Modulated Crystallization and Reduced Voc Deficit of Mixed Lead-Tin Perovskite Solar Cells with Antioxidant Caffeic Acid

Mixed lead-tin (Pb-Sn) perovskite photovoltaics have attracted great attention for reducing toxic lead and tuning optical bandgaps. However, the main challenges are the uncontrolled crystallization rate of perovskite films and easy oxidation of Sn2+, which can give rise to rough morphology and unwanted p-type doping. Herein, we precisely modulated the crystallization process of the mixed Pb-Sn perovskite by adjusting the energy barrier of nucleation with the help of caffeic acid (CA), a natural antioxidant, which is introduced into the perovskite precursor solution. We demonstrated CA also could depress the oxidation of Sn2+ to Sn4+ effectively by reducing hydroxyl functional groups, leading to the reduction of background carriers and hole trap densities. Therefore, an efficiency of 19.85% was obtained with an impressive open-circuit voltage of 0.855 V for mixed Pb-Sn perovskite solar cells with high reproducibility.

Automated summary

By introducing caffeic acid into the perovskite precursor solution, the crystallization process of mixed Pb-Sn perovskite was precisely modulated, reducing the oxidation of Sn2+ effectively and leading to the reduction of background carriers and hole trap densities successfully.