Molecular electronic structure plays a vital role in the photovoltaic performances in polymer solar cells (PSCs) due to their influences on light-harvesting, charge carrier transfer, π–π stacking, etc. Indacenodithiophene as a star unit has been well studied in PSCs; various structural derivation methods have been tried, but they are still not efficient in improvement of power conversion efficiencies (PCE) due to the narrow optical absorptions. In this contribution, a novel planar DMIDT with extended lateral π-electron delocalization is efficiently synthesized via introduction of sp2 hybrid carbons as the bridge atoms. Based on this novel building block, a two-dimensional conjugated polymer PDMIDT-TPD is prepared, and the unique structure improves the conjugation at the lateral direction, enlarges the electron delocalization area, and greatly broadens the absorption spectrum with a full coverage from 350 to 700 nm. Finally, a PCE of 8.26% is achieved when blended with PC71BM, which is the highest result among the IDT-based polymer donors. Meanwhile, PDMIDT-TPD also presents good compatibility with the non-fullerene acceptor, and a preliminary PCE of 6.88% is obtained. In all, this work not only provides an excellent donor material but also offers a general and simple derivation strategy for fused aromatic building blocks.

We have developed a kind of novel fused-ring small molecular acceptor, whose planar conformation can be locked by intramolecular noncovalent interaction. The formation of planar supramolecular fused-ring structure by conformation locking can effectively broaden its absorption spectrum, enhance the electron mobility, and reduce the nonradiative energy loss. Polymer solar cells (PSCs) based on this acceptor afforded a power conversion efficiency (PCE) of 9.6%. In contrast, PSCs based on similar acceptor, which cannot form a flat conformation, only gave a PCE of 2.3%. Such design strategy, which can make the synthesis of small molecular acceptor much easier, will be promising in developing a new acceptor for high efficiency polymer solar cells.

Conjugated polymers with three components, P1-1 and P1-2, were prepared by one-pot Stille polymerization. The two-component polymer P1-0 is only composed of a 5-fluoro-6-alkyloxybenzothiadiazole (AFBT) acceptor unit and a thiophene donor unit, while the three-component polymers P1-1 and P1-2 contain 10% and 20% 5,6-difluorobenzothiadiazole (DFBT), respectively, as the third component. The incorporation of the third component, 5,6-difluorobenzothiadiazole, makes the side chains discretely distributed in the polymer backbones, which can enhance the π–π stacking of polymers in film, markedly increase the hole mobility of active layers, and improve the power-conversion efficiency (PCE) of devices. Influence of the third component on the morphology of active layer was also studied by X-ray diffraction (XRD), resonant soft X-ray scattering (R-SoXS), and transmission electron microscopy (TEM) experiments. P1-1/PC71BM-based PSCs gave a high PCE up to 7.25%, whereas similarly fabricated devices for P1-0/PC71BM only showed a PCE of 3.46%. The PCE of P1-1/PC71BM-based device was further enhanced to 8.79% after the use of 1,8-diiodooctane (DIO) as the solvent additive. Most importantly, after the incorporation of 10% 5,6-difluorobenzothiadiazole unit, P1-1 exhibited a marked tolerance to the blend film thickness. Devices with a thickness of 265 nm still showed a PCE above 8%, indicating that P1-1 is promising for future applications.Keywords: film thickness; morphology; power-conversion efficiency; side chains; solar cells; three-component conjugated polymers;

A series of conjugated polymers P0, P5, and P7 containing 0, 5, and 7 mol % 2,5-difluorobenzene units, respectively, were prepared and utilized as electron donors in polymer solar cells. Incorporation of a small amount of 2,5-difluorobenzene unit into the backbone of donor polymers can significantly increase their planarity and crystallinity as well as decrease their solubility. The improved molecular conformation can markedly affect the morphology of polymer:PC71BM blend films. After incorporation of 5 mol % 2,5-difluorobenzene unit into the backbone of donor polymers, the domain size of blend films became smaller and the hole mobility increased. Increasing the content of 2,5-difluorobenzene to 7 mol % can further decrease the solubility of resulting polymers and resulted in poor solution processability. As a result, P5-based devices achieved a power conversion efficiency (PCE) of 8.5%, whereas P0 based devices gave a PCE of 7.8%.Keywords: 2,5-difluorobenzene; conjugated polymers; crystallinity; fluorinated benzothiadiazole; polymer solar cells; random copolymerization;

To develop novel hole-transport materials (HTMs) with less synthetic steps is still a great challenge. Here, a small molecule hexakis[4-(N,N-di-p-methoxyphenylamino)phenyl]benzene (F-1) was successfully synthesized by a relatively simple scenario. F-1 exhibits a deep highest occupied molecular orbital energy level of −5.31 eV. Notably, F-1 also features 2 times higher hole mobility of 4.98 × 10–4 cm2 V–1 s–1 than that of the mostly used 2,2′,7,7′-tetrakis(N,N-bis(4-methoxyphenyl)amino)-9,9′-spirobifluorene (spiro-OMeTAD). Consequently, F-1-based perovskite solar cells (PSCs) show markedly improved performance compared with spiro-OMeTAD-based ones. These results indicate such a material can be a promising HTM candidate to boost the overall performance of the PSC.Keywords: deep energy level; high efficiency; high mobility; hole-transport material synthesis; perovskite solar cell;

Novel polymers comprising a 3-fluoro-5-alkylthiophenyl benzodithiophene donor unit and a 5-fluoro-6-alkoxy (or alkylthio)-2,1,3-benzothiadiazole (BT) acceptor unit were synthesized. Both POF and PSF possess low HOMO and LUMO energy levels due to the incorporation of fluorine atoms. Additionally, alkoxy and alkylthio substitution on the BT unit also had a great influence on the molecular packing and the energy level of the resulting polymers. The introduction of the alkylthio side chains on the BT unit of PSF led to a significant downshift of the HOMO energy level in comparison to that of POF with an alkoxy substituent due to the weaker electron-donating properties of the sulfur atom than that of oxygen. However, the steric hindrance caused by the large sulfur atoms resulted in reduced planarity of the backbone of PSF, which might influence the charge transport and the morphology of the blend film. As a result, POF based NF-PSCs exhibited a PCE of 7.28%, with a Voc of 0.86 V, a Jsc of 14.9 mA cm−2, and an FF of 0.47, while a low PCE of 1.55% with a Voc of 0.95 V, a Jsc of 5.6 mA cm−2, and an FF of 0.29 was obtained for PSF based non-fullerene polymer solar cells (NF-PSCs). Therefore, the side chain engineering of the donor polymer is crucial for maximizing both Jsc and Voc values to achieve high performance polymer solar cells.

