Brominated Polythiophene Reduces the Efficiency‐Stability‐Cost Gap of Organic and Quantum Dot Hybrid Solar Cells

Abstract The emerging solution‐processed solar cells have attracted worldwide effort in the last decade. Developing efficient, stable, and cost‐effective solar cells is strongly desirable in countering the growing global warming. Nevertheless, the photovoltaic performance and stability of hybrid solar cells based on low‐cost polythiophenes are far from satisfactory, due to their high‐lying energy levels and excessive aggregation. Herein, it is shown that brominated polythiophene (P3HT‐Br), prepared via a facile two‐step approach can effectively facilitate charge transport and suppress recombination in quantum dot (QD)/organic heterojunctions. Accordingly, the power conversion efficiency of the optimized hybrid polythiophene/QD cell is boosted from 8.7% to 11% (a 26% increase) with markedly reduced energy loss. More strikingly, the device achieves record‐high thermal stability with a lifetime of over 400 h maintaining 80% of the initial performance. Both device efficiency and stability are the best reported for polythiophene/QD hybrid solar cells. Moving forward, brominated polythiophenes hold great application in perovskite solar cells with significantly improved performance and offer new opportunities for other emerging solar cells.