Molecular Buffers to Regulate Vapor Deposition Dynamics of Copper Phthalocyanines Enabling Efficient Charge Extraction in Perovskite Photovoltaics

Abstract Copper phthalocyanine (CuPc) boasts the advantages of high stability and low materials cost, thus holding great promise for applications in perovskite solar cells (PSCs). Although the CuPc thin films produced through thermal evaporation offer precise thickness control and high uniformity, interface incompatibility between CuPc and perovskite exerts a profound influence on the interfacial charge extraction and device performance. Here, a buffer layer strategy is developed by coating phosphorylcholine (PC) on the perovskite to modulate the vapor deposition growth of CuPc film and mitigate the mismatches at the contact interfaces. The PC functionalization promotes the transform of the perovskite surface to p‐type characteristics, realizing optimal energy band alignment and facilitating the hole extraction. Concurrently, the PC buffer layer enables the adjustment of molecular stacking modes toward a favorable face‐on orientation, which endows the PC‐modified CuPc film with elevated electrical conductivity for carrier transport. Consequently, the resulting PSCs based on PC achieve notable efficiency improvement from 11.24% to 20.23%, which represents the highest reported performance for conventional PSCs using vapor‐processed undoped hole transport materials. Most crucially, the unsealed PSCs retain more than 95% of their maximal efficiency after 4000 h of storage.