Efficient Stabilization and Passivation for Low-Temperature-Processed γ-CsPbI Solar Cells.

The inorganic CsPbI perovskite has attracted tremendous attention in the photovoltaic fields for its chemical stability and suitable band gap. Generally, CsPbI solar cells with decent performances adopted high annealing temperature to form high-quality black-phase perovskite films. The high-temperature process hinders its practical application and further development. Hence, fabricating stable black-phase CsPbI at low temperature is imperative and necessary. In this work, a new additive -xylilenediamine bromide (PhDMADBr) is reported to facilitate the synthesis of solution-processed, high-quality, and stable γ-CsPbI films at a surprisingly low temperature of 60 °C. The additive with an appropriate content can effectively improve both the film morphology and crystallinity of γ-CsPbI perovskite films. PhDMADBr anchors to the perovskite surface or grain boundaries as a protection through hydrogen bonding between its ammonium cations and CsPbI. In addition, the Br element introduced by the additive passivates I vacancies in perovskite films, resulting in the improvement of both phase stability and devices' performance. Finally, the PSCs based on the modified γ-CsPbI perovskite film achieve a champion efficiency of 12.71%. Moreover, the device retains 85% of its original efficiency after being kept for 1000 h.