Synergistic Crystallization and Passivation by a Single Molecular Additive for High Performance Perovskite Solar Cells

With its power conversion efficiency suddenly surpassed those of all other thin film solar cells only a few years after its invention, the perovskite solar cell has become a superstar for the next generation of photovoltaics. It is known that controlling the intermediate phase of crystallization is a key to obtain high-quality perovskite films for high-efficiency perovskite solar cells. Herein, a single molecule additive, N, N-Dimethylimidodicarbonimidic diamide hydroiodide (DIAI), is incorporated into the perovskite precursor to eliminate the influence of intermediate phases during the film formation process. By taking advantage of interaction of DIAI and dimethyl sulfoxide (DMSO) solvent, the intermediate phase FAI-PbI2-DMSO complex is eliminated, and the δ-FAPbI3 phase is entirely converted to the desired α-FAPbI3 phase during the crystallization step, resulting in enlarged grain size and significantly improved crystalline quality. This is the first observation in solution method that FAPbI3 can be obtained without an intermediate phase for high-performance perovskite solar cells with increased efficiency and stability. Furthermore, the DIAI is found to be effective at passivating the surface defects, resulting in reduced defect density, improved perovskite film quality and increased carrier lifetime, and thus comprehensively improved device efficiency and stability. The champion device achieved an efficiency of 24.13%, one of the highest in the field. Furthermore, the bare device without any encapsulation maintains 94.1% of its initial efficiency after ambient exposure for over 1000 hours. This work contributes a strategy of synergistic crystallization and passivation to directly form α-FAPbI3 from the precursor solution without the influence of intermediate impurities for high performance perovskite applications.