Co-reporter:Yong Cui, Huifeng Yao, Bowei Gao, Yunpeng Qin, Shaoqing Zhang, Bei Yang, Chang He, Bowei Xu, and Jianhui Hou
Journal of the American Chemical Society May 31, 2017 Volume 139(Issue 21) pp:7302-7302
Publication Date(Web):May 12, 2017
DOI:10.1021/jacs.7b01493
Fabricating organic solar cells (OSCs) with a tandem structure has been considered an effective method to overcome the limited light absorption spectra of organic photovoltaic materials. Currently, the most efficient tandem OSCs are fabricated by adopting fullerene derivatives as acceptors. In this work, we designed a new non-fullerene acceptor with an optical band gap (Egopt) of 1.68 eV for the front subcells and optimized the phase-separation morphology of a fullerene-free active layer with an Egopt of 1.36 eV to fabricate the rear subcell. The two subcells show a low energy loss and high external quantum efficiency, and their photoresponse spectra are complementary. In addition, an interconnection layer (ICL) composed of ZnO and a pH-neutral self-doped conductive polymer, PCP-Na, with high light transmittance in the near-IR range was developed. From the highly optimized subcells and ICL, solution-processed fullerene-free tandem OSCs with an average power conversion efficiency (PCE) greater than 13% were obtained.
Co-reporter:Liyan Yang, Shaoqing Zhang, Chang HeJianqi Zhang, Huifeng Yao, Yang Yang, Yun Zhang, Wenchao Zhao, Jianhui Hou
Journal of the American Chemical Society 2017 Volume 139(Issue 5) pp:1958-1966
Publication Date(Web):January 12, 2017
DOI:10.1021/jacs.6b11612
A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (Egopt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of −5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (Voc = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor–acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.
Co-reporter:Yunpeng Qin;Yu Chen;Yong Cui;Shaoqing Zhang;Huifeng Yao;Jiang Huang;Wanning Li;Zhong Zheng
Advanced Materials 2017 Volume 29(Issue 24) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adma.201606340
Tandem organic solar cells (TOSCs), which integrate multiple organic photovoltaic layers with complementary absorption in series, have been proved to be a strong contender in organic photovoltaic depending on their advantages in harvesting a greater part of the solar spectrum and more efficient photon utilization than traditional single-junction organic solar cells. However, simultaneously improving open circuit voltage (Voc) and short current density (Jsc) is a still particularly tricky issue for highly efficient TOSCs. In this work, by employing the low-bandgap nonfullerene acceptor, IEICO, into the rear cell to extend absorption, and meanwhile introducing PBDD4T-2F into the front cell for improving Voc, an impressive efficiency of 12.8% has been achieved in well-designed TOSC. This result is also one of the highest efficiencies reported in state-of-the-art organic solar cells.
Co-reporter:Huifeng Yao;Long Ye;Junxian Hou;Bomee Jang;Guangchao Han;Yong Cui;Gregory M. Su;Cheng Wang;Bowei Gao;Runnan Yu;Hao Zhang;Yuanping Yi;Han Young Woo;Harald Ade
Advanced Materials 2017 Volume 29(Issue 21) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adma.201700254
A new acceptor–donor–acceptor-structured nonfullerene acceptor ITCC (3,9-bis(4-(1,1-dicyanomethylene)-3-methylene-2-oxo-cyclopenta[b]thiophen)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d′:2,3-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene) is designed and synthesized via simple end-group modification. ITCC shows improved electron-transport properties and a high-lying lowest unoccupied molecular orbital level. A power conversion efficiency of 11.4% with an impressive V OC of over 1 V is recorded in photovoltaic devices, suggesting that ITCC has great potential for applications in tandem organic solar cells.
Co-reporter:Sunsun Li;Long Ye;Wenchao Zhao;Xiaoyu Liu;Jie Zhu;Harald Ade
Advanced Materials 2017 Volume 29(Issue 46) pp:
Publication Date(Web):2017/12/01
DOI:10.1002/adma.201704051
AbstractImproving the fill factor (FF) is known as a challenging issue in organic solar cells (OSCs). Herein, a strategy of extending the conjugated area of end-group is proposed for the molecular design of acceptor–donor–acceptor (A–D–A)-type small molecule acceptor (SMA), and an indaceno[1,2-b:5,6-b′]dithiophene-based SMA, namely IDTN, by end-capping with the naphthyl fused 2-(3-oxocyclopentylidene)malononitrile is synthesized. Benefiting from the π-conjugation extension by fusing two phenyls, IDTN shows stronger molecular aggregation, more ordered packing structure, thus over one order of magnitude higher electron mobility relative to its counterpart. By utilizing the fluorinated polymer (PBDB-TF) as the electron donor, the corresponding device exhibits a high efficiency of 12.2% with a record-high FF of 0.78, which is approaching the theoretical limit of OSCs. Compared with the reference molecule, such a high FF in the IDTN system can be mainly attributed to the more ordered π–π packing of acceptor aggregates, higher domain purity and symmetric carrier transport in the blend. Hence, enlarging the conjugated area of the terminal-group in these A–D–A-type SMAs is a promising approach not only for enhancing the electron mobility, but also for improving the blend morphology, and both of them are conducive to the fill-factor breakthrough.
Co-reporter:Hao Zhang;Shaoqing Zhang;Ke Gao;Feng Liu;Huifeng Yao;Bei Yang;Chang He;Thomas P. Russell
Journal of Materials Chemistry A 2017 vol. 5(Issue 21) pp:10416-10423
Publication Date(Web):2017/05/30
DOI:10.1039/C7TA01250K
A new conjugated polymer utilizing diketopyrrolopyrrole (DPP) and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) units as the backbone framework was designed, synthesized, and applied in polymer solar cells. A high efficiency of 9.18% was obtained using phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor, which was among the best results obtained for DPP-based photovoltaic polymers. Absorption spectra indicated that the new polymer exhibits a narrow optical band-gap and strong aggregation behavior in the solution state. It was found that by dissolving the donor and acceptor in different solvents and then mixing them before film casting, better performing solar cell devices and distinct film morphology could be achieved, rather than by dissolution in one solvent. Small-angle neutron scattering (SANS) profiles showed that PC71BM in solution impaired polymer aggregate formation, because of its favorable interaction with the polymer chain. This study demonstrated the importance of manipulating the aggregation state in bulk heterojunction solar cell fabrication and revealed the influence of polymer-fullerene interplay on the blend film morphology.
Co-reporter:Li-Peng Zhang;Wenchao Zhao;Xiaoyu Liu;Ke-Jian Jiang;Feng-Ting Li;Lian-Ming Yang
New Journal of Chemistry (1998-Present) 2017 vol. 41(Issue 18) pp:10237-10244
Publication Date(Web):2017/09/11
DOI:10.1039/C7NJ01971H
Perylenediimide (PDI) possesses intense absorption, a low-lying energy level, and a high electron mobility. However, its highly planar conformation and thus strong intermolecular π–π stacking prevents its application as an electron acceptor used in efficient bulk heterojunction (BHJ) organic solar cells (OSCs). Herein, we report a structurally non-planar molecule TRIP-PDI3, in which a rigid and shape-persistent triptycene (TRIP) unit is employed as a central unit to collect three PDI arms at the periphery. As an electron acceptor, TRIP-PDI3 exhibits a low-lying LUMO energy level of −3.81 eV similar to that of conventional PCBM, but with an intensive light absorption in the range of 450–600 nm. BHJ OSCs were fabricated using TRIP-PDI as an electron acceptor and a low band gap polymer PBDT-TS1 as an electron donor, exhibiting a power conversion efficiency (PCE) of 4.53%. The result demonstrates that TRIP is a promising building block for the construction of structurally non-planar PDI derivatives as non-fullerene (NF) electron acceptors for efficient OSCs.
Co-reporter:Wenchao Zhao 赵文超;Long Ye 叶龙;Sunsun Li 李荪荪;Xiaoyu Liu 刘晓宇
Science China Materials 2017 Volume 60( Issue 8) pp:697-706
Publication Date(Web):07 August 2017
DOI:10.1007/s40843-017-9080-x
Though the power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been boosted to 12%, the use of highly pollutive halogenated solvents as the processing solvent significantly hinders the mass production of OSCs. It is thus necessary to achieve high-efficiency OSCs by utilizing the halogen-free and environmentally-friendly solvents. Herein, we applied a halogen-free solvent system (oxylene/1-phenylnaphthalene, XY/PN) for fabricating fullerene-free OSCs, and a high PCE of 11.6% with a notable fill factor (FF) of 72% was achieved based on the PBDB-T:IT-M blend, which is among the top efficiencies of halogen-free solvent processed OSCs. In addition, the influence of different halogen-free solvent additives on the blend morphology and device performance metrics was studied by synchrotron-based tools and other complementary methods. Morphological results indicate the highly ordered molecular packing and highest average domain purity obtained in the blend films prepared by using XY/PN co-solvent are favorable for achieving increased FFs and thus higher PCEs in the devices. Moreover, a lower interaction parameter (χ) of the IT-M:PN pair provides a good explanation for the more favorable morphology and performance in devices with PN as the solvent additive, relative to those with diphenyl ether and N-methylpyrrolidone. Our study demonstrates that carefully screening the non-halogenated solvent additive plays a vital role in realizing the efficient and environmentally-friendly solvent processed OSCs.虽然近年来有机太阳能电池的能量转换效率已经超过13%, 但是加工高效率有机太阳能电池的溶剂大多数是含卤溶剂, 这些溶剂体系阻碍了有机太阳能电池的进一步发展. 因此, 探索使用绿色溶剂制备高效率电池具有重要意义. 本文在非卤溶剂邻二甲苯作为主溶剂的前提下,通过筛选不同非卤溶剂作为添加剂制备高效有机太阳能电池, 在PBDB-T:IT-M共混材料体系中, 取得了11.6%的能量转换效率, 该效率是使用非卤溶剂加工有机太阳能电池的最高效率之一. 我们通过一系列形貌测试将共混薄膜形貌的相区尺寸, 相区纯度以及结晶性等重要形貌参数与器件性能进行关联, 这对非富勒烯有机太阳能电池的性能优化具有指导意义. 本研究表明, 通过细致筛选非卤溶剂添加剂调节共混薄膜的形貌, 从而可以获得高性能的有机太阳能电池.
Co-reporter:Hao Zhang;Xiaohui Wang;Liyan Yang;Shaoqing Zhang;Yun Zhang;Chang He;Wei Ma
Advanced Materials 2017 Volume 29(Issue 42) pp:
Publication Date(Web):2017/11/01
DOI:10.1002/adma.201703777
AbstractAn all-small-molecule ternary solar cell is achieved with a power conversion efficiency of 10.48% by incorporating phenyl-C71-butyric-acid-methyl ester (PC71BM) into a nonfullerene binary system. The addition of PC71BM is found to modulate the film morphology by improving the domain purity and decreasing the domain size. This modulation facilitates charge generation and suppresses charge recombination, as manifested by the significantly enhanced short-circuit current density and fill factor. The results correlate the domain characteristics with the device performance and offer new insight from the perspective of morphology modulation for constructing efficient ternary devices.
Co-reporter:Yu Chen;Yunpeng Qin;Yang Wu;Cheng Li;Huifeng Yao;Ningning Liang;Xiaochen Wang;Weiwei Li;Wei Ma
Advanced Energy Materials 2017 Volume 7(Issue 17) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/aenm.201700328
Ternary blend is proved to be a potential contender for achieving high efficiency in organic photovoltaics, which can apparently strengthen the absorption of active layer so as to better harvest light irradiation. Much of the previous work in ternary polymer solar cells focuses on broadening the absorption spectrum; however, a new insight is brought to study the third component, which in tiny amounts influents the small-molecule acceptor-based device performance. Without contributing to complementing the absorption, a minute amount of fullerene derivative, Bis-PC70BM, can effectively play an impressive role as sensitizer in enhancing the external quantum efficiency of the host binary blend, especially for polymeric donor. Detailed investigations reveal that the minute addition of Bis-PC70BM can realize morphology modification as well as facilitate electron transfer from polymeric donor to small molecule acceptor via cascade energy level modulation, and therefore lead to an improvement in device efficiency.
Co-reporter:Sunsun Li;Long Ye;Wenchao Zhao;Shaoqing Zhang;Harald Ade
Advanced Energy Materials 2017 Volume 7(Issue 17) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/aenm.201700183
Molecular engineering of nonfullerene electron acceptors is of great importance for the development of organic photovoltaics. In this study, a series of methoxyl-modified dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene-based small-molecule acceptor (SMA) isomers are synthesized and characterized to determine the effect of substitution position of the terminal group in these acceptor–donor–acceptor-type SMAs. Minor changes in the substitution position are demonstrated to greatly influence the optoelectronic properties and molecular packing of the isomers. Note that SMAs with planar molecular backbones show more ordered molecular packing and smaller π–π stacking distances, thus dramatically higher electron mobilities relative to their counterparts with distorted end-groups. By utilizing polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophen)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione)] (PBDB-T) as an electron donor, an optimum power conversion efficiency (PCE) of 11.9% is achieved in the device based on PBDB-T:IT-OM-2, which is among the top efficiencies reported as of yet. Moreover, the PCE stays above 10% as the film thickness increases to 250 nm, which is very advantageous for large-area printing. Overall, the intrinsic molecular properties as well as the morphologies of blends can be effectively modulated by manipulating the substituent position on the terminal groups, and the structure–property relationships gleaned from this study will aid in designing more efficient SMAs for versatile applications.
Co-reporter:Shaoqing Zhang;Liyan Yang;Delong Liu;Chang He;Jianqi Zhang
Science China Chemistry 2017 Volume 60( Issue 10) pp:1340-1348
Publication Date(Web):15 September 2017
DOI:10.1007/s11426-017-9121-0
Two benzo[1,2-b:4,5-b′]dithiophene (BDT)-based small molecule (SM) donor materials with identical conjugated backbones but different substitution groups, named as DRTB-O and DRTB-T, were well explored to demonstrate the influence of the replacement of alkoxy with alkylthienyl on their photovoltaic properties in fullerene-based and fullerene-free organic solar cells (OSCs). The study shows that the two SM donors possess similar absorption spectra and energy levels but different crystalline structures in solid films. The carrier transport property and phase separation morphologies of the blend films have also been fully investigated. By employing PC71BM as the acceptor, the power conversion efficiency (PCE) of DRTB-O:PC71BM and DRTB-T:PC71BM based devices were 4.91% and 7.08%, respectively. However, by blending with IDIC, the two SM donors exhibited distinctly different photovoltaic properties in fullerene-free OSCs, and the PCE of DRTB-O:IDIC and DRTB-T:IDIC based devices were 0.15% and 9.06%, respectively. These results indicate that the replacement of alkoxyl with alkylthienyl in designing SM donor materials plays an important role in the application of fullerene-free OSCs.
Co-reporter:Xiaoyu Liu;Long Ye;Wenchao Zhao;Shaoqing Zhang;Sunsun Li;Gregory M. Su;Cheng Wang;Harald Ade
Materials Chemistry Frontiers 2017 vol. 1(Issue 10) pp:2057-2064
Publication Date(Web):2017/09/27
DOI:10.1039/C7QM00182G
Owing to the use of cost-effective materials and excellent stability, nonfullerene polymer solar cells (PSCs) have great potential for realizing large-area industrial production. In contrast to fullerene-based devices, non-fullerene PSCs have exhibited a superior photovoltaic performance with up to 12% efficiency and long-term thermal stability. Presently, one of the major factors hindering industrial production is the high sensitivity of the power conversion efficiency (PCE) to thickness variations, which can significantly affect the manufacturing yields and production costs of roll-to-roll processing. Specifically, the device fill factors and PCEs of many high-efficiency nonfullerene PSCs show a significant loss when the thickness of the active layer is over 100 nm. In order to achieve high output capabilities earlier, there is an urgent need to find a processing method to fabricate high-efficiency thick-film nonfullerene PSCs. Controlling the morphology and performance sensitivity in thick-film non-fullerene devices is a great challenge in the field. Here, we present a simple morphology optimization method via thermal annealing to fabricate highly efficient thickness-insensitive non-fullerene PSCs. After this treatment, PBDB-T/IT-M-based nonfullerene PSCs can afford an impressive PCE of up to ∼9.4% at an active layer thickness of 250 nm. In addition, the devices with an active layer thickness of 400 nm still maintain a high efficiency close to 9%. The photovoltaic properties and morphology parameters resolved from hard and soft X-ray scattering clearly indicate that thermal annealing plays a key role in improving the film thickness insensitivity for non-fullerene PSCs.
