Lianjie Zhang

Name:

Organization: South China University of Technology

Department: Institute of Polymer Optoelectronic Materials & Devices, State Key Laboratory of Luminescent Materials & Devices

Title:

TOPICS

Polymer

Polymer Solar Cells

Chemicals
References

A Highly Crystalline Wide-Band-Gap Conjugated Polymer toward High-Performance As-Cast Nonfullerene Polymer Solar Cells

Co-reporter:Haiying Jiang, Zhen Wang, Lianjie Zhang, Anxing Zhong, Xuncheng Liu, Feilong Pan, Wanzhu Cai, Olle Inganäs, Yi Liu, Junwu Chen, and Yong Cao

ACS Applied Materials & Interfaces October 18, 2017 Volume 9(Issue 41) pp:36061-36061

Publication Date(Web):September 25, 2017

DOI:10.1021/acsami.7b10059

A new wide-band-gap conjugated polymer PBODT was successfully synthesized that showed high crystallinity and was utilized as the active material in nonfullerene bulk-heterojunction polymer solar cells (PSCs). The photovoltaic devices based on the as-cast blend films of PBODT with ITIC and IDIC acceptors showed notable power conversion efficiencies (PCEs) of 7.06% and 9.09%, with high open-circuit voltages of 1.00 and 0.93 V that correspond to low energy losses of 0.59 and 0.69 eV, respectively. In the case of PBODT:ITIC, lower exciton quenching efficiency and monomolecular recombination are found for devices with small driving force. On the other hand, the relatively higher driving force and suppressed monomolecular recombination for PBODT:IDIC devices are identified to be the reason for their higher short-circuit current density (Jsc) and higher PCEs. In addition, when processed with the nonchlorinated solvent 1,2,4-trimethylbenzene, a good PCE of 8.19% was still achieved for the IDIC-based device. Our work shows that such wide-band-gap polymers have great potential for the environmentally friendly fabrication of highly efficient PSCs.Keywords: bulk-heterojunction polymer solar cells; charge-transfer state; crystallinity; energy loss; nonfullerene acceptor; wide-band-gap polymer;

Alternating dithienobenzoxadiazole-based conjugated polymers for field-effect transistors and polymer solar cells

Co-reporter:Haitao Wang, Yongxiang Zhu, Zhulin Liu, Lianjie Zhang, Junwu Chen, Yong Cao

Organic Electronics 2016 Volume 31() pp:1-10

Publication Date(Web):April 2016

DOI:10.1016/j.orgel.2015.12.030

•Alternating conjugated polymers based on dithienobenzoxadiazole (DTfBO).•High hole mobility up to 0.54 cm2/(V s).•Good power conversion efficiency up to 5.63% for 250 nm thick active layer.Three new alternating copolymers derived from dithienobenzoxadizole (DTfBO) and different thiophene-based π-spacers, including terthiophene, quarterthiophene, and dithienyl flanked thienothiophene, were successfully synthesized. The DTfBO-based polymers possess optical band-gaps in the range of 1.84–1.89 eV and exhibit relatively deep HOMO levels between −5.36 eV and −5.50 eV. Due to strong interchain aggregation, DTfBO-based polymers could not be well dissolved in chlorobenzene at room temperature, but they could be processed with hot chlorobenzene solutions of ∼100 °C. Evolutions of UV absorption spectra of polymer solutions during heating process could differentiate their different aggregation ability, among which a repeating unit based on a DTfBO and a terthiophene could supply the strongest inter-chain interaction. Notably, the three DTfBO-based polymers displayed high field-effect hole mobilities between 0.21 and 0.54 cm2/(V s). In polymer solar cells (PSCs) with the three polymers as the donors, high open-circuit voltages between 0.87 and 0.93 V could be realized. For active layer thickness of 80 nm, the PSCs displayed power conversion efficiency (PCE) between 2.85% and 5.07%. A very high fill factor of 75.4% was achieved for the polymer comprising dithienyl flanked thienothiophene. With thicker ative layers of 250 nm, the three DTfBO-based polymers exhibited comparable PCEs of ∼5.61% due to obviously increased short-circuit currents. Our results suggest that DTfBO, a big coplanar heterocycle, is a promising building block to construct high mobility conjugated polymers for efficient thick-film PSCs.

