Alkali chloride doped SnO2 electron-transporting layers for boosting charge transfer and passivating defects in all-inorganic CsPbBr3 perovskite solar cells

Abstract

An electron-transporting layer (ETL) with improved charge extraction-transfer kinetics and a perovskite film with improved quality highly determine the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, various alkali chlorides (MCl, M = Li, Na, K, Rb and Cs) are employed as passivators to simultaneously modulate the electronic properties of the underlying SnO₂ ETL and to regulate the quality of the upper all-inorganic CsPbBr₃ perovskite film. The primary results demonstrate that the detrimental oxygen vacancies at the SnO₂ surface and under-coordinated Pb²⁺ in the perovskite film are counterbalanced by alkali chlorides, benefiting the PCE promotion of the carbon electrode based CsPbBr₃ PSC. Because of the accelerated charge extraction, the reduced defects and the suppressed nonradiative recombination, the best device free of encapsulation tailored by the SnO₂–RbCl ETL achieves a champion PCE as high as 10.04% with improved long-term stability under 80% relative humidity over 15 days, which is much higher than the 7.88% for the reference device. The proposed strategy demonstrates great promise for the development of highly-efficient PSCs with a defect engineering related concept.