•Two nonfullerene acceptors with different linkage, PDI-V and PDI-E were synthesized.•The impact of the linkage between two PDI units on the photovoltaic performance were investigated.•The PCE for PSCs based on PTB7-Th:PDI-V is almost two times higher than that of PTB7-Th:PDI-E based devices.•It gains deeper insight into the design of new nonfullerene small molecular acceptors for high efficiency PSCs.Vinylene (V)- and ethynylene (E)-bridged perylene diimide dimers (PDI-V and PDI-E) were designed, synthesized and used as nonfullerene acceptors for polymer solar cells. Our researches revealed that the linkage between two PDI units has a great impact on the molecular geometry, the optical properties, the blend film morphology, the molecular packing orientation, and the photovoltaic performance. Computational calculations via density functional theory (DFT) showed that PDI-E and PDI-V possessed planar and twisted geometric structures, respectively. TEM investigations showed that PTB7-Th:PDI-V based blend film exhibited a uniform morphology with small domain size and PTB7-Th:PDI-E based one showed apparent phase separation with large domain size. GIWAXS results revealed that the PDI-V can influence PTB7-Th to take on a face-on orientation, which is beneficial for vertical charge transport to increase Jsc. A PCE of 4.51% with a Voc of 0.76 V, a Jsc of 10.03 mA cm−2, and an FF of 0.59 was obtained for PSCs based on PTB7-Th:PDI-V, which is almost two times higher than that of PTB7-Th:PDI-E based devices, which showed a PCE of 2.66%, a Voc of 0.66 V, a Jsc of 7.33 mA cm−2, and an FF of 0.55. These results help to gain deeper insight into the design of new nonfullerene small molecular acceptors for high efficiency PSCs.Download high-res image (167KB)Download full-size image

•Two non-fullerene small molecular acceptors with a carbazole core were synthesized.•Effects of different side chains on the device performance of non-fullerene acceptors have been investigated.•A high open circuit voltage about 1 V can be achieved in devices based on these two acceptors.•OSCs based on carbazole-cored acceptors exhibit a good performance even though the ΔELUMO and ΔEHOMO are both small.Two novel carbazole-cored small molecules CzC6C8 and CzC8 bearing different side chains and two 3-ethylrhodanine end-capping groups were synthesized and used as electron acceptors in organic solar cells (OSCs). Devices based on these two acceptors showed a high open circuit voltage (Voc) about 1 V. Due to more closely molecular stacking and improved film morphology, CzC8 bearing a linear alkyl side chain showed a better photovoltaic performance than CzC6C8 bearing a branched one. CzC8 based OSCs can still exhibit a good performance even though the ΔELUMO and ΔEHOMO between donor and acceptor are both small. Three polymer donors (PBT, PTB7-Th, and PTFBDT) with a similar LUMO level but various HOMO levels were tested and they all showed good PCE values larger than 4.6%. Among them, PTB7-Th:CzC8 based devices afforded the highest PCE of 4.91% and PTFBDT:CzC8 based ones gave the highest Voc of 1.16 V.

•Three novel copolymers based on DTQx and IDT were synthesized.•PHF based PSCs gave a PCE of 7.2% with fluorination on side chain of DTQx.•Fluorination position and number result in varied morphology of active layers.To explore the influence of fluoro substitution position and number on optical, electrochemical and photovoltaic properties, three novel donor-acceptor (D-A) alternative copolymers (PHF, PFH and PFF) were synthesized by Stille polycondensation of 2,3-diphenyl-5,8-di(thiophen-2-yl)quinoxaline (DTQx) acceptor unit and indacenodithiophene (IDT) donor unit. As films, PHF and PFF comprising two fluoro substituents on the lateral phenyl groups displayed a broad absorption ranging from 350 to 700 nm; whereas PFH containing two fluorine atoms on the polymer main chain exhibited a slightly narrower absorption ranging from 350 to 650 nm. In addition, fluoro substitution on the polymer main chain can lower the HOMO level of the resulted polymers. As expected, PFH and PFF possess deeper HOMO energy level than PHF. Polymer solar cells (PSCs) were fabricated with these three polymers as donor materials and PC71BM as acceptor material. PHF based PSCs gave a power conversion efficiency (PCE) of 7.2% with a Voc of 0.84 V, a Jsc of 12.46 mA/cm2 and an FF of 0.69. And PFH based PSCs showed a PCE of 6.19% with a Voc of 0.93 V, a Jsc of 9.57 mA/cm2 and an FF 0.70. However, a PCE of only 2.9% with a Voc of 0.92 V, a Jsc of 4.61 mA/cm2 and an FF of 0.68 was obtained for PFF based PSCs. Transmission electron microscopy (TEM) and resonant soft X-ray scattering (R-SoXS) studies indicated that the introduction of four fluorine atoms at each repeating unit can spoil the morphology of active layer. These results highlight the importance of fluorination position and number to the performance of PSCs.Three novel donor-acceptor (D-A) alternative copolymers PHF, PFH and PFF were synthesized and applied for polymer solar cells (PSCs) to explore the influence of fluoro substitution position and number on optical, electrochemical and photovoltaic properties. PHF, PFH and PFF based PSCs gave power conversion efficiencies of 7.2%, 6.19% and 2.9%, respectively. TEM and R-SoXS studies indicated that the introduction of four fluorine atoms at each repeating unit can spoil the morphology of active layer.Download high-res image (249KB)Download full-size image

A novel class of amphiphilic dendrons with a pyrene functional group at the focal point was designed and synthesized. The self-assembly and DNA condensation behaviors of these pyrene-functionalized amphiphilic dendrons were investigated in detail. The size of dendritic wedges, together with the fluorescent pyrene hydrophobe significantly influenced their supramolecular assembly behaviors and DNA condensation. Anisotropic 1D nanostructures were formed owing to their amphiphilic nature and the synergic effect of non-covalent interactions. Furthermore, the complexes formed by the cationic dendrons and DNA were well characterized, demonstrating these dendritic amphiphiles as promising candidates for efficient and functional gene carriers. Interestingly, the condensation efficiency of these pyrene based supramolecular nanostructures towards DNA could be conveniently controlled by the generation of dendrons, which will make them potentially applicable in many fields of medicinal science and biotechnology.

Three planar nonfullerene acceptors (FTIC-C8C6, FTIC-C6C6 and FTIC-C6C8) comprising a central fluorenedicyclopentathiophene (FT) core and two 2-methylene-(3-(1,1-dicyanomethylene)-indanone) terminal groups are designed and synthesized. The coplanarity of the molecular backbone can be maintained through a locked conformation via intramolecular noncovalent interactions. The solubility of these nonfullerene acceptors is very good because the FT core can bear enough flexible aliphatic side-chain substitutions. Thus, the dilemma of the planarity–solubility tradeoff can be minimized. Through changing the length of the six flexible aliphatic side chains at the central FT core, we can easily adjust the π–π interactions of nonfullerene acceptors and optimize the nanoscale morphology of the photoactive layers. Among these three small molecular acceptors, FTIC-C6C8 based active layers show the best morphology together with the highest electron and hole mobility. These inherent advantages of FTIC-C6C8 guarantee it a high power conversion efficiency of 11.12% when used in non-fullerene polymer solar cells with a wide-bandgap polymer donor PBDB-T. Our results provide an appropriate molecular design strategy for building high-performance nonfullerene acceptors and show that optimizing alkyl-side chains is a very effective way to further improve the photovoltaic performance of devices.

For the first time, a hyperbranched polymer acceptor, HP-PDI, was designed, synthesized and applied in polymer solar cells (PSCs). Devices based on HP-PDI showed a power conversion efficiency of 2.15%, which is 14 times higher than that of devices based on the small molecular acceptor SM-PDI. The hyperbranched structure can effectively suppress the aggregation of PDI molecules preventing them from forming large domains. Our preliminary results have demonstrated that high efficiency PSCs could be achieved by using a hyperbranched polymer acceptor.

AbstractA kind of new fused-ring electron acceptor, IDT-OB, bearing asymmetric side chains, is synthesized for high-efficiency thick-film organic solar cells. The introduction of asymmetric side chains can increase the solubility of acceptor molecules, enable the acceptor molecules to pack closely in a dislocated way, and form favorable phase separation when blended with PBDB-T. As expected, PBDB-T:IDT-OB-based devices exhibit high and balanced hole and electron mobility and give a high power conversion efficiency (PCE) of 10.12%. More importantly, the IDT-OB-based devices are not very sensitive to the film thickness, a PCE of 9.17% can still be obtained even the thickness of active layer is up to 210 nm.

