Fabrication of High V_OC Organic Solar Cells with a Non-Halogenated Solvent and the Effect of Substituted Groups for “Same-A-Strategy” Material Combinations

We report a class of high-voltage organic solar cells (OSCs) processed by the environmentally friendly solvent tetrahydrofuran (THF), where four benzotriazole (BTA)-based p-type polymers (PE31, PE32, PE33, and J52-Cl) and a BTA-based small molecule BTA5 are applied as p-type and n-type materials, respectively, according to “Same-A-Strategy” (SAS). The single-junction OSCs based on all four material blends exhibit a high open-circuit voltage (VOC) above 1.10 V. We systematically study the impact of the three different substituents (−OCH3, −F, −Cl) on the BTA unit of the polymer donors. Interestingly, PE31 containing the unsubstituted BTA unit shows the efficient hole transfer and more balanced charge mobilities, thus leading to the highest power conversion efficiency (PCE) of 10.08% with a VOC of 1.11 V and a JSC of 13.68 mA cm–2. Due to the upshifted highest electron-occupied molecular orbital (HOMO) level and the weak crystallinity of the methoxy-substituted polymer PE32, the resulting device shows the lowest PCE of 7.40% with a slightly decreased VOC of 1.10 V. In addition, after the chlorination and fluorination, the HOMO levels of the donor materials PE33 and J52-Cl are gradually downshifted, contributing to increased VOC values of 1.16 and 1.21 V, respectively. Our results prove that an unsubstituted p-type polymer can also afford high voltage and promising performance via non-halogenated solvent processing, which is of great significance for simplifying the synthesis steps and realizing the commercialization of OSCs.