Wide-bandgap polymer donors for non-fullerene organic solar cells

Abstract

High-performance wide-bandgap (WBG) polymer donors are one of the key factors in determining the power conversion efficiencies (PCEs) of non-fullerene organic solar cells (OSCs). To date, thousands of polymer donors with different building blocks have been synthesized, but the reported efficient polymers need to be classified and analyzed to achieve better photovoltaic performances. Accordingly, in this work, we present a brief survey of the developments of WBG polymers and classify these efficient polymers into five categories. Moreover, the correlation among their chemical structures and optical properties, electronic properties, aggregation behavior, and photovoltaic performance are summarized and discussed. (i) PBDB-T and the fluorinated derivative PM6 are the most widely used polymer donors for evaluating photovoltaic properties and conducting theoretical research in OSCs. (ii) The D18 series polymers, which were first reported by Ding's group, are among the best polymer materials with over 19% PCEs in ternary OSCs. (iii) Polythiophenes (PTs) are the cheapest donors for commercial OSCs but exhibit intrinsically inferior photovoltaic performance compared with other D–A copolymers. However, the introduction of electron-withdrawing groups has enhanced the performance of PTs, achieving PCEs of over 17%. (iv) Quinoxaline (Qx)-based polymers exhibit excellent photovoltaic performance. Especially, PTQ10 shows great potential for commercial production due to its low cost and high performance. (v) There are also many other polymers with decent photovoltaic performances, such as lactone and 1,3,4-thiadiazole-based polymers. These results indicate the diversity of conjugated polymers and can inspire chemists to develop more effective polymer materials for commercialization. Finally, some perspectives for the further development of WBG polymers are provided and the bright future of OSCs is emphasized.