Converting Residual Unstable PbI ₂ into Robust 2D Perovskite via Spacer Cation Engineering Toward Operationally Stable Perovskite Solar Cells

Abstract Addressing light instability challenges induced by residual PbI 2 is essential for simultaneously achieving high power conversion efficiency and excellent stability. Herein, we report an effective management strategy of residual photoactive PbI 2 based on dimensional engineering. The guanfacine hydrochloride (GUFCl) as additive or interface modifier is used to modulate perovskite films, converting residual PbI 2 at grain boundaries (GBs) into stable 2D perovskites, which suppresses the photodecomposition of perovskite films, inhibits ion migration and thus stabilizes GBs. The formation of 2D perovskites can result in reduced defect density and facilitated carrier transport and extraction, thereby mitigating carrier nonradiative recombination. As a result, the p‐i‐n inverted perovskite solar cells (PSCs) incorporating GUFCl achieve a champion efficiency of 26.19% with significantly improved operational stability. The unencapsulated inverted PSC maintains 92% of its initial efficiency after 1100 h of maximum power point (MPP) continuous tracking. This work provides a simple yet effective method to solve the residual PbI 2 ‐induced intrinsic instability issue, aiming to realize efficient, operationally stable perovskite photovoltaics.