Co-reporter:Jie Zhu;Sunsun Li;Xiaoyu Liu;Huifeng Yao;Fenghao Wang;Shaoqing Zhang;Mingliang Sun
Journal of Materials Chemistry A 2017 vol. 5(Issue 29) pp:15175-15182
Publication Date(Web):2017/07/25
DOI:10.1039/C7TA04431C
Four dithienoindaceno[1,2-b:5,6-b′]dithiophene (DT-IDT) based small molecules IT-O1, IT-O2, IT-O3 and IT-O4 with increasing alkoxyl chain length from methoxy to butoxy on the terminal-groups were synthesized to investigate the end-group side-chain effects on these acceptor–donor–acceptor-type small molecule electron acceptors. The optical absorption and energy levels of the four molecules, blend morphologies, carrier mobilities, and photovoltaic performances of the devices blended with the polymer PBDB-T are systematically investigated. Interestingly, both the solubility and electron mobility are enhanced for these materials with decrease in side chain length, which lead to ideal morphologies and balanced charge transport. Hence, increased Jsc and FF, and thus distinctly higher PCEs of 11.6% were obtained from the PBDB-T:IT-O1-based devices.
Co-reporter:Chen Sun;Zhihong Wu;Zhanhao Hu;Jingyang Xiao;Wenchao Zhao;Ho-Wa Li;Qing-Ya Li;Sai-Wing Tsang;Yun-Xiang Xu;Kai Zhang;Hin-Lap Yip;Fei Huang;Yong Cao
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 8) pp:1784-1791
Publication Date(Web):2017/08/09
DOI:10.1039/C7EE00601B
Non-fullerene polymer solar cells have attracted extensive attention due to their potential for overcoming the performance bottleneck currently encountered in fullerene-based photovoltaics. Herein, we report non-fullerene polymer solar cells with a maximal power conversion efficiency of over 11% by introducing an n-type water/alcohol soluble conjugated polymer as a cathode interlayer. We found that the contact between the n-type interlayer and the donor provides an extra interface for charge dissociation and the matching of energy levels between the n-type interlayer and the acceptor allows efficient electron extraction from the bulk heterojunction, which eventually leads to much improved performance. This study proposes a significant design rule for designing new interfaces for high performance non-fullerene photovoltaics.
Co-reporter:Delong Liu;Bei Yang;Bomee Jang;Bowei Xu;Shaoqing Zhang;Chang He;Han Young Woo
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 2) pp:546-551
Publication Date(Web):2017/02/15
DOI:10.1039/C6EE03489F
Two p-type conjugated polymers with disparate optical and electronic properties, PB3T and PB2T, were developed and applied in fullerene-free polymer solar cells (PSCs). The photovoltaic performance of the PB3T-based PSC device processed by anisole achieved a high power conversion efficiency of 11.9% with a Jsc of 18.8 mA cm−2 and Voc of 1.00 V.
Co-reporter:Huifeng Yao, Long Ye, Hao Zhang, Sunsun Li, Shaoqing Zhang, and Jianhui Hou
Chemical Reviews 2016 Volume 116(Issue 12) pp:7397
Publication Date(Web):June 2, 2016
DOI:10.1021/acs.chemrev.6b00176
Advances in the design and application of highly efficient conjugated polymers and small molecules over the past years have enabled the rapid progress in the development of organic photovoltaic (OPV) technology as a promising alternative to conventional solar cells. Among the numerous OPV materials, benzodithiophene (BDT)-based polymers and small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking 10% efficiency barrier in the single junction OPV devices. Remarkably, the OPV device featured by BDT-based polymer has recently demonstrated an impressive PCE of 11.21%, indicating the great potential of this class of materials in commercial photovoltaic applications. In this review, we offered an overview of the organic photovoltaic materials based on BDT from the aspects of backbones, functional groups, alkyl chains, and device performance, trying to provide a guideline about the structure-performance relationship. We believe more exciting BDT-based photovoltaic materials and devices will be developed in the near future.
Co-reporter:Wenchao Zhao;Deping Qian;Shaoqing Zhang;Sunsun Li;Olle Inganäs;Feng Gao
Advanced Materials 2016 Volume 28( Issue 23) pp:4734-4739
Publication Date(Web):
DOI:10.1002/adma.201600281
Co-reporter:Bowei Xu;Zhong Zheng;Kang Zhao
Advanced Materials 2016 Volume 28( Issue 3) pp:434-439
Publication Date(Web):
DOI:10.1002/adma.201502989
Co-reporter:Zhong Zheng;Shaoqing Zhang;Jianqi Zhang;Yunpeng Qin;Wanning Li;Runnan Yu;Zhixiang Wei
Advanced Materials 2016 Volume 28( Issue 25) pp:5133-5138
Publication Date(Web):
DOI:10.1002/adma.201600373
Co-reporter:Shaoqing Zhang, Long Ye, Hao Zhang, Jianhui Hou
Materials Today 2016 Volume 19(Issue 9) pp:533-543
Publication Date(Web):November 2016
DOI:10.1016/j.mattod.2016.02.019
Solution-processable organic photovoltaics (OPV) has emerged as a promising clean energy-generating technology due to its potential for low-cost manufacturing with a high power/weight ratio. The state-of-the-art OPV devices are processed by hazardous halogenated solvents. Fabricating high-efficiency OPV devices using greener solvents is a necessary step toward their eventual commercialization. In this review, recent research efforts and advances in green-solvent-processable OPVs are summarized, and two basic strategies including material design and solvent selection of light-harvesting layers are discussed. In particular, the most recent green-solvent-processable OPVs with high efficiencies in excess of 9% are highlighted.
Co-reporter:Shaoqing Zhang;Long Ye
Advanced Energy Materials 2016 Volume 6( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/aenm.201502529
With the advances in organic photovoltaics (OPVs), the invention of model polymers with superior properties and wide applicability is of vital importance to both the academic and industrial communities. The recent inspiring advances in OPV research have included the emergence of poly(benzodithiophene-co-thieno[3,4-b]thiophene) (PBDTTT)-based materials. Through the combined efforts on PBDTTT polymers, over 10% efficiencies have been realized recently in various types of OPV devices. This review attempts to critically summarize the recent advances with respect to five well-known PBDTTT polymers and their design considerations, basic properties, photovoltaic performance, as well as device application in conventional, inverted, tandem solar cells. These PBDTTT polymers also make great contributions to the rapid advances in the field of emerging ternary blends and fullerene-free OPVs with top performances. Addtionally, new challenges in developing novel photovoltaic polymers with more superior properties are prospected. More importantly, the research of highly efficient PBDTTT-based polymers provides useful insights and builds fundamentals for new types of OPV applications with various architectures.
Co-reporter:Ningning Liang;Kai Sun;Zhong Zheng;Huifeng Yao;Guangpeng Gao;Xiangyi Meng;Zhaohui Wang;Wei Ma
Advanced Energy Materials 2016 Volume 6( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/aenm.201600060
Co-reporter:Sunsun Li;Hao Zhang;Wenchao Zhao;Long Ye;Huifeng Yao;Bei Yang;Shaoqing Zhang
Advanced Energy Materials 2016 Volume 6( Issue 5) pp:
Publication Date(Web):
DOI:10.1002/aenm.201501991
To realize high power conversion efficiencies (PCEs) in green-solvent-processed all-polymer solar cells (All-PSCs), a long alkyl chain modified perylene diimide (PDI)-based polymer acceptor PPDIODT with superior solubility in nonhalogenated solvents is synthesized. A properly matched PBDT-TS1 is selected as the polymer donor due to the red-shifted light absorption and low-lying energy level in order to achieve the complementary absorption spectrum and matched energy level between polymer donor and polymer acceptor. By utilizing anisole as the processing solvent, an optimal efficiency of 5.43% is realized in PBDT-TS1/PPDIODT-based All-PSC with conventional configuration, which is comparable with that of All-PSCs processed by the widely used binary solvent. Due to the utilization of an inverted device configuration, the PCE is further increased to over 6.5% efficiency. Notably, the best-performing PCE of 6.58% is the highest value for All-PSCs employing PDI-based polymer acceptors and green-solvent-processed All-PSCs. The excellent photovoltaic performance is mainly attributed to a favorable vertical phase distribution, a higher exciton dissociation efficiency (Pdiss) in the blend film, and a higher electrode carrier collection efficiency. Overall, the combination of rational molecular designing, material selection, and device engineering will motivate the efficiency breakthrough in green-solvent-processed All-PSCs.
Co-reporter:Hao Zhang;Huifeng Yao;Wenchao Zhao;Long Ye
Advanced Energy Materials 2016 Volume 6( Issue 6) pp:
Publication Date(Web):
DOI:10.1002/aenm.201502177
Co-reporter:Huifeng Yao;Runnan Yu;Tae Joo Shin;Hao Zhang;Shaoqing Zhang;Bomee Jang;Mohammad Afsar Uddin;Han Young Woo
Advanced Energy Materials 2016 Volume 6( Issue 15) pp:
Publication Date(Web):
DOI:10.1002/aenm.201600742
Co-reporter:Long Ye, Yuan Xiong, Huifeng Yao, Abay Gadisa, Hao Zhang, Sunsun Li, Masoud Ghasemi, Nrup Balar, Adrian Hunt, Brendan T. O’Connor, Jianhui Hou, and Harald Ade
Chemistry of Materials 2016 Volume 28(Issue 20) pp:7451
Publication Date(Web):September 22, 2016
DOI:10.1021/acs.chemmater.6b03083
Solution processable conjugated organic materials have gained tremendous interest motivated by their potential of low cost, lightweight and especially easy manufacturing of large-area and flexible electronics. Toxic halogen-containing solvents have been widely used in the processing of organic electronics, particularly organic photovoltaics (OPVs). To transition this technology to more commercially attractive manufacturing approaches, removing these halogenated solvents remains one of the key challenges. Our morphological (hard/soft X-ray scattering) and calorimetric characterizations reveal that using o-methylanisole, a certified food additive, as processing solvent can achieve similar crystalline properties and domain spacing/purity with that achieved by widely used binary halogenated solvents (chlorobenzene and 1,8-diiodooctane), thus yielding comparable photovoltaic performance in spin-casted films. To move a step forward, we further present the potential of o-methylanisole as processing solvent in the blade-coating of several cases of OPVs in air. Remarkably, this single nonhazardous solvent yields ∼8.4% and ∼5.2% efficiency in OPVs by respectively blade-coating PBDT-TSR:PC71BM and all-polymeric PBDT-TS1:PPDIODT in ambient air, which are among the highest values for the respective kind of device. We postulate this simple nonhazardous solvent approach will also be applicable in the large area roll-to-roll coating and industrial scale printing of high-efficiency OPVs in air.
Co-reporter:Long Ye, Xuechen Jiao, Wenchao Zhao, Shaoqing Zhang, Huifeng Yao, Sunsun Li, Harald Ade, and Jianhui Hou
Chemistry of Materials 2016 Volume 28(Issue 17) pp:6178
Publication Date(Web):August 15, 2016
DOI:10.1021/acs.chemmater.6b02222
All-polymer solar cells (All-PSCs) are of great interest as a renewable and economically viable energy technology, which has shown potential advantages in practical photovoltaic applications due to the highly tunable optical, electronic, and mechanical properties. A quantitative understanding of the domain composition variations and orientational ordering of all-polymeric films affected by solvent additives had been unattainable until now. This study demonstrates how the use of trace amount solvent additive can indeed manipulate domain purity and molecular orientational ordering as revealed by polarized soft X-ray scattering (P-SoXS). Additionally, the BDDT/PNDI all-polymeric blend exhibits enhanced average domain purity with the use of a trace amount of solvent additive and thus improved charge mobility, device fill factor and power conversion efficiency. A high power conversion efficiency of ∼7.1% was obtained in the All-PSC mainly contributed by this morphology control strategy. Manipulation of domain purity and orientation ordering, both of which are impacted by the aggregation kinetics, may be a key to further boost the efficiency of new fullerene-free solar cells and all-anisotropic materials-based devices.
Co-reporter:Huifeng Yao, Wenchao Zhao, Zhong Zheng, Yong Cui, Jianqi Zhang, Zhixiang Wei and Jianhui Hou
Journal of Materials Chemistry A 2016 vol. 4(Issue 5) pp:1708-1713
Publication Date(Web):22 Dec 2015
DOI:10.1039/C5TA08614K
In this study, a regioregular copolymer (PBDT-TSR) based on alkythio-substituted two dimensional conjugated benzodithiophene (2D-BDT) and asymmetric thienothiophene (TT) was synthesized through two steps. Compared with its random counterpart PBDT-TS1, the PBDT-TSR shows improved absorption properties and enhanced inter-chain π–π packing effects. The hole mobility of PBDT-TSR is higher than that of PBDT-TS1. What's more, the enhancement of regioregularity does not have great influence on its molecular energy levels of the polymer and its miscibility with the acceptor material, PC71BM. The polymer solar cell (PSC) device fabricated by using PBDT-TSR shows a high power conversion efficiency of 10.2% with a short-circuit current density (JSC) of 17.99 mA cm−2, while the PBDT-TS1 shows a PCE of 9.74%. Overall, these results suggest that it is of great importance to investigate the influence of backbone configuration on photovoltaic performance for high efficiency conjugated polymers based on asymmetric conjugated building blocks, and to improve the regioregularity of this type of polymer should be a feasible approach to enhance their photovoltaic properties.
Co-reporter:Yahui Liu, Wenchao Zhao, Yang Wu, Jicheng Zhang, Guangwu Li, Wenhua Li, Wei Ma, Jianhui Hou and Zhishan Bo
Journal of Materials Chemistry A 2016 vol. 4(Issue 21) pp:8097-8104
Publication Date(Web):25 Apr 2016
DOI:10.1039/C6TA02622B
Two kinds of new conjugated polymers (P1 and P2) with benzothiadiazole as the acceptor unit and thiophene as the donor unit were designed, synthesized and used as donor materials for polymer solar cells (PSCs). These polymers show a broad absorption in the visible region, a medium band gap of about 1.75 eV, and a low-lying HOMO energy level of about −5.65 eV. The open-circuit voltage (Voc) of both P1 and P2 was greatly improved to 0.85 V mainly due to the introduction of a carboxylate group at the 3-position of the thiophene spacer. Fluoro substitution on the polymer backbone of P2 can greatly enhance the interchain interaction, leading to a huge increase of short-circuit current density (Jsc). P2-based devices with the active layer spin-coated from 1,2-diclorobenzene (DCB) solutions that contain 1% 1,8-diiodooctane (DIO) and washed with methanol showed a synergistic positive effect, resulting in a significant enhancement of the power conversion efficiency (PCE) up to 8.67%. The PCE could be further improved by constructing inverted devices and the best efficiency of 9.26% was finally obtained. In addition, the mechanism for achieving such a high PCE for P2 based devices was also proposed based on the morphological analysis of the blend films by atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incident angle X-ray scattering (GIWAXS) and resonant soft X-ray scattering (RSoXS). The improvement can be ascribed to the enhanced molecular packing and proper phase separation of the blend films and the reduced charge recombination.
