8.30% Efficiency P3HT-based all-polymer solar cells enabled by a miscible polymer acceptor with high energy levels and efficient electron transport

P3HT stands out from numerous polymer donors owing to the merits of low cost and high scalability of synthesis. However, the photovoltaic performance of P3HT-based blends lags significantly behind the state-of-the-art systems, especially for all-polymer solar cells (APSCs) that generally show efficiency of around 3%–4% due to the lack of matched polymer acceptors. Herein, a polymer acceptor, named IDTBTC8-CN, was designed and synthesized with indacenodithiophene (IDT) and mono-cyano (CN)-substituted benzothiadiazole (BT-CN) as building blocks. Introducing a CN group endowed the polymer with decreased bandgap, and apparent n-type charge transport character despite the relatively high energy levels. Additionally, IDTBTC8-CN showed largely improved miscibility with P3HT, compared with that of BT-based control polymer IDTBTC8. The high miscibility between P3HT and IDTBTC8-CN as well as the amorphous aggregation behavior of IDTBTC8-CN enabled a broad manipulation room for the blend film to acquire favorable morphology. Eventually, a champion efficiency of 8.30% was achieved, in sharp contrast to that of the IDTBTC8-based system (1.21%). Such efficiency is a new record for P3HT-based APSCs reported so far. Moreover, P3HT:IDTBTC8-CN blend film also exhibited excellent mechanical robustness. This study implies the guidance of molecular design of the polymer acceptors and morphology control for P3HT-based APSCs. [Figure not available: see fulltext.]