Alcohol Vapor Post-Annealing for Highly Efficient Sb₂S₃ Planar Heterojunction Solar Cells

Solution-processed Sb₂S₃ planar heterojunction solar cells have shown great progress in power conversion efficiency (PCE) in recent years. However, a conventional solution process yields Sb₂S₃ films with a small grain size. Herein, an alcohol vapor post-annealing strategy is reported that uses alcohol vapors to facilitate grain growth of Sb₂S₃ films during annealing, achieving films with a larger grain size and better crystallinity. A series of alcohols with different polarities are used for the vapor post-annealing. Methanol with the highest polarity provides films with the largest grain size. As a result, the Sb₂S₃ films prepared via vapor post-annealing show enhanced light absorption, longer carrier lifetime, and less carrier recombination, which are verified by photoluminescence, transient photovoltage, suns-short-circuit photocurrent density, and suns-open-circuit voltage measurements. The Sb₂S₃ solar cells post-annealed with methanol vapor exhibit a PCE of 5.27%, showing a drastic improvement of 31% compared with the non-treated devices. The alcohol vapor post-annealing approach presents a new avenue toward controlling the morphology and crystallinity of solution-processed Sb₂S₃ films and achieving efficient Sb₂S₃ solar cells.