Co-reporter:Kang Zhao, Qi Wang, Bowei Xu, Wenchao Zhao, Xiaoyu Liu, Bei Yang, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2016 vol. 4(Issue 24) pp:9511-9518
Publication Date(Web):23 May 2016
DOI:10.1039/C6TA03288E
Two wide band gap (WBG) polymers based on thiophene-thiazolothiazole (TTz) units, PBT-TTz and PBT-S-TTz, were synthesized. Both polymers showed absorption onsets at 635 nm in solid films. Although PBT-TTz and PBT-S-TTz are WBG materials with relatively narrow absorption spectra, they have great potential for constructing high-performance polymer solar cells (PSCs). By replacing the alkyl side chain of PBT-TTz with an alkylthiol side chain, the HOMO level of PBT-S-TTz was lowered to −5.45 eV. A PCE of 7.92% was then obtained in a single-junction PSC device based on a PBT-S-TTz:PC71BM active layer. Moreover, high-performance fullerene-free PSCs were fabricated using these polymers and a high PCE of 8.22% was achieved. This work demonstrates that TTz-based polymers PBT-TTz and PBT-S-TTz are promising candidates as efficient WBG polymers for constructing high-performance PSC devices.
Co-reporter:Huifeng Yao, Hao Zhang, Long Ye, Wenchao Zhao, Shaoqing Zhang, and Jianhui Hou
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 6) pp:3575
Publication Date(Web):September 11, 2015
DOI:10.1021/acsami.5b07311
Dialkylthio-substituted thienyl-benzodithiophene (BDT-DST) was designed and synthesized as a building block to modulate the molecular levels of the conjugated polymers, and three copolymers named PDST-BDD, PDST-TT and PDST-DPP were prepared and applied in polymer solar cells (PSCs). Theoretical calculations and electrochemical cyclic voltammetry (CV) measurement suggested that the dialkylthio group could decrease the molecular energy levels of the resulting polymers distinctly. The open-circuit voltage (VOC) of PSC devices based on PDST-BDD, PDST-TT, and PDST-DPP are as high as 1.0, 0.98, and 0.88 V, respectively, which are ∼0.15 V higher than those of the corresponding alky-substituted analogues. Moreover, the influence of the dialkylthio group on the absorption spectra, crystalline properties, hole mobilities, and blend morphologies of the polymers was also investigated. The results indicate that the dialkythio substitution is an effective method to modulate the molecular energy levels and that the BDT-DST unit has potential for constructing high-efficiency photovoltaic polymers.Keywords: conjugated polymer; dialkylthio substitution; molecular energy levels; photovoltaic polymer; polymer solar cell
Co-reporter:Sunsun Li, Long Ye, Qi Wang, Shaoqing Zhang, Wenchao Zhao, Jianhui Hou
Organic Electronics 2016 Volume 28() pp:39-46
Publication Date(Web):January 2016
DOI:10.1016/j.orgel.2015.10.004
•Sulfonyl group was introduced by a post-polymerization method.•Two oxidants have been explored to convert the alkylthio group.•The open-circuit voltage of photovoltaic polymer is increased.Molecular designing of photovoltaic polymers based on benzodithiophene (BDT) building blocks for high power conversion efficiency (PCE) in polymer solar cells (PSCs) arouse much attention in the past few years. To meliorate the energy levels of photovoltaic polymers featuring alkylthio substituted BDT units, a novel post-polymerization oxidation method was proposed applied in converting sulfur atom into sulfonyl group on side chains of the pristine polymer PBT-S. After treating with tiny amount of meta-chloroperoxybenzoic acid (m-CPBA) and hydrogen peroxide (H2O2), two batches of the target polymers, namely, PBT-SO2-M and PBT-SO2-H were prepared for the first time, respectively. The photochemical and electrochemical results indicate that both the HOMO levels are distinctly dropped with almost no influence on band gaps by introducing strong electron-withdrawing sulfonyl groups on side chains of BDT. Accordingly, the photovoltaic results reveal that the Voc of devices based on PBT-SO2-M and PBT-SO2-H are 0.81, 0.71 V which are 0.17 and 0.07 V higher than that of pristine polymer PBT-S, respectively. Moreover, the Jsc and PCE of PBT-SO2-H devices are comparable with those of the devices based on PBT-S. Overall, this work suggests that the molecular energy levels of D–A copolymers can be effectively tuned by a post-oxidation method.
Co-reporter:Xia Guo, Maojie Zhang, Wei Ma, Shaoqing Zhang, Jianhui Hou and Yongfang Li
RSC Advances 2016 vol. 6(Issue 57) pp:51924-51931
Publication Date(Web):23 May 2016
DOI:10.1039/C6RA06020J
Photovoltaic properties of polymer solar cells (PSCs) are strongly affected by surface and bulk morphologies of their active layers. Herein, three solvent additives with different boiling points (BP) and asymmetric solvencies with respect to the polymer donor and fullerene-based acceptor were used to control the surface and bulk morphologies of the blend active layers based on PBDTTT-C-T and PC71BM. Based on the detailed results obtained from photovoltaic measurements and morphological characterization, the correlations between the nature of the solvent additives, the surface and bulk morphologies of the blend films and the photovoltaic performance of the devices are rationally demonstrated. We found that the Voc is determined by the contact surface potential, which is affected by the donor/acceptor composition at the top surface, while the Jsc and FF are heavily influenced by the sizes and the relative compositional fluctuations of the aggregations in the blends. It was also found that the relative solvencies of the additives to the solutes and the large difference of saturated vapor pressure (Po) values between the host solvent (o-dichlorobenzene, o-DCB) and the guest solvent (additives with high BP) play the key roles in affecting surface and bulk morphologies of the PBDTTT-C-T:PC71BM blend films. Overall, this work provides informative and useful guidance to select the best solvent additive for morphology control of polymer solar cells.
Co-reporter:Zhiguo Zhao, Yun Zhang, Yidan Wang, Xiaojun Qin, Junbo Wu, Jianhui Hou
Organic Electronics 2016 Volume 28() pp:178-183
Publication Date(Web):January 2016
DOI:10.1016/j.orgel.2015.11.001
Photovoltaic properties of the two polymers (named as PBQ-0F and PBQ-4F) were investigated by employing [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor and a water-alcohol-soluble polymer interlayer material (named as PFNBr) to fabricate photovoltaic devices. For the PBQ-0F:PC71BM blend, the device using Ca/Al as cathode showed very similar efficiency as the device using PFNBr/Al as cathode, while for the PBQ-0F:PC71BM blend, photovoltaic performance of the device can be distinctly improved by replacing Ca/Al with PFNBr/Al. As a result, the best PCE of the PBQ-4F:PC71BM based devices reached 9.04%, which is much higher than that of the PBQ-0F:PC71BM based devices. The results obtained from the quantum chemistry calculations and water contact angle measurements demonstrate that these two polymers are low polar materials, and also the films based on them have hydrophobic surfaces. Since PFNBr has an amphipathic structure (hydrophobic backbone and hydrophilic side chain) and the blend films of PBQ-4F:PC71BM and PBQ-4F:PC71BM have different surface energies, the PFNBr organization atop these two blend types of should be different, which will affect device photovoltaic performance.The device with a PFNBr/Al cathode showed a similar efficiency as the device with a Ca/Al cathode for the PBQ-0F:PC71BM-based devices, while efficiency of the PBQ-4F:PC71BM-based devices was significantly improved by using PFNBr as an n-type interlayer material.
Co-reporter:Wenchao Zhao;Shaoqing Zhang
Science China Chemistry 2016 Volume 59( Issue 12) pp:1574-1582
Publication Date(Web):2016 December
DOI:10.1007/s11426-016-0198-0
In this work, photovoltaic properties of the PBDB-T:ITIC based-NF-PSCs were fully optimized and characterized by tuning the morphology of the active layers and changing the device architecture. First, donor/acceptor (D/A) weight ratios were scanned, and then further optimization was performed by using different additives, i.e. 1,8-diiodooctane (DIO), diphenyl ether (DPE), 1-chloronaphthalene (CN) and N-methyl-2-pyrrolidone (NMP), on the basis of best D/A ratio (1:1, w/w), respectively. Finally, the conventional or inverted device architectures with different buffer layers were employed to fabricate NF-PSC devices, and meanwhile, the morphology of the active layers was further optimized by controlling annealing temperature and time. As a result, a record efficiency of 11.3% was achieved, which is the highest result for NF-PSCs. It’s also remarkable that the inverted NF-PSCs exhibited long-term stability, i.e. the best-performing devices maintain 83% of their initial PCEs after over 4000 h storage.
Co-reporter:Shaoqing Zhang, Bei Yang, Delong Liu, Hao Zhang, Wenchao Zhao, Qi Wang, Chang He, and Jianhui Hou
Macromolecules 2016 Volume 49(Issue 1) pp:120-126
Publication Date(Web):December 28, 2015
DOI:10.1021/acs.macromol.5b02416
Conjugated polymers have rigid backbones and strong interchain π–π interaction in aggregation state, so their morphologies in thin films could be significantly affected by backbone conformation. In this work, taking two highly efficient photovoltaic polymers (PDTBT-TT and PBT4T) as example, we investigated the correlations among the chemical structure of backbone units, thermodynamic stability of backbone conformation, backbone curvature, phase transformation kinetics, and crystalline properties by utilizing quantum chemistry calculation, differential scanning calorimetry, temperature-dependent UV–vis absorption spectroscopy, and X-ray diffraction. The results indicated that compared to PBT4T, PDTBT-TT possesses more rigid backbone, more stable backbone conformation, and curvature, so PDTBT-TT has higher melting and crystallization temperatures but smaller phase transformation enthalpy than PBT4T. Furthermore, polymer solar cells (PSCs) based on these two polymers were fabricated and characterized with a simple conventional device structure. In our measurements, the PSCs based on PBT4T showed a best PCE of 8.38%, which is coincident with the reported results; the PSCs based on PDTBT-TT exhibited a best PCE of 9.18%, indicating PDTBT-TT is a promising photovoltaic polymer material. Overall, the results and discussion in this work suggest a new perspective for molecular design of polymer photovoltaic materials.
Co-reporter:Shaoqing Zhang, Yunpeng Qin, Mohammad Afsar Uddin, Bomee Jang, Wenchao Zhao, Delong Liu, Han Young Woo, and Jianhui Hou
Macromolecules 2016 Volume 49(Issue 8) pp:2993-3000
Publication Date(Web):April 8, 2016
DOI:10.1021/acs.macromol.6b00248
Here, taking a polythiophene derivative (PBDD4T) as a starting polymer, we tried to increase the rotation barrier and hence stabilize its backbone conformation by introducing fluorine into the β- and β′-position of the α-linked bithiophene segments and then synthesized a new polymer named as PBDD4T-2F. Our results demonstrate that the rotation barrier between the α-linked bithiophene significantly increases after the fluorination, so PBDD4T-2F has a more stable backbone conformation than PBDD4T. Compared to PBDD4T, PBDD4T-2F shows stronger aggregation effect in solution state and more compact π–π stacking in solid thin film and also possesses deeper HOMO level. These properties make PBDD4T-2F being an ideal donor material in PSCs. When blended with PC71BM, a fullerene acceptor, the PBDD4T-2F-based device showed a power conversion efficiency (PCE) of 9.04%, which is 38% higher than that of the PBDD4T-based device; when blended with ITIC, a non-fullerene acceptor, the PBDD4T-2F-based device showed a PCE of 8.69%, which is almost 20 times higher than that of the PBDD4T-based device. What is more, the tandem cell, in which the blend of PBDD4T-2F:PC61BM was used for making the front subcell, exhibited a high PCE of 10.12%. The photovoltaic results indicate that the fluorination is an effective method to enhance interchain π–π interaction for the polythiophene and hence to tune its photovoltaic properties in PSCs, especially for the fullerene-free device based on ITIC.
Co-reporter:Yong Cui, Bowei Xu, Bei Yang, Huifeng Yao, Sunsun Li, and Jianhui Hou
Macromolecules 2016 Volume 49(Issue 21) pp:8126-8133
Publication Date(Web):October 28, 2016
DOI:10.1021/acs.macromol.6b01595
Three pH neutral conjugated polymers based on thiophene and benzene derivatives, namely PCP-Na, PCF-Na, and PFS-Na, were designed and synthesized. In the three polymers, PCP-Na exhibited a self-doping effect in aqueous solution, and the thin film of PCP-Na demonstrated a high electrical conductivity of 1.66 × 10–3 S/cm and a deep HOMO level of −5.22 eV; these properties make it an ideal anode interfacial layer (AIL) material in polymer solar cells (PSCs). The single-junction PSC modified with PCP-Na AIL showed a PCE of 9.89%, which is comparable to that of the PEDOT:PSS-modified device (PCE = 9.53%). Notably, PCP-Na AIL exhibited excellent thickness insensitivity in fabricating PSC devices; i.e., the PSC devices with very thick PCP-Na interlayers over 300 nm still demonstrated a high fill factor over 70%, indicating the PCP-Na layer has excellent charge collection and transport properties. Furthermore, the homo-tandem PSC device was fabricated using a new connecting interlayer, which consists of PCP-Na as the hole collection layer and ZnO as the electron collection layer, and a PCE of 10.54% was achieved in the homo-tandem device.
Co-reporter:Long Ye;Xuechen Jiao;Meng Zhou;Shaoqing Zhang;Huifeng Yao;Wenchao Zhao;Andong Xia;Harald Ade
Advanced Materials 2015 Volume 27( Issue 39) pp:6046-6054
Publication Date(Web):
DOI:10.1002/adma.201503218
Co-reporter:Feng Gao;Scott Himmelberger;Mattias Andersson;David Hanifi;Yuxin Xia;Shaoqing Zhang;Jianpu Wang;Alberto Salleo;Olle Inganäs
Advanced Materials 2015 Volume 27( Issue 26) pp:3868-3873
Publication Date(Web):
DOI:10.1002/adma.201405913
Co-reporter:Zhong Zheng;Shaoqing Zhang;Maojie Zhang;Kang Zhao;Long Ye;Yu Chen;Bei Yang
Advanced Materials 2015 Volume 27( Issue 7) pp:1189-1194
Publication Date(Web):
DOI:10.1002/adma.201404525
Co-reporter:Maojie Zhang;Xia Guo;Wei Ma;Harald Ade
Advanced Materials 2015 Volume 27( Issue 31) pp:4655-4660
Publication Date(Web):
DOI:10.1002/adma.201502110
Co-reporter:Wenchao Zhao, Long Ye, Shaoqing Zhang, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2015 vol. 3(Issue 24) pp:12723-12729
Publication Date(Web):08 May 2015
DOI:10.1039/C4TA07029A
Power conversion efficiencies (PCEs) of state-of-the-art polymer solar cells (PSCs) have been promoted to over 9%. However, halogenated solvents like chlorobenzene (CB), o-dichlorobenzene (DCB), 1,8-diiodooctane (DIO) or their mixtures are still predominately used in the fabrication of these high performance PSCs. With the rapid progress in PCEs, removing the halogenated solvents from the fabrication processes of PSCs becomes an urgent task for the practical utilization of PSC technology. In this study, a halogen-free solvent system consisting of o-xylene (XY) and N-methylpyrrolidone (NMP) was successfully applied in the fabrication of the PSCs based on a variety of highly efficient polymers including PBDT-TS1 and other eight types of photovoltaic polymers. Notably, utilizing an XY–2% NMP mixture as a processing solvent, the PBDT-TS1/PC71BM-based PSC realized a PCE of 9.47%, which has been the highest value in halogen-free solvent processed PSCs until now. The photovoltaic properties and nanoscale morphology clearly indicated that the halogen-free solvent system featuring the XY–NMP mixture can replace the role of the widely utilized halogenated solvents in fabricating environmentally friendly PSCs with high efficiency.
