Tungstate-mediated In-situ Passivation of Grain Boundary Grooves in Perovskite Solar Cells.

Possessed with advantageous optoelectronic properties, perovskites have boosted the rapid development of solution-processed solar cells. The performance of perovskite solar cells (PSCs) is significantly weakened by the carrier loss at grain boundary grooves (GBGs); however, it receives limited attention and there lacks effective approach to solve this issue. Herein, for the first time, we constructed the tungstate/perovskite heterointerface via a "two step" in-situ reaction approach that provides effective defect passivation and ensures efficient carrier dynamics at the GBGs. The exposed perovskite at grain boundaries is converted to wide-band-gap PbWO4 via an in-situ reaction between Pb2+ and tungstate ions, which passivate defects due to the strong ionic bonding. Moreover, recombination loss is further suppressed via the heterointerface energetics modification based on an additional transformation from PbWO4 to CaWO4. PSCs based on this groove modification strategy showed good universality in both normal and inverted structure, with an improved efficiency of 23.25% in the n-i-p device and 23.33% in the p-i-n device. Stable power output of the modified device could maintain 91.7% after ~1100 h, and the device efficiency could retain 92.5% after aging in air for ~ 2110 h, and 93.1% after aging at 85 °C in N2 for 972 h.