Effects of chlorine and carbon on Cu2ZnSnS4 thin film solar cells prepared by spray pyrolysis deposition

Abstract Cu 2 ZnSnS 4 (CZTS) thin film solar cells were fabricated under non-vacuum conditions, wherein the absorption layer was prepared by the spray pyrolysis deposition method. By using a chlorine (Cl)-free solution instead of a Cl-containing solution, the solar cell efficiency was improved from 0.18% to 0.35%. On the CZTS surface deposited from the Cl-containing solution, Cl-containing precipitates with size of 10 μm were present and were found to degrade the solar cell efficiency. The still low efficiency of 0.35% was caused by a layer containing small grains that existed between the CZTS layer and the Mo electrode, which included a significant amount of carbon. By optimizing the pre-annealing process, the small-grained layer became thinner and the efficiency was improved to 0.63%. Finally, by adjusting the chemical composition of the Cl-free solution and the CdS buffer layer deposition conditions, the cell efficiency was improved to 0.94%.