Non-hydrazine solution processed CuIn(Se,S)2 photovoltaic device

Solution processing of CuIn(Se,S)₂ or Cu(InGa)S₂ has proven to be one of the most promising strategies for low-cost, high-efficiency photovoltaic devices. With hydrazine as the sole solvent for dissolving Cu₂S and In₂Se₃, power conversion efficiencies can achieve up to 12.2%, which is dramatically better than those through using Cu or In chloride or nitrate precursor dissolved in organic solvents, such as butylamine. Although the hydrazine-based process produces the CISS absorber layer with less impurity, the reactivity and toxicity of hydrazine limit the further investigation and application in industry. Here, we demonstrate an alternative for hydrazine-based process by using suitable mixture of ethanolamine (EA) and dimethyl sulfoxide (DMSO) to dissolve Cu and In hydrazinium precursor. Control experiments suggest that sulfur in DMSO coordinates with Cu or In in precursors, while EA stabilizes the dissolved Cu-In complex. XRD and Raman characterization indicate the formation of the CISS phase after annealing. Amorphous carbon in the as-formed film, which comes from the decomposition of solvents, can be removed by selenization of the film. Optimized devices exhibit a power conversion efficiency of 3.83% with only ~300 nm-thick CISS absorber layer, which is comparable to that in N₂H₄-based device with similar thickness.