Solution-Processed Trigonal Cu₂BaSnS₄ Thin-Film Solar Cells

Recently, Cu2BaSnS4 (CBTS) thin film has emerged as a promising candidate for single- or multiple-junction photovoltaics (PVs) due to its excellent optical and electrical properties, and earth-abundant, nontoxic constituents. In this study, a molecular solution-based nonvacuum process has been employed to prepare CBTS thin films for solar cells. The obtained CBTS films show trigonal structure with band gap of 2.01 eV and p-type conductivity. The solar cell device with configuration of Mo-coated glass/CBTS/CdS/i-ZnO/ITO has achieved a power conversion efficiency (PCE) of 1.72% for CBTS with a Ba/Sn atomic ratio of 1.30. An abrupt band gap cutoff in external quantum efficiency (EQE) data coupled with the very small offset (only 10 meV) in band gap between EQE and photoluminescence (PL) measurements reveals that band tailing is not the limiting factor in CBTS.