Hydrophilic Conjugated Polymers with Large Bandgaps and Deep-Lying HOMO Levels as an Efficient Cathode Interlayer in Inverted Polymer Solar Cells

Co-reporter:Yuanyuan Kan;Yongxiang Zhu;Zhulin Liu;Junwu Chen;Yong Cao

Macromolecular Rapid Communications 2015 Volume 36( Issue 15) pp:1393-1401

Publication Date(Web):

DOI:10.1002/marc.201500163

Efficient Blue Light-Emitting Diodes Based on Conjugated Polymers with Fluorinated Silole Chemically Doped in Fluorene–Carbazole Main Chain

Co-reporter:Lianjie Zhang;Zhulin Liu;Xiaofei Zhang

Journal of Inorganic and Organometallic Polymers and Materials 2015 Volume 25( Issue 1) pp:64-72

Publication Date(Web):2015 January

DOI:10.1007/s10904-014-0078-0

A series of random conjugated copolymers PFCFS1-20 with 2,5-diphenyl-3,4-bis(3-fluorophenyl)-silole (fluorinated TPS) chemically doped in 2,7-fluorene-2,7-carbazole main chain were successfully synthesized and characterized. Polymers PFCFS1-20 with fluorinated TPS contents from 1 to 20 % possess high weight-average molecular weights between 63.5 and 114.1 kg mol−1. The absorption spectra of THF solutions and films of PFCFS1-20 are very similar, showing peaks around 385 nm and optical band gaps around 2.87 eV. Almost no red-shifts of the absorption peaks from a solution to a solid state film for the four copolymers indicate that their interchain interactions are extremely weak. PFCFS1-20 solutions show blue emissions with very limited intrachain excitation energy transfers. The films of PFCFS1-20 also display blue emissions with main peaks at 449 nm for PFCFS1 and 475 nm for PFCFS20, suggesting that the fluorinated TPS may comprise more twisted phenyl peripherals. Two types of electroluminescence (EL) devices with configurations of ITO/PEDOT:PSS/PFCFS/CsF/Al and ITO/PEDOT:PSS/PFCFS/TPBI/CsF/Al were investigated. It was found that PFCFS1-20 in the two types of EL devices could show blue to sky-blue emissions. Among PFCFS1-20, for EL devices without TPBI layer, PFCFS5 possesses the best device performances with maximum luminous efficiency (LEmax) of 1.46 cd A−1 and maximum external quantum efficiency (EQEmax) of 0.93 %. The insertion of TPBI as the electron transport layer remarkably improves the EL performances. Also PFCFS5 displays the best LEmax of 4.59 cd A−1 and EQEmax of 3.21 %. The latter one is among the best efficiency so far reported for silole-containing polymers. Our results suggest that the fluorinated TPS is an efficient chromophore for constructions of blue-emissive conjugated polymers.

Low band-gap benzodithiophene-thienothiophenecopolymers: the effect of dual two-dimensional substitutions on optoelectronic properties

Co-reporter:Zhulin Liu;Jiangman Sun;Yongxiang Zhu;Peng Liu

Science China Chemistry 2015 Volume 58( Issue 2) pp:267-275

Publication Date(Web):2015 February

DOI:10.1007/s11426-014-5223-7

Two new conjugated copolymers, PBDT-T6-TTF and PBDT-T12-TTF, were derived from a novel 4-fluorobenzoyl thienothiophene (TTF). In addition, two types of benzodithiophene (BDT) units with 2,3-dihexylthienyl (T6) and 2,3-didodecylthienyl (T12) substituents, respectively, were successfully synthesized. The effect of the dual two-dimensional (2D) substitutions of the building blocks upon the optoelectronic properties of the polymers was investigated. Generally, the two polymers exhibited good solubility and broad absorption, showing similar optical band gaps of ∼1.53 eV. However, PBDT-T6-TTF with its shorter alkyl chain length possessed a larger extinction coefficient in thin solid film. The highest occupied molecular orbital (HOMO) level of PBDT-T6-TTF was located at −5.38 eV while that of PBDT-T12-TTF was at −5.51 eV. In space charge-limited-current (SCLC) measurement, PBDT-T6-TTF and PBDT-T12-TTF displayed respective hole mobilities of 3.0×10−4 and 1.6×10−5 cm2 V−1s−1. In polymer solar cells, PBDT-T6-TTF and PBDT-T12-TTF showed respective power conversion efficiencies (PCEs) of 2.86% and 1.67%. When 1,8-diiodooctane (DIO) was used as the solvent additive, the PCE of PBDT-T6-TTF was remarkably elevated to 4.85%, but the use of DIO for the PBDT-T12-TTF-blend film resulted in a lower PCE of 0.91%. Atomic force microscopy (AFM) indicated that the superior efficiency of PBDT-T6-TTF with 3% DIO (v/v) should be related to the better continuous phase separation of the blend film. Nevertheless, the morphology of the PBDT-T12-TTF deteriorated when the 3% DIO (v/v) was added. Our results suggest that the alkyl-chain length on the 2D BDT units play an important role in determining the optoelectronic properties of dual 2D BDT-TT-based polymers.

