A Triphenylamine-Functionalized Co-Assembly Material for Record Efficiency Inverted CsPbI₃ Perovskite Solar Cells

The precise regulation of self-assembled monolayer (SAM) distribution and interfacial modification is pivotal for advancing the performance of p-i-n inverted perovskite solar cells (PSCs). Here, a new co-assembly material, 4-(aminomethyl)-N,N-diphenylaniline iodide (TPAI), is developed to make SAM orderly assembled. Density functional theory (DFT) calculation and sum frequency generation (SFG) spectroscopy reveal that TPAI binds with SAM via π-π interactions, effectively suppressing SAM aggregation and enhancing the orderliness of self-assembly. Further characterization by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) demonstrates that ─NH₃ group in TPAI coordinates with undercoordinated Pb²⁺ to passivate defects of cesium lead triiodide (CsPbI₃) film. The TPAI modification creates a defect-minimized buried interface with optimized energy alignment, significantly improving hole extraction and transport kinetics. Consequently, the TPAI-treated CsPbI₃ PSCs achieve a high power conversion efficiency (PCE) of 21.60%, the highest reported value for inverted CsPbI₃ PSCs, maintaining 96.71% initial PCE after tracking at maximum power point (MPP) for 1400 h. This work provides a molecular-level strategy for interfacial engineering, advancing the development of efficient and durable perovskite photovoltaics.