Efficient and Stable MA-Free Sn─Pb Perovskite Solar Cells With Exceptional VOC 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 Sn2+ 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 Sn2+/Pb2+ 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 Sn2+ 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 (VOC) losses. As a result, the MA-free Sn─Pb PSC achieves a champion power conversion efficiency (PCE) of 23.2% with a remarkably high VOC 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.