Suppressing Cation Migration in Passivation Layers for Perovskite Solar Cells

Two-dimensional (2D) and three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells. However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks, leading to degradation in performance over time. We hypothesized that perovskitoids, with robust organic–inorganic networks enabled by edge- and face-sharing, could impede ion migration. We explored a set of perovskitoids of varying dimensionality and found that cation migration within perovskitoid–perovskite heterostructures was suppressed compared with the 2D–3D perovskite case. Increasing the dimensionality of perovskitoids improves charge transport when they are interfaced with 3D perovskite surfaces—this is the result of enhanced octahedral connectivity and out-of-plane orientation. The 2D perovskitoid provides efficient passivation of perovskite surfaces and enables uniform large-area perovskite films. Devices based on perovskitoid–perovskite heterostructures achieve a record certified quasi-steady-state power conversion efficiency of 24.6% for centimetre-area perovskite solar cells. We removed the fragile hole transport layers and showed stable operation of the underlying perovskitoid–perovskite heterostructure at 85°C for 1250 hours for encapsulated large-area devices in ambient air.