Optimum chemical composition of antimony sulfide selenide for thin film solar cells

Antimony sulfide (Sb2S3) with an optical bandgap (Eg) of 1.88 eV and antimony selenide (Sb2Se3) with Eg 1.1 eV, both of orthorhombic crystalline structure, offer a unique opportunity to prepare solar cell absorbers of Eg, 1.3–1.6 eV poised toward economically viable, non-toxic and 'earth-abundant" devices. We prepared chemical precipitates of Sb-S-Se from solutions containing potassium antimony tartrate, thioacetamide and selenosulfate, which were used as sources in vacuum thermal evaporation to produce thin films (280–300 nm) of composition, Sb2SxSe3−x (x = 0.7–2). The Eg of 1.43–1.6 eV and photoconductivity, 4 × 10−5 and 8 × 10−7 Ω−1 cm−1, respectively of these films help to combine a high open circuit voltage (Voc) of 0.609 V with a conversion efficiency (η) 5.5% or a Voc of 0.503 V with η of 6.2%. A dual-crucible thermal evaporation system allowed the preparation of absorber films of varying composition (x) in the cell structure, SnO2:F (FTO)/CdS/Sb2SxSe3−x/C-Ag. The cell area were, 0.2–0.8 cm2. A prototype module of seven series-connected cells of area 1 cm2 each produced a Voc of 3.5 V, short circuit current 12 mA at η, 2.4%. Evaluation of the composition of the Sb2SxSe3−x films through gracing incidence X-ray diffraction is illustrated; and device parameters and solar cell perspectives of these materials are presented.