Co-reporter:Long Ye, Chengyue Zhou, Haifeng Meng, Heng-Hsin Wu, Chi-Ching Lin, Hua-Hsien Liao, Shaoqing Zhang and Jianhui Hou
Journal of Materials Chemistry A 2015 vol. 3(Issue 3) pp:564-569
Publication Date(Web):26 Nov 2014
DOI:10.1039/C4TC02449D
Along with the advances in polymer solar cells (PSCs), the accurate evaluation of novel photovoltaic polymers with various band gaps is an important issue that should be concerned, as well as needs to be addressed at various research laboratories in the world. In this work, we have focused on PSCs by employing some of the most efficient and well-known low band gap (LBG) polymers, for instance, PBDTTT-C-T, PBDTBDD, PDPP3T, PTB7-Th, PSBTBT and PBDTTPD, and obtained the corresponding spectral-mismatch factors (MMFs) under various reference cell/solar simulator combinations. Generally, there still exists ±25% spectral error even for a simulator whose spectrum grade is labeled as AAA. The best way to accurately evaluate the power conversion efficiencies (PCEs) of LBG polymers is by choosing a combination of a spectral-matched-silicon-solar-cell (match to LBG polymer's spectral responsivity spectrum) and a Class AAA solar simulator. Furthermore, our results could provide guidance for the accurate measurements of organic molecules, perovskites, and related photovoltaic technologies.
Co-reporter:Kang Zhao, Long Ye, Wenchao Zhao, Shaoqing Zhang, Huifeng Yao, Bowei Xu, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:9565-9571
Publication Date(Web):11 Aug 2015
DOI:10.1039/C5TC02172C
In this contribution, a novel cathode interlayer material (NDIO) based on naphthalene diimide was successfully prepared by a facile two-step reaction from commercially available compounds. NDIO exhibited excellent water solubility, high transparency in the visible light region, and well-matched molecular energy levels. By incorporating this novel water processed cathode interlayer, a high power conversion efficiency of 9.51% was recorded in PBDT-TS1/PC71BM-based polymer photovoltaic cells (PPCs), and the value is nearly 2-fold the device efficiency of PPCs without the cathode interlayer. More importantly, the insertion of the NDIO interlayer promotes the device efficiency of polymer/polymer photovoltaic cells based on PBDTTT-EFT/N2200 from 3.23% up to 5.77%. The successful applications in both polymer/PCBM and polymer/polymer blend-based inverted PPCs make NDIO a promising cathode interlayer for realizing aqueous processed polymer photovoltaic cells with high performance.
Co-reporter:Long Ye, Kai Sun, Wei Jiang, Shaoqing Zhang, Wenchao Zhao, Huifeng Yao, Zhaohui Wang, and Jianhui Hou
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 17) pp:9274
Publication Date(Web):April 28, 2015
DOI:10.1021/acsami.5b02012
Among the diverse nonfullerene acceptors, perylene bisimides (PBIs) have been attracting much attention due to their excellent electron mobility and tunable molecular and electronic properties by simply engineering the bay and head linkages. Herein, guided by two efficient small molecular acceptors, we designed, synthesized, and characterized a new nonfullerene small molecule PPDI with fine-tailored alkyl chains. Notably, a certificated PCE of 5.40% is realized in a simple structured fullerene-free polymer solar cell comprising PPDI as the electron acceptor and a fine-tailored 2D-conjugated polymer PBDT-TS1 as the electron donor. Moreover, the device behavior, morphological feature, and origin of high efficiency in PBDT-TS1/PPDI-based fullerene-free PSC were investigated. The synchronous selection and design of donor and acceptor materials reported here offer a feasible strategy for realizing highly efficient fullerene-free organic photovoltaics.Keywords: donor polymers; nonfullerene acceptor; perylene bisimides; polymer solar cells;
Co-reporter:Shaoqing Zhang, Mohammad Afsar Uddin, Wenchao Zhao, Long Ye, Han Young Woo, Delong Liu, Bei Yang, Huifeng Yao, Yong Cui and Jianhui Hou
Polymer Chemistry 2015 vol. 6(Issue 14) pp:2752-2760
Publication Date(Web):25 Feb 2015
DOI:10.1039/C5PY00071H
Alkyl side chains play critical roles in the molecular design of conjugated polymers for applications in bulk-heterojunction (BHJ) polymer solar cells (PSCs). Recently, the introduction of alkylthio substituents onto poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-b]thiophene) (PBDTTT)-based conjugated polymers has been proved to be an effective method to improve the photovoltaic properties of the polymers. In this contribution, three alkylthiothiophene-substituted benzodithiophene (BDT-TS) based polymers, named PBDT-TS1, PBDT-TS2 and PBDT-TS3, were synthesized and applied as donor materials in PSCs. In these three polymers, octyl, 2-ethylhexyl and 3,7-dimethyloctyl are used on their BDT units, respectively. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), electrochemical cyclic voltammetry (CV) and grazing-incidence wide-angle X-ray scattering (GI-WAXS), and also their photovoltaic properties in PSCs were studied and compared. The results reveal that the alkyls have little influence on absorption spectra and molecular energy levels of the polymers. The GI-WAXS results show that PBDT-TS1 has stronger and tighter π–π stacking than the other two polymers, implying that linear alkyls may reduce steric hindrance than branched alkyl chains in an aggregation state. As a consequence of the strong π–π inter-chain packing of PBDT-TS1, an increased short circuit current density (JSC) and fill factor (FF) as well as a power conversion efficiency of over 9.5% are achieved in single-cell BHJ devices, which are obviously higher than those for devices based on the other two polymers. Overall, the results of this work suggest that alkyl side groups play an important role in affecting the π–π stacking of the conjugated polymers, i.e., the linear octyl has weaker steric hindrance for the inter-chain π–π stack than the branched 2-ethylhexyl and 3,7-dimethyloctyl, and for the highly efficient polymer based on the 2-alkylthiothiophene-substituted BDT, PBDT-TS1 has the optimal structure.
Co-reporter:Yu Chen, Yong Cui, Shaoqing Zhang and Jianhui Hou
Polymer Chemistry 2015 vol. 6(Issue 22) pp:4089-4095
Publication Date(Web):05 May 2015
DOI:10.1039/C5PY00431D
A novel BDT-based conjugated polymer, PBDTTT-S-TEG, and a series of new fullerene derivatives were designed, synthesized and applied to green solvent processable polymer solar cells. By rationally screening processing solvents, a PCE of 4.50% was firstly achieved with definitely low toxic, non-halogenated and safe solvent fabrication, which is almost identical to that processed with o-dichlorobenzene.
Co-reporter:Delong Liu, Zaiyu Wang, Shaoqing Zhang, Zhong Zheng, Bei Yang, Wei Ma and Jianhui Hou
RSC Advances 2015 vol. 5(Issue 85) pp:69567-69572
Publication Date(Web):10 Aug 2015
DOI:10.1039/C5RA14013G
High-efficiency polymer solar cells (PSCs) based on a conjugated polymer named PBQ-4 were fabricated by employing 1,2-dichlorobenzene (o-DCB), o-xylene and anisole as primary solvents. We rationally selected three solvent additives, 1,8-diiodooctane (DIO), N-methylpyrrolidone (NMP) and diphenyl ether (DPE) to tune the morphologies of the blend films. The power conversion efficiency (PCE) of 8.47% and 7.62% were realized by using o-DCB/DIO and o-xylene/NMP as processing solvent, respectively. The PSC with a PCE of 8.37% was fabricated using the environmentally friendly solvents of anisole/DPE. To the best of our knowledge, the PCE of 8.37% is not only among the highest values reported for PSCs with Eg > 1.7 eV but also the highest value for a PSC processed using a biodegradable solvents with low toxicity. Therefore, these results open the new paths for the fabrication of highly efficient PSCs by green processes.
Co-reporter:Long Ye, Wei Jiang, Wenchao Zhao, Shaoqing Zhang, Yong Cui, Zhaohui Wang, Jianhui Hou
Organic Electronics 2015 Volume 17() pp:295-303
Publication Date(Web):February 2015
DOI:10.1016/j.orgel.2014.12.020
•Donor selection is a feasible strategy to realize high efficiency for non-fullerene acceptors.•A high Voc of 1.04 V was achieved in PBDTTPD/SDIPBI-based PSC.•A high PCE of 4.5% was recorded for PBDTTT-EFT/SDIPBI-based PSC.Recently, perylene bisimides have been explored and developed as potential candidates for non-fullerene acceptors and power conversion efficiencies (PCEs) exceeding 3% were realized in the non-fullerene polymer solar cells (NF-PSCs) featuring perylene bisimides as acceptors. Considering that only a few donor polymers like P3HT and PBDTTT-C-T were utilized in non-fullerene PSCs, screening donor polymers with well-matched energy levels, absorption spectrum as well as hole mobility in NF-PSCs will be the key to promote the current PCEs. Herein, four high performance donor polymers including PBDTTPD, PBDTTT-EFT, PDPP3T, PSBTBT were employed for the optimization of single bond-linked perylene bisimide (SDIPBI)-based NF-PSCs. A clear criterion in selection of donor polymers has been established for the SDIPBI-based NF-PSCs. Suitable energy level differences, finer morphology, and broad absorption ranges could be successively screened for donor polymers. Interestingly, NF-PSCs based on PBDTTPD/SDIPBI delivers a high Voc of 1.04 V and a desirable PCE of 3.4%. Moreover, the SDIPBI-based NF-PSC employing PBDTTT-EFT as donor polymer exhibits a high PCE up to 4.5%. The results implicate that to select donor polymers is a feasible strategy to boost the photovoltaic performance of NF-PSCs further.
Co-reporter:Jian Liu;Xinchen Li;Shaoqing Zhang;Xingang Ren;Jiaqi Cheng;Lu Zhu;Di Zhang;Lijun Huo;Wallace C. H. Choy
Advanced Materials Interfaces 2015 Volume 2( Issue 17) pp:
Publication Date(Web):
DOI:10.1002/admi.201500324
Currently, most of the promising organic solar cells (OSCs) are based on low bandgap polymer donors with deep-lying highest occupied molecular orbit (HOMO) levels, which impose the challenges for device architecture design. In terms of fast charge extraction and suppression of bimolecular recombination, elaborate interface design in low bandgap OSCs is of significance to further boost their ultimate efficiency. In this work, a facile solution-processed functionalized single wall carbon nanotube (f-SWCNT) mesh/self-assembled molecule (SAM) hybrid structure is reported as hole transport layer (HTL) in low bandgap OSCs. The effectiveness of such hybrid HTL originates from two aspects: (i) SAM layer can effectively realize Ohmic contact between f-SWCNT and low bandgap polymer donors with deep-lying HOMO levels due to the reduction of interface energy barrier; (ii) f-SWCNT mesh can provide fast hole extraction pathways to quickly sweep out photogenerated charges. As a consequence of synergic effects of such hybrid HTL, both photocurrent and fill factor are greatly enhanced due to the reduced bimolecular recombination. Together with careful light management by using ZnO optical spacer, a high efficiency of 10.5% has been achieved. This work offers an excellent choice for large-scale processable and effective HTL toward the application in low bandgap OSCs with deep-lying energy levels.
Co-reporter:Hao Zhang;Long Ye
Polymer International 2015 Volume 64( Issue 8) pp:957-962
Publication Date(Web):
DOI:10.1002/pi.4895
Abstract
Open-circuit voltage (Voc) is one of the key parameters in determining the photovoltaic performance of polymer solar cells (PSCs). Although significant advances in materials and device physics of PSCs have been achieved in the past decade, the low Voc values still hamper the enhancement of power conversion efficiencies (PCEs) of PSCs based on the widely known polymers like polythiophenes (PTs) and poly(benzo[1,2-b:4,5-b′]dithiophene-co-thieno[3,4-b]thiophene) (PBDTTT) polymers. In order to pursue high PCE, more efforts should be directed towards improving Voc through molecular design of conjugated polymers, i.e. to reduce the highest occupied molecular orbital levels without sacrificing optical absorption properties. In this mini-review, some feasible and effective strategies, such as inserting conjugated side groups with various electron-withdrawing effects, manipulating alkyl chains and introducing functional substituents, to improve Voc of PSCs based on some highly efficient photovoltaic polymers, especially PTs and PBDTTT polymers, are summarized and discussed. Owing to these strategies, PCEs of PSCs based on PTs and PBDTTT polymers can be further boosted to ca 7% and ca 10%, respectively. Apparently, these strategies offer opportunities for achieving new breakthroughs in other π-conjugated photovoltaic materials. © 2015 Society of Chemical Industry
Co-reporter:Long Ye, Xuechen Jiao, Hao Zhang, Sunsun Li, Huifeng Yao, Harald Ade, and Jianhui Hou
Macromolecules 2015 Volume 48(Issue 19) pp:7156-7163
Publication Date(Web):September 23, 2015
DOI:10.1021/acs.macromol.5b01537
All polymer photovoltaic cells offer unique potentials owing to the chemical and electronic tunability of both polymer donors and polymer acceptors. Compared with the numerous π-conjugated polymer donors, choices of π-conjugated polymer acceptors are limited for photovoltaic applications. Although 2D-conjugated benzo[1,2-b:4,5-b′]dithiophene (BDT) units are widely used as building blocks in highly efficient donor polymers in recent years, polymer acceptors based on these units have not been reported yet. Herein, a novel 2D-conjugated polymer acceptor (PBDTNDI-T) based on naphthalene diimide (NDI) and alkylthiothiophene-substituted BDT was designed, synthesized, and in-depth characterized. The polymers’ photophysical, electrical, crystallinity, and morphological properties are addressed in homopolymer and blend films and well correlated with device performance. Under the weight ratio of 1.5:1 and 3 vol % of 1-chloronaphthalene, the PBDTNDI-T-based all polymer photovoltaic device exhibited a desirable PCE of nearly 3%, which is ascribed to the relatively high domain purity and small domain characteristic length observed by resonant soft X-ray scattering (R-SoXS) characterizations. These results demonstrated PBDTNDI-T is a novel polymer acceptor and also promising candidate material for efficient energy-related applications.
Co-reporter:Wenchao Zhao
The Journal of Physical Chemistry C 2015 Volume 119(Issue 49) pp:27322-27329
Publication Date(Web):November 13, 2015
DOI:10.1021/acs.jpcc.5b09575
Here we report a successful efficiency improvement strategy in both conventional and inverted polymer solar cells (PSCs) based on multiple polymer blends, using a feasible and commercially available cathode buffer layer (CBL), namely barium hydroxide [Ba(OH)2], to modify the photoactive blend and cathode contacts. High performance PSCs with an identical Ba(OH)2 buffer layer were fabricated based on the multiple light-harvesting PBDT-TS1:PC71BM, PffBT4T-2OD:PC71BM, and PBDT-TS1:N2200 blends. The conventional PSC with Ba(OH)2 as the CBL showed a higher power conversion efficiency (PCE) of 9.65% based on the PBDT-TS1:PC71BM system under the illumination of 100 mW/cm2. For the inverted cells based on the PffBT4T-2OD:PC71BM system, the PCE can be improved from 4.26% (without CBL) to 9.02% after inserting the Ba(OH)2 buffer layer. More importantly, the Ba(OH)2 buffer layer presents similar positive effects in the conventional and inverted all-polymer devices based on a new combination, i.e., the PBDT-TS1:N2200 system. The dramatic enhancement in device performance resulted from the suitable work function of Ba(OH)2, extremely high transmittance, and excellent film-forming capability. Therefore, inserting Ba(OH)2 as the CBL is a simple, low-cost, and widely applicable method to simultaneously improve the conventional and inverted photovoltaic device performance.
