Impurity-healing interface engineering for efficient perovskite submodules.

An issue that affects the scaling-up development of perovskite photovoltaics is the marked efficiency drop when enlarging the device area, caused by the inhomogeneous distribution of defected sites. In the narrow band gap formamidinium lead iodide (FAPbI), the native impurities of PbI and δ-FAPbI non-perovskite could induce unfavoured non-radiative recombination, as well as inferior charge transport and extraction. Here we develop an impurity-healing interface engineering strategy to address the issue in small-area solar cells and large-scale submodules. With the introduction of a functional cation, 2-(1-cyclohexenyl)ethyl ammonium, two-dimensional perovskite with high mobility is rationally constructed on FAPbI to horizontally cover the film surface and to vertically penetrate the grain boundaries of three-dimensional perovskites. This unique configuration not only comprehensively transforms the PbI and δ-FAPbI impurities into stable two-dimensional perovskite and realizes uniform defect passivation but also provides interconnecting channels for efficient carrier transport. As a result, the FAPbI-based small-area (0.085 cm) solar cells achieve a champion efficiency of more than 25.86% with a notably high fill factor of 86.16%. The fabricated submodules with an aperture area of 715.1 cm obtain a certified record efficiency of 22.46% with a good fill factor of 81.21%, showcasing the feasibility and effectualness of the impurity-healing interface engineering for scaling-up promotion with well-preserved photovoltaic performance.