Boron Trioxide‐Assisted Post‐Annealing Enables Vertical Oriented Recrystallization of Sb2Se3 Thin Film for High‐Efficiency Solar Cells

Abstract Crystallization process is critical for enhancing the crystallinity, regulating the crystal orientation of polycrystalline thin films, as well as repairing defects within the films. For quasi‐1D Sb 2 Se 3 photovoltaic materials, the preparation of Sb 2 Se 3 thin films still faces great challenges in adjusting orientation and defect properties, which limits the device performance. In this study, a novel post‐treatment strategy is developed that uses a low melting point B 2 O 3 coating layer as a flux to drive the recrystallization of Sb 2 Se 3 , thereby regulating the micro‐orientation of thermal evaporation‐derived Sb 2 Se 3 films and optimizing their electrical properties. Mechanistic investigations show that B 2 O 3 exhibits stronger adsorption with (hk1) planes of Sb 2 Se 3 to induce a vertical orientation growth of the film, while blocking the volatilization channels of Se and inhibiting Se vacancy defects by interacting with Sb 2 Se 3 . The Sb 2 Se 3 film with [hk1] preferential orientation and suppressed deep‐level defects promotes the effective transport of charge carriers in solar cells. As a result, the B 2 O 3 ‐treated device delivers a champion efficiency of 9.37% without MgF 2 anti‐reflection coating, which is currently the highest efficiency in Sb 2 Se 3 solar cells achieved by thermal evaporation method. This study provides a new method and mechanism for regulating optical and electrical properties of low‐dimensional inorganic thin films.