Multifunctional Buried Interface Modification Enables Efficient Tin Perovskite Solar Cells

Abstract Tin perovskite solar cells (PSCs) are considered promising candidates to promote lead‐free perovskite photovoltaics. However, their power conversion efficiency (PCE) is limited by the easy oxidation of Sn 2+ and low quality of tin perovskite film. Herein, an ultra‐thin 1‐carboxymethyl‐3‐methylimidazolium chloride (ImAcCl) layer is used to modify the buried interface in tin PSCs, which can induce multifunctional improvements and remarkably enhance the PCE. The carboxylate group (CO) and the hydrogen bond donor (NH) in ImAcCl can interact with tin perovskites, thus significantly suppressing the oxidation of Sn 2+ and reducing the trap density in perovskite films. The interfacial roughness is reduced, which contributes to a high‐quality tin perovskite film with increased crystallinity and compactness. In addition, the buried interface modification can modulate the crystal dimensionality, favoring the formation of large bulk‐like crystals instead of low‐dimensional ones in tin perovskite films. Therefore, the charge carrier transport is effectively promoted and the charge carrier recombination is suppressed. Eventually, tin PSCs show a remarkably enhanced PCE from 10.12% to 12.08%. This work highlights the importance of buried interface engineering and provides an effective way to realize efficient tin PSCs.