Inhomogeneous Halide Anions Distribution along Out-of-Plane Direction in Wide-Bandgap Perovskite Solar Cells and Its Effect on Open Circuit Voltage Loss and Phase Segregation.

The large open circuit voltage ( V OC ) loss and phase segregation are two main obstacles hindering the development of wide-bandgap perovskite solar cells (PSCs). Even though substantial progress has been made through crystallization regulation and surface modification on perovskite, the mechanism of V OC loss and phase segregation has rarely been studied. In this paper, we first investigate the halide ions distribution along the out-of-plane direction and find the initial inhomogeneous distribution of halide ions during the crystallization process is an important reason. It leads to the formation of an unfavorable potential well in PSCs, resulting in V OC loss as well as generation of strong strain exacerbating phase segregation. Through introducing melatonin (MT) into perovskite precursors, a homogeneous distribution of halide anions is realized due to the well-regulated crystallization. Consequently, the treated PSCs exhibit an optimized power conversion efficiency (PCE) of 22.88% with a V OC loss as low as 0.38 V, which are the best values for wide-bandgap PSCs up to now.