Efficient and Stable MA‐Free Sn─Pb Perovskite Solar Cells With Exceptional V OC by Bioavailable Phytophenol Sinapic Acid

Narrow‐bandgap Sn─Pb perovskite solar cells (PSCs) are vital for advancing high‐efficiency tandem photovoltaics and near‐infrared optoelectronic devices, yet their performance is limited by Sn 2+ oxidation, defective crystallization, and instability, particularly in thermally stable methlyammonium (MA)‐free systems. We introduce a transformative approach using sinapic acid (SA), a bioavailable phytophenol, as a multifunctional additive to address these challenges in MA‐free Sn─Pb PSCs. SA forms Lewis acid‐base adducts with Sn 2+ /Pb 2+ ions, slowing crystallization kinetics to produce compact, uniform films with minimal grain boundary defects. Its electron‐rich functional groups selectively coordinate with uncoordinated metal ions, effectively suppressing Sn 2+ oxidation and passivating deep trap states that cause non‐radiative recombination. This dual action significantly enhances optoelectronic quality and energy‐level alignment, reducing open‐circuit voltage ( V OC ) losses. As a result, the MA‐free Sn─Pb PSC achieves a champion power conversion efficiency (PCE) of 23.2% with a remarkably high V OC of 0.893 V, ranking among the highest reported PCEs for Sn─Pb PSCs. In addition, the device exhibits impressive long‐term stability, retaining over 90% of its initial PCE after 5200 h. These findings represent a pivotal advancement in Sn─Pb PSCs development, offering new prospects for highly efficient tandem photovoltaics and narrow‐bandgap perovskites for near‐infrared applications.