Dye-sensitized solar cells based on donor-π-acceptor fluorescent dyes with a pyridine ring as an electron-withdrawing-injecting anchoring group

A new‐type of donor–acceptor π‐conjugated (D‐π‐A) fluorescent dyes NI3 – NI8 with a pyridine ring as electron‐withdrawing‐injecting anchoring group have been developed and their photovoltaic performances in dye‐sensitized solar cells (DSSCs) are investigated. The short‐circuit photocurrent densities and solar energy‐to‐electricity conversion yields of DSSCs based on NI3 – NI8 are greater than those for the conventional D‐π‐A dye sensitizers NI1 and NI2 with a carboxyl group as the electron‐withdrawing anchoring group. The IR spectra of NI3 – NI8 adsorbed on TiO₂ indicate the formation of coordinate bonds between the pyridine ring of dyes NI3 – NI8 and the Lewis acid sites (exposed Tiⁿ⁺ cations) of the TiO₂ surface. This work demonstrates that the pyridine rings of D‐π‐A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO₂ surface are promising candidates as not only electron‐withdrawing anchoring group but also electron‐injecting group, rather than the carboxyl groups of the conventional D‐π‐A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO₂ surface.     

Donor‐π‐Acceptors Containing the 10‐(1,3‐Dithiol‐2‐ylidene)anthracene Unit for Dye‐Sensitized Solar Cells

Two donor–acceptor molecular tweezers incorporating the 10‐(1,3‐dithiol‐2‐ylidene)anthracene unit as donor group and two cyanoacrylic units as accepting/anchoring groups are reported as metal‐free sensitizers for dye‐sensitized solar cells. By changing the phenyl spacer with 3,4‐ethylenedioxythiophene (EDOT) units, the absorption spectrum of the sensitizer is red‐shifted with a corresponding increase in the molar absorptivity. Density functional calculations confirmed the intramolecular charge‐transfer nature of the lowest‐energy absorption bands. The new dyes are highly distorted from planarity and are bound to the TiO₂ surface through the two anchoring groups in a unidentate binding form. A power‐conversion efficiency of 3.7 % was obtained with a volatile CH₃CN‐based electrolyte, under air mass 1.5 global sunlight. Photovoltage decay transients and ATR‐FTIR measurements allowed us to understand the photovoltaic performance, as well as the surface binding, of these new sensitizers.     

Organic Dyes with Well‐Defined Structures for Highly Efficient Dye‐Sensitised Solar Cells Based on a Cobalt Electrolyte

Seven SGT organics dyes, containing bis‐dimethylfluoreneyl amino groups with a dialkoxyphenyl unit as an electron donor and a cyanoacrylic acid group as an anchoring group, connected with oligothiophenes, fused thiophenes and benzothiadiazoles as π‐bridges, were designed and synthesised for applications in dye‐sensitised solar cells (DSSCs). The photovoltaic performance of DSSCs based on organic dyes with oligothiophenes depends on the molecular structure of the dyes, in terms of the length change of the π‐bridging units. The best performance was found with a π‐bridge length of about 6 Å. To further enhance the photovoltaic performance associated with this concept, cyclopenta[1,2‐b:5,4‐b′]dithiophene (CPDT) and benzothiadiazole were introduced into the π‐bridge unit. As a result, the DSSC based on the organic dye containing the CPDT moiety showed the best photovoltaic performance with a short‐circuit photocurrent density (J_sc) of 14.1 mA cm^?2, an open‐circuit voltage (V_oc) of 0.84 V and a fill factor (FF) of 0.72, corresponding to an overall conversion efficiency (η) of 8.61 % under standard AM 1.5 irradiation.     

