In situ Surface Polishing Enables VOC Approaching 95% of the Theoretical Limit for Efficient Inverted Perovskite Solar Cells

Surface modification of perovskite films by conventional chemical additives suffers from the complexity of the process and the risk of secondary contamination, which limits the open-circuit voltage (VOC) of the perovskite solar cells (PSCs). The utilization of the clean-passivate strategy for the polishing of perovskite films has garnered considerable attention in recent years. Nevertheless, this method necessitates the incorporation of additives and does not ensure their complete removal, which may potentially compromise the stability of the devices. Here, a simple additive-free in situ surface polishing (ISSP) strategy is proposed to reconstruct the surface of perovskite films and mitigate VOC loss. The ISSP treatment, based on a green polishing agent of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), has demonstrated its effectiveness in reducing surface defects, optimizing energy level alignment, and improving interfacial contacts. The ISSP-treated PSCs exhibit a minimal VOC loss of 0.35 V, approaching 95% of the theoretical VOC limit. As a result, the PSCs exhibit high power conversion efficiency (PCE) and stability, with a high PCE of 24.13% and maintaining 91.1% of the initial PCE after over 2,500 h of N2 storage (ISOS-D-1). Furthermore, the ISSP treatment is applicable to flexible PSCs (FPSCs) to obtain both high efficiency and mechanical robustness.