Co-reporter:Long Ye;Benhu Fan;Shaoqing Zhang;Sunsun Li;Bei Yang
Science China Materials 2015 Volume 58( Issue 12) pp:953-960
Publication Date(Web):2015 December
DOI:10.1007/s40843-015-0102-x
In the past several years, conjugated polymers and organometal halide perovskites have become regarded as promising light-absorbing materials for next-generation photovoltaic devices and have attracted a great deal of interest. As the main part of this contribution, we describe the enhancement of near-infrared (NIR) photoresponse of well-known CH3NH3PbI3−xClx-based solar cells by the integration of bulk heterojunction (BHJ) small band gap polymer:fullerene absorbers. Particularly, the integration of a commercially available polymer PDPP3T and PCBM-based BHJ boosts the peak external quantum efficiency (EQE) by up to 46% in the NIR region (800−1000 nm), which is outside of the photoresponsive region (300−800 nm) of conventional perovskite solar cells. This substantial improvement in the EQE over the NIR region offers an additional current density of ∼5 mA cm−2 for the control perovskite solar cell, and a high power conversion efficiency (PCE) of over 12% was obtained in the perovskite/BHJ-based solar cells. In addition, the insertion of the BHJ absorber consisting of a small band gap polymer PDTP-DFBT and PCBM also results in nearly 40% EQE for the perovskite/BHJ solar cell. The results also reveal that controlling over the polymer/PCBM weight ratio for a BHJ absorber is the key to achieving the optimal efficiency for this type of perovskite-polymer hybrid solar cell.近年来, 共轭聚合物和钙钛矿型有机金属卤化物被视为极具潜力的光伏材料, 引起了广泛的研究兴趣. 本文通过引入两种本体异质结(BHJ)聚合物: 富勒烯活性层, 大幅提高了基于CH3NH3PbI3−x的钙钛矿太阳能电池的近红外光响应特性. 其中, 基于窄带隙聚合物PDPP3T的钙钛矿/BHJ杂化太阳能电池在近红外区域(800∼1000 nm)内的外量子效率(EQE)峰值高达46%, 且该区域已经超出了CH3NH3PbI3−x型太阳能电池的光响应范围(300∼800 nm). 相较于参照的钙钛矿太阳能电池, 近红外区域大幅提升的EQE为钙钛矿/BHJ杂化太阳能电池贡献了额外的电流密度(∼5 mA cm−2), 因此其光电转换效率达到了12%以上. 此外, 引入基于聚合物PDTP-DFBT的BHJ也可以使钙钛矿太阳能电池在近红外区域的EQE达到40%以上. 研究结果也表明优化BHJ的聚合物: 富勒烯比例是提高这类钙钛矿-聚合物杂化太阳能电池性能的关键.
Co-reporter:Shaoqing Zhang;Long Ye;Wenchao Zhao;Bei Yang;Qi Wang
Science China Chemistry 2015 Volume 58( Issue 2) pp:248-256
Publication Date(Web):2015 February
DOI:10.1007/s11426-014-5273-x
The low band gap polymer based on benzodithiophene (BDT)-thieno[3,4-b]thiophene (TT) backbone, PBDT-TS1, was synthesized following our previous work and the bulk heterojunction (BHJ) material comprising PBDT-TS1/PC71BM was optimized and characterized. By processing the active layer with different additives i.e. 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN) and 1, 8-octanedithiol (ODT) and optimizing the ratio of each additive in the host solvent, a high PCE of 9.98% was obtained under the condition of utilizing 3% DIO as processing additive in CB. The effect of varied additives on photovoltaic performance was illustrated with atomic force microscopy (AFM) and transmission electron microscope (TEM) measurements that explained changes in photovoltaic parameters. These results provide valuable information of solvent additive choice in device optimization of PBDTTT polymers, and the systematic device optimization could be applied in other efficient photovoltaic polymers. Apparently, this work presents a great advance in single junction PSCs, especially in PSCs with conventional architecture.
Co-reporter:Huifeng Yao;Long Ye;Benhu Fan;Lijun Huo
Science China Materials 2015 Volume 58( Issue 3) pp:213-222
Publication Date(Web):2015 March
DOI:10.1007/s40843-015-0036-3
Three conjugated polymers based on thienyl-substituted benzodithiophene (BDT) and 4,7-bis-thienyl-benzothiadiazole (DTBT) with varied substitution positions of the alkyl side chains were synthesized to investigate the correlations between the structure and photovoltaic performance of the polymer photovoltaic materials. The three polymers named PBDTDTBT-p, PBDTDTBT-o and PBDTDTBT-m were characterized by a set of methods including absorption spectroscopy, cyclic voltammetry, thermogravimetric analysis, X-ray diffraction, density functional theory and photovoltaic measurements. The results show that the steric hindrance caused by the different substitution positions of the alky chains has a significant influence on the photovoltaic properties of the polymers. The open-circuit voltage (Voc) of the photovoltaic devices based on the three polymers could range from 0.67 to 0.90 V. Clearly, this finding provides us a feasible strategy to optimize the photovoltaic properties by simply changing the positions of the alkyl chains.本文将具有不同取代位点的二维共轭支链引入到PBDTDTBT类聚合物的苯并二噻吩单元上, 设计和合成了三种骨架相同的两维共轭聚合物, 即PBDTDTBT-p, PBDTDTBT-o和PBDTDTBT-m, 并在此基础上探究了烷基链取代位点对共轭聚合物的光伏性质以及器件性能的影响. 通过吸收光谱、 循环伏安、 热失重分析、 X射线衍射、 光伏测试以及理论计算等手段对比研究了三种聚合物光伏材料, 结果表明由不同烷基链取代位点引起的分子空间位阻作用对三种聚合物的光物理性质、 微观形貌以及光伏性能有着重要的影响. 基于三种聚合物制备的光伏器件的开路电压可从0.67 V变化到0.90 V, 其光伏效率也相应地从3.48%提高到5%以上. 调节烷基链取代位点是一种简单有效制备高性能聚合物光伏材料的优化策略.
Co-reporter:Delong Liu, Wenchao Zhao, Shaoqing Zhang, Long Ye, Zhong Zheng, Yong Cui, Yu Chen, and Jianhui Hou
Macromolecules 2015 Volume 48(Issue 15) pp:5172-5178
Publication Date(Web):July 24, 2015
DOI:10.1021/acs.macromol.5b00829
We present the synthesis and photovoltaic application of four conjugated polymers composed of benzo[1,2-b:4,5-b′]dithiophene (BDT)-based and 2,3-diphenyl-5,8-di(thiophen-2-yl)quinoxaline (DTQx)-based units. Fluorination of the DTQx units and the conjugated side groups of the BDT unit shows synergistic effect on molecular energy level modulation of the polymers, and as a result, the polymer PBQ-4 exhibits the deepest HOMO and LUMO levels in these four polymers. The characterizations of the photovoltaic properties of the polymer solar cells (PSCs) based on these four polymers reveal that the fluorination has little influence on short-circuit current density (JSC) and fill factor (FF) but is very helpful to enhance open-circuit voltage (VOC) of the devices. Benefiting from the synergistic effect of the fluorination, the device based on PBQ-4 shows a high VOC of 0.90 V, which is 0.26 V higher than the polymer without fluorine and ca. 0.10 V higher than the other two polymers with less fluorine. As a result, a power conversion efficiency (PCE) of 8.55% was recorded in the PBQ-4 based device, which is much higher than those of the other three polymers and also the highest one for the BDT-Qx-based polymers.
Co-reporter:Huifeng Yao, Hao Zhang, Long Ye, Wenchao Zhao, Shaoqing Zhang, and Jianhui Hou
Macromolecules 2015 Volume 48(Issue 11) pp:3493-3499
Publication Date(Web):May 19, 2015
DOI:10.1021/acs.macromol.5b00649
(E)-5-(2-(5-(Alkylthio)thiophen-2-yl)vinyl)thiophene-2-yl functional groups were introduced onto 4- and 8-positions of BDT units, and this building block was used to construct a new derivative polymer of PTB7, named as PBT-TVT. Benefiting from the prolonged conjugation of the conjugated side groups on BDT units, the optical absorption property of PBT-TVT can be improved greatly compared to that of PTB7, so an inspiring result of 7.67% was obtained by using PBT-TVT as the donor and PC61BM as the acceptor in polymer solar cells (PSCs), which is much higher than that of the PTB7:PC61BM-based device and also one of the highest results for PSCs with PC61BM. In electrochemical cyclic voltammetry (CV) measurements, PBT-TVT showed a deeper HOMO level than PTB7 so the device based on the former exhibits higher open circuit voltage than the latter. Moreover, in comparison with PTB7, the new polymer PBT-TVT exhibited stronger interchain π–π interaction and thus higher hole mobility. Overall, the results in this work indicated that PBT-TVT is a promising donor polymer, and the strategy used in this work will be beneficial for molecular design of polymer photovoltaic materials for large-scale production of PSCs.
Co-reporter:Long Ye, Shaoqing Zhang, Lijun Huo, Maojie Zhang, and Jianhui Hou
Accounts of Chemical Research 2014 Volume 47(Issue 5) pp:1595
Publication Date(Web):April 29, 2014
DOI:10.1021/ar5000743
As researchers continue to develop new organic materials for solar cells, benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymers have come to the fore. To improve the photovoltaic properties of BDT-based polymers, researchers have developed and applied various strategies leading to the successful molecular design of highly efficient photovoltaic polymers. Novel polymer materials composed of two-dimensional conjugated BDT (2D-conjugated BDT) have boosted the power conversion efficiency of polymer solar cells (PSCs) to levels that exceed 9%.In this Account, we summarize recent progress related to the design and synthesis of 2D-conjugated BDT-based polymers and discuss their applications in highly efficient photovoltaic devices. We introduce the basic considerations for the construction of 2D-conjugated BDT-based polymers and systematic molecular design guidelines. For example, simply modifying an alkoxyl-substituted BDT to form an alkylthienyl-substituted BDT can improve the polymer hole mobilities substantially with little effect on their molecular energy level. Secondly, the addition of a variety of chemical moieties to the polymer can produce a 2D-conjugated BDT unit with more functions. For example, the introduction of a conjugated side chain with electron deficient groups (such as para-alkyl-phenyl, meta-alkoxyl-phenyl, and 2-alkyl-3-fluoro-thienyl) allowed us to modulate the molecular energy levels of 2D-conjugated BDT-based polymers. Through the rational design of BDT analogues such as dithienobenzodithiophene (DTBDT) or the insertion of larger π bridges, we can tune the backbone conformations of these polymers and modulate their photovoltaic properties. We also discuss the influence of 2D-conjugated BDT on polymer morphology and the blends of these polymers with phenyl-C61 (or C71)-butyric acid methyl ester (PCBM). Finally, we summarize the various applications of the 2D-conjugated BDT-based polymers in highly efficient PSC devices.Overall, this Account correlates the molecular structures of the 2D-conjugated BDT-based polymers with their photovoltaic properties. As a result, this Account can guide the molecular design of organic photovoltaic materials and the development of organic materials for other types of optoelectronic devices.
Co-reporter:Maojie Zhang;Xia Guo;Wei Ma;Harald Ade
Advanced Materials 2014 Volume 26( Issue 33) pp:5880-5885
Publication Date(Web):
DOI:10.1002/adma.201401494
Co-reporter:Xia Guo;Maojie Zhang;Wei Ma;Long Ye;Shaoqing Zhang;Shengjian Liu;Harald Ade;Fei Huang
Advanced Materials 2014 Volume 26( Issue 24) pp:4043-4049
Publication Date(Web):
DOI:10.1002/adma.201400411
Co-reporter:Maojie Zhang;Xia Guo;Wei Ma;Shaoqing Zhang;Lijun Huo;Harald Ade
Advanced Materials 2014 Volume 26( Issue 13) pp:2089-2095
Publication Date(Web):
DOI:10.1002/adma.201304631
Co-reporter:Maojie Zhang;Xia Guo;Shaoqing Zhang
Advanced Materials 2014 Volume 26( Issue 7) pp:1118-1123
Publication Date(Web):
DOI:10.1002/adma.201304427
Co-reporter:Yu Chen;Shaoqing Zhang;Yue Wu
Advanced Materials 2014 Volume 26( Issue 17) pp:2744-2749
Publication Date(Web):
DOI:10.1002/adma.201304825
Co-reporter:Wei Ma;John R. Tumbleston;Long Ye;Cheng Wang;Harald Ade
Advanced Materials 2014 Volume 26( Issue 25) pp:4234-4241
Publication Date(Web):
DOI:10.1002/adma.201400216
Co-reporter:Zhan'ao Tan;Liangjie Li;Fuzhi Wang;Qi Xu;Shusheng Li;Gang Sun;Xiaohe Tu;Xuliang Hou;Yongfang Li
Advanced Energy Materials 2014 Volume 4( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/aenm.201300884
Co-reporter:Long Ye, Shaoqing Zhang, Wenchao Zhao, Huifeng Yao, and Jianhui Hou
Chemistry of Materials 2014 Volume 26(Issue 12) pp:3603
Publication Date(Web):June 12, 2014
DOI:10.1021/cm501513n
Co-reporter:Wei Jiang, Long Ye, Xiangguang Li, Chengyi Xiao, Fang Tan, Wenchao Zhao, Jianhui Hou and Zhaohui Wang
Chemical Communications 2014 vol. 50(Issue 8) pp:1024-1026
Publication Date(Web):30 Oct 2013
DOI:10.1039/C3CC47204C
A series of bay-linked perylene bisimides as non-fullerene acceptors for organic solar cells are designed. The best power conversion efficiency up to 3.63% based on s-diPBI (1b) is demonstrated by fine-tuning optoelectronic properties resulting from different degrees of twisting and flexibility by bay-linkages.
Co-reporter:Xia Guo, Maojie Zhang, Chaohua Cui, Jianhui Hou, and Yongfang Li
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 11) pp:8190
Publication Date(Web):May 9, 2014
DOI:10.1021/am500836u
The photovoltaic performance of poly(3-hexylthiophene) (P3HT) has been improved greatly by using indene–C60 bisadduct (ICBA) as acceptor instead of phenyl-C61-butyric acid methyl ester (PCBM). However, the solvent of dichlorobenzene (DCB) used in fabricating polymer solar cells (PSCs) limited the application of the PSCs, because of the environmental problem caused by the harmful halogenated solvent. In this work, we fabricated the PSCs based on P3HT/ICBA processed with four low-harmful non-halogenated solvents of toluene, o-xylene, m-xylene, and p-xylene. The PSCs based on P3HT/ICBA (1:1, w/w) with toluene as the solvent exhibit the optimized power conversion efficiency (PCE) of 4.5% with open-circuit voltage (Voc) of 0.84 V, short circuit current density (Jsc) of 7.2 mA/cm2, and fill factor (FF) of 71%, under the illumination of AM 1.5G at 100 mW/cm2. Upon using 1% N-methyl pyrrolidone (NMP) as a solvent additive in the toluene solvent, the PCE of the PSCs was greatly improved to 6.6% with a higher Jsc of 10.3 mA/cm2 and a high FF of 75%, which is even higher than that of the devices fabricated with halogenated DCB solvent. The X-ray diffraction (XRD) measurement shows that the crystallinity of P3HT increased with the NMP additive. The investigations on morphology of the active layers by atomic force microscopy (AFM) and transmission electron microscopy (TEM) indicate that the NMP additive promotes effective phase separation and formation of nanoscaled interpenetrating network structure of the active layer, which is beneficial to the improvement of Jsc and PCE for the PSCs fabricated with toluene as the solvent.Keywords: indene−C60 bisadduct; N-methyl pyrrolidone additive; non-halogenated solvents; polymer solar cells; toluene solvent;
Co-reporter:Guangzheng Zuo, Zhaojun Li, Maojie Zhang, Xia Guo, Yue Wu, Shaoqing Zhang, Bo Peng, Wei Wei and Jianhui Hou
Polymer Chemistry 2014 vol. 5(Issue 6) pp:1976-1981
Publication Date(Web):12 Dec 2013
DOI:10.1039/C3PY01231J
Two conjugated polymers, PBDT–TBT and PBDT–TTBT, were designed and synthesized. PBDT–TBT has a zigzagged chain conformation (Z-type), while PBDT–TTBT has a linear chain conformation (L-type). The results show that the polymer chain conformation significantly affects the optoelectronic properties of the polymers. With the conformation change from Z-type to L-type, the J-aggregation of the polymer was enhanced greatly, i.e. PBDT–TTBT shows a much more prominent absorption shoulder peak at the long wavelength direction compared to PBDT–TBT. In the X-ray diffraction analysis, it was found that the L-type polymer shows much stronger crystallinity than the Z-type polymer. Benefiting from the enhanced inter-chain π–π stacking effect, the blend of PBDT–TTBT/PC71BM showed higher hole mobility compared to the blend of PBDT–TBT/PC71BM. The power conversion efficiencies (PCEs) of the polymer solar cells based on PBDT–TTBT/PC71BM and PBDT–TTBT/PC71BM are 6.3% and 4.9%, respectively. These results clearly reveal that the backbone conformation is an important issue for improving the intermolecular interaction of conjugated polymers, and hence provides a guideline for the molecular design of conjugated polymers.
