Interfacial Engineering via Polishing and Dipolar Synergy Toward Efficient Inverted CsPbI ₃ Perovskite Solar Cells

ABSTRACT Cesium lead triiodide perovskite (CsPbI ₃ ) has garnered widespread attention owing to its great potential for developing high‐efficiency single‐junction and tandem perovskite solar cells (PSCs). However, the intrinsic lead‐poor surface of the CsPbI ₃ layer, coupled with the energy level mismatch at the interface between the perovskite layer and electron transport layer (ETL), causes the device performance to remain far below its theoretical limit. To address the above issues, we herein propose a synergistic strategy integrating surface polishing and interfacial dipolar modulation at the perovskite interface, where 1, 4‐butanediamine (BDA) serves as the polishing agent and pentafluorobenzoic acid (5‐FBA) as the dipolar agent. As a result, the inverted CsPbI ₃ ‐based PSCs achieve a champing power conversion efficiency (PCE) of 20.71%, which is significantly higher than that of the control device (12.93%). Notably, the BDA+5‐FBA‐modified devices exhibit a high fill factor (FF) value for inverted CsPbI ₃ ‐based PSCs, reaching up to 83.92%. Furthermore, stability measurements demonstrate that the devices with BDA+5‐FBA treatment retain over 99% of their initial efficiency after 1200 h of storage in a nitrogen (N ₂ ) atmosphere.