Distinct Reaction Route toward High Photovoltaic Performance: Perovskite Salts versus Crystals

The synthetical strategy of methylamine (MA) molecular treatment for fabricating perovskite film has been attracting increasing attention because of the ease of fabrication feature and the high-throughput process. In this approach, we found both of perovskite salts (MAI and PbI2) and crystals have been used as the source materials for the interaction with MA molecules. Even though both alternatives are applicable, the reaction routes toward perovskite crystalline film are distinct, which correlates with the photovoltaic performance and the fabrication process design. Therefore, we systematically studied the difference between perovskite salts and crystals with respect to precursor solubility, crystallization dynamics, perovskite crystal structure, and photoelectric properties. The results show the configuration and the crystallization dynamic of the salts and crystal-derived solution are different. The salt-derived solution consists of iodoplumbate complexes, while the crystal-derived solution is composed of perovskite sheet intermediates. Because of the ordered stacking behavior of the perovskite sheet intermediates, the crystal-derived perovskite films showed faster crystallization and preferred crystal orientation, which results in superior charge carrier transport properties and higher conversion efficiency. The disclosure of the distinct features between salts and crystals provides guidelines to modulate the solution chemistry for higher photovoltaic performance.