Gallium content-dependent efficiency limits of CIGS solar cells at AM1.5G solar irradiance

The gallium content-dependent theoretical limit of the efficiencies of Cu ( In , Ga ) Se2 solar cells were studied using a MATLAB model developed based on the Shockley–Queisser detailed balance. The developed model included the temperature dependence of the bandgap according to the gallium content. The original Shockley–Queisser detailed-balance and the developed model at the ASTM G173-03 AM1.5G solar irradiance were used to calculate the gallium content and solar cell temperature-dependent theoretical efficiency limits of a Cu ( In1 − xGax ) Se2-based solar cell. Due to the spectral distribution of the solar irradiance, there were two “peaks” of efficiency: one at values of x around 0.2 prevails at lower temperatures and the other at values of x around 0.6 higher at temperatures above 0°C. Consequently, there is a “pit” with a minimum at x of around 0.5. Values of x corresponding to these values are higher for the temperature-dependent bandgap model. The calculated relative difference between the ultimate efficiency limit and the theoretical efficiency at x = 0.3 at 310 K is