Co-reporter:Shaoqing Zhang, Long Ye, Wenchao Zhao, Delong Liu, Huifeng Yao, and Jianhui Hou
Macromolecules 2014 Volume 47(Issue 14) pp:4653-4659
Publication Date(Web):July 9, 2014
DOI:10.1021/ma500829r
Recently, the benzodithiophene- (BDT-) based polymers with conjugated side groups attracted considerable attention due to their superior properties in polymer solar cells (PSCs), so the investigation of the side chain effects on the photovoltaic properties of this type of polymers is an interesting and important topic for molecular design. Herein, three conjugated polymers based on BDT and thieno[3,4-b]thiophene units with furan, thiophene and selenophene as side groups, named as PBDTTT-EFF, PBDTTT-EFT, and PBDTTT-EFS, were synthesized and applied in polymer solar cells. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), density functional theory (DFT), ultraviolet photoemission spectroscopy (UPS), X-ray diffraction (XRD), and photovoltaic measurements. The results show that the dihedral angles between the BDT and conjugated side groups play important roles in affecting the absorption bands, HOMO levels, crystallinities, and aggregation sizes of the polymers. The photovoltaic results indicate that PBDTTT-EFT and PBDTTT-EFS show similar photovoltaic characteristics in device, and PCEs of 9.0% and 8.78% were obtained, respectively. The device of PBDTTT-EFF shows a Voc of 0.69 V and a Jsc of 11.77 mA/cm2, which are lower than those in the devices based on the other two polymers. Overall, this work suggests that the photovoltaic properties of the BDT-based polymers can be effectively tuned by introducing conjugated side groups with varied steric hindrance.
Co-reporter:Xin Zhang;Zhenhuan Lu;Long Ye;Chuanlang Zhan;Shaoqing Zhang;Bo Jiang;Yan Zhao;Jianhua Huang;Shanlin Zhang;Yang Liu;Qiang Shi;Yunqi Liu;Jiannian Yao
Advanced Materials 2013 Volume 25( Issue 40) pp:5791-5797
Publication Date(Web):
DOI:10.1002/adma.201300897
Co-reporter:Deping Qian ; Wei Ma ; Zhaojun Li ; Xia Guo ; Shaoqing Zhang ; Long Ye ; Harald Ade ; Zhan’ao Tan
Journal of the American Chemical Society 2013 Volume 135(Issue 23) pp:8464-8467
Publication Date(Web):May 24, 2013
DOI:10.1021/ja402971d
A novel polythiophene derivative, PBT1, was designed, synthesized, and applied in polymer solar cells (PSCs). This work provides a successful example of using molecular structure as a tool to realize optimal photovoltaic performance with high polymer content, thus enabling the realization of efficient photoabsorption in very thin films. As a result, an efficiency of 6.88% was recorded in a PSC with a 75 nm active layer.
Co-reporter:Zhi-Guo Zhang, Hui Li, Boyuan Qi, Dan Chi, Zhiwen Jin, Zhe Qi, Jianhui Hou, Yongfang Li and Jizheng Wang
Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:9624-9629
Publication Date(Web):05 Jul 2013
DOI:10.1039/C3TA12478A
An easy-accessible amine group functionalized fullerene derivative, DMAPA-C60, is explored as a cathode buffer layer (CBL) in polymer solar cells (PSCs) for our presently tested three different material systems, namely P3HT:PCBM, PBDTTT-C:PC70BM and PBDTTT-C-T:PC70BM. The power conversion efficiencies of the three systems with DMAPA-C60 as the CBL reach 3.88%, 6.29% and 7.42%, respectively, which are much higher than those of the corresponding PSCs with the Al-only cathode and even slightly higher than those of the corresponding Ca/Al devices of these systems. The DMAPA-C60 CBL also allows high work function metals (Ag, Cu, and Au) as cathodes.
Co-reporter:Wei Ma, Long Ye, Shaoqing Zhang, Jianhui Hou and Harald Ade
Journal of Materials Chemistry A 2013 vol. 1(Issue 33) pp:5023-5030
Publication Date(Web):27 Jun 2013
DOI:10.1039/C3TC30679H
Thermal annealing and additive processing are employed and compared using alkoxy substituted (QxO) and extended π conjugated alkythienyl substituted (QxT) benzo[1,2-b:4,5 b′]dithiophene based heterojunction (BHJ) solar cells. The characteristic median length of the morphology, average composition fluctuations, interface structure, crystallinity and molecular miscibility are investigated based on these two processes. Our results suggest that focusing on single structural, morphological or thermodynamic measurements is not sufficient to explain differences in device performance. In the current work, no blends are close to the ideal morphology containing either domains that are too large, too mixed or too pure. An optimization strategy is proposed to improve those devices. Importantly, we find that domain size and relative domain purity are overall correlated with molecular miscibility, i.e. the more immiscible system induces larger and purer domains irrespective of the processing and even in non-equilibrium structures. This indicates that the relative domain size and purity, and device performance can be potentially predicted by the donor–acceptor molecular miscibility, a factor not yet widely considered when designing new materials for BHJ devices.
Co-reporter:Weina Yong, Maojie Zhang, Xiaodong Xin, Zhaojun Li, Yue Wu, Xia Guo, Zhou Yang and Jianhui Hou
Journal of Materials Chemistry A 2013 vol. 1(Issue 45) pp:14214-14220
Publication Date(Web):09 Sep 2013
DOI:10.1039/C3TA12229H
A novel small molecule with a acceptor–donor–acceptor (A–D–A) structure, IDT(BTTh2)2, containing an electron-rich indacenodithiophene (IDT) unit as core, flanked by electron-deficient 2,1,3-benzothiadiazole (BT) units and end-capped with hexyl-substituted bithiophene units, has been synthesized for photovoltaic application. IDT(BTTh2)2 shows a broad absorption in the visible range with an optical band gap of ca. 1.80 eV and possesses a relatively deep HOMO level at −5.21 eV. The solution-processed bulk heterojunction solar cells based on the blend of IDT(BTTh2)2/PC71BM (1:3, w/w) without using any treatment such as a solvent additive or thermal annealing, showed a power conversion efficiency (PCE) of 4.25% with a high open-circuit voltage (Voc) of 0.93 V, a short-circuit current (Jsc) of 9.42 mA cm−2 and a fill factor (FF) of 48.5%, under the illumination of AM 1.5G at 100 mW cm−2. These results indicate that indacenodithiophene-based small molecules are promising for bulk heterojunction solar cells.
Co-reporter:Qi Xu, Fuzhi Wang, Deping Qian, Zhan’ao Tan, Liangjie Li, Shusheng Li, Xiaohe Tu, Gang Sun, Xuliang Hou, Jianhui Hou, and Yongfang Li
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 14) pp:6591
Publication Date(Web):June 19, 2013
DOI:10.1021/am401263m
An integrated device architecture was constructed via vertical combination of planar and bulk heterojunctions by solution processing, where a cross-linked D-A copolymer (PBDTTT-Br25) was inserted between a PEDOT:PSS layer and the blended photoactive layer. PBDTTT-Br25 can readily undergo photo crosslinking to form an insoluble robust film via ultraviolet irradiation after solution–deposition, which enables the subsequent solution processing of a photoactive layer on the robust surface. The insertion of a pure PBDTTT-Br25 layer to build an integrated heterojunction could provide an additional donor/acceptor interface, which enables hole transport to the anode without interruption, thereby reducing the charge carrier recombination probability. The power conversion efficiency (PCE) of the polymer solar cell (PSC) with the integrated architecture reaches 5.24% under an AM1.5G illumination of 100 mW/cm2, which is increased by 65%, in comparison with that of the reference single heterojunction device (3.17%), under the same experimental conditions.Keywords: bulk heterojunction solar cells; D-A copolymer; integrated architecture; photo-cross-linkable conjugated polymers; planar solar cells;
Co-reporter:Long Ye, Yan Jing, Xia Guo, Hao Sun, Shaoqing Zhang, Maojie Zhang, Lijun Huo, and Jianhui Hou
The Journal of Physical Chemistry C 2013 Volume 117(Issue 29) pp:14920-14928
Publication Date(Web):July 11, 2013
DOI:10.1021/jp404395q
Undesirable efficiency reproducibility was sometimes observed in fabrication of high performance polymer solar cell devices incorporating high boiling point additives. The anomalous results originated from the slow drying of additives not only reduced the controllability of device performance but also impeded the studies of device physics and material design. How to remove the residual additives and achieve stable interface properties is crucial for both the academic and industrial community. Herein, we demonstrated that the morphological stability is enhanced and efficiency reproducibility is increased obviously from 7.07 ± 0.27% to 7.53 ± 0.12% after spin-coating inert solvents for the PBDTTT-C-T/PCBM system. The relationship between processing conditions and photovoltaic performance was well explored and demonstrated via multiple techniques including atomic force microscopy, Kelvin probe force microscopy, transmission electron microscopy, and X-ray photospectroscopy. Most importantly, this method was successfully employed in more than five representative donor polymers. Our study suggested that the slow drying process of the residual high boiling point additives could induce undesirable morphological variation as well as unfavorable interfacial contact, and by washing with low boiling point “inert” solvent, like methanol, the negative influence caused by the residual additive can be avoided and hence the additives would perform more efficiently in the optimization of device performance of highly efficient PSCs.
Co-reporter:Deping Qian;Qi Xu;Xuliang Hou;Fuzhi Wang;Zhan'ao Tan
Journal of Polymer Science Part A: Polymer Chemistry 2013 Volume 51( Issue 15) pp:3123-3131
Publication Date(Web):
DOI:10.1002/pola.26695
ABSTRACT
Novel bromine-functionalized photocrosslinkable low-bandgap copolymers, PBDTTT-Br25 and PBDTTT-Br50, are synthesized via Stille cross-coupling polymerization for the purpose of stabilizing the film morphology in polymer solar cells (PSCs). Photocrosslinking of PBDTTT-Br25 and PBDTTT-Br50 copolymers dramatically improves the solvent resistance of the active layer without disrupting the molecular ordering and charge transport, which is confirmed by the insolubility of the films washed by organic solvents and by their thermal behavior. As a result, the formation of large aggregations of fullerene is suppressed in polymer:fullerene blend films even after prolonged thermal annealing, and the stability of the device is enhanced when compared with cells based on noncrosslinkable PBDTTT. The power conversion efficiency of the PSCs based on PBDTTT-Br25 and PBDTTT-Br50 reaches 5.17% and 4.48%, respectively, which is improved obviously in comparison with that (4.26%) of the PSCs based on the control polymer PBDTTT. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3123–3131
Co-reporter:Long Ye, Shaoqing Zhang, Deping Qian, Qi Wang, and Jianhui Hou
The Journal of Physical Chemistry C 2013 Volume 117(Issue 48) pp:25360-25366
Publication Date(Web):November 25, 2013
DOI:10.1021/jp409216e
In recent years, fullerene bis-adducts have gained significant interest within the academic community due to their high-lying LUMO level. Herein, we carried out device optimization of the photovoltaic performances of novel photovoltaic polymer PBDTBDD with Bis-PCBM, and several characterization techniques including photoluminescence quench analysis, X-ray diffraction patterns, and atomic force microscopy were employed. As the synergistic result of balanced mobility, better crystallinity, efficient exciton dissociation, and charge transport efficiency, high fill factor and short-circuit current density as well as power conversion efficiency were achieved in the PBDTBDD/Bis-PCBM device. In addition, the optimized PSC device based on PBDTBDD:Bis-PCBM (1:1, wt/wt) with 3 vol % DIO yielded a high PCE of 6.07% with Voc of 1.00 V, Jsc of 10.02 mA/cm2, and FF of 60.54% under the illumination of AM1.5G, 100 mW/cm2. Therefore, we reported that polymer/Bis-PCBM-based polymer solar cells obtain both high efficiency ∼6% and high Voc ≈ 1 V, which exhibited PBDTBDD/Bis-PCBM and is a promising blue absorber unit for tandem devices, and also paved a path to optimization of other polymer/Bis-PCBM systems.
Co-reporter:Xia Guo, Maojie Zhang, Lijun Huo, Feng Xu, Yue Wu and Jianhui Hou
Journal of Materials Chemistry A 2012 vol. 22(Issue 39) pp:21024-21031
Publication Date(Web):21 Aug 2012
DOI:10.1039/C2JM32931J
New low band gap copolymers PBDTT–DTTBT and PBDTT–DTBT using BDT-T and BT as donor and acceptor, with different π-bridge units thieno[3,2-b]thiophene and thiophene, respectively, were synthesized. The absorption spectra, electronic energy levels, and photovoltaic properties of the polymers were characterized. PBDTT–DTTBT and PBDTT–DTBT films show broad absorption in the visible range with an absorption edge at over 751 nm, and possess relatively low-lying HOMO levels at −5.11 eV and 5.15 eV. A high hole mobility of 1.97 × 10−3 cm2 V−1 s−1 was recorded for PBDTT–DTTBT, that is two orders of magnitude higher than PBDTT–DTBT (1.58 × 10−5 cm2 V−1 s−1), which is ascribed to the application of thieno[3,2-b]thiophene as π-bridge units. The PCE of the PSC device based on PBDTT–DTTBT/PC70BM (1:1, w/w) reached 6.03% with a Jsc of 12.46 mA cm−2, a Voc of 0.78 V and a FF of 0.62, while PBDTT–DTBT/PC70BM (1:1, w/w) only has a PCE of 2.34% with a Voc of 0.82 V, a Jsc of 5.78 mA cm−2 and a FF of 0.495 under the illumination of AM 1.5 G, 100 mW cm−2. These results indicate that PBDTT–DTTBT is a promising photovoltaic material. Furthermore, it can be concluded that extending the conjugation of the backbone units, as demonstrated in this work, has little influence on the molecular energy levels, but can be seen as a feasible strategy to improve the photovoltaic properties of D–π–A conjugated polymers by enhancing intermolecular interactions.
Co-reporter:Yue Wu, Zhaojun Li, Xia Guo, Huili Fan, Lijun Huo and Jianhui Hou
Journal of Materials Chemistry A 2012 vol. 22(Issue 40) pp:21362-21365
Publication Date(Web):31 Aug 2012
DOI:10.1039/C2JM34629J
A feasible synthetic route to alkoxy-substituted DTBDT was designed and the first DTBDT-based polymer was prepared and applied in organic solar cells. The preliminary results indicate that the DTBDT unit can be used as a potential building block in organic semiconductor materials.
