Hydrothermal Deposition of Antimony Selenosulfide on Titanium Oxide Nanoparticle Films for Cadmium-Free Solar Cells

A hydrothermal deposition approach was recently developed for the preparation of antimony selenosulfide (Sb2(S,Se)3) film on a CdS substrate and leads to an efficiency breakthrough in Sb2(S,Se)3 solar cells. However, the toxicity and narrow bandgap of CdS pose a challenge for practical applications and sufficient light harvesting. TiO2, with a wide bandgap and nontoxic elements, is an ideal alternative electron extraction layer to CdS, while the growth of Sb2(S,Se)3 on a TiO2 substrate via a hydrothermal method has been unsuccessful owing to the lattice mismatch and strong bond energy of Ti–O. Here, we show that TiO2 nanoparticle thin film with an amorphous structure is able to initiate the nucleation because of the abundant anchor sites for the Sb2(S,Se)3 nucleus adherence. This characteristic in turn enables the formation of a compact Sb2(S,Se)3 thin film, along with a preferred [hkl] orientation and reduced deep-level defects. Notably, the light harvesting is enhanced in the short wavelength region, which is usually lost in a CdS-based solar cell. Finally, we achieved the highest power conversion efficiency in hydrothermal-method-derived Sb2(S,Se)3 with a TiO2 substrate. This study provides new insight into interface-enabled film deposition with improved morphology, defect characteristics, and preferred crystal orientation.