Benzotriazole Unit Research Articles

Polymer Based on Asymmetrically Halogenated Benzotriazole Enables High Performance Organic Solar Cells Prepared in Nonhalogenated Solvent.

Halogenation on the A unit of the D-π-A-type polymer donor has been proven as an effective strategy to improve the performance of organic solar cells (OSCs). Compared with fluorination, chlorination usually increases the open-circuit voltage because of the downward shift of energy levels, but decreases the charge transport ability due to the large steric hindrance of the chlorine atom. We reported herein a method to balance the energy loss and charge transport through asymmetric halogenation on the benzotriazole (BTA) unit of the polymer. The designed PE3-FCl based on the BTA unit containing fluorine and chlorine atoms rendered the highest power conversion efficiency (PCE) of 17.83% when eC9-2Cl-γ and o-xylene were used as the electron acceptor and solvent, respectively. The performance is obviously higher than that of the polymer PE3 containing a difluorinated BTA unit (16.65%) and polymer PE3-2Cl with dichlorinated BTA (14.65%) due to the manipulated morphology by preaggregation, improved and more balanced charge carrier transport, and reduced recombination loss. Notably, this PCE is a breakthrough for the BTA-based polymers processed by nonhalogenated solvent. This work gives deep insight into the asymmetric halogenation of polymer donors for high-performance green solvent-processed OSCs.

Control of Multi-Fluorination Number and Position in D-π-A Type Polymers and Their Impact on High-Voltage Organic Photovoltaics.

Exploring the structure-performance relationship of high-voltage organic solar cells (OSCs) is significant for pushing material design and promoting photovoltaic performance. Herein, we chose a D-π-A type polymer composed of 4,8-bis(thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene (BDT-T) and benzotriazole (BTA) units as the benchmark to investigate the effect of the fluorination number and position of the polymers on the device performance of the high-voltage OSCs, with a benzotriazole-based small molecule (BTA3) as the acceptor. F00, F20, and F40 are the polymers with progressively increasing F atoms on the D units, while F02, F22, and F42 are the polymers with further attachment of F atoms to the BTA units based on the above three polymers. Fluorination positively affects the molecular planarity, dipole moment, and molecular aggregations. Our results show that VOC increases with the number of fluorine atoms, and fluorination on the D units has a greater effect on VOC than on the A unit. F42 with six fluorine atom substitutions achieves the highest VOC (1.23 V). When four F atoms are located on the D units, the short-circuit current (JSC) and fill factor (FF) plummet, and before that, they remain almost constant. The drop in JSC and FF in F40- and F42-based devices may be attributed to inefficient charge transfer and severe charge recombination. The F22:BTA3 system achieves the highest power conversion efficiency of 9.5% with a VOC of 1.20 V due to the excellent balance between the photovoltaic parameters. Our study provides insights for the future application of fluorination strategies in molecular design for high-voltage organic photovoltaics.

Dual-state emission and two-wavelength amplified spontaneous emission behaviors observed from symmetric dyes based on functionalized fluorene and benzotriazole units.

Structurally symmetric dyes using functionalized fluorenes and benzotriazole as the main building moieties have been synthesized and found to exhibit efficient dual-state emission (DSE) and interesting two-wavelength or dual amplified spontaneous emission (dual-ASE) behaviors in the solution phase, which may benefit the development of organic gain materials with dual-wavelength amplification.

An A′–A–DA′D–A–A′-type acceptor enables organic solar cells with high VOC and low nonradiative voltage loss

A novel A′–A–DA′D–A–A′ typed acceptor was developed, where the benzotriazole unit was used as the A′ unit both on the central core and terminal groups, to reduce the voltage loss and to increase the open-circuit voltage in efficient organic solar cells.

Subtle structural modification of thiophene-fused benzotriazole unit to simultaneously improve the JSC and VOC of OSCs

A new electron-accepting unit has been designed through introducing two F atoms at α,β-positions of the thiophene fused benzotriazole unit to build a new D–A polymer donor with 4,8-bis(5-alkyl-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene unit.