Enhanced Charge Separation Efficiency in Pyridine‐Anchored Phthalocyanine‐Sensitized Solar Cells by Linker Elongation

A series of zinc phthalocyanine sensitizers ( PcS22 – 24 ) having a pyridine anchoring group are designed and synthesized to investigate the structural dependence on performance in dye‐sensitized solar cells. The pyridine‐anchor zinc phthalocyanine sensitizer PcS23 shows 79 % incident‐photon to current‐conversion efficiency (IPCE) and 6.1 % energy conversion efficiency, which are comparable with similar phthalocyanine dyes having a carboxylic acid anchoring group. Based on DFT calculations, the high IPCE is attributed with the mixture of an excited‐state molecular orbital of the sensitizer and the orbitals of TiO₂. Between pyridine and carboxylic acid anchor dyes, opposite trends are observed in the linker‐length dependence of the IPCE. The red‐absorbing PcS23 is applied for co‐sensitization with a carboxyl‐anchor organic dye D131 that has a complementary spectral response. The site‐selective adsorption of PcS23 and D131 on the TiO₂ surface results in a panchromatic photocurrent response for the whole visible‐light region of sun light.     

Bandgap Modulation in Efficient n‐Thiophene Absorbers for Dye Solar Cell Sensitization

Five new sensitizers for dye sensitized solar cells have been designed consisting of conjugated thienylenevinylene units threaded with alkyl chains to improve solubility and cyanoacetic acid as anchoring group. The conjugation length was increased from 2 to 6 thienylenevinylene units, which resulted in a red‐shift of the optical absorption of the dyes from 550 to 750 nm, improving the spectral overlap with the solar spectrum. The photovoltaic performance of these dyes as sensitizers in mesoporous TiO₂ solar cells shows a clear correlation of increasing photocurrent with the extension of the conjugation up to an optimal length. Further extension of the conjugation increases the absorption but additional effects like self‐quenching or recombination processes reduce the photocurrent and photovoltages and consequently the overall efficiency of the DSC.     

Dye‐Sensitized Solar Cells Based on a Donor–Acceptor System with a Pyridine Cation as an Electron‐Withdrawing Anchoring Group

New hemicyanine dyes ( CM101 , CM102 , CM103 , and CM104 ) in which tetrahydroquinoline derivatives are used as electron donors and N‐(carboxymethyl)‐pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye‐sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N‐(carboxymethyl)‐pyridinium has a stronger electron‐withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101 – CM104 markedly depends on the molecular structures of the dyes in terms of the n‐hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0 % (J_sc=13.4 mA cm^?2, V_oc=704 mV, FF=74.8 %) under AM 1.5 irradiation (100 mW cm^?2). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4 % (J_sc=6.2 mA cm^?2, V_oc=730 mV, FF=74.8 %). Under the same conditions, the cell fabricated with N719 sensitized porous TiO₂ exhibited an efficiency of 7.9 % (J_sc=15.4 mA cm^?2, V_oc=723 mV, FF=72.3 %). The dyes CM101 – CM104 show a broader spectral response compared with the reference dyes CMR101 – CMR104 and have high IPCE exceeding 90 % from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100 % during this region.     

The Influence of Substituent Orientation on the Photovoltaic Performance of Phthalocyanine‐Sensitized Solar Cells

Phthalocyanines (Pcs) are used as sensitizers in dye‐sensitized solar cells (DSSCs) because of their stability and intense absorption in the red and near‐IR regions. Impressive progress has been made in photovoltaic efficiencies by introduction of bulky peripheral substituents to help suppress macrocycle aggregation. To reach benchmark efficiencies reported for other related dyes, new designs need to be explored. Single carboxy‐ZnPc regioisomers substituted at the non‐peripheral positions by rigid aryl groups have now been studied, which has shed light on the influence of steric hindrance and/or orientation of the substituent around the anchoring group on the photovoltaic response. The regioisomer bearing the aryl group far away from the anchoring group produces a more effective sensitization of the TiO₂ films and higher short‐circuit photocurrent density (J_sc). Taking advantage of the good photovoltaic performance in the near‐IR region of this ZnPc, it was combined with another appropriate dye for panchromatic sensitization of the mesoporous photoelectrode and an increase of the overall device efficiency.     

