Enhanced interface regulation via π-conjugated heterojunctions for high-efficiency inverted perovskite solar cells

Abstract

Self-assembled monolayers (SAMs) are increasingly utilized as effective hole-collecting material to boost the efficiency of inverted perovskite solar cells (PSCs). However, issues such as incomplete surface coverage and suboptimal interfacial bonding persist, leading to non-radiative recombination and compromise long-term stability. To address these challenges, we developed an innovative strategy by integrating 1-benzyl-3-methylimidazolium tetrafluoroborate (BzMIMBF4) onto the SAM, optimizing the buried interface and enhancing perovskite crystallization. BzMIMBF4 enhances SAM surface coverage through BzMIM+ interactions, forming a robust π-conjugated heterojunction with [4-(3,6-dimethyl-9H-carbazol-9-yl) butyl] phosphonic Acid (Me-4PACz) SAM that optimizes interfacial bonding, inhibits detrimental Pb2+/I- ion migration, and safeguards the bottom electrode. BzMIMBF4 stabilizes crystal nucleation, minimizing defect-related non-radiative recombination, promotes rapid α-phase formation, and enhances (100) plane alignment and charge carrier transfer to the hole-transport layer (HTL). Besides, time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling confirms the distribution of BF4- anions throughout the perovskite film. Simultaneously, BF4- anions effectively passivate perovskite surface and bulk defects, such as uncoordinated Pb2⁺ ions and iodine vacancies, thereby suppressing non-radiative recombination centers. The resulting perovskite films exhibit a pinhole-free structure, increased grain sizes, smoother surfaces, and significantly reduced residual strain. Consequently, BzMIMBF4-treated devices achieve remarkable power conversion efficiencies of up to 26.45% (certified 26.37%) and retain 90.8% of their initial efficiency after 700 hours of operation under one-sun illumination, demonstrating excellent stability. This approach paves the way for high-performance, durable PSCs and their potential in advanced photovoltaic applications.