This data contains additional data related to the article “Influence of Substrate Temperature on the Film Morphology and Photovoltaic Performance of Non-fullerene Organic Solar Cells” (Jicheng Zhang et al., In press) [1]. Data include measurement and characterization instruments and condition, detail condition to fabricate norfullerene solar cell devices, hole-only and electron-only devices. Detail condition about how to control the film morphology of devices via tuning the temperature of substrates was also displayed. More information and more convincing data about the change of film morphology for active layers fabricated from different temperature, which is attached to the research article of “Influence of Substrate Temperature on the Film Morphology and Photovoltaic Performance of Non-fullerene Organic Solar Cells” was given.

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.

A novel diketopyrrolopyrrole (DPP)-based conjugated polymer (PCDPP) was designed, synthesized and used as a donor material for polymer solar cells (PSCs). By increasing the planarity of polymer chains and reducing the energy loss in devices, we have simultaneously acquired a high short-circuit current (Jsc) and a large open-circuit voltage (Voc) in PSCs based on PCDPP, which is a regular alternating ternary conjugated polymer. This polymer has a medium optical band gap (1.55 eV) with low-lying HOMO and LUMO energy levels. In addition, PCDPP exhibits a very good planarity from density functional theory (DFT) calculations and forms a fibrillar network in the active layer of solar cells. Because of these integrated favourable effects, PCDPP-based photovoltaic devices exhibit a high power conversion efficiency (PCE) of 9.02% which is among the highest values reported so far for devices based on DPP-containing polymers. More importantly, the Voc of our PCDPP-based devices can reach as high as 0.86 V, which is much higher than that (<0.7 V) of high-efficiency solar cells based on other DPP polymers. These results provide a promising way to minimize the energy loss and to realize high Voc and Jsc values at the same time in devices to obtain high power conversion efficiencies.

Two novel polymers PTFBDT-BZS and PTFBDT-BZO with 4-alkyl-3,5-difluorophenyl substituted benzodithiophene as the donor unit, benzothiadiazole or benzooxadiazole as the acceptor unit, and thiophene as the spacer have been synthesized and used as donor materials for polymer solar cells (PSCs). These two polymers exhibited wide optical band gaps of about 1.8 eV. PSCs with the blend of PTFBDT-BZS:PC71BM (1:2, by weight) as the active layer fabricated without using any processing additive and any postannealing treatment showed power conversion efficiency (PCE) of 8.24% with an open circuit voltage (Voc) of 0.89 V, a short circuit current (Jsc) of 12.67 mA/cm2, and a fill factor (FF) of 0.73 under AM 1.5G illumination, indicating that PTFBDT-BZS is a very promising donor polymer for PSCs. The blend of PTFBDT-BZO:PC71BM showed a lower PCE of 5.67% with a Voc of 0.96 V, a Jsc of 9.24 mA/cm2, and an FF of 0.64. One reason for the lower PCE is probably due to that PTFBDT-BZO has a smaller LUMO offset with PC71BM, which cannot provide enough driving force for charge separation. And another reason is probably due to that PTFBDT-BZO has a lower hole mobility in comparison with PTFBDT-BZS.Keywords: bulk heterojunction; donor materials; fluorinated polymers; polymer solar cells; wide band gap polymers

With the efficient synthesis of the crucial dibenzopyran building block, a series of PDBPTBT polymers containing different alkyl side chains and/or fluorine substitution were designed and synthesized via the microwave-assisted Suzuki polycondensation. Quantum chemistry calculations based on density functional theory indicated that different substitutions have significant impacts on the planarity and rigidity of the polymer backbones. Interestingly, the alkyloxy chains of PDBPTBT-4 tend to stay in the same plane with the benzothiadiazole unit, but the others appear to be out of plane. With the S···O and F···H/F···S supramolecular interactions, the conformations of the four polymers will be locked in different ways as predicted by the quantum chemistry calculation. Such structural variation resulted in varied solid stacking and photophysical properties as well as the final photovoltaic performances. Conventional devices based on these four polymers were fabricated, and PDBPTBT-5 displayed the best PCE of 5.32%. After optimization of the additive types, ratios, and the interlayers at the cathode, a high PCE of 7.06% (Voc = 0.96 V, Jsc = 11.09 mA/cm2, and FF = 0.67) is obtained for PDBPTBT-5 with 2.0% DIO as the additive and PFN-OX as the electron-transporting layer. These results indicated DBP-based conjugated polymers are promising wide band gap polymer donors for high-efficiency polymer solar cells.Keywords: dibenzopyran; electron-transporting layer; polymer solar cells; quantum chemistry calculations; supramolecular interaction; wide band gap

A new 1,8-naphthalimide based planar small molecular acceptor and two benzothiadiazole based wide band gap (WBG) polymer donors P1 and P2 were synthesized for nonfullerene organic photovoltaic cells (OPVs). Devices based on fluorinated polymer P2 achieved a highly improved PCE of 3.71% with an open circuit voltage (Voc) of 1.07 V, which is beyond the currently known levels for nonfullerene OPVs with the Voc higher than 1 V.

Four small molecular acceptors (SM1–4) comprising a central benzene core, two thiophene bridges and two 1,8-naphthalimide (NI) terminal groups were designed and synthesized by direct C–H activation. SM1 has a planar chemical structure and forms H-aggregation as films. By attachment of different substituents on the central benzene ring, the dihedral angles between the two NI end groups of SM1–4 gradually increased, leading to a gradual decrease of planarity. SM1–4 all possess a high-lying LUMO level, matching with wide band gap (WBG) polymer donors which usually have a high-lying LUMO level. When used in OSCs, devices based on SM1 and WBG donor PCDTBT-C12 gave higher electron mobility, superior film morphology and better photovoltaic performance. After optimization, a PCE of 2.78% with a Voc of 1.04 V was achieved for SM1 based devices, which is among the highest PCEs with a Voc higher than 1 V. Our results have demonstrated that NI based planar small molecules are potential acceptors for WBG polymer based OSCs.Keywords: C−H activation; H-aggregation; high open circuit voltage; nonfullerene acceptor; organic solar cells; planar small molecules; wide band gap polymer

Three asymmetrical dithienosilole monomers with different electron withdrawing groups (nonanoyl group, octyl cyanoacetate or malononitrile) were synthesized and a series of silicon containing conjugated polymers (PBDTDTSi-1, PBDTDTSi-2 to PBDTDTSi-3) were prepared from these asymmetrical dithienosilole building blocks via microwave assisted polymerization. Density functional theory (DFT) quantum chemistry calculations were employed for the optimization of molecular structures, deep understanding of the electronic structures and their photophysical properties. When these polymers were utilized as the donor materials for polymer solar cells (PSCs), the influence of side chains on the photovoltaic performance was investigated and all the polymers presented high open-circuit voltage above 1.0 V. PSCs with a blend of PBDTDTSi-1:PC71BM (1:4, by weight) as the active layer showed the highest power conversion efficiency of 3.29%, with an open-circuit voltage of 1.07 V, a short-circuit current density of 7.53 mA cm−2, and a fill factor of 0.41. Our research revealed that the variation of substituents on the dithienosilole moieties had a great influence on the morphology of blend films and charge carrier mobilities, which are crucial to the performance of PSCs.