Benzotriazole-based copolymers with an interlocked conformation for mitigating the correlation of thermoelectric parameters

As for thermoelectric materials, a strong trade-off relationship between the electrical conductivity (σ) and the Seebeck coefficient (S) is a huge obstacle to maximization of their thermoelectric (TE) performances, especially for polymeric semiconductors with a single component. Recently, some of intensive efforts were made to explore effective methods for decoupling TE parameters of organic semiconductors. In this work, a novel type of D–A non-fused-ring copolymers were designed and synthesized from the Stille coupling polymerization of cyclopentadithiophene and benzotriazole units (fluorinated or non-fluorinated). The incorporation of fluorine atoms into the polymer backbone constructed skillfully a fully interlocked coplanar conformation via the dual assistance of the F···S and N···H noncovalent interactions, significantly enhancing the ordered degree of molecular stacking and thus the σ and S values. More importantly, the two polymers achieved a simultaneous increase in both the σ and S within a certain doping time, probably due to that the bimodal orientation of polymers played a crucial role in decoupling the correlation between σ and S. Consequently, FeCl3-doped P(CPD-BTA-2F) harvested an optimal power factor of 7.77 ± 0.77 μW m−1 K−2, which is one order of magnitude higher than that of P(CPD-BTA). This work, albeit only a modest power factor (PF) was attained, offered a valuable insight into the molecular engineering for breaking through the trade-off relationship between σ and S, and shed some light on the development of promising polymeric TE materials.

Design of benzotriazole-based A2-A1-D-A1-A2-type fully non-fused non-fullerene acceptors for P3HT

Designing fitted acceptors for the homopolymer poly(3-hexylthiophene) (P3HT) has been a hot topic in research field of organic solar cells (OSCs) because of its unique advantages of low-cost, stability and simplicity of synthesis. In resent years, we have been committed to the development of fused non-fullerene acceptors (NFA) containing benzotriazole (BTA) unit in order to achieve high power conversion efficiency (PCE). The modulation of the crystallinity of P3HT in the active layer affecting exciton dissociation, charge transfer and recombination has always been a challenge. Here, two simple non-fused NFAs containing BTA with different terminal units were easily prepared. P3HT:BTA31 device delivered an initial PCE of 3.95 % due to the unbalanced charge mobility and adverse trap-assisted recombination. Due to the efficient charge separation and suppressed charge recombination, P3HT:BTA33 device showed an increased PCE of 5.68 %. Our results suggest that these non-fused NFAs are promising candidates for application of P3HT-based OSCs.

Benzotriazole-based 3D 4-Arm Small Molecules Enable 19.1% Efficiency for PM6:Y6-based Ternary Organic Solar Cells.

The third component featuring a planar backbone structure similar to the binary host molecule has been the empirical formula for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3-dimensional structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three 4-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials into the classical system PM6: Y6, the resulting ternary devices obtained ultra-high power conversion efficiencies (PCEs) of 19.1%, 18.7%, and 18.8%, respectively, compared with the binary OSCs (PCE = 17.4%). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.

Benzotriazole‐Based 3D Four‐Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6‐Based Ternary Organic Solar Cells

AbstractA third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D‐structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal‐modified (rhodanine, thiazolidinedione, and dicyano‐substituted rhodanine) benzotriazole (BTA) units, affording three four‐arm molecules, SF‐BTA1, SF‐BTA2, and SF‐BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra‐high power‐conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF‐BTA1‐3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF‐BTA1‐3 also acts to enhance charge generation. Introducing SF‐BTA1‐3 could form acceptor alloys to modify the molecular energy level and inhibit the self‐aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi‐arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi‐arm materials could make OSCs more stable and efficient.

