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

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.