Co-reporter:Ye Huang, Mingqian Zhang, Long Ye, Xia Guo, Charles C. Han, Yongfang Li and Jianhui Hou
Journal of Materials Chemistry A 2012 vol. 22(Issue 12) pp:5700-5705
Publication Date(Web):13 Feb 2012
DOI:10.1039/C2JM16474D
An investigation on the opto-electronic and photovoltaic properties of a pair of alkoxy substituted quinoxaline-based copolymers PTTQx is performed in order to describe the effect of changing the position of alkoxy substituents on the peripheral phenyl rings. The copolymer with meta-positioned alkoxy showed lower HOMO and LUMO levels and a higher Voc of 0.73 V, while the copolymer with para-positioned alkoxy displayed higher HOMO and LUMO levels and lower Voc of 0.60 V when a polymer/PC71BM blend film was used as the active layer in polymer solar cells (PSCs) under AM 1.5 G irradiation (100 mW cm−2). With the good agreement between theoretical calculation and experimental observation, it has been observed that the effect of the substituents depends on the position of the alkoxy group which exhibits a stronger electron donating effect in the para-position than in the meta-position. The resonance electron donating effect of the alkoxy group on the para-position can elevate the HOMO and LUMO levels simultaneously, while this effect is not obviously reflected on the meta-position. Therefore, PTTQx-m exhibits lower HOMO level, higher Voc correspondingly and thereby higher PCE of the PSCs based on it.
Co-reporter:Lijun Huo, Ye Huang, Benhu Fan, Xia Guo, Yan Jing, Maojie Zhang, Yongfang Li and Jianhui Hou
Chemical Communications 2012 vol. 48(Issue 27) pp:3318-3320
Publication Date(Web):13 Feb 2012
DOI:10.1039/C2CC17708K
A new building block of benzo[1,2-b:4,5-b′]difuran (BDF) was firstly designed and synthesized. The newly designed unit was applied for constructing a new photovoltaic low band gap polymer, PBDFDTBT, which exhibited promising power conversion efficiency of 5.0%.
Co-reporter:Ruomeng Duan, Long Ye, Xia Guo, Ye Huang, Peng Wang, Shaoqing Zhang, Jianping Zhang, Lijun Huo, and Jianhui Hou
Macromolecules 2012 Volume 45(Issue 7) pp:3032-3038
Publication Date(Web):March 20, 2012
DOI:10.1021/ma300060z
Two new donor–acceptor (D–A) alternative copolymers, PBDTDTQx-T and PBDTDTQx-O, were designed and synthesized to investigate the influence of two-dimensional conjugated structure on photovoltaic properties of conjugated polymers. In these two polymers, PBDTDTQx-O was used as control material, which is an alternative copolymer based on a quinoxaline derivative (DTQx) and alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-O) unit; PBDTDTQx-T has an identical conjugated backbone as PBDTDTQx-O, but a simple two-dimensional conjugated BDT unit (BDT-T) was used to replace the alkoxy-BDT. The polymers were characterized by TGA, UV–vis absorption, electrochemical cyclic voltammetry, hole mobility of space-charge-limited current (SCLC) model, and photovoltaic measurements. It was found that PBDTDTQx-T exhibits similar molecular energy levels and higher hole mobility than PBDTDTQx-O. The power conversion efficiency (PCE) of the polymer solar cells (PSCs) based on PBDTDTQx-T: [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) = 1/2 (w/w) reached ∼5%, which is 60% higher than that of PBDTDTQx-O-based PSC. On the basis of these results, it can be concluded that the application of two-dimensional conjugated structure would be a feasible approach to improve photovoltaic properties of conjugated polymers.
Co-reporter:Deping Qian, Long Ye, Maojie Zhang, Yongri Liang, Liangjie Li, Ye Huang, Xia Guo, Shaoqing Zhang, Zhan’ao Tan, and Jianhui Hou
Macromolecules 2012 Volume 45(Issue 24) pp:9611-9617
Publication Date(Web):December 6, 2012
DOI:10.1021/ma301900h
A new conjugated polymer based on 5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, named as PBDTBDD, was designed, synthesized, and applied in polymer solar cells (PSCs). A power conversion efficiency (PCE) of 6.67% was obtained from the PBDTBDD/PC61BM-based PSC, which is a remarkable result for the PSCs using PC61BM as electron acceptor. The PBDTBDD/PC61BM-based device exhibits a narrow absorption band and excellent quantum efficiency in the range from 500 to 700 nm. Furthermore, PBDTBDD shows a strong aggregation effect in solution state, and the study indicates that although the temperature used in solution preparation has little influence on molecular orientation as well as crystallinity of the D/A blend, it plays an important role in forming proper domain size in the blend. This work provides a good example to reveal the correlation between the morphology of the blend films and the processing temperature of the solution preparation. Furthermore, the study in this work suggests an interesting and feasible approach to modulate domain size without changing crystallinity of the blend films in PSCs.
Co-reporter:Xia Guo, Maojie Zhang, Lijun Huo, Chaohua Cui, Yue Wu, Jianhui Hou, and Yongfang Li
Macromolecules 2012 Volume 45(Issue 17) pp:6930-6937
Publication Date(Web):August 23, 2012
DOI:10.1021/ma301269f
A new D–A copolymer, poly(thieno[3,2-b]thiophene-alt-bithiazole) (PTTBTz), based on thieno[3,2-b]thiophene donor unit and bithiazole acceptor unit, was synthesized by the Pd-catalyzed Stille-coupling reaction for the application as donor material in polymer solar cells (PSCs). PTTBTz film possesses high thermal stability with 5% weight-loss temperature at 450 °C, a lower-lying HOMO energy level at −5.20 eV, a higher hole mobility of 6.45 × 10–3 cm2/(V s), and a crystalline structure. Photovoltaic performance of the polymer was investigated with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) or indene-C60 bisadduct (ICBA) as acceptor and with 3% DIO additive. The power conversion efficiency (PCE) of the PSC based on PTTBTz:ICBA (1:1 w/w) reached 5.35% with a high Voc of 1.03 V, a Jsc of 8.55 mA/cm2, and an FF of 0.608, whereas the PCE of the PSC based on PTTBTz:PC70BM (1:1 w/w) was 4.57% with a Voc of 0.82 V, a Jsc of 9.89 mA/cm2, and an FF of 0.563, under the illumination of AM1.5, 100 mW/cm2. PTTBTz is one of the D–A copolymers that shows better photovoltaic performance with ICBA as acceptor than PC70BM. PTTBTz/ICBA could be a promising front active layer for high-efficiency tandem PSC because of its high Voc.
Co-reporter:Lijun Huo, Long Ye, Yue Wu, Zhaojun Li, Xia Guo, Maojie Zhang, Shaoqing Zhang, and Jianhui Hou
Macromolecules 2012 Volume 45(Issue 17) pp:6923-6929
Publication Date(Web):August 22, 2012
DOI:10.1021/ma301254x
In order to investigate the influence of two-dimensional (2D) conjugated structure on photovoltaic properties of benzo[1,2-b:4,5-b′]difuran (BDF)-based polymers, two low band gap photovoltaic polymers, named PBDFTT-CF-O and PBDFTT-CF-T, were designed and synthesized. These two polymers have the same backbones and different side groups. Although these two polymers show similar optical band gaps (ca. 1.5 eV), the polymer with alkylthienyl side groups, PBDFTT-CF-T, exhibits stronger absorption in long wavelength direction than the polymer with alkoxyl side groups, PBDFTT-CF-O. Meanwhile, PBDFTT-CF-T exhibits a HOMO level of −5.21 eV, which is 0.23 eV lower than that of PBDFTT-CF-O due to weaker electron-donating ability of alkylthienyl side groups than that of aloxyl side groups. The hole mobility of the blend of PBDFTT-CF-T/PC71BM (1:1.5, w/w) is 0.128 cm2 V–1 s–1, which is 1 order of magnitude higher than that of the blend of PBDFTT-CF-O/PC71BM. Density functional theory (DFT) model shows thiophene pendants on dithienyl-BDF are more coplanar than it on dithienyl-BDT. These results indicate that the 2D-conjugated structure is helpful for molecular structure design of the BDF-based polymers in enhancing the intermolecular π–π stacking and improving charge transport property. Furthermore, the photovoltaic devices based on these two polymers show similar short circuit density and fill factor values, while the open circuit voltage of the PBDFTT-CF-T-based device is 0.78 V, which is 0.15 V higher than that of the PBDFTT-CF-O-based device. Therefore, the efficiencies of the devices based PBDFTT-CF-T/PC71BM and PBDFTT-CF-O/PC71BM are 6.26% and 5.22%, respectively. The results in this work demonstrate that the weak electron-donating ability of alkylthienyl side groups can be seen as an effective strategy to improve photovoltaic properties of the BDF-based polymers and the 2D-conjugated molecular structure is favorable to improve hole mobility.
Co-reporter:Ye Huang, Lijun Huo, Shaoqing Zhang, Xia Guo, Charles C. Han, Yongfang Li and Jianhui Hou
Chemical Communications 2011 vol. 47(Issue 31) pp:8904-8906
Publication Date(Web):20 Jun 2011
DOI:10.1039/C1CC12575C
A strong electron-withdrawing group, sulfonyl, was firstly introduced to a semiconducting polymer, PBDTTT-S. The PCE of the PBDTTT-S device reached 6.22% with a high open-circuit voltage of 0.76 V. The sulfonyl group is thus a promising candidate as a strong electron-withdrawing group applied to high-efficiency PSCs.
Co-reporter:Lijun Huo, Xia Guo, Yongfang Li and Jianhui Hou
Chemical Communications 2011 vol. 47(Issue 31) pp:8850-8852
Publication Date(Web):28 Jun 2011
DOI:10.1039/C1CC12643A
A planar benzodithiophene with lower HOMO was copolymerized with the thieno[3,4-b]thiophene unit to obtain a new low band gap polymer of PBDPTT-C, which exhibited a higher open-circuit voltage (Voc) of 0.8 V and a promising efficiency of 5.2%.
Co-reporter:Lijun Huo and Jianhui Hou
Polymer Chemistry 2011 vol. 2(Issue 11) pp:2453-2461
Publication Date(Web):10 Aug 2011
DOI:10.1039/C1PY00197C
To pursue high power conversion efficiency (PCE) of polymer solar cells (PSCs), more and more new active layer materials, especially polymeric photovoltaic materials, have been developed in the past several years, and benzo[1,2-b:4,5-b′]dithiophene (BDT) plays a very important role in these polymer materials. The applications of these new polymer materials boost the PCE of polymer solar cells greatly, and recent results indicate that 7–8% PCEs have been achieved by using BDT-based polymers. In this review, we summarize the recent works related to BDT-based polymers for the applications in PSCs and try to reveal the correlations of molecular structures of BDT-based polymers with their band gaps and molecular energy levels.
Co-reporter:Lijun Huo, Xia Guo, Shaoqing Zhang, Yongfang Li, and Jianhui Hou
Macromolecules 2011 Volume 44(Issue 11) pp:4035-4037
Publication Date(Web):May 5, 2011
DOI:10.1021/ma200743b
Co-reporter:Dr. Lijun Huo;Shaoqing Zhang;Xia Guo;Feng Xu; Yongfang Li; Jianhui Hou
Angewandte Chemie International Edition 2011 Volume 50( Issue 41) pp:9697-9702
Publication Date(Web):
DOI:10.1002/anie.201103313
Co-reporter:Wanning Li, Shaoqing Zhang, Hao Zhang, Jianhui Hou
Organic Electronics (May 2017) Volume 44() pp:42-49
Publication Date(Web):May 2017
DOI:10.1016/j.orgel.2017.01.036
Co-reporter:Wei Jiang, Long Ye, Xiangguang Li, Chengyi Xiao, Fang Tan, Wenchao Zhao, Jianhui Hou and Zhaohui Wang
Chemical Communications 2014 - vol. 50(Issue 8) pp:NaN1026-1026
Publication Date(Web):2013/10/30
DOI:10.1039/C3CC47204C
A series of bay-linked perylene bisimides as non-fullerene acceptors for organic solar cells are designed. The best power conversion efficiency up to 3.63% based on s-diPBI (1b) is demonstrated by fine-tuning optoelectronic properties resulting from different degrees of twisting and flexibility by bay-linkages.
Co-reporter:Lijun Huo, Ye Huang, Benhu Fan, Xia Guo, Yan Jing, Maojie Zhang, Yongfang Li and Jianhui Hou
Chemical Communications 2012 - vol. 48(Issue 27) pp:NaN3320-3320
Publication Date(Web):2012/02/13
DOI:10.1039/C2CC17708K
A new building block of benzo[1,2-b:4,5-b′]difuran (BDF) was firstly designed and synthesized. The newly designed unit was applied for constructing a new photovoltaic low band gap polymer, PBDFDTBT, which exhibited promising power conversion efficiency of 5.0%.
Co-reporter:Lijun Huo, Xia Guo, Yongfang Li and Jianhui Hou
Chemical Communications 2011 - vol. 47(Issue 31) pp:NaN8852-8852
Publication Date(Web):2011/06/28
DOI:10.1039/C1CC12643A
A planar benzodithiophene with lower HOMO was copolymerized with the thieno[3,4-b]thiophene unit to obtain a new low band gap polymer of PBDPTT-C, which exhibited a higher open-circuit voltage (Voc) of 0.8 V and a promising efficiency of 5.2%.
Co-reporter:Ye Huang, Lijun Huo, Shaoqing Zhang, Xia Guo, Charles C. Han, Yongfang Li and Jianhui Hou
Chemical Communications 2011 - vol. 47(Issue 31) pp:NaN8906-8906
Publication Date(Web):2011/06/20
DOI:10.1039/C1CC12575C
A strong electron-withdrawing group, sulfonyl, was firstly introduced to a semiconducting polymer, PBDTTT-S. The PCE of the PBDTTT-S device reached 6.22% with a high open-circuit voltage of 0.76 V. The sulfonyl group is thus a promising candidate as a strong electron-withdrawing group applied to high-efficiency PSCs.
Co-reporter:Kang Zhao, Qi Wang, Bowei Xu, Wenchao Zhao, Xiaoyu Liu, Bei Yang, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2016 - vol. 4(Issue 24) pp:NaN9518-9518
Publication Date(Web):2016/05/23
DOI:10.1039/C6TA03288E
Two wide band gap (WBG) polymers based on thiophene-thiazolothiazole (TTz) units, PBT-TTz and PBT-S-TTz, were synthesized. Both polymers showed absorption onsets at 635 nm in solid films. Although PBT-TTz and PBT-S-TTz are WBG materials with relatively narrow absorption spectra, they have great potential for constructing high-performance polymer solar cells (PSCs). By replacing the alkyl side chain of PBT-TTz with an alkylthiol side chain, the HOMO level of PBT-S-TTz was lowered to −5.45 eV. A PCE of 7.92% was then obtained in a single-junction PSC device based on a PBT-S-TTz:PC71BM active layer. Moreover, high-performance fullerene-free PSCs were fabricated using these polymers and a high PCE of 8.22% was achieved. This work demonstrates that TTz-based polymers PBT-TTz and PBT-S-TTz are promising candidates as efficient WBG polymers for constructing high-performance PSC devices.
Co-reporter:Wenchao Zhao, Long Ye, Shaoqing Zhang, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2015 - vol. 3(Issue 24) pp:NaN12729-12729
Publication Date(Web):2015/05/08
DOI:10.1039/C4TA07029A
Power conversion efficiencies (PCEs) of state-of-the-art polymer solar cells (PSCs) have been promoted to over 9%. However, halogenated solvents like chlorobenzene (CB), o-dichlorobenzene (DCB), 1,8-diiodooctane (DIO) or their mixtures are still predominately used in the fabrication of these high performance PSCs. With the rapid progress in PCEs, removing the halogenated solvents from the fabrication processes of PSCs becomes an urgent task for the practical utilization of PSC technology. In this study, a halogen-free solvent system consisting of o-xylene (XY) and N-methylpyrrolidone (NMP) was successfully applied in the fabrication of the PSCs based on a variety of highly efficient polymers including PBDT-TS1 and other eight types of photovoltaic polymers. Notably, utilizing an XY–2% NMP mixture as a processing solvent, the PBDT-TS1/PC71BM-based PSC realized a PCE of 9.47%, which has been the highest value in halogen-free solvent processed PSCs until now. The photovoltaic properties and nanoscale morphology clearly indicated that the halogen-free solvent system featuring the XY–NMP mixture can replace the role of the widely utilized halogenated solvents in fabricating environmentally friendly PSCs with high efficiency.
