Anethole Regulated Crystallization for High Efficiency Carbon‐Based Perovskite Solar Cells

Abstract Two‐step sequential deposition is a widespread technique for the fabrication of perovskite films, renowned for its better control of the crystallization process. However, achieving a well‐controlled and complete reaction of PbI 2 by organic ammonium salts remains a key challenge. Previous studies have predominantly focused on regulating the properties of the PbI 2 layer while paying less attention to the high reactivity of organic ammonium salts. In this study, the natural molecule anethole is first explored to control perovskite crystallization during two‐step sequential deposition, focusing on the reactivity modulation of organic formamidine ion (FA + ). It is demonstrated that FA + exhibits strong hydrogen bond interactions with anethole, inhibiting the high reactivity of FA + and effectively delaying the rapid reaction between FAI and PbI 2 . This decelerates the crystallization kinetics of perovskite films, facilitating the orderly and complete reaction of PbI 2 by FAI while suppressing detrimental δ‐phase formation. Consequently, FA‐based perovskite films with high crystallinity, preferred orientation, and low defect state density are obtained. The fabricated planar hole transport layer‐free carbon electrode perovskite solar cells deliver an efficiency of 20.41% (certified efficiency of 20.0%), which is a new record for this kind of solar cell.