•Three novel polymers have branched side chains with varied branching positions.•The bifurcation positions influnce intermolecular stacking and film morphology.•The bifurcation positions influnce charge mobility and photovoltaic performance.•The best PCE of 5.67% is achieved by adjusting the bifurcation points position.Three novel copolymers (PTTAFBT-C0, PTTAFBT-C1 and PTTAFBT-C2) based on thieno[3,2-b]thiophene and 5-alkoxy-6-fluorobenzo-[c][1,2,5]thiadiazole (AFBT) bearing branched alkoxy chains with varied branching positions are synthesized. The influences of the bifurcation positions on intermolecular stacking, charge mobility, film morphology and photovoltaic performance are systematically investigated. 2D-GIWAXS analyses of the optimized polymer:PC71BM blend films exhibit the crystallinity increases from PTTAFBT-C0 to PTTAFBT-C1 and PTTAFBT-C2 is more prone to form the edge-on orientation than PTTAFBT-C1, which result in a dramatic difference in film morphologies. TEM image of PTTAFBT-C1:PC71BM blend films exhibits a suitable morphology with favorable interpenetrating networks, which is in favor of high performance. The best PCE of 5.67% with a device configuration of ITO/PEDOT: PSS/PTTAFBT-C1:PC71BM/LiF/Al under AM 1.5G solar radiation (100 mW cm−2) is achieved. These results indicate that higher PCE can be obtained by adjusting the bifurcation points of the branched side chains away from the polymer backbone.

The use of environmentally friendly halogen-free organic solvents for the fabrication of polymer solar cells will be of great importance for future practical applications. In this work, a new alternative conjugated polymer with 3,4-bis(octyloxy)-phenyl substituted benzo[1,2-b:4,5-b]dithiophene as the donor unit and benzo[c][1,2,5]thiadiazole as the acceptor unit was synthesized and used as the donor material for polymer solar cells. This polymer showed good solubility in halogen-free solvents such as toluene, o-xylene and so on. The blend film morphology, charge mobility and photovoltaic performance were investigated in halogen-free solvents. The photovoltaic devices fabricated from o-xylene with N-methyl-2-pyrrolidone as additive provided the best power conversion efficiency of 4.57%, comparable to that fabricated from halogenated solvents such as 1,2-dichlorobenzene/1,8-diiodooctane with a power conversion efficiency of 4.33%. Our results demonstrate that halogen-free solvents are promising for the fabrication of high efficiency polymer solar cells.

In the past few years, ternary polymer solar cells (PSCs) have emerged as a promising structure to simultaneously improve all solar cell parameters compared with traditional binary PSCs. The third component in ternary PSCs can play versatile functions to enhance the device performance. In this review, we summarize the design rules for fabricating high-performance ternary PSCs and introduce the recent progress in this field. In addition, the characterization methods for determining the role of the third component played in ternary PSCs are described.过去几年, 三元共混聚合物太阳能电池作为一种新型的共混结构电池, 由于其优秀的潜质受到国内外研究学者的广泛关注. 相较于 传统的二元共混聚合物太阳能电池, 这种三元共混结构能有效地提高太阳能电池的各项参数, 从而使电池的光电转换效率有了大幅度的提 升. 本综述主要总结了制备高效率三元共混太阳能电池的设计思路并介绍了这一领域的最新进展, 讨论了三元共混聚合物太阳能电池中 第三组分的主要作用和表征方法.

Lettuce-like CuxS micron particles were successfully prepared by a colloidal hot-injection method, and the preliminary evaluation of the light-gating artificial ionic nanochannels designed using these particles was also demonstrated. A likely underlying mechanism behind the formation of the lettuce architecture was tentatively proposed via monitoring the evolution process. These particles are hydrophobic and possess a high surface area that can readily absorb the light-responsive 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran (Spiro) molecules. Finally, the heterogeneous nanochannels were constructed by spin-coating the preprepared CuxS particles loaded with Spiro onto the commercially available anodic alumina (AAO) substrate. The AAO-CuxS/Spiro heterogeneous nanochannels “close” under illumination of ultraviolet light (365 nm) and then “open” by visible light irradiation, which exhibits a regulated ionic transport property with good responsive switchability and stability.Keywords: copper sulfide; heterogeneous nanochannels; lettuce architecture; light-gating

A novel type of π-extended 1,10-phenanthroline, specifically with fused thiophene groups at the less exploited 3-, 4-, 7-, and 8-positions of the phenanthroline ring, and its conjugated polymers were designed and synthesized. The current developed route is based on the Bischler–Napieralski cyclization of the (1,2-phenylene)diamide precursor, which offers a facile and versatile strategy for preparing soluble and well-defined 1,10-phenanthroline derivatives and their analogues. High molecular weight poly(phenanthroline-co-fluorene)s with good solubility in common organic solvents or water were prepared by palladium-catalyzed Suzuki–Miyaura–Schlüter polycondensation. The optical responsive properties of these thiophene-fused 1,10-phenanthroline-containing polymers have demonstrated these polymers could be a good candidate for potential applications as luminescent chemosensor materials thanks to the specific repeating unit along the backbone.

In living systems, ion conduction plays a major role in numerous cellular processes and can be controlled by biological ion channels in response to specific environmental stimuli. This article describes biomimetic ionic gates for ion conduction based on sodium and potassium activated nanochannels. The Na+ activated ionic gate and K+ activated ionic gate were developed by immobilizing the alkali metal cation-responsive functional molecules, 4′-aminobenzo-15-crown-5 and 4′-aminobenzo-18-crown-6, respectively, onto the conical polyimide nanochannels. When the ionic gate was in the presence of the specific alkali metal cation, positively charged complexes formed between the crown ether and the alkali metal cation. On the basis of the resulting changes in surface charge, wettability and effective pore size, the nanochannel can achieve reversible switching. The switching behaviors of the two complexes differed due to the differences in binding strength between the two complexes. The Na+ activated ionic gate is able to open and close to control the ion conduction through the nanochannel, and the K+ activated ionic gate enables selective cation and anion conduction through the nanochannel. The Na+ and K+ activated ionic gates show great promise for use in clinical medicine, biosensors and drug delivery based on their high sensitivity and selectivity of being activated, and good stability.

Three novel copolymers P1–3 with alkylthiophenyl substituted benzodithiophene as the donor unit, thiophene as the spacer, and benzothiadiazole as the acceptor unit have been designed, synthesized, and used as donor materials for polymer solar cells. Polymer solar cells with P3:PC71BM blends as the active layer exhibited a high power conversion efficiency (PCE) of 7.7% and a good tolerance to the change of film thickness. PCE higher than 7.3% can be obtained with the thickness of the active layer ranging from 90 to 380 nm, indicating that P3 is a very promising donor material for practical application.

A novel small molecule NI-T-NI with a thiophene core and two 1,8-naphthalimide terminal groups was synthesized via direct C–H activation and used as the acceptor for polymer solar cells. NI-T-NI exhibits a good crystallinity and can form H-aggregates in the solid state. NI-T-NI has a rather high-lying LUMO level, which is beneficial for achieving a high Voc. In cooperation with a high-lying LUMO level polymer PCDTBT-C12, a PCE of 2.01% with a high Voc of 1.30 V has been achieved. As far as we know, a Voc of 1.30 V is the highest value reported for single junction organic solar cells. Our results have demonstrated that 1,8-naphthalimide could be a useful building block for the synthesis of promising acceptor materials for polymer solar cells.

