Chemical Dynamics of Back Contact with MoO3 Interfacial Layer in Kesterite Solar Cells: Microstructure Evolution and Photovoltaic Performance

A back contact interface in a kesterite Cu2ZnSn(S,Se)(4) (CZTSSe) photovoltaic device plays an important role in fabricating high quality semiconducting photoactive layers and improving carrier extraction efficiency. However, uncontrolled decomposition reactions between the CZTSSe absorber layer and Mo electrode result in high series resistance and recombination at the back interface. The insertion of high work function MoO3 as an interfacial layer is considered as a promising way to engineer the back contact. This highlights the importance of elucidating the chemistry and dynamics of MoO3 at the Mo/kesterite interface in the CZTSSe annealing process. Herein, A detailed investigation of the elemental diffusion and chemistry of the back contact with the MoO3 intermediate layer during selenization is carried out. The results demonstrate that the presence of the MoO3 interfacial layer largely suppresses the chemical reaction between Mo and CZTSSe in the annealing process, inducing high quality CZTSSe absorbing films with fewer voids and reducing the thickness of MoSe2 from 209 to 84 nm when the optimized thickness of MoO3 is 10 nm. This finally leads to the increase in device efficiency from 9.02% to 10.92%, and the best performance where an efficiency of 11.37% is achieved.