Degradation and device physics modeling of TiO2/CZTS ultrathin film photovoltaics

A hybrid solar cell of a nonporous n-type-TiO2 nanolayer and a p-type semiconductor Cu2(Zn,Sn)Se4 (CZTS) ultrathin film has been numerically simulated using SCAPS-1D program. The device physics including carrier generation, charge collection and current-voltage characteristics are investigated and the degradation rate of the electrical parameters under the normal operation condition is considered through a time dependent approach. The simulation analyzes are based on the experimental data reported in literature. An ultrathin (d≤1 μm) instead of a thin CZTS layer is considered due to high absorption coefficient of such materials which allows a sub-micron layer to be adequate for complete photoabsorption. The defect density/levels significantly reduce the efficiency over time. The results are interpreted with a device physics proposed in in literature on the tunneling recombination at the interface of such structure. The TiO2 layer was selected to be 50 nm only.