Synthesis of Cu2ZnSnS4 film by air-stable molecular-precursor ink for constructing thin film solar cells

Abstract

Cu₂ZnSnS₄ (CZTS) precursor ink routes have been demonstrated to open up new possible ways to fabricate low-cost and high-efficiency CZTS film solar cells, and a prerequisite is to investigate and develop precursor inks. Herein, we report the synthesis of air-stable molecular precursor ink for the construction of CZTS film solar cells. The precursor ink was prepared by dissolving Cu(acac)₂, Zn(acac)₂, and SnC₂O₄ and sulfur powder in pyridine, which yielded a viscous black solution. Subsequently, the precursor ink was spin-coated on a Mo-coated glass substrate, and the resulting film was heated in the air to burn off organics, producing an oxide film. The oxide film was subjected to the sulfurization process, in which the effects of sulfurization conditions on composition were investigated. CZTS film was obtained with Cu/(Zn + Sn) = 0.87 and Zn/Sn = 1.09, which is a composition that is close to the previously proposed composition for high-efficiency CZTS film solar cells. This CZTS thin film was used to construct a solar cell, and it exhibited an initial power conversion efficiency of 2.30%. Further improvement of the efficiency can be expected by the optimization of the ink composition, the composition/morphology/thickness/phase of the CZTS layer, and the device structure.