D-A type ambipolar electrochromic copolymers based on dithienopyrrole, 3,4-propylenedioxythiophene and benzotriazole units with dual fading processes

Three donor–acceptor (D-A) type electrochromic copolymers (PDPB-1, PDPB-2 and PDPB-3), employing dithieno[3,2-b:2′,3′-d]pyrrole (DTP) and 3,4-propylenedioxythiophene (ProDOT) units as donors as well as benzotriazole (BTz) units as acceptor, were synthesized by chemical polymerization with different feed molar ratios of the monomers. The three polymers possess double-doping (p-type and n-type doping) electrochromic feature and relatively narrow optical band gaps (about 1.70 eV). Their solid films display slightly different blue colors in the neutral states including dark navy blue (PDPB-1), navy blue (PDPB-2 and PDPB-3), and all switch to light blue-gray after oxidation as well as to gray after reduction. The polymers also exhibit favorable kinetic properties, especially showing high optical contrasts and desired coloring efficiencies in the near-infrared (NIR) region. D-A type ambipolar electrochromic polymers with dual fading processes which display oxidized and reduced gray states are rarely reported in the literatures and such materials are obtained in this work by utilizing DTP units which are rarely used as building blocks for electrochromic copolymers.

P-nitrophenol-terminated alkyl side chain substituted polymer as high dielectric constant polymer additive enables efficient organic solar cells

Herein, we introduced p-nitrophenol-terminated alkyl side chain into the benzotriazole unit and synthesized a high dielectric constant polymer PBTA-NO2 (εr = 7.1). The properties as absorption spectra, energy levels, aggregation, dielectric constant, photovoltaic performance, etc. of PBTA-NO2 were analyzed and compared with its controlled polymer PBTA-C10H21. It is found that the PBTA-NO2 exhibits a similar absorption spectrum, lower highest occupied molecular orbital (HOMO) energy level, stronger aggregation characteristic and higher dielectric constant at 1 kHz in contrast to that of PBTA-C10H21. Beyond that, the PBTA-NO2 was adopted as a high dielectric constant polymer additive into the active layer of the PM6:Y6 based polymer solar cells (PSCs). The incorporation of 5 wt% PBTA-NO2 slightly increased the relative dielectric constant (εr) of the blend film from 4.4 to 4.8 and simultaneously improved the morphology of the active layer, which promoted the exciton dissociation and carrier transport, inhibited bimolecular recombination, and eventually increased the power conversion efficiency (PCE) by 6% as compared to the original device.

PTB7-Th-Based Organic Photovoltaic Cells with a High VOC of over 1.0 V via Fluorination and Side Chain Engineering of Benzotriazole-Containing Nonfullerene Acceptors.

PTB7-Th is considered one of the most classic donor polymers for organic photovoltaic (OPV) cells. However, the power conversion efficiency (PCE) of PTB7-Th-based OPV is lagging behind that of other promising polymers mainly because of the relatively low open-circuit voltage (VOC). To increase the VOC and PCE of PTB7-Th-based OPV, the development of nonfullerene acceptors (NFAs) and studies of structure-property-performance relationship are vital. Here, three A2-A1-D-A1-A2-type acceptors, namely BTA45, F-BTA45, and F-BTA5, were developed by fluorination on the benzotriazole (BTA) unit and regulating alkoxy or alkyl phenyl side chains. Compared with BTA45, light absorption and π-π packing can be simultaneously improved for the two fluorinated BTA acceptors, resulting in an increased JSC and FF. Moreover, the F-BTA5-based blend film exhibits better phase separation morphology and electron transport than those of BTA45 and F-BTA45, which contribute to a device efficiency of 10.36% with a VOC of 1.03 V. In addition, the ΔE2 values of the three blends are less than 0.15 eV, together with their moderate ΔE3, efficiently decreasing their energy loss. These results highlight the importance of fluorination and side chain engineering for NFAs to boost the VOC and PCE for low-band gap photovoltaic polymers.

Side-Chain Substituents on Benzotriazole-Based Polymer Acceptors Affecting the Performance of All-Polymer Solar Cells.

