Over 12% efficient low-bandgap CuIn(S, Se)₂ solar cells with the absorber processed from aqueous metal complexes solution in air

Fabrication of the absorber from environmentally benign solution in ambient air is the ideal approach to address the cost and environmental issues that limit chalcopyrite solar cell commercialization. Here, we report CuIn(S,Se)₂ (CISSe) solar cells with the absorber fabricated from an aqueous solution using metal thiourea complexes CuTU₃Cl and InTU₃Cl₃ as precursors. The direct bonding of all metal ions with sulphur in the complexes prevents the hydrolysis of indium and promote the formation of metal sulphide upon thermal annealing. High quality low band gap CISSe absorber material with film thickness penetrating large grains and smooth surface is fabricated from the simple aqueous solution in air. CISSe solar cell with a power conversion efficiency of 12.3% is achieved.