Cesium Lead Chloride Nanocrystals Interface Blocking Layer Enables Stable and Efficient Perovskite Solar Cells

Abstract The efficiency of perovskite solar cells is significantly improved, but the instability issues persist hindering their further development and applications. When subjected to external stimuli, the migration of iodine ions easily occurs in the perovskite, which affects the structural stability of the perovskite and leads to a decrease in device stability and efficiency. Here, a cesium lead chloride nanocrystal layer at the buried interface can suppress iodine ion diffusion and thereby enhance the stability. Temperature‐dependent electrical conductivity and space charge limited current demonstrated that this layer elevates the activation energy increase from 0.47 to 0.75 eV, and the trap density value reduce from 1.5 × 10 16 to 9.8 × 10 15 cm −3 . A set of I 2 diffusion experiments indicated that this layer can prevent the extravasation of iodine from the perovskite via the formation of a CsI 2 film. Furthermore, the blocking layer can passivate oxygen vacancies in SnO 2 and promote the increase of perovskite crystallinity. Therefore, the power conversion efficiency is increased from 22.06% to 24.66%, and an ≈8‐times improved T 80 lifetime operation under ultraviolet irradiation, and a ≈7‐times improved T 80 lifetime of heat‐light test. This work provides a new route to stabilize and enhance the efficiency of perovskite photovoltaics.