The synergistic effect of dry air and surfactants enables water to be a promising green solvent for stable and efficient perovskite solar cells

Abstract

In recent years, perovskite has emerged as a prominent mineral to compete with all other existing PV materials. However, its fabrication typically involves the use of toxic organic solvents. A desirable solution would be to replace these harmful solvents with the genial water. Unfortunately, the high surface tension of water often results in the growth of Pb(NO₃)₂ crystals resembling islands, leading to morphological imperfections in the final perovskite film. In this study, the detailed Pb(NO₃)₂ crystallization process under different relative humidity is examined. It is found that moisture in the ambient air plays a pivotal role in the spreading dynamics of aqueous inks and the nucleation rate of Pb(NO₃)₂. Potassium oleate (PO), a long-alkyl chain anionic surfactant, is therefore designed to reduce the surface tension of water. Through the synergistic effect of dry air and oleate anion, a high-quality, pinhole-free conformal perovskite film with enlarged grain size can be readily obtained. Meanwhile, crystallinity regulation of Pb(NO₃)₂ by PO is proven to boost the further crystallization of PbI₂ and improve the formation kinetics of perovskite. Consequently, PO treated PSCs exhibit a power conversion efficiency (PCE) of 24.14% (0.09 cm²), one of the highest PCEs among all water-processed PSCs. More importantly, benefitting from the wetting-controlled strategy, a PCE of 22.09% is achieved for the first time on a large area (1 cm²). The bare device without any protection shows outstanding stability under continuous thermal stress and light illumination. This triumph is expected to shed light on the scalable production of PSCs using a minimal quantity of harmful organic solvents.