Recently, the strategy of polymerized small-molecule acceptors (PSMAs) has attracted extensive attention for applications in all-polymer solar cells (all-PSCs). Although side-chain engineering is considered as a simple and effective strategy for manipulating polymer properties, the corresponding effect on photovoltaic performance of PSMAs in all-PSCs has not been systemically investigated. Herein, a series of PSMAs based on the benzotriazole (BTz)-core fused SMAs with different N-alkyl chains including branched 2-butyloctyl, linear n-octyl, and methyl on the BTz unit, namely PZT-C12, PZT-C8, and PZT-C1, respectively, is presented. Comparative studies show that the size of alkyl chains has a significant impact on the solid-state behavior of PZT polymers, which in turn affects their light absorption and charge transporting capacities, and subsequently the all-PSC performances. When combining with the polymer donor PBDB-T, PZT-C1 affords a champion power conversion efficiency of 14.9%, compared to 13.1% of PZT-C12, and 13.8% of PZT-C8 in the resultant all-PSCs, mainly benefiting from its better crystallinity and the more favorable blend morphology. This work emphasizes the importance of optimizing side-chain substituents on PSMAs for improving the device efficiency of all-PSCs.

The Subtle Structure Modulation of A2 -A1 -D-A1 -A2 Type Nonfullerene Acceptors Extends the Photoelectric Response for High-Voltage Organic Photovoltaic Cells.

Molecular structural modifications are utilized to improve the short-circuit current (JSC ) of high-voltage organic photovoltaics (OPVs). Herein, the classic non-fullerene acceptor (NFA), BTA3, is chosen as a benchmark, with BTA3b containing the linear alkyl chains on the middle core and JC14 fusing thiophene on the benzotriazole (BTA) unit as a contrast. The photovoltaic devices based on J52-F: BTA3b and J52-F: JC14 achieve wider external quantum efficiency responses with band edges of 730 and 800nm, respectively than that of the device based on J52-F: BTA3 (715 nm). The correspondingJSC increases to 14.08 and 15.78mA cm-2 , respectively, compared to BTA3 (11.56mA cm-2 ). The smaller Urbach energy and higher electroluminescence efficiency guarantee J52-F: JC14 a decreased energy loss (0.528eV) and a high open-circuit voltage (VOC ) of 1.07V. Finally, J52-F: JC14 combination achieves an increased power conversion efficiency (PCE) of 10.33% than that of J52-F: BTA3b (PCE = 9.81%) and J52-F: BTA3 (PCE = 9.04%). Overall, the research results indicate that subtle structure modification of NFAs, especially introducing fused rings, is a simple and effective strategy to extend the photoelectric response, boosting theJSC and ensuring a high VOC beyond 1.0V.

Linear and second‐order nonlinear optical properties of non‐fullerene acceptor derivatives with A–D–A structure

AbstractIn this paper, in order to study the relationship between structure and performance, four new non‐fullerene acceptor (NFA) derivatives were designed based on the two reported NFA molecules BO‐4Cl and BTP‐S2 by replacing the benzothiadiazole unit with a less‐electron deficient benzotriazole unit and inserting another ethylene double bond between the central core and the terminal groups. Density functional theory (DFT) and Time‐dependent DFT were applied to investigate linear and nonlinear optical (NLO) properties, such as electronic structure, electronic absorption, reorganization energy, and the second‐order NLO properties. The investigation demonstrates that they are all narrow bandgap derivatives, the absorption spectrum extends to the near‐infrared region and using two ethylene double bond is the most effective way to reduce the energy gap, redshift the maximum absorption peak and the middle absorption band, and enhance second‐order NLO response. Considering the smaller electron and hole reorganization energy and the larger static first hyperpolarizability value, the studied NFA derivatives have great potential to become ambipolar charge transport materials and large second‐order NLO materials.

Effects of Halogenation on the Benzotriazole Unit of Non-Fullerene Acceptors in Organic Solar Cells with High Voltages.

