Crystallization manipulation and morphology evolution for highly efficient perovskite solar cell fabrication via hydration water induced intermediate phase formation under heat assisted spin-coating

A delicate control of crystallization and morphology of perovskite absorbers is critical to obtain high performance hybrid perovskite solar cells (PSCs). Here, we have developed a novel crystallization strategy which involves hydration water induced intermediate phase formation under heat assisted spin-coating processing (HASP) to manipulate the morphology and grain size of perovskite films, and thus it can avoid the use of toxic and volatile antisolvents used in conventional one-step solution processes to make PSCs. During HASP, impressive morphological evolution of films occurs with the formation of CH3NH3PbI3·xH2O perovskite intermediate phases. With ingenious control of the crystallization kinetics, highly crystalline perovskite films with fewer defect states and high carrier lifetimes are obtained. The corresponding PSCs exhibit a power conversion efficiency (PCE) of 19.12% with a stabilized power output efficiency of 18.89% at the maximum power point, which is a 70% enhancement compared to that of conventional one-step process based PSCs. Furthermore, the PSC fabricated by the HASP method achieved a PCE of 15.47% with an active area of 1.2 cm2. Moreover, the flexible PSCs fabricated by the HASP method achieved a record efficiency of 14.87% with negligible hysteresis for PEDOT:PSS-based flexible inverted PSCs. Our work opens up a new avenue for morphology and crystallization control through hydration water induced intermediate phase formation under HASP, which paves the way toward further enhancing the device performance of perovskite solar cells.