Mixed Pb-Sn perovskite solar cells have recently demonstrated photoconversion efficiencies (PCEs) comparable to those of fully Pb-based halide perovskite devices. The main advantages of the Sn-containing composition are reduced toxicity and enhanced light absorbance over a wider wavelength range. Furthermore, the narrow bandgap of approximately 1.25 eV gives Pb–Sn perovskites the potential to surpass the photoelectric conversion efficiency of lead halide perovskite solar cells. However, the practical application of these devices is currently limited by the easy oxidation of Sn²⁺. Avoiding this oxidation is one of the requirements to achieve efficient and stable Sn-based perovskite solar cells (PSCs). The few recent reports have shown that some amino acids used as additives in the Pb-Sn mixtures can effectively passivate defects thanks to their zwitterions properties and also reduce Sn⁴⁺ cations that present in precursor solutions as impurities [1]. Therefore, this study is dedicated to optimizing a strategy for employing amino acid salts in mixed Pb-Sn perovskite solar cells to improve their performance and stability.

Chloride salts of L-lysine, L-aspartic acid, L-histidine, and other amino acids were introduced into the precursor solutions, followed by interface passivation on the perovskite surface. A comparative study of the structural, photoluminescent and morphological properties of perovskite films and the photovoltaic properties of solar cells allowed us to determine which amino acid salt is the most effective in defect passivation and suppression of Sn⁴⁺ formation.

In particular, the incorporation of L-lysine·HCl as an additive in Sn–Pb perovskite solar cells resulted in a power conversion efficiency of 18.4% for single-junction devices. These results suggest that amino acid salts represent a promising strategy for enhancing both the efficiency and stability of single-junction Sn-Pb perovskite solar cells. We acknowledge the support provided by the GOPV project RdS2019-21 CSEAA_00011 - TIPO A - Ministry of Environment and Energy Security (MASE) – CUP E83C23000840001

[1] Zhou, S., Fu, S., Wang, C. et al. Aspartate all-in-one doping strategy enables efficient all-perovskite tandems. Nature 624, 69–73 (2023).