A series of new conjugated polymers (P1–P3) with 3,6-difluorocarbazole as a donor unit and benzoxadiazole as an acceptor unit were synthesized and used as donor materials for polymer solar cells (PSCs). The morphology of blend films was regulated by controlling the drying process via tuning the solubility of polymers and using solvent additives. Enhancing the solubility of polymers via increasing the volume of side chains can decrease the domain size of polymers and using 1,8-diiodooctane (DIO) as a solvent additive can give an even better vertical phase separation, leading to a significant enhancement of the power conversion efficiency (PCE) of up to 5.71% for P3 based PSCs. The improving of the interface between polymers and PC71BM phases as well as the formation of vertical phase separation after using DIO as an additive are probably responsible for the high open circuit voltage (Voc) of devices.

Four planar conjugated polymers called CZ-BO8, CZ-BO12, CZ-BT8 and CZ-BT12 with carbazole as the donor unit and benzooxadiazole or benzothiadiazole as the acceptor unit have been synthesized and characterized. These four polymers have medium band gaps (1.95–1.97 eV), low lying highest occupied molecular orbital energy levels (below −5.5 eV), relatively high hole mobilities (in the range of 0.026–0.1 cm2 V−1 s−1), and on/off current ratio of 106 without any post-treatment. Furthermore, high performance thin film phototransistors based on these four polymers have also been fabricated with high photocurrent/dark current ratios (5.7 × 103–8.2 × 103). Interestingly, phototransistors based on CZ-BO8 and CZ-BO12 show a faster photoresponse than that based on CZ-BT8 and CZ-BT12, providing valuable molecular design guidelines for high performance photoresponse polymers.

The use of a commercially available nucleating agent as the additive for the fabrication of polymer:PC71BM-based active layers by solution-processing can greatly enhance the power conversion efficiency (PCE) of bulk heterojunction polymer solar cells (BHJ PSCs). The enhancement of device performance is mainly due to the addition of nucleating agent, which is able to regulate the drying process of the active layer and decrease the oversized domain size of conjugated polymers. Via this effective strategy to optimize the film morphology, the designed device exhibits an enhancement as great as 30.8%.Keywords: conjugated polymers; domain size; morphology control; nucleating agent; polymer solar cells

Three conjugated polymers (P1–P3) with benzodithiophene derivatives as the donor unit, 5-fluoro-6-(2-hexyldecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole as the acceptor unit and thiophene as the spacer were designed, synthesized, and used as donor materials for polymer solar cells (PSCs). The influence of side chains at the benzodithiophene unit on the performance of PSCs was investigated. PSCs with the blend of P2:PC71BM (1:2, by weight) as the active layer show the highest power conversion efficiency (PCE) of 6.88%, with an open circuit voltage (Voc) of 0.76 V, a short circuit current (Jsc) of 14.67 mA/cm2, and a fill factor (FF) of 0.62. Our research revealed that the variation of side chains had a great influence on the morphology of blend films, which is crucial to the performance of PSCs. As indicated by transmission electron microscopy, the blends of P1:PC71BM (1:2) and P2:PC71BM (1:2) formed nanofibers, whereas the blends of P3:PC71BM (1:2) formed spherical domains. Therefore, we concluded that formation of a more interpenetrating phase-separated donor–acceptor network with a larger interfacial area and proper percolation in the blends from P1 to P2 is mainly responsible for better performance in the corresponding devices.Keywords: 5-fluoro-6-alkyloxybenzothiadiazole; benzodithiophene; mobility; polymer solar cells;

Solution processable star-shaped donor–acceptor (D–A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping.

Two conjugated polymers with benzodithiophene derivatives as the donor unit and planar difluoro-substituted dibenzo[a,c]phenazine as the acceptor unit P1, P2-L and P2-H were designed, synthesized, and used as the donor material in polymer solar cells. P2-H exhibits the highest hole mobility of 1.54 × 10−2 cm2 V−1 s−1. Polymer solar cells (PSCs) with a blend of P1:PC71BM (1:1.5, by weight) as the active layer show the highest power conversion efficiency (PCE) of 6.0% with an open circuit voltage (Voc) of 0.74 V, a short circuit current (Jsc) of 12.50 mA cm−2, and a fill factor (FF) of 0.65.

•Star-shaped D-A molecules were synthesized by direct C–H activation and Suzuki cross-coupling.•Star-shaped molecules were used as donor materials for organic solar cells.•1,8-Naphthalimide, triphenylamine, and oligothiophene were used the acceptor, the donor and the spacer, respectively.A series of novel star-shaped small molecules with triphenylamine as the core, oligothiophene as the spacer and 1,8-naphthalimide as the electron withdrawing end-group were synthesized and used as donor materials for solution-processed organic solar cells. Direct arylation and Suzuki cross-coupling were used to synthesize the key intermediates and star-shaped molecules. The star-shaped molecules showed good thermal stability, intense absorption in the range of 300–700 nm, and deep HOMO energy level. A bulk heterojunction organic solar cell with one of the star shaped molecules in combination with PC71BM as the active layer gave a power conversion efficiency of 2.32% with a high open-circuit voltage up to 0.94 V. The influence of the spacer between the triphenylamine core and the peripheral 1,8-naphthalimide function group on the optical and photovoltaic properties was also investigated. Our studies indicated that 1,8-naphthalimide can be used as a promising building block for the synthesis of novel donor materials for organic solar cells.

Two conjugated polymers HXS-1 and PDFCDTBT were prepared by direct C-H activation and Suzuki polycondensation and their chemical structures were characterized by 1H NMR spectroscopy. The molecular weight of conjugated polymer synthesized by direct C-H activation is lower than the corresponding polymers prepared by Suzuki polycondensation. Conjugated polymers synthesized by direct C-H activation have considerable solubility in common organic solvents and form amorphous film. The photovoltaic property of conjugated polymers synthesized by direct C-H activation is inferior to the corresponding polymers synthesized by Suzuki polycondensation.

•Poly(fluorinated acenaphthoquinoxaline-co-benzodithiophene) was synthesized and PCE of 4.72% was obtained for solar cells.•Polymer solar cells with the blend of P1 and PC71BM as the active layer showed a PCE of 4.72%.•P1 based devices have the highest PCE report for acenaphtho[1,2-b]quinoxaline based polymer solar cells.A new low band gap polymer P1 with fluorinated acenaphtho[1,2-b]quinoxaline (AQ) as the acceptor unit and benzo[1,2-b:4,5-b′]dithiophene as the donor unit has been designed and synthesized. Comparing with its non-fluorinated analog polymer P2, P1 shows a lower band gap of 1.76 eV with a deeper HOMO energy level of −5.54 eV. Polymer solar cells with the blend of P1 and PC71BM as the active layer without the additive or annealing showed a PCE of 4.72%, which was higher than P2 based devices with a PCE of 1.65%. Obviously, P1 can endow devices with a Voc of 0.77 V and a Jsc of 10.75 mA cm−2, which are higher than that of P2 based devices with a Voc of 0.75 V and aJsc of 4.41 mA cm−2, such an enhanced photovoltaic performance can be attributed to the broader absorption, the improvement of film morphology, and the higher charge mobility. Thus, fluorinated AQ can be a useful acceptor unit to construct narrow band gap conjugated polymers. To the best of our knowledge, this is the highest PCE report for AQ based polymer solar cells.

