Chemical-Bath-Deposited Zn(S,O) Buffer Achieves 12.0% Efficient Solution-Processed CIGS Solar Cells

The state-of-the-art copper indium gallium selenide Cu(In,Ga)Se2 (CIGS) thin-film solar cells are fabricated based on vacuum methods and use cadmium sulfide as the buffer layer. Considering the cost-effective production and environmental safety, fabrication of a CIGS absorber via the solution process and using a cadmium-free buffer layer is desirable. Here, we report engineering of a chemical-bath-deposited zinc sulfoxide Zn(S,O) buffer layer for solution-processed CIGS solar cells. Our results show that optimization of the deposition time and annealing process of the Zn(S,O) film to avoid cracking is critical to obtain a dense and uniform Zn(S,O) buffer layer. Benefited from the large band gap of Zn(S,O) and light-soaking-induced device performance improvement, a champion CIGS solar cell with a power conversion efficiency of 12.0% (without antireflection coating) has been achieved. This is the first time that the Zn(S,O) buffer layer has been applied to a solution-processed CIGS absorber and achieves highly efficient CIGS solar cells. The effect of light-soaking on the heterojunction property and the stability of device performance are discussed.