Thermal degradation and light capture performance of CuInGaSe2 (CIGS) and c-Si photovoltaic devices

The thermal degradation and light capture performance of CuInGaSe₂ (CIGS) and c-Si photovoltaic devices were explored. Typically thin-film polycrystalline materials such as CIGS are hypothesized to be advantaged over single crystal Si solar cells as having lower thermal performance and improved light capture response. To this end, we present our evaluation of the thermal and light capture performance of three different CIGS devices, having different absorber layer stoichiometry and bandgap (E_g), and a c-Si device. Our results indicate that at the cell level these CIGS and c-Si photovoltaic devices have similar thermal degradation and light capture performance. The thermal performance of the c-Si and three CIGS materials explored were on average 0.40, 0.47, 0.51, and 0.48 % efficiency/°C, respectively. At low light levels (~150 W/m²) the voltages generated by each device were within 90% of those generated at full light intensity (1000 W/m²). The current levels generated by each device trended linearly with the irradiance, and the Rs for each device increased with the irradiance although no intentional changes were made to the electrical contacts. These results indicate that both CIGS-based and c-Si devices will perform equally well in comparable real-world conditions. With regards to the performance relative to the CIGS bandgap, tuning the CIGS material stoichiometry, i.e. making it closer to CGS, should broaden the materials spectral response and provide beneficial improvements to the thermal degradation rate and the light capture performance of CIGS devices.