Benzothiadiazole Containing D‐π‐A Conjugated Compounds for Dye‐Sensitized Solar Cells: Synthesis,Properties, and Photovoltaic Performances

Two D ‐π‐A conjugated molecules, BzTCA and BzTMCA , were developed through facile synthetic approaches for dye‐sensitized solar cells. The investigation of the photophysical properties of BzTCA and BzTMCA both in dilute solutions and in thin films indicates that their absorption exhibits a wide coverage of the solar spectrum. The absorption features for BzTCA and BzTMCA commence at about 710 nm in solution, and at about 800 nm in the solid state. The absorption maxima (λ_max) for both BzTCA and BzTMCA on TiO₂ film are almost the same as those in dilute solution. Their HOMOs and LUMOs were found to partly overlap at the center of these dyes, which guarantees appreciable interactions between the donors and acceptors. The investigation of the performance of dye‐sensitized solar cells fabricated from BzTCA and BzTMCA indicated that the power‐conversion efficiencies are 6.04 % and 4.68 %, respectively, which could be comparable with the normal sensitizer N3. BzTMCA showed lower incident photon‐to‐electron conversion efficiency (IPCE) and J_sc values relative to BzTCA , which is probably because of the weaker driving force of dye regeneration and electron injection process of BzTMCA . The IPCE responsive area reached nearly 800 nm, which provides great potential for further improvement of the photocurrent density and power‐conversion efficiency. Our investigations demonstrate that both dyes BzTCA and BzTMCA could be promising candidates for dye‐sensitized solar cells.     

Computational studies on optoelectronic and charge transfer properties of some perylene‐based donor‐π‐acceptor systems for dye sensitized solar cell applications

We report DFT studies on some perylene‐based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor‐π‐acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the π‐bridge and cyanoacrylic group as the acceptor. The effect of different π‐bridges and various substituents on the perylene donor was evaluated in terms of opto‐electronic and photovoltaic parameters such as HOMO‐LUMO energy gap, λ_max, light harvesting efficiency(LHE), electron injection efficiency (Ø_inject), excited state dye potential (E^dye*), reorganization energy(λ), and free energy of dye regeneration (). The effect of various substituents on the dye–I₂ interaction and hence recombination process was also evaluated. We found that the furan‐based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto‐electronic and transport parameters of the TiO₂‐dye assembly after anchoring the dyes on the model TiO₂ cluster assembly.     

Molecular Design Principle of All‐organic Dyes for Dye‐Sensitized Solar Cells

All‐organic dyes have shown promising potential as an effective sensitizer in dye‐sensitized solar cells (DSSCs). The design concept of all‐organic dyes to improve light‐to‐electric‐energy conversion is discussed based on the absorption, electron injection, dye regeneration, and recombination. How the electron‐donor–acceptor‐type framework can provide better light harvesting through bandgap‐tuning and why proper arrangement of acceptor/anchoring groups within a conjugated dye frame is important in suppressing improper charge recombination in DSSCs are discussed. Separating the electron acceptor from the anchoring unit in the donor–acceptor‐type organic dye would be a promising strategy to reduce recombination and improve photocurrent generation.     

Dye‐sensitized solar cells based on zinc(II) phthalocyanines bearing 3‐pyridin‐3‐ylpropoxy anchoring groups

