Two-step perovskite crystallization assisted with F-containing additives enables over 23% efficiency in perovskite solar cells

The two-step preparation of perovskite solar cells (PSCs) has attracted the interest of many researchers because this method can better control the nucleation and growth of perovskite thin films. This work proposes a crystallization management strategy to improve the quality of active layer with the assistant of F-containing additives with low boiling point. Hexafluorobenzene (HFB) is introduced into lead iodide (PbI2) precursor solutions, and HFB aggregation forms due to its low surface energies. As the result, nano porous PbI2 films are obtained after the evaporation of HFB during annealing process, leading to pinhole free perovskite films with large grain size and low defect states. As the consequence, the best power conversion efficiency (PCE) of 23.01% is obtained for the PSCs with HFB assisted perovskite films. Meanwhile HFB modified unencapsulated device maintains 88% of its initial PCE after aging for over 1440 h at 25 °C and 30% relative humidity in ambient conditions.