Li‐Doping and Ag‐Alloying Interplay Shows the Pathway for Kesterite Solar Cells with Efficiency Over 14%

Abstract Kesterite photovoltaic technologies are critical for the deployment of light‐harvesting devices in buildings and products, enabling energy sustainable buildings, and households. The recent improvements in kesterite power conversion efficiencies have focused on improving solution‐based precursors by improving the material phase purity, grain quality, and grain boundaries with many extrinsic doping and alloying agents (Ag, Cd, Ge…). The reported progress for solution‐based precursors has been achieved due to a grain growth in more electronically intrinsic conditions. However, the kesterite device performance is dependent on the majority carrier density and sub‐optimal carrier concentrations of 10 14 –10 15 cm −3 have been consistently reported. Increasing the majority carrier density by one order of magnitude would increase the efficiency ceiling of kesterite solar cells, making the 20% target much more realistic. In this work, LiClO 4 is introduced as a highly soluble and highly thermally stable Li precursor salt which leads to optimal (>10 16 cm −3 ) carrier concentration without a significant impact in other relevant optoelectronic properties. The findings presented in this work demonstrate that the interplay between Li‐doping and Ag‐alloying enables a reproducible and statistically significant improvement in the device performance leading to efficiencies up to 14.1%.