In this study, nonperipherally tetra‐substituted ( 2 ), peripherally tetra‐substituted ( 3 ), and peripherally octa‐substituted ( 4 ) zinc(II) phthalocyanines were synthesized as sensitizers for dye‐sensitized solar cells (DSSCs) in which 3‐pyridin‐3‐ylpropoxy substituent acts as anchoring unit to bind TiO₂ surface. The optical results indicated that there is an interaction between the dyes and the TiO₂ surface. The photovoltaic performances of the DSSCs based on these dyes were found to depend on both the position and number of the substituents. Despite the more red‐shifted absorption, the DSSC based on 2 showed the conversion efficiency of 0.68%, which is lower than 1.36% and 0.92% for 3 and 4 , respectively, under one sun (AM 1.5G). The vertical orientation of the dye on TiO₂ surface could be the main reason for the higher photovoltaic performance of complex 3 , which is beneficial for not only injecting the electrons into the conduction band of TiO₂ but also reducing the charge recombination. Overall, these results demonstrate that the peripherally tetra‐substituted 3‐pyridin‐3‐ylpropoxy zinc(II) phthalocyanine complex ( 3 ) as a sensitizer can more efficiently utilize the photons in the red/near‐infrared region with respect to the other complexes studied.     

New Dual Donor–Acceptor (2D‐π‐2A) Porphyrin Sensitizers for Stable and Cost‐Effective Dye‐Sensitized Solar Cells

A series of porphyrin sensitizers that featured two electron‐donating groups and dual anchoring groups that were connected through a porphine π‐bridging unit have been synthesized and successfully applied in dye‐sensitized solar cells (DSSCs). The presence of electron‐donating groups had a significant influence on their spectroscopic, electrochemical, and photovoltaic properties. Overall, the dual anchoring groups gave tunable electronic properties and stronger attachment to TiO₂. These new dyes were readily synthesized in a minimum number of steps in gram‐scale quantities. Optical and electrochemical data confirmed the advantages of these dyes for use as sensitizers in DSSCs. Porphyrins with electron‐donating amino moieties provided improved charge separation and better charge‐injection efficiencies for the studied dual‐push–pull dyes. Attenuated total reflectance–Fourier‐transform infrared (ATR‐FTIR) and X‐ray photoelectron spectroscopy of the porphyrin dyes on TiO₂ suggest that both p‐carboxyphenyl groups are attached onto TiO₂, thereby resulting in strong attachment. Among these dyes, cis-Zn2BC2A , with two electron‐donating 3,6‐ditertbutyl‐phenyl‐carbazole groups and dual‐anchoring p‐carboxyphenyl groups, showed the highest efficiency of 4.07 %, with J_SC=9.81 mA cm^?2, V_OC=0.63 V, and FF=66 %. Our results also indicated a better photostability of the studied dual‐anchored sensitizers compared to their mono‐anchored analogues under identical conditions. These results provide insight into the developments of a new generation of high‐efficiency and thermally stable porphyrin sensitizers.     

Molecular design of organic dyes with diketopyrrolopyrrole for dye‐sensitized solar cell: A theoretical approach

Three designed metal‐free dyes based on 3‐(10‐butyl‐8‐(methylthio)‐10H‐phenothiazin‐3‐yl)‐2‐cyanoacrylic acid (V5) are investigated by density functional theory (DFT) and time‐dependent DFT to improve the efficiency of V5‐based solar cell devices. We have studied the geometrical structures, excitations, electronic structures, and conduction band shift caused by dye adsorption. The results indicate that the designed dyes have several merits compared with V5 including: (i) smaller energy band gaps and the LUMO closer to conduction band of TiO₂; (ii) wider absorption spectra and higher oscillator strength; (iii) larger dipole moment that lead to higher V_oc value. Our work suggests that the modification of π‐bridge with diketopyrrolopyrrole unit is very effective for designing novel metal‐free dyes with improved performance for dye‐sensitized solar cells (DSSCs). These findings are expected to provide a bright way to design new efficient metal‐free organic DSSCs. © 2014 Wiley Periodicals, Inc.     

