Ionic-Liquid-Perovskite Capping Layer for Stable 24.33%-Efficient Solar Cell

Metal-halide perovskite has emerged as an effective photovoltaic material for its high power conversion efficiency (PCE), low cost and straightforward fabrication techniques. Unfortunately, its long-term operational durability, mainly affected by halide ion migration and undercoordinated Pb2+ is still the bottleneck for its large-scale commercialization. In this work, an ionic liquid (IL) is designed to effectively cap the grain surface for improved stability and reduced trap density. More specifically, the Br- in the IL passivates the undercoordinated Pb2+ by chemically bonding to it, resulting in a thin layer of ionic-liquid-perovskite formed on the surface, leading to improved photovoltaic performance and better stability. Specifically, the solar cell exhibits an open-circuit voltage of 1.192 V and PCE of 24.33% under one-sun illumination with negligible hysteresis, and a large area (10.75 cm(2)) integrated module achieves PCE of 20.33%. Moreover, the bare device maintains over 90% of its initial efficiency after 700 h of aging at 65 degrees C. It also shows outstanding stability with only about 10% degradation after being exposed to the ambient environment for 1000 h. The superior efficiency and stability demonstrate that the present IL passivating strategy is a promising approach for high-performance large area perovskite solar cell applications.