Plant‐Derived l‐Theanine for Ultraviolet/Ozone Resistant Perovskite Photovoltaics

Abstract As the efficiency of perovskite solar cell has skyrocketed to as high as 25.7%, their stability has become the biggest obstacle to commercialization. Preliminary analyses suggest that additive engineering may be effective in improving both solar cell efficiency and its stability. Herein, the plant‐derived natural green additive of l ‐Theanine (Thea) is selected to improve the crystal quality of the perovskite absorber and obtain high‐performance perovskite solar cells (PSCs) with ultraviolet/ozone (UV/O 3 ) resistance. The characterization results reveal that the CO group in Thea can effectively inhibit the precipitation of metal Pb 0 , passivate undercoordinated Pb 2+ ions, and promote the nucleation and crystallization of perovskite. In addition, the combination of the NH group and I − in the form of a hydrogen bond cooperatively reduce the probability of nonradiative recombination of photogenerated carriers and effectively improves the extraction ability of carriers from perovskite absorber. With the cooperation of CO and NH 2 groups in Thea, the champion efficiency is improved from 22.29% in the control device to 24.58%. More importantly, Thea significantly alleviates the perovskite phase transition and film decomposition induced by UV/O 3 treatment. The study provides exploratory research for the application of plant‐derived green additives in the UV/O 3 resistance field of perovskite photovoltaics.