Effect of source–substrate separation and thermal ramp on Sb2Se3 thin films growth via close-space sublimation

Antimony selenide (Sb 2 Se 3 ) is a promising absorber layer for thin-film solar cells owing to its excellent optoelectronic properties, low toxicity, and earth abundance. According to the Shockley–Queisser limit, a theoretical maximum efficiency close to 33% is achievable; however, the current record barely exceeds 10%, primarily due to defects such as pinholes, selenium deficiency, and improper crystal orientation. In this study, a deposition strategy is presented to optimize Sb 2 Se 3 thin films using a modified Close-Space Sublimation (CSS) process. The influence of substrate temperature ( T sub ) and, for the first time, source–substrate separation on the properties of Sb 2 Se 3 films deposited by CSS was investigated. Our main results demonstrate that a larger source–substrate separation (2.0 cm) minimizes radiative heating, preventing uncontrolled re-evaporation. Based on these results and using thermal ramps of T sub from 250 °C to 450 °C, we achieved compact, void-free films with large columnar grains. Furthermore, these optimized conditions yielded a slight Se excess and a near-ideal direct optical bandgap of 1.36 eV for photovoltaic applications. This strategy offers a reproducible pathway to fabricate high-quality Sb 2 Se 3 absorbers without post-deposition treatments.