Efficient and stable inorganic perovskite solar cells fabricated via the promotion of grain boundary regrowth

Inorganic CsPbIXBr3−X (1 ≤ X ≤ 3) perovskites are highly susceptible to moisture, presenting a significant challenge to the advancement of inorganic perovskite solar cells. To address this issue, the present study employs 2-methylthio-2-imidazoline hydroiodate (MTIH) for post-treatment of the upper interface of the CsPbI2Br film. The treatment induces secondary grain boundary growth in the CsPbI2Br film, facilitated by the inherent soft lattice characteristics of the perovskite, leading to lattice expansion and a notable reduction in grain boundary gaps, which enhances the wet stability of the films. Furthermore, the formation of a small amount of δ-CsPbI2Br is uniformly distributed on the film, further improving the stability of the film. Concurrently, a substantial increase in the Fermi level elevates the internal potential, thereby enhancing the open-circuit voltage. Therefore, compared to the untreated CsPbI2Br film, the MTIH-treated CsPbI2Br film exhibits significantly improved stability in a high relative humidity (RH) environment of 75 ± 5 % and a high-temperature environment of 90 °C. Ultimately, the device subjected to MTIH heat treatment achieves an optimal power conversion efficiency of 14.25 %, with 89.78 % of the initial efficiency retained after 1152 h of storage in ambient air at 20 ± 5 % RH.