Solar cells and prototype modules of variable bandgap antimony sulfide selenide thin films made by chemical deposition

Abstract

Antimony sulfide (Sb₂S₃) with a bandgap (E_g) of 1.88 eV and antimony selenide (Sb₂Se₃) with an E_g, 1.1 eV, both of orthorhombic crystalline structure, can form thin films of Sb₂S_xSe_3-x of variable bandgap, 1.1 – 1.88 eV. In chemical deposition, thin films of Sb₂S_2.3Se_0.7 (film, C) with E_g, 1.58 eV and Sb₂S_0.46Se_2.54 (film, H) with E_g, 1.31 eV were obtained by varying the selenosulfate – to – thioacetamide (SS:TA) ratio from 0.033 (C) to 0.3 (H) in the deposition bath. Solar cell structures of fluorine-doped tin oxide (FTO)/CdS (75 – 80 nm)/Sb₂S_xSe_3-x (90 – 180 nm)/graphite were made with colloidal graphite paint applied on an area 0.25 cm² and heated in nitrogen (20 torr pressure) for 30 min. Silver paint was applied on the FTO around the demarked cells and on the graphite electrode. Under standard test conditions, the Sb₂S_2.3Se_0.7 solar cell (C) gave: V_oc of 0.552 V, J_sc of 8.6 mA/cm², fill factor (FF) 0.32 and efficiency (η) of 1.52 %. Solar cell of Sb₂S_0.46Se_2.54 (H) gave: 0.427 V, J_sc of 23.1 mA cm ^{– 2}, and FF of 0.54, with η of 5.32 %. Solar cell prepared with variable bandgap C-H films improved η to 6 % with V_oc of 0.461 V, and J_sc of 24.73 mA cm ^{– 2}. Prototype modules of six series connected cells of variable bandgap absorbers of Sb₂S_xSe_3-x, each of 0.9 cm² in area (active area, 5.4 cm²), gave under standard operating condition, V_oc of 2.8 V, with short circuit current (I_sc) 17.24 mA, FF of 0.46 with η of 4 %. Variable bandgap Sb₂S_xSe_3-x prototype modules produced by chemical deposition is a viable option for their continued improvement.