Influence of Solvent and Bridge Structure in Alkylthio‐Substituted Triphenylamine Dyes on the Photovoltaic Properties of Dye‐Sensitized Solar Cells

Three new triphenylamine dyes that contain alkylthio‐substituted thiophenes with a low bandgap as a π‐conjugated bridge unit were designed and synthesized for organic dye‐sensitized solar cells (DSSCs). The effects of the structural differences in terms of the position, number, and shape of the alkylthio substituents in the thiophene bridge on the photophysical properties of the dye and the photovoltaic performance of the DSSC were investigated. The introduction of an alkylthio substituent at the 3‐position of thiophene led to a decrease in the degree of redshift and the value of the molar extinction coefficient of the charge‐transfer band, and the substituent with a bridged structure led to a larger redshift than that of the open‐chain structure. The introduction of bulky and hydrophobic side chains decreased the short‐circuit photocurrent (J_sc), which was caused by the reduced amount of dye adsorbed on TiO₂. This resulted in a decrease in the overall conversion efficiency (η), even though it could improve the open‐circuit voltage (V_oc) due to the retardation of charge recombination. Furthermore, the change in solvents for TiO₂ sensitization had a critical effect on the performance of the resulting DSSCs due to the different amounts of dye adsorbed. Based on the optimized dye bath and molecular structure, the ethylene dithio‐substituted dye ( ATT3 ) showed a prominent solar‐to‐electricity conversion efficiency of 5.20 %.     

The Role of π Bridges in High‐Efficiency DSCs Based on Unsymmetrical Squaraines

A series of squaraine‐based sensitizers with various π bridges and anchors were prepared and examined in dye‐sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4‐di‐n‐hexyl‐cyclopentadithiophene group that is directly attached onto the π bridge, JD10 , exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem‐di‐n‐hexyl substituents, which extend above and below the π‐conjugated dye plane. Dye JD10 demonstrates a power‐conversion efficiency of 7.3 % for liquid‐electrolyte dye‐sensitized solar cells and 7.9 % for cells that are co‐sensitized by another metal‐free dye, D35 , which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident‐photon‐to‐current‐conversion efficiency curve is realized for this dye with an excellent short‐circuit current of 18.0 mA cm^?2. This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5 000 M ^?1 cm^?1 from 400 nm to the long‐wavelength onset of 724 nm for dye JD10 .     

Tuning the Spectroscopic,Electrochemical, and Photovoltaic Properties of Triaryl Amine Based Sensitizers through Ring‐Fused Thiophene Bridges

The ring‐fused thiophene derivatives benzo[c]thiophene and its precursor bicyclo[2.2.2]octadiene (BCOD) have been introduced as π‐conjugated spacers for organic push–pull sensitizers with dihexyloxy‐substituted triphenylamine as donor and cyanoacrylic acid as acceptor ( OL1 , OL2 , OL3 , OL4 , OL5 , OL6 ). The effects of the fused ring on the spectroscopic and electrochemical properties of these sensitizers and their photovoltaic performance in dye‐sensitized solar cells have been evaluated. Introduction of a binary benzo[c]thiophene and ethylenedioxy thiophene as π bridge caused a significant red shift of the characteristic intramolecular charge‐transfer band to 642 nm. It is found that the sensitizer OL3 , which contains one benzo[c]thiophene unit as π linker, gives the highest overall conversion efficiency of 5.03 % among all these dyes.     

A Computational and Experimental Study of Thieno[3,4‐b]thiophene as a Proaromatic π‐Bridge in Dye‐Sensitized Solar Cells

Four D ‐π‐A dyes (D=donor, A=accpetor) based on a 3,4‐thienothiophene π‐bridge were synthesized for use in dye‐sensitized solar cells (DSCs). The proaromatic building block 3,4‐thienothiophene is incorporated to stabilize dye excited‐state oxidation potentials. This lowering of the excited‐state energy levels allows for deeper absorption into the NIR region with relatively low molecular weight dyes. The influence of proaromatic functionality is probed through a computational analysis of optimized bond lengths and nucleus independent chemical shifts (NICS) for both the ground‐ and excited‐ states. To avoid a necessary lowering of the TiO₂ semiconductor conduction band (CB) to promote efficient dye–TiO₂ electron injection, strong donor functionalities based on triaryl‐ and diarylamines are employed in the dye designs to raise both the ground‐ and excited‐state oxidation potentials of the dyes. Solubility, aggregation, and TiO₂ surface protection are addressed by examining an ethylhexyl alkyl chain in comparison to a simple ethyl chain on the 3,4‐thienothiophene bridge. Power conversion efficiencies of up to 7.8 % are observed.     

