Postassembly Multifunctional Boric Acid Molecular-Modulated Buried Interface for High-Performance Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) have been widely used in high-efficiency inverted perovskite solar cells (PSCs) as a hole-selective layer. However, the inherent amphiphilic nature of SAMs, exemplified by molecules such as [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), drives self-aggregation behavior. This tendency results in pivotal interfacial challenges, including nonuniform surface coverage, defective perovskite crystallization, and compromised device stability. In this work, we innovatively propose a postassembly strategy (po-SAM). The primary Me-4PACz SAM is preferentially anchored onto the nickel oxide (NiOx) substrate to obviate competitive adsorption. Subsequently, 1,4-phenylenediboronic acid (PB) undergoes secondary assembly within the exposed voids via its boronic acid groups, thereby constructing a dense heterogeneous po-SAM architecture. This approach concurrently reduces the surface energy, optimizing the perovskite precursor wettability and inhibiting nonuniform nucleation. Simultaneously, the boronic acid groups form robust coordination bonds with Pb2+, effectively modulating the crystallization kinetics, passivating buried interfacial defects, and reinforcing interfacial anchoring. Consequently, the optimized device achieves a power conversion efficiency (PCE) of 25.61%, accompanied by a fill factor (FF) of 84.35% and an open-circuit voltage (VOC) of 1.184 V. Furthermore, the encapsulated device retains 86% of its initial PCE after 1200 h of aging under ISOS-D-2 protocols. Importantly, this approach overcomes the performance unpredictability inherent to traditional co-SAM caused by competitive adsorption, thereby establishing a new paradigm for interfacial engineering in high-performance PSCs.