Solvent‐Induced Surface Passivation and Reconstruction for Efficient Carbon‐Based HTL‐Free Perovskite Solar Cells

Carbon‐based perovskite solar cells (C‐PSCs) have garnered significant research interest due to their simplified hole transport layer (HTL)‐free configuration, low cost, and superior stability. However, the absence of an HTL results in serious interfacial issues at perovskite/carbon electrode interface, such as restricted carrier transport and severe non‐radiative recombination, which significantly hinder the development of C‐PSCs. Herein, we introduce a solvent‐induced interfacial engineering strategy that simultaneously achieves surface defect passivation and optimization of perovskite/carbon electrode interfacial contact. The utilization of acetonitrile (ACN) with weak coordination enables large organic cations (5‐ammonium valeric acid [5‐AVA]) to retain high reactivity, thereby more effectively passivating surface defects in perovskite compared to isopropanol (IPA)‐based post‐treatment. Additionally, the inherent properties of ACN, including strong polarity, low boiling point, and high volatility, facilitate rapid surface reconstruction of perovskite while optimizing the perovskite/carbon electrode interfacial contact. C‐PSCs based on 5‐ammonium valeric acid iodide (5‐AVAI)/ACN post‐treatment exhibit a power conversion efficiency (PCE) of 15.14%, significantly surpassing the 12.82% and 14.65% of the control and 5‐AVAI/IPA‐treated devices, respectively. Remarkably, unencapsulated devices retain 90% of the initial PCE following 1200‐h ambient aging (22°C, 45% RH). This work demonstrates the synergistic effects of solvent‐induced surface passivation and reconstruction, advancing the development of HTL‐free C‐PSCs.