Non-fullerene acceptors (NFAs) can be simply divided into three categories: A-D-A, A-DA'D-A, and A2-A1-D-A1-A2 according to their chemical structures. Benefiting from the easily modified 1,1-dicyanomethylene-3-indanone end groups, the halogenation on the first two types of materials has been proved to be very effective to modulate their optoelectronic properties and improve their photovoltaic performance. Hence, in this work, we systematically investigate the effect of halogenation on the classic NFA molecule of BTA3, which has the linear A2-A1-D-A1-A2-type backbone. After fluorination and chlorination, F-BTA3 and Cl-BTA3 have similar optical band gaps but lower energy levels than BTA3. When blending with a linear copolymer PE25 composed of benzodifuran and chlorinated benzotriazole (BTA) according to "Same-A-Strategy", the corresponding VOC of the halogenated NFAs gradually decreases (1.13 V for F-BTA3 and 1.09 V for Cl-BTA3), compared with that of the BTA3-based device (VOC = 1.22 V). This tendency mainly comes from the lower lowest unoccupied molecular orbital energy levels due to the strong electron-withdrawing ability of halogen atoms and the larger nonradiative energy loss. However, the power conversion efficiencies of the halogenated materials are slightly improved, from 9.08% for PE25: BTA3 to 10.45% for PE25: F-BTA3 and 10.75% for PE25: Cl-BTA, with the nonhalogenated solvent tetrahydrofuran as the processing solvent. The improved photovoltaic performance of F-BTA3 and Cl-BTA3 should come from the higher carrier mobility, weaker bimolecular recombination, and higher fluorescence quenching rate. This study illustrates that halogenation on the A1 unit is a promising strategy for developing novel and effective A2-A1-D-A1-A2-type NFAs.

Polymerized small-molecule acceptors based on vinylene as π-bridge for efficient all-polymer solar cells

Two near-infrared (NIR) polymer acceptors (PAs, PYV, and PYV-Tz) based on fused-ring 2,1,3-benzothiadiazole (BT)- or benzotriazole (BTz)-based A′-DAD-A′ structure as electron-deficient-core and vinylene as the linking units, were designed and synthesized. The structure-property relationships of the all-polymer solar cells (all-PSCs) with a wide bandgap PBDB-T as donor were investigated systematically. Compared to the BT-based PA PYV, using BTz unit as the central core in PA PYV-Tz leads to the red-shifted absorption spectra and higher absorption coefficient in the PYV-Tz neat film. In addition, PYV-Tz also exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level and better electron mobility. Consequently, the PBDB-T:PYV-Tz all-PSCs displayed a PCE of 13.02%, under the illumination of AM 1.5G, 100 mW cm-2, which is much higher than that of the PBDB-T:PYV device (11.51%). The measurements of relevant physical dynamics and blend morphologies further demonstrated the photovoltaic performance differences between PBDB-T:PYV and PBDB-T:PYV-Tz. This result indicates that PYV-Tz is a promising polymer acceptor material for the potential application of all-PSCs.

Compatibility between Solubility and Enhanced Crystallinity of Benzotriazole-Based Small Molecular Acceptors with Less Bulky Alkyl Chains for Organic Solar Cells.

Optimizing the molecular structures of organic solar cell (OSC) materials and boosting the power conversion efficiencies are the eternal theme in the solar energy region. A series of fused benzotriazole (BTA)-based A-DA'D-A structures of nonfullerene acceptors (such as Y18) were developed for application in efficient OSCs, in which high quantum efficiencies and low voltage losses could be achieved because of the optimized electron-deficient core and specific molecular geometry. Here, based on the BTA core, the bulky alkyl chain on the BTA unit was further tailored to minimize the lateral alkyl chains and enhance the crystallinity while maintaining an adequate solubility. The resulting NFAs of BTA-C1, BTA-C5, and BTA-C6 are synthesized. Compared with the well-designed molecular Y18 (BTA-C8), we found that simply replacing the 2-ethylhexyl chain with a single methyl (BTA-C1) can easily improve the fill factor up to 77%, but its poor light absorption capacity and large domain size impeded further efficiency improvement. In particular, the BTA-C5, with a shortened branch alkyl chain of 2-methylbutyl, achieves suitable solubility and enhanced crystallinity. Significantly, owing to the balanced charge carrier mobility and suitable phase separation, the BTA-C5-based binary single-junction OSCs achieve a high efficiency of 17.11%, which is one of the top values in BTA-based OSCs.

