Correlation between deep defect states and device parameters in CuIn1-xGaxSe2 photovoltaic devices

Sub-bandgap defect densities and minority carrier collection properties have been characterized for a series of CuIn_1-xGa_xSe₂ devices with varying device efficiencies. Samples fabricated using reduced substrate temperatures during growth have also been studied, and show additional defect response. Transient photocapacitance and photocurrent spectroscopies were employed to deduce the defect distributions and minority carrier mobilities. Drive-level capacitance profiling was used to determine the spatial and thermal energy distributions of the majority carrier traps. Photovoltaic device parameters were determined for all samples. It appears that the device efficiency is not clearly controlled by any single sub-bandgap defect population.