Novel Thiazolo[5,4‐d]thiazole‐Based Organic Dyes for Quasi‐Solid‐State Dye‐Sensitized Solar Cells

A series of novel metal‐free organic dyes containing the thiazolo[5,4‐d]thiazole moiety were designed and synthesized for quasi‐solid‐state dye‐sensitized solar cells (DSSCs). Different alkoxy chains were introduced into the electron donor part of the dye molecules for comparison. The optical, electrochemical, and photovoltaic properties for all sensitizers were systematically investigated. It was found that the sensitizers with the different alkoxy groups have similar photophysical and electrochemical properties, such as absorbance and energy levels, owing to their close chemical structures. However, the quasi‐solid‐state DSSCs based on the resulting sensitizers exhibit different performance parameters. The quasi‐solid‐state DSSC based on sensitizer FNE74 with two octyloxy chains possessed the highest solar energy conversion efficiency of 5.10 % under standard AM 1.5G sunlight illumination without the use of coadsorbant agents.     

Bi‐anchoring Organic Dyes that Contain Benzimidazole Branches for Dye‐Sensitized Solar Cells: Effects of π Spacer and Peripheral Donor Groups

Benzimidazole‐branched bi‐anchoring organic dyes that contained triphenylamine/phenothiazine donors, 2‐cyanoacrylic acid acceptors, and various π linkers were synthesized and examined as sensitizers for dye‐sensitized solar cells. The structure–activity relationships in these dyes were systematically investigated by using absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The wavelength of the absorption peak was more‐heavily influenced by the nature of the π linker than by the nature of the donor. For a given donor, the absorption maximum (λ_max) was red‐shifted on changing the π linker from phenyl to 2,2′‐bithiophene, whilst the dyes that contained triphenylamine units displayed higher molar extinction coefficients (?) than their analogous phenothiazine‐based triphenylamine dyes, which led to good light‐harvesting properties in the triphenylamine‐based dyes. Electrochemical data for the dyes indicated that the triphenylamine‐based dyes possessed relatively low‐lying HOMOs, which could be beneficial for suppressing back electron transfer from the conduction band of TiO₂ to the oxidized dyes, owing to facile regeneration of the oxidized dye by the electrolyte. The best performance in the DSSCs was observed for a dye that possessed a triphenylamine donor and 2,2′‐bithiophene π linkers. Electron impedance spectroscopy (EIS) studies revealed that the use of triphenylamine as the donor and phenyl or 2,2′‐bithiophene as the π linkers was beneficial for disrupting the dark current and charge‐recombination kinetics, which led to a long electron lifetime of the injected electrons in the conduction band of TiO₂.     

New Bithiazole‐Based Sensitizers for Efficient and Stable Dye‐Sensitized Solar Cells

A series of new push–pull organic dyes ( BT‐I – VI ), incorporating electron‐withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye‐sensitized solar cells (DSSCs). In comparison with the model compound T1 , these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π–π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT‐I ‐based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon‐to‐current conversion efficiency (IPCE) of 81.1 %, a short‐circuit photocurrent density (J_sc) of 15.69 mA cm^?2, an open‐circuit photovoltage (V_oc) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long‐term stability of the BT‐I – III ‐based DSSCs with ionic‐liquid electrolytes under 1000 h of light soaking was demonstrated and BT‐II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.