Deep defects limiting the conversion efficiency of Sb₂Se₃ thin-film solar cells

Quasi-one-dimensional (Q1D) semiconductor antimony selenide (Sb₂Se₃) shows great potential in the photovoltaic field, but the photoelectric conversion efficiency (PCE) of Sb₂Se₃-based solar cells has shown no obvious breakthrough during the past several years, of which the intrinsic reasons are pending experimentally. Here, we prepare high-quality Q1D Sb₂Se₃ thin films via the vapor transport deposition technique. By investigating the bandedge electronic level structure and carrier relaxation/recombination dynamics, we find that (i) the optimized Se-rich growth conditions can highly improve the crystal quality of the Q1D Sb₂Se₃ thin films, the carrier lifetime of which is substantially increased up to ∼8.3 μs; (ii) the Se-rich growth conditions have advantages to annihilate the deep selenium vacancies V_Sei (i = 1 and 3 for non-equivalent Se atomic sites) but is not effective for the deep donor V_Se2, which locates at ∼0.3 eV (300 K) below the conduction band and intrinsically limits the PCE value of devices below ∼7.63%. This work suggests that further optimizing the Se-rich conditions to technically eliminate this kind of deep defect is still essential for preparing high-performance Sb₂Se₃ film solar cells.