9-Arylidene-9H-fluorene containing donor–acceptor (D–A) alternating polymers P1 and P2 were synthsized and used for the fabrication of polymer solar cells (PSCs). High and low molecular weight P1 (HMW-P1 and LMW-P1) and high molecular weight P2 were prepared to study the influence of molecular weight and the position of alkoxy chains on the photovoltaic performance of PSCs. HMW-P1:PC71BM-based PSCs fabricated from 1,2-dichlorobenzene (DCB) solutions showed a power conversion efficiency (PCE) of 6.26%, while LMW-P1:PC71BM-based PSCs showed poor photovoltaic performance with a PCE of only 2.75%. PCE of HMW-P1:PC71BM-based PSCs was further increased to 6.52% with the addition of 1,8-diiodooctane (DIO) as the additive. Meanwhile, PCE of only 2.51% was obtained for P2:PC71BM-based PSCs. The results indicated that the position of alkoxy substituents on the 9-arylidene-9H-fluorene unit and the molecular weight of polymers are very crucial to the photovoltaic performance of PSCs.Keywords: benzothiadiazole; bulk heterojunction; conjugated polymers; donor−acceptor alternating polymers; polymer solar cells; Suzuki polycondensation;

Three novel isoindigo based donor–acceptor (D–A) conjugated polymers P1–3 have been synthesized by Suzuki polycondensation and utilized as donor materials for polymer solar cells (PSCs). These three polymers are of the same backbone, but have different substituents. All these polymers exhibit high thermal stability and broad absorption in the range of 300 to 770 nm. Hole mobilities of polymer films spin coated from 1,2-dichlorobenzene (DCB) solutions are 7.00 × 10−4, 2.37 × 10−3 and 2.90 × 10−4 cm2 V−1 s−1 for P1, P2 and P3, respectively. PSCs based on P2:PC71BM (1:2 by weight) with a 2% DIO additive displayed a power conversion efficiency (PCE) of 3.41% with a short-circuit current density (Jsc) of 7.57 mA cm−2, an open-circuit voltage (Voc) of 0.85 V, and a fill factor (FF) of 53%, under the illumination of AM 1.5G (100 mW cm−2). XRD diffraction measurements have shown that these polymers have a short π–π stacking distance in the solid state. The results demonstrate that these conjugated polymers could be promising donor materials in the application of polymer solar cells.

Fluorine is one of the human body’s required trace elements. Imbalanced fluoride levels severely affect the normal functioning of living organisms. In this article, an anion-regulated synthetic nanochannel is described. A fluoride-driven ionic gate was developed by immobilizing a fluoride-responsive functional molecule, 4-aminophenylboronic acid, onto a single conical polyimide nanochannel. When the ionic gate was in the presence of fluoride, the boron bound F–, and the hybridization of the boron center changed from sp2 to sp3. Thus, negatively charged monofluoride adduct (RB(OH)2F–), difluoride adduct (RB(OH)F2–), and trifluoride adduct (RBF3–) modified surfaces with different wettability would be formed successively by increasing the concentration of F–. On the basis of the variation of surface charge and wettability, the nanochannel can actualize reversible switching between the “off” state and the “on” state in the absence and presence of F–, respectively. As an anion-regulated synthetic nanochannel, this fluoride-driven ionic gate was characterized by measuring ionic current, which possesses high sensitivity, fine selectivity, and strong stability. Thus, this gate may show great promise for use in biosensors, water quality monitoring, and drug delivery.Keywords: 4-aminophenylboronic acid; fluoride-driven; gate; nanochannel;

Three donor–acceptor (D–A) alternating conjugated polymers with silafluorene as the donor unit, 5-alkyloxy-6-fluorobenzothiadiazole as the acceptor unit, and thiophene as the spacer has been synthesized and used as donor materials for polymer solar cells (PSCs). The introduction of a fluorine atom on the benzothiadiazole unit can lower the HOMO and LUMO energy level of the resulted polymers to afford higher open circuit voltage (Voc); whereas the introduction of a flexible alkyloxy chain on benzothiadiazole unit can increase the solubility of the resulted polymers without interfering the close packing of polymer chains in the solid state. High molecular weight polymers P-1a, P-1b, and P-1c, which are fully soluble in 1,2-dichorobenzene (DCB) at elevated temperature, have been prepared by Suzuki polycondensation. Among these polymers, P-1c exhibited the highest hole mobility up to 1.36 × 10–2 cm2 V–1 s–1. PSCs based P-1b:PC71BM demonstrated the highest Voc up to 0.98 V. P-1a:PC71BM based PSCs gave the highest power conversion efficiency (PCE) of 6.41%, which is the highest value among solar cells with benzothiadiazole- and silafluorene-containing polymers as the donor material.

Two new triindole-cored star-shaped molecules SM-1 and SM-2 have been designed and synthesized, and their optical, electrochemical, thermal, transport and photovoltaic properties have been investigated in detail. SM-1 and SM-2 exhibited good thermal stability, intensive absorption in a broad region, and relatively high hole mobility. Photovoltaic performances of these two molecules were investigated by fabricating bulk heterojunction solar cell devices with a blend film of SM-1:PC71BM or SM-2:PC71BM as the active layer. Organic solar cells (OSCs) based on SM-1:PC71BM and SM-2:PC71BM gave power conversion efficiencies (PCEs) of 2.05% and 2.29%, respectively. A PCE of 2.29% is the best result for all the reported triindole-based photovoltaic materials, indicating that triindole-based small molecules could become promising donor materials for solution-processed OSCs.

Alcohol soluble fullerene derivative (FN-C60) has been synthesized and used as a cathode interfacial layer for high-efficiency polymer solar cells (PSCs). To examine the function of the FN-C60 interfacial layer, polymer solar cells were fabricated with blends of P3:PC71BM, HXS-1:PC71BM, PDFCDTBT:PC71BM, and PDPQTBT:PC71BM as the active layer. In comparison to the bare Al electrode, power conversion efficiencies (PCEs) of P3:PC71BM, HXS-1:PC71BM, PDFCDTBT:PC71BM, and PDPQTBT:PC71BM based PSCs were increased from 3.50 to 4.64%, 4.69 to 5.25%, 2.70 to 4.60%, and 1.52 to 2.29%, respectively, when FN-C60/Al was used as the electrode. Moreover, the overall photovoltaic performances of PSCs with the FN-C60/Al electrode were better than those of cells with LiF/Al electrode, indicating that FN-C60 is a potential interfacial layer material to replace LiF.Keywords: alcohol soluble; fullerene derivative; interfacial layer; photovoltaic performance; polymer solar cells; power conversion efficiency;

Three new isoindigo containing donor–acceptor (D–A) type conjugated polymers were synthesized by palladium catalyzed Suzuki polycondensation and used as donor materials for polymer solar cells (PSCs) and field effect transistors (FETs). All the polymers possess good solubility in common organic solvents, high thermal stability, and broad absorption in the range of 300 to 750 nm. These polymers have narrow band gaps (1.66 to 1.70 eV) and low lying HOMO energy levels (5.15 to 5.31 eV). Hole mobilities of these polymers are in the range of 1.78 × 10−3 to 2.62 × 10−3 cm2 V−1 s−1. PSCs based on P3:PC71BM (1:2, by weight) gave the best device performance with a power conversion efficiency (PCE) of 1.75%, a short-circuit current density (Jsc) of 4.74 mA cm−2, an open-circuit voltage (Voc) of 0.81 V, and a fill factor (FF) of 0.45, indicating these polymers can be promising donor polymers for polymer solar cells.

High molecular weight thiophene-containing conjugated polymers were successfully synthesized by Suzuki polycondensation of aryl dibromides and 2,5-thiophenebis(boronic acid) derivatives by using a new thiophene-containing bulky phosphorous compound as the ligand for a zerovalent palladium catalyst.