Modulating the middle and end-capped units of A2-A1-D-A1-A2 type non-fullerene acceptors for high VOC organic solar cells

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been improved rapidly in the last few years, due to the development of excellent non-fullerene acceptor (NFA) materials. However, compared to the high PCE, the open-circuit voltage ( V OC ) of OSCs is still relatively low. Recently, we have demonstrated that the “Same-A-Strategy” (SAS) is feasible to achieve high V OC , where the same electron-accepting (A) unit is utilized to construct polymer donor and NFA. To investigate the structure-properties relationship, here we chose six benzotriazole-based NFAs (BTA1, BTA11, BTA3, BTA13, BTA7 and BTA17) with A 2 -A 1 -D-A 1 -A 2 type molecular backbone, where indacenodithiophene (IDT) and indacenodithieno[3,2- b ]thiophene (IDTT) as middle electron-donating unit, rhodanine (R), 2-(1,1-dicyanomethylene)rhodanine (RCN), and malononitrile (M) as the terminal A 2, respectively. When paired with a p-type polymer J52-Cl containing BTA unit, OSCs based on six material combinations can realize ultra-high V OC of 1.09–1.33 V with PCEs of 0.13–10.5%. The results indicate that the middle and end-capped units play a vital role to extend the application of SAS, and IDT and RCN are promising choices as the core and end-capped groups. Six benzotriazole-based non-fullerene acceptors are combined with a benzotriazole-based polymer J52-Cl for high-voltage organic solar cells. The results indicate IDT and RCN are better choices as the middle and end-capped groups for “Same-A-Strategy” material combinations. • By modulating the middle and end capped units, six benzotriazole (BTA)-based non-fullerene acceptors are developed to combine with a BTA-based polymer. • Organic solar cell based on all the six material combinations can achieve high V oc of 1.09–1.33V. • The PCEs of OSCs based on these six non-fullerene acceptors various from 0.13% to 10.5%.

New 3-Ethynylaryl Coumarin-Based Dyes for DSSC Applications: Synthesis, Spectroscopic Properties, and Theoretical Calculations.

A set of 3-ethynylaryl coumarin dyes with mono, bithiophenes and the fused variant, thieno [3,2-b] thiophene, as well as an alkylated benzotriazole unit were prepared and tested for dye-sensitized solar cells (DSSCs). For comparison purposes, the variation of the substitution pattern at the coumarin unit was analyzed with the natural product 6,7-dihydroxycoumarin (Esculetin) as well as 5,7-dihydroxycomarin in the case of the bithiophene dye. Crucial steps for extension of the conjugated system involved Sonogashira reaction yielding highly fluorescent molecules. Spectroscopic characterization showed that the extension of conjugation via the alkynyl bridge resulted in a strong red-shift of absorption and emission spectra (in solution) of approximately 73–79 nm and 52–89 nm, respectively, relative to 6,7-dimethoxy-4-methylcoumarin (λabs = 341 nm and λem = 410 nm). Theoretical density functional theory (DFT) calculations show that the Lowest Unoccupied Molecular Orbital (LUMO) is mostly centered in the cyanoacrylic anchor unit, corroborating the high intramolecular charge transfer (ICT) character of the electronic transition. Photovoltaic performance evaluation reveals that the thieno [3,2-b] thiophene unit present in dye 8 leads to the best sensitizer of the set, with a conversion efficiency (η = 2.00%), best VOC (367 mV) and second best Jsc (9.28 mA·cm−2), surpassed only by dye 9b (Jsc = 10.19 mA·cm−2). This high photocurrent value can be attributed to increased donor ability of the 5,7-dimethoxy unit when compared to the 6,7 equivalent (9b).