Herein, we demonstrate a facile technique for transforming a low‐energy‐converting quinoxaline‐based polymer into an efficient polymeric donor for non‐fullerene acceptor‐based organic solar cells (NFA‐OSCs). Alternating copolymers, namely P(BDTSi‐DTfQ), incorporating electron‐rich 4,8‐bis(triisopropylsilylethynyl)‐benzo[1,2‐b:4,5‐′]dithiophene (BDTSi) and electron‐deficient 2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (DTfQ) units were synthesized. The properties of P(BDTSi‐DTfQ) were thoroughly studied and briefly compared to those of the reported polymers, namely P(BDTSi‐DTffQ), made up of BDTSi and 2,3‐didodecyl‐6,7‐difluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (DTffQ) units. Polymer P(BDTSi‐DTfQ) exhibited a lower bandgap (Eg) and higher highest occupied and lowest unoccupied energy levels (HOMO and LUMO) than P(BDTSi‐DTffQ). The estimated Eg and HOMO/LUMO for P(BDTSi‐DTfQ) were 1.90 eV and −5.46 eV/−3.56 eV, respectively, and for P(BDTSi‐DTffQ) the same were 1.94 eV and −5.58 eV/−3.64 eV, respectively. Interestingly, the NFA‐OSCs made from P(BDTSi‐DTfQ) as the donor and NFA, namely ITIC, as the acceptor, gave a power conversion efficiency (PCE) of 3.68%, which is much higher than the PCE obtained (⁓0.75%) for the OSCs prepared by using the P(BDTSi‐DTffQ):ITIC blend. Noticeably, the energy levels of P(BDTSi‐DTfQ) were found to be favorable for efficient charge separation when it was blended with ITIC. This blend not only allowed a better charge separation at the donor/acceptor interfaces but also significantly lowered bimolecular recombination. The overall effect was to provide a higher PCE. However, P(BDTSi‐DTffQ) showed mismatched energy levels with ITIC resulting in a higher bimolecular recombination and lower PCE.

A new medium bandgap polymer incorporating electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene (BDTT) and electron‐deficient 2,3‐didodecyl‐6,7‐difluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TffQ) units in an alternate manner, namely P(BDTT‐2TffQ), was prepared for organic solar cell (OSC) applications. The optical and electrochemical properties of P(BDTT‐2TffQ) were found to be suitable to use it as an electron donor in OSCs. The absorption band covers the region from 300 to 600 nm with an optical bandgap (Eg) of 1.84 eV, and it highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) were found to be positioned at −5.36 and − 3.52 eV. The OSCs prepared by using P(BDTT‐2TffQ):[6,6]‐Phenyl‐C71‐butyric acid methyl ester (PC70BM) and P(BDTT‐2TffQ):2,2′‐((2Z,2'Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6) blends provided a maximum power conversion efficiency (PCE) of 5.50% and 11.65%, respectively. The differences in the photovoltaic performances of OSCs are mainly attributed to their dissimilar short‐circuit current (Jsc), which depends on their absorption spectrum. Herein, we also compared the properties of P(BDTT‐2TffQ) with a structurally similar polymer, namely P(BDTT‐2TfQ), made up of BDTT and 2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TfQ) units, for better understanding the effects of the incorporation of additional fluorine atom on the backbone of quinoxaline‐based polymers.

Here, we studied the potential of 2,3‐didodecyl‐6‐fluoroquinoxaline–based polymer as an electron‐donor in binary and ternary organic solar cell (OSC) applications. A new wide bandgap polymeric donor, namely poly(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline) (P(BDTT‐TfQT)), is prepared. Polymer P(BDTT‐TfQT) showed intense absorption between 300 and 650 nm with an optical band gap of 1.83 eV. The determined highest occupied and lowest unoccupied molecular orbitals (highest occupied molecular orbital/lowest unoccupied molecular orbital = −5.28 eV/−3.45 eV) for P(BDTT‐TfQT) are found to be suitable to utilize as an electron donor along with widely used fullerene and non‐fullerene acceptors. The OSCs prepared by using P(BDTT‐TfQT):fullerene blend gave a maximum power conversion efficiency (PCE) of 4.64%, and the PCE further increased to 6.77% by using a non‐fullerene acceptor instead of fullerene. Overall, the improved light absorption results in higher photo‐current and PCE for P(BDTT‐TfQT):non‐fullerene blend compared to that of P(BDTT‐TfQT):fullerene blend. In contrast, the inclusion of 10 vol% of P(BDTT‐TfQT) as a third component in a high energy converting polymer: non‐fullerene blend is found to lower the performance from 16.03% to 14.50% for the resulting ternary OSCs.

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