A novel donor–acceptor (D–A) copolymer PDFCDTBT with 3,6-difluoro substituted carbazole as the donor unit and dialkoxy substituted benzothiadiazole as the acceptor unit has been synthesized and used as a donor material for bulk heterojunction polymer solar cells (BHJ PSCs). PDFCDTBT possesses a band gap of 1.75 eV, a low-lying HOMO energy level of −5.23 eV, and a good thermal and electrochemical stability. In comparison with the corresponding non-fluoro substituted HXS-1, which has a HOMO energy level of 5.21 eV, a LUMO energy level of 3.35 eV, and an optical band gap of 1.86 eV, the incorporation of two fluoro atoms in the carbazole donor unit lowers the HOMO and the LUMO energy levels of the polymer, which results in simultaneously decreasing the band gap of the polymer and increasing the Voc of polymer solar cells. The fluoro-containing polymer PDFCDTBT also shows strong intramolecular interactions and forms close packing in the solid state. Polymer solar cells based on PDFCDTBT and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) demonstrate a power conversion efficiency (PCE) of 4.8% with a Voc of 0.91 V, a Jsc of 9.5 mA cm−2, and an FF of 0.55. In comparison with HXS-1, the better stability, higher Voc, and narrower band gap indicate that PDFCDTBT is a very promising donor material for high efficiency polymer solar cells.

6,7-Dialkoxy-2,3-diphenylquinoxaline based narrow band gap conjugated polymers, poly[2,7-(9-octyl-9H-carbazole)-alt-5,5-(5,8-di-2-thinenyl-(6,7-dialkoxy-2,3-diphenylquinoxaline))] (PCDTQ) and poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,8-di-2-thinenyl-(6,7-dialkoxy-2,3-diphenylquinoxaline))] (PFDTQ), have been synthesized by Suzuki polycondensation. Their optical, electrochemical, transport and photovoltaic properties have been investigated in detail. Hole mobilities of PCDTQ and PFDTQ films spin coated from 1,2-dichlorobenzene (DCB) solutions are 1.0 × 10−4 and 4.1 × 10−4 cm2V−1 s−1, respectively. Polymer solar cells were fabricated with the as-synthesized polymers as the donor and PC61BM and PC71BM as the acceptor. Devices based on PCDTQ:PC71BM (1:3) and PFDTQ:PC71BM (1:3) fabricated from DCB solutions demonstrated a power conversion efficiency (PCE) of 2.5% with a Voc of 0.95 V and a PCE of 2.5% with a Voc of 0.98 V, respectively, indicating they are promising donor materials.

The controlled preparation of organic nanotubesviaself-assembly of polycyclic aromatics is a contemporary challenge for supramolecular science. Here, we show that the self-assembly of pyrene-containing cationic amphiphiles, 3-(4-(pyren-6-yl)phenoxy)propan-1-ammonium salts (PyPA-Cl, PyPA-Br, and PyPA-SO44), can form high aspect ratio nanotubes with a uniform diameter distribution. We have also demonstrated that the counter anions also play an important role in the self-assembling results. The self-assembly of pyrene-containing cationic amphiphilic molecules with monovalent anions (Cl−− and Br−−) forms exclusively uniform nanotubes; whereas the self-assembly of amphiphiles with bivalent counter anions (SO42−) forms exclusively high aspect ratio nanoribbons. Furthermore, we have found that the diameter of the PyPA-Brnanotubes is larger than that of the PyPA-Clnanotubes. The research results reported herein represent an important step towards the preparation of functional nanostructures with controlled 1D architectures.

Three D–A alternating copolymers P1–3 with 3,7-linked 2,8-bis(alkoxy)dibenzothiophene as the donor unit and benzothiadiazole (P1 and P2) or 3,4-bis(octyloxy)benzothiadiazole (P3) as the acceptor unit have been designed and synthesized. P1–3 show two broad absorption peaks in the visible region, and the internal charge transfer (ICT) absorptions at about 530 nm in solutions and 560 nm in films of P3 are much stronger than that of P1 and P2. All the polymers show narrow band gaps below 2.0 eV and the low-lying HOMO energy levels of approximately −5.30 eV. The hole mobilities of polymer films spin-cast from 1,2-dichlorobenzene (DCB) solutions are 3.0 × 10–4, 2.7 × 10–4, and 2.3 × 10–3 cm2 V–1 s–1 for P1, P2, and P3, respectively. Under simulated solar illumination of AM 1.5G (100 mW/cm2), a PCE of 4.48% with a Voc of 0.83 V, a Jsc of 9.30 mA/cm2, and an FF of 0.58 has been achieved for PSCs with the P3:PC71BM blend (1:3, by weight) as the active layer in simply processed devices, whereas after the optimization, PCEs of only 1.02% and 1.71% have been obtained for P1- and P2-based devices, respectively. This is the first report on dibenzothiophene-based conjugated polymers used for high efficiency polymer solar cells, demonstrating that photovoltaic performance can be improved by fine-tuning the conjugated polymer structure.

A new alternating copolymer (PSFDTBT) based on spirobifluorene, thiophene, and benzothiadiazole units has been synthesized. PSFDTBT has an optical band gap of 1.97 eV with the low-lying HOMO energy level at −5.4 eV. The hole mobility of the pristine PSFDTBT film spin-cast from o-dichlorobenzene (DCB) solution is 7.26 × 10–3 cm2 V–1 s–1 with on/off ratios in the order of 105. Polymer solar cell devices based on the blend films of PSFDTBT and PC71BM show a high open-circuit voltage of 0.94 V and a power conversion efficiency of 4.6% without any post-treatment. All the device measurements were performed in air without encapsulation. This is the first report on spirobifluorene-based conjugated polymers used for polymer solar cells, demonstrating the great potential of spirobifluorene moiety as an electron-donating unit for the construction of main chain donor–acceptor alternating conjugated polymers for high performance polymer solar cells.

For the first time, a hyperbranched polymer acceptor, HP-PDI, was designed, synthesized and applied in polymer solar cells (PSCs). Devices based on HP-PDI showed a power conversion efficiency of 2.15%, which is 14 times higher than that of devices based on the small molecular acceptor SM-PDI. The hyperbranched structure can effectively suppress the aggregation of PDI molecules preventing them from forming large domains. Our preliminary results have demonstrated that high efficiency PSCs could be achieved by using a hyperbranched polymer acceptor.

A new 1,8-naphthalimide based planar small molecular acceptor and two benzothiadiazole based wide band gap (WBG) polymer donors P1 and P2 were synthesized for nonfullerene organic photovoltaic cells (OPVs). Devices based on fluorinated polymer P2 achieved a highly improved PCE of 3.71% with an open circuit voltage (Voc) of 1.07 V, which is beyond the currently known levels for nonfullerene OPVs with the Voc higher than 1 V.

Solution processable star-shaped donor–acceptor (D–A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping.

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.

Four planar conjugated polymers called CZ-BO8, CZ-BO12, CZ-BT8 and CZ-BT12 with carbazole as the donor unit and benzooxadiazole or benzothiadiazole as the acceptor unit have been synthesized and characterized. These four polymers have medium band gaps (1.95–1.97 eV), low lying highest occupied molecular orbital energy levels (below −5.5 eV), relatively high hole mobilities (in the range of 0.026–0.1 cm2 V−1 s−1), and on/off current ratio of 106 without any post-treatment. Furthermore, high performance thin film phototransistors based on these four polymers have also been fabricated with high photocurrent/dark current ratios (5.7 × 103–8.2 × 103). Interestingly, phototransistors based on CZ-BO8 and CZ-BO12 show a faster photoresponse than that based on CZ-BT8 and CZ-BT12, providing valuable molecular design guidelines for high performance photoresponse polymers.