Low band-gap DA conjugated copolymers based on anthradithiophene and diketopyrrolopyrrole for polymer solar cells and field-effect transistors

Co-reporter:Jun Huang;Yongxiang Zhu;Ping Cai;Xiaofeng Xu;Junwu Chen;Yong Cao

Journal of Polymer Science Part A: Polymer Chemistry 2014 Volume 52( Issue 12) pp:1652-1661

Publication Date(Web):

DOI:10.1002/pola.27163

ABSTRACT

Two conjugated copolymers PADT-DPP and PADT-FDPP based on anthradithiophene and diketopyrrolopyrrole, with thiophene and furan as the π-conjugated bridge, respectively, were successfully synthesized and characterized. The number-averaged molecular weights of the two polymers are 38.7 and 30.2 kg/mol, respectively. Polymers PADT-DPP and PADT-FDPP exhibit broad absorption bands and their optical band gaps are 1.44 and 1.50 eV, respectively. The highest occupied molecular orbital energy level of PADT-DPP is located at −5.03 eV while that of PADT-FDPP is at −5.16 eV. In field-effect transistors, PADT-DPP and PADT-FDPP displayed hole mobilities of 4.7 × 10⁻³ and 2.7 × 10⁻³ cm²/(V s), respectively. In polymer solar cells, PADT-DPP and PADT-FDPP showed power conversion efficiency (PCE) of 3.44% and 0.29%, respectively. Atomic force microscopy revealed that the poor efficiency of PADT-FDPP should be related to the large two-phase separation in its active layer. If 1,8-diiodooctane (DIO) was used as the solvent additive, the PCE of PADT-DPP remained almost unchanged due to very limited morphology variation. However, the addition of DIO could remarkably elevate the PCE of PADT-FDPP to 2.62% because of the greatly improved morphology. Our results suggest that the anthradithiophene as an electron-donating polycyclic system is useful to construct new D–A alternating copolymers for efficient polymer solar cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1652–1661

Donoracceptor copolymers based on phenanthrene as electron-donating unit: Synthesis and photovoltaic performances

Co-reporter:Zhenhui Chen;Ping Cai;Yongxiang Zhu;Xiaofeng Xu;Jiangman Sun;Jun Huang;Xuncheng Liu;Junwu Chen;Hongzheng Chen;Yong Cao

Journal of Polymer Science Part A: Polymer Chemistry 2013 Volume 51( Issue 23) pp:4966-4974

Publication Date(Web):

DOI:10.1002/pola.26948

ABSTRACT

Using 9,10-bis(dodecyloxy)phenanthrene as electron-donating unit and 4,7-dithienyl-5,6-bis(dodecyloxy)benzothiadiazole, 4,7-dithienyl-5,6-bis(octyloxy)benzoxadiazole, 5,8-dithienyl-2,3-bis(para-octyloxyphenyl)quinoxaline, and 5,8-dithienyl-2,3-bis(meta-octyloxyphenyl)quinoxaline as electron-accepting unit, four D–A copolymers PPA-DTBT, PPA-DTBX, PPA-p-DTQ, and PPA-m-DTQ, respectively, were successfully synthesized as new polymeric donors for photovoltaic cells. All the alternating copolymers can show two absorption bands, both in solutions and thin films. The optical bandgaps of the polymers are quite close, which are between 1.93 and 2.00 eV. The HOMO and LUMO levels of the polymers are also comparable of −5.52 ± 0.03 eV and −3.57 ± 0.03 eV, respectively. Thus, using the dialkoxyphenanthrene as the D unit could afford D–A copolymers with deep-lying HOMO levels, which would be an important factor to achieve high open-circuit voltages (V_oc) in bulk-heterojunction solar cells. With the copolymers as the donor and PC₇₁BM as the acceptor, the resulting solar cells could display good V_oc between 0.86 and 0.88 V. Among the four copolymers, PPA-DTBT containing the dialkoxybenzothiadiazole unit showed the best power conversion efficiency of 3.03% because of its relatively higher hole mobility and better phase separation. The results suggest that dialkoxyphenanthrene is a valuable electron-donating unit in the constructions of D–A copolymers for efficient solar cells with high V_oc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4966–4974