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

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 Sb2Se3 photovoltaic materials, the preparation of Sb2Se3 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 B2O3 coating layer as a flux to drive the recrystallization of Sb2Se3, thereby regulating the micro-orientation of thermal evaporation-derived Sb2Se3 films and optimizing their electrical properties. Mechanistic investigations show that B2O3 exhibits stronger adsorption with (hk1) planes of Sb2Se3 to induce a vertical orientation growth of the film, while blocking the volatilization channels of Se and inhibiting Se vacancy defects by interacting with Sb2Se3. The Sb2Se3 film with [hk1] preferential orientation and suppressed deep-level defects promotes the effective transport of charge carriers in solar cells. As a result, the B2O3-treated device delivers a champion efficiency of 9.37% without MgF2 anti-reflection coating, which is currently the highest efficiency in Sb2Se3 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.