A novel small molecule NI-T-NI with a thiophene core and two 1,8-naphthalimide terminal groups was synthesized via direct C–H activation and used as the acceptor for polymer solar cells. NI-T-NI exhibits a good crystallinity and can form H-aggregates in the solid state. NI-T-NI has a rather high-lying LUMO level, which is beneficial for achieving a high Voc. In cooperation with a high-lying LUMO level polymer PCDTBT-C12, a PCE of 2.01% with a high Voc of 1.30 V has been achieved. As far as we know, a Voc of 1.30 V is the highest value reported for single junction organic solar cells. Our results have demonstrated that 1,8-naphthalimide could be a useful building block for the synthesis of promising acceptor materials for polymer solar cells.

A series of new conjugated polymers (P1–P3) with 3,6-difluorocarbazole as a donor unit and benzoxadiazole as an acceptor unit were synthesized and used as donor materials for polymer solar cells (PSCs). The morphology of blend films was regulated by controlling the drying process via tuning the solubility of polymers and using solvent additives. Enhancing the solubility of polymers via increasing the volume of side chains can decrease the domain size of polymers and using 1,8-diiodooctane (DIO) as a solvent additive can give an even better vertical phase separation, leading to a significant enhancement of the power conversion efficiency (PCE) of up to 5.71% for P3 based PSCs. The improving of the interface between polymers and PC71BM phases as well as the formation of vertical phase separation after using DIO as an additive are probably responsible for the high open circuit voltage (Voc) of devices.

The controlled preparation of organic nanotubesviaself-assembly of polycyclic aromatics is a contemporary challenge for supramolecular science. Here, we show that the self-assembly of pyrene-containing cationic amphiphiles, 3-(4-(pyren-6-yl)phenoxy)propan-1-ammonium salts (PyPA-Cl, PyPA-Br, and PyPA-SO44), can form high aspect ratio nanotubes with a uniform diameter distribution. We have also demonstrated that the counter anions also play an important role in the self-assembling results. The self-assembly of pyrene-containing cationic amphiphilic molecules with monovalent anions (Cl−− and Br−−) forms exclusively uniform nanotubes; whereas the self-assembly of amphiphiles with bivalent counter anions (SO42−) forms exclusively high aspect ratio nanoribbons. Furthermore, we have found that the diameter of the PyPA-Brnanotubes is larger than that of the PyPA-Clnanotubes. The research results reported herein represent an important step towards the preparation of functional nanostructures with controlled 1D architectures.

Two new triindole-cored star-shaped molecules SM-1 and SM-2 have been designed and synthesized, and their optical, electrochemical, thermal, transport and photovoltaic properties have been investigated in detail. SM-1 and SM-2 exhibited good thermal stability, intensive absorption in a broad region, and relatively high hole mobility. Photovoltaic performances of these two molecules were investigated by fabricating bulk heterojunction solar cell devices with a blend film of SM-1:PC71BM or SM-2:PC71BM as the active layer. Organic solar cells (OSCs) based on SM-1:PC71BM and SM-2:PC71BM gave power conversion efficiencies (PCEs) of 2.05% and 2.29%, respectively. A PCE of 2.29% is the best result for all the reported triindole-based photovoltaic materials, indicating that triindole-based small molecules could become promising donor materials for solution-processed OSCs.

Three novel copolymers P1–3 with alkylthiophenyl substituted benzodithiophene as the donor unit, thiophene as the spacer, and benzothiadiazole as the acceptor unit have been designed, synthesized, and used as donor materials for polymer solar cells. Polymer solar cells with P3:PC71BM blends as the active layer exhibited a high power conversion efficiency (PCE) of 7.7% and a good tolerance to the change of film thickness. PCE higher than 7.3% can be obtained with the thickness of the active layer ranging from 90 to 380 nm, indicating that P3 is a very promising donor material for practical application.

A novel diketopyrrolopyrrole (DPP)-based conjugated polymer (PCDPP) was designed, synthesized and used as a donor material for polymer solar cells (PSCs). By increasing the planarity of polymer chains and reducing the energy loss in devices, we have simultaneously acquired a high short-circuit current (Jsc) and a large open-circuit voltage (Voc) in PSCs based on PCDPP, which is a regular alternating ternary conjugated polymer. This polymer has a medium optical band gap (1.55 eV) with low-lying HOMO and LUMO energy levels. In addition, PCDPP exhibits a very good planarity from density functional theory (DFT) calculations and forms a fibrillar network in the active layer of solar cells. Because of these integrated favourable effects, PCDPP-based photovoltaic devices exhibit a high power conversion efficiency (PCE) of 9.02% which is among the highest values reported so far for devices based on DPP-containing polymers. More importantly, the Voc of our PCDPP-based devices can reach as high as 0.86 V, which is much higher than that (<0.7 V) of high-efficiency solar cells based on other DPP polymers. These results provide a promising way to minimize the energy loss and to realize high Voc and Jsc values at the same time in devices to obtain high power conversion efficiencies.

Novel polymers comprising a 3-fluoro-5-alkylthiophenyl benzodithiophene donor unit and a 5-fluoro-6-alkoxy (or alkylthio)-2,1,3-benzothiadiazole (BT) acceptor unit were synthesized. Both POF and PSF possess low HOMO and LUMO energy levels due to the incorporation of fluorine atoms. Additionally, alkoxy and alkylthio substitution on the BT unit also had a great influence on the molecular packing and the energy level of the resulting polymers. The introduction of the alkylthio side chains on the BT unit of PSF led to a significant downshift of the HOMO energy level in comparison to that of POF with an alkoxy substituent due to the weaker electron-donating properties of the sulfur atom than that of oxygen. However, the steric hindrance caused by the large sulfur atoms resulted in reduced planarity of the backbone of PSF, which might influence the charge transport and the morphology of the blend film. As a result, POF based NF-PSCs exhibited a PCE of 7.28%, with a Voc of 0.86 V, a Jsc of 14.9 mA cm−2, and an FF of 0.47, while a low PCE of 1.55% with a Voc of 0.95 V, a Jsc of 5.6 mA cm−2, and an FF of 0.29 was obtained for PSF based non-fullerene polymer solar cells (NF-PSCs). Therefore, the side chain engineering of the donor polymer is crucial for maximizing both Jsc and Voc values to achieve high performance polymer solar cells.

Three planar nonfullerene acceptors (FTIC-C8C6, FTIC-C6C6 and FTIC-C6C8) comprising a central fluorenedicyclopentathiophene (FT) core and two 2-methylene-(3-(1,1-dicyanomethylene)-indanone) terminal groups are designed and synthesized. The coplanarity of the molecular backbone can be maintained through a locked conformation via intramolecular noncovalent interactions. The solubility of these nonfullerene acceptors is very good because the FT core can bear enough flexible aliphatic side-chain substitutions. Thus, the dilemma of the planarity–solubility tradeoff can be minimized. Through changing the length of the six flexible aliphatic side chains at the central FT core, we can easily adjust the π–π interactions of nonfullerene acceptors and optimize the nanoscale morphology of the photoactive layers. Among these three small molecular acceptors, FTIC-C6C8 based active layers show the best morphology together with the highest electron and hole mobility. These inherent advantages of FTIC-C6C8 guarantee it a high power conversion efficiency of 11.12% when used in non-fullerene polymer solar cells with a wide-bandgap polymer donor PBDB-T. Our results provide an appropriate molecular design strategy for building high-performance nonfullerene acceptors and show that optimizing alkyl-side chains is a very effective way to further improve the photovoltaic performance of devices.