Co-reporter:Weina Yong, Maojie Zhang, Xiaodong Xin, Zhaojun Li, Yue Wu, Xia Guo, Zhou Yang and Jianhui Hou
Journal of Materials Chemistry A 2013 - vol. 1(Issue 45) pp:NaN14220-14220
Publication Date(Web):2013/09/09
DOI:10.1039/C3TA12229H
A novel small molecule with a acceptor–donor–acceptor (A–D–A) structure, IDT(BTTh2)2, containing an electron-rich indacenodithiophene (IDT) unit as core, flanked by electron-deficient 2,1,3-benzothiadiazole (BT) units and end-capped with hexyl-substituted bithiophene units, has been synthesized for photovoltaic application. IDT(BTTh2)2 shows a broad absorption in the visible range with an optical band gap of ca. 1.80 eV and possesses a relatively deep HOMO level at −5.21 eV. The solution-processed bulk heterojunction solar cells based on the blend of IDT(BTTh2)2/PC71BM (1:3, w/w) without using any treatment such as a solvent additive or thermal annealing, showed a power conversion efficiency (PCE) of 4.25% with a high open-circuit voltage (Voc) of 0.93 V, a short-circuit current (Jsc) of 9.42 mA cm−2 and a fill factor (FF) of 48.5%, under the illumination of AM 1.5G at 100 mW cm−2. These results indicate that indacenodithiophene-based small molecules are promising for bulk heterojunction solar cells.
Co-reporter:Kang Zhao, Long Ye, Wenchao Zhao, Shaoqing Zhang, Huifeng Yao, Bowei Xu, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN9571-9571
Publication Date(Web):2015/08/11
DOI:10.1039/C5TC02172C
In this contribution, a novel cathode interlayer material (NDIO) based on naphthalene diimide was successfully prepared by a facile two-step reaction from commercially available compounds. NDIO exhibited excellent water solubility, high transparency in the visible light region, and well-matched molecular energy levels. By incorporating this novel water processed cathode interlayer, a high power conversion efficiency of 9.51% was recorded in PBDT-TS1/PC71BM-based polymer photovoltaic cells (PPCs), and the value is nearly 2-fold the device efficiency of PPCs without the cathode interlayer. More importantly, the insertion of the NDIO interlayer promotes the device efficiency of polymer/polymer photovoltaic cells based on PBDTTT-EFT/N2200 from 3.23% up to 5.77%. The successful applications in both polymer/PCBM and polymer/polymer blend-based inverted PPCs make NDIO a promising cathode interlayer for realizing aqueous processed polymer photovoltaic cells with high performance.
Co-reporter:Ye Huang, Mingqian Zhang, Long Ye, Xia Guo, Charles C. Han, Yongfang Li and Jianhui Hou
Journal of Materials Chemistry A 2012 - vol. 22(Issue 12) pp:NaN5705-5705
Publication Date(Web):2012/02/13
DOI:10.1039/C2JM16474D
An investigation on the opto-electronic and photovoltaic properties of a pair of alkoxy substituted quinoxaline-based copolymers PTTQx is performed in order to describe the effect of changing the position of alkoxy substituents on the peripheral phenyl rings. The copolymer with meta-positioned alkoxy showed lower HOMO and LUMO levels and a higher Voc of 0.73 V, while the copolymer with para-positioned alkoxy displayed higher HOMO and LUMO levels and lower Voc of 0.60 V when a polymer/PC71BM blend film was used as the active layer in polymer solar cells (PSCs) under AM 1.5 G irradiation (100 mW cm−2). With the good agreement between theoretical calculation and experimental observation, it has been observed that the effect of the substituents depends on the position of the alkoxy group which exhibits a stronger electron donating effect in the para-position than in the meta-position. The resonance electron donating effect of the alkoxy group on the para-position can elevate the HOMO and LUMO levels simultaneously, while this effect is not obviously reflected on the meta-position. Therefore, PTTQx-m exhibits lower HOMO level, higher Voc correspondingly and thereby higher PCE of the PSCs based on it.
Co-reporter:Wei Ma, Long Ye, Shaoqing Zhang, Jianhui Hou and Harald Ade
Journal of Materials Chemistry A 2013 - vol. 1(Issue 33) pp:NaN5030-5030
Publication Date(Web):2013/06/27
DOI:10.1039/C3TC30679H
Thermal annealing and additive processing are employed and compared using alkoxy substituted (QxO) and extended π conjugated alkythienyl substituted (QxT) benzo[1,2-b:4,5 b′]dithiophene based heterojunction (BHJ) solar cells. The characteristic median length of the morphology, average composition fluctuations, interface structure, crystallinity and molecular miscibility are investigated based on these two processes. Our results suggest that focusing on single structural, morphological or thermodynamic measurements is not sufficient to explain differences in device performance. In the current work, no blends are close to the ideal morphology containing either domains that are too large, too mixed or too pure. An optimization strategy is proposed to improve those devices. Importantly, we find that domain size and relative domain purity are overall correlated with molecular miscibility, i.e. the more immiscible system induces larger and purer domains irrespective of the processing and even in non-equilibrium structures. This indicates that the relative domain size and purity, and device performance can be potentially predicted by the donor–acceptor molecular miscibility, a factor not yet widely considered when designing new materials for BHJ devices.
Co-reporter:Xia Guo, Maojie Zhang, Lijun Huo, Feng Xu, Yue Wu and Jianhui Hou
Journal of Materials Chemistry A 2012 - vol. 22(Issue 39) pp:NaN21031-21031
Publication Date(Web):2012/08/21
DOI:10.1039/C2JM32931J
New low band gap copolymers PBDTT–DTTBT and PBDTT–DTBT using BDT-T and BT as donor and acceptor, with different π-bridge units thieno[3,2-b]thiophene and thiophene, respectively, were synthesized. The absorption spectra, electronic energy levels, and photovoltaic properties of the polymers were characterized. PBDTT–DTTBT and PBDTT–DTBT films show broad absorption in the visible range with an absorption edge at over 751 nm, and possess relatively low-lying HOMO levels at −5.11 eV and 5.15 eV. A high hole mobility of 1.97 × 10−3 cm2 V−1 s−1 was recorded for PBDTT–DTTBT, that is two orders of magnitude higher than PBDTT–DTBT (1.58 × 10−5 cm2 V−1 s−1), which is ascribed to the application of thieno[3,2-b]thiophene as π-bridge units. The PCE of the PSC device based on PBDTT–DTTBT/PC70BM (1:1, w/w) reached 6.03% with a Jsc of 12.46 mA cm−2, a Voc of 0.78 V and a FF of 0.62, while PBDTT–DTBT/PC70BM (1:1, w/w) only has a PCE of 2.34% with a Voc of 0.82 V, a Jsc of 5.78 mA cm−2 and a FF of 0.495 under the illumination of AM 1.5 G, 100 mW cm−2. These results indicate that PBDTT–DTTBT is a promising photovoltaic material. Furthermore, it can be concluded that extending the conjugation of the backbone units, as demonstrated in this work, has little influence on the molecular energy levels, but can be seen as a feasible strategy to improve the photovoltaic properties of D–π–A conjugated polymers by enhancing intermolecular interactions.
Co-reporter:Hao Zhang, Shaoqing Zhang, Ke Gao, Feng Liu, Huifeng Yao, Bei Yang, Chang He, Thomas P. Russell and Jianhui Hou
Journal of Materials Chemistry A 2017 - vol. 5(Issue 21) pp:NaN10423-10423
Publication Date(Web):2017/04/29
DOI:10.1039/C7TA01250K
A new conjugated polymer utilizing diketopyrrolopyrrole (DPP) and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) units as the backbone framework was designed, synthesized, and applied in polymer solar cells. A high efficiency of 9.18% was obtained using phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor, which was among the best results obtained for DPP-based photovoltaic polymers. Absorption spectra indicated that the new polymer exhibits a narrow optical band-gap and strong aggregation behavior in the solution state. It was found that by dissolving the donor and acceptor in different solvents and then mixing them before film casting, better performing solar cell devices and distinct film morphology could be achieved, rather than by dissolution in one solvent. Small-angle neutron scattering (SANS) profiles showed that PC71BM in solution impaired polymer aggregate formation, because of its favorable interaction with the polymer chain. This study demonstrated the importance of manipulating the aggregation state in bulk heterojunction solar cell fabrication and revealed the influence of polymer-fullerene interplay on the blend film morphology.
Co-reporter:Yue Wu, Zhaojun Li, Xia Guo, Huili Fan, Lijun Huo and Jianhui Hou
Journal of Materials Chemistry A 2012 - vol. 22(Issue 40) pp:NaN21365-21365
Publication Date(Web):2012/08/31
DOI:10.1039/C2JM34629J
A feasible synthetic route to alkoxy-substituted DTBDT was designed and the first DTBDT-based polymer was prepared and applied in organic solar cells. The preliminary results indicate that the DTBDT unit can be used as a potential building block in organic semiconductor materials.
Co-reporter:Long Ye, Chengyue Zhou, Haifeng Meng, Heng-Hsin Wu, Chi-Ching Lin, Hua-Hsien Liao, Shaoqing Zhang and Jianhui Hou
Journal of Materials Chemistry A 2015 - vol. 3(Issue 3) pp:NaN569-569
Publication Date(Web):2014/11/26
DOI:10.1039/C4TC02449D
Along with the advances in polymer solar cells (PSCs), the accurate evaluation of novel photovoltaic polymers with various band gaps is an important issue that should be concerned, as well as needs to be addressed at various research laboratories in the world. In this work, we have focused on PSCs by employing some of the most efficient and well-known low band gap (LBG) polymers, for instance, PBDTTT-C-T, PBDTBDD, PDPP3T, PTB7-Th, PSBTBT and PBDTTPD, and obtained the corresponding spectral-mismatch factors (MMFs) under various reference cell/solar simulator combinations. Generally, there still exists ±25% spectral error even for a simulator whose spectrum grade is labeled as AAA. The best way to accurately evaluate the power conversion efficiencies (PCEs) of LBG polymers is by choosing a combination of a spectral-matched-silicon-solar-cell (match to LBG polymer's spectral responsivity spectrum) and a Class AAA solar simulator. Furthermore, our results could provide guidance for the accurate measurements of organic molecules, perovskites, and related photovoltaic technologies.
Co-reporter:Zhi-Guo Zhang, Hui Li, Boyuan Qi, Dan Chi, Zhiwen Jin, Zhe Qi, Jianhui Hou, Yongfang Li and Jizheng Wang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN9629-9629
Publication Date(Web):2013/07/05
DOI:10.1039/C3TA12478A
An easy-accessible amine group functionalized fullerene derivative, DMAPA-C60, is explored as a cathode buffer layer (CBL) in polymer solar cells (PSCs) for our presently tested three different material systems, namely P3HT:PCBM, PBDTTT-C:PC70BM and PBDTTT-C-T:PC70BM. The power conversion efficiencies of the three systems with DMAPA-C60 as the CBL reach 3.88%, 6.29% and 7.42%, respectively, which are much higher than those of the corresponding PSCs with the Al-only cathode and even slightly higher than those of the corresponding Ca/Al devices of these systems. The DMAPA-C60 CBL also allows high work function metals (Ag, Cu, and Au) as cathodes.
Co-reporter:Yahui Liu, Wenchao Zhao, Yang Wu, Jicheng Zhang, Guangwu Li, Wenhua Li, Wei Ma, Jianhui Hou and Zhishan Bo
Journal of Materials Chemistry A 2016 - vol. 4(Issue 21) pp:NaN8104-8104
Publication Date(Web):2016/04/25
DOI:10.1039/C6TA02622B
Two kinds of new conjugated polymers (P1 and P2) with benzothiadiazole as the acceptor unit and thiophene as the donor unit were designed, synthesized and used as donor materials for polymer solar cells (PSCs). These polymers show a broad absorption in the visible region, a medium band gap of about 1.75 eV, and a low-lying HOMO energy level of about −5.65 eV. The open-circuit voltage (Voc) of both P1 and P2 was greatly improved to 0.85 V mainly due to the introduction of a carboxylate group at the 3-position of the thiophene spacer. Fluoro substitution on the polymer backbone of P2 can greatly enhance the interchain interaction, leading to a huge increase of short-circuit current density (Jsc). P2-based devices with the active layer spin-coated from 1,2-diclorobenzene (DCB) solutions that contain 1% 1,8-diiodooctane (DIO) and washed with methanol showed a synergistic positive effect, resulting in a significant enhancement of the power conversion efficiency (PCE) up to 8.67%. The PCE could be further improved by constructing inverted devices and the best efficiency of 9.26% was finally obtained. In addition, the mechanism for achieving such a high PCE for P2 based devices was also proposed based on the morphological analysis of the blend films by atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incident angle X-ray scattering (GIWAXS) and resonant soft X-ray scattering (RSoXS). The improvement can be ascribed to the enhanced molecular packing and proper phase separation of the blend films and the reduced charge recombination.
Co-reporter:Huifeng Yao, Wenchao Zhao, Zhong Zheng, Yong Cui, Jianqi Zhang, Zhixiang Wei and Jianhui Hou
Journal of Materials Chemistry A 2016 - vol. 4(Issue 5) pp:NaN1713-1713
Publication Date(Web):2015/12/22
DOI:10.1039/C5TA08614K
In this study, a regioregular copolymer (PBDT-TSR) based on alkythio-substituted two dimensional conjugated benzodithiophene (2D-BDT) and asymmetric thienothiophene (TT) was synthesized through two steps. Compared with its random counterpart PBDT-TS1, the PBDT-TSR shows improved absorption properties and enhanced inter-chain π–π packing effects. The hole mobility of PBDT-TSR is higher than that of PBDT-TS1. What's more, the enhancement of regioregularity does not have great influence on its molecular energy levels of the polymer and its miscibility with the acceptor material, PC71BM. The polymer solar cell (PSC) device fabricated by using PBDT-TSR shows a high power conversion efficiency of 10.2% with a short-circuit current density (JSC) of 17.99 mA cm−2, while the PBDT-TS1 shows a PCE of 9.74%. Overall, these results suggest that it is of great importance to investigate the influence of backbone configuration on photovoltaic performance for high efficiency conjugated polymers based on asymmetric conjugated building blocks, and to improve the regioregularity of this type of polymer should be a feasible approach to enhance their photovoltaic properties.
Co-reporter:Jie Zhu, Sunsun Li, Xiaoyu Liu, Huifeng Yao, Fenghao Wang, Shaoqing Zhang, Mingliang Sun and Jianhui Hou
Journal of Materials Chemistry A 2017 - vol. 5(Issue 29) pp:NaN15182-15182
Publication Date(Web):2017/06/23
DOI:10.1039/C7TA04431C
Four dithienoindaceno[1,2-b:5,6-b′]dithiophene (DT-IDT) based small molecules IT-O1, IT-O2, IT-O3 and IT-O4 with increasing alkoxyl chain length from methoxy to butoxy on the terminal-groups were synthesized to investigate the end-group side-chain effects on these acceptor–donor–acceptor-type small molecule electron acceptors. The optical absorption and energy levels of the four molecules, blend morphologies, carrier mobilities, and photovoltaic performances of the devices blended with the polymer PBDB-T are systematically investigated. Interestingly, both the solubility and electron mobility are enhanced for these materials with decrease in side chain length, which lead to ideal morphologies and balanced charge transport. Hence, increased Jsc and FF, and thus distinctly higher PCEs of 11.6% were obtained from the PBDB-T:IT-O1-based devices.
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