Growth mechanism of Sb2Se3 thin films for photovoltaic application by vapor transport deposition

Sb2Se3 is a rapidly advancing sustainable thin film solar cell technology demonstrating 9.2% conversion efficiency recently. Because of its unique quasi-1D crystal structure, the orientation of absorbers plays a key role in charged carrier transport and therefore in solar cell performance. However, deeper understanding how deposition conditions affect film orientation and ability to control it are missing. Herein using vapor transport deposition (VTD) method we studied growth process of Sb2Se3 on Mo, MoSe2, CdS, ZnO and TiO2 substrates. We varied the temperature of substrate and source to imitate various growth conditions. We have found three distinct growth regimes at which films exhibit characteristic features. Compact and large grained morphology with explicit (hkl, l≠0) orientation was achieved when high growth rate regime governed by evolution selection principle was induced on all substrates. Proposed growth model takes into account the influence of substrate and provides directions to obtain Sb2Se3 films with desired morphology and orientation. In conclusion, we have compared morphological properties of Sb2Se3 films synthesized by various evaporation based methods in literature with the properties predicted by the model. A fair agreement was found, proposing that this model can serve as a guideline for Sb2Se3 thin film optimization using evaporation based methods.