Over 23% power conversion efficiency of planar perovskite solar cells via bulk heterojunction design

The planar organic-inorganic hybrid perovskite solar cells (PSCs) have in recent years had remarkable success due to their superior optoelectronic performance. However, their power conversion efficiency is significantly inferior compared to mesoporous structure PSCs. Unlike most other advances focusing on non-perovskite materials to improve device performance, herein a multifunctional double perovskite material, Cs2PtI6, is proposed as the grain boundary modifier of organic-inorganic hybrid perovskite films. Results show three main benefits of introducing Cs2PtI6 into perovskite films: (1) it prompts growth of perovskite crystals, resulting in improved crystallinity and enlarged crystals; (2) it suppresses the trap assisted recombination at grain boundaries thanks to the formation of heterojunction and interface passivation; (3) it raises the efficiency of carrier collection and transport at grain boundaries owing to the high carrier mobility of Cs2PtI6. Consequently, a PCE of 23.56% is achieved. The unencapsulated devices show less than 10% degradation compared to the initial performance after storage in ambient (approximate to 30%) humidity for 2000 h. This study outlines a simple yet effective strategy for boosting the performance of planar PSCs.