Numerical thickness optimization study of CIGS based solar cells with wxAMPS

In this paper, a numerical investigation of the effects of thickness of absorber and buffer layers for a typical CIGS based solar cell was carried out for the first time, employing the wxAMPS software which is a new custom-designed software package for solar cell simulation. We have examined how the output parameters change with absorber and buffer thicknesses and suggested four different cell structures. By using the baseline structure, an optimum band gap value of 1.4 eV was determined for the CIGS absorber layer prior to do thickness study. Optimum absorber thickness value has been determined as 2500 nm from the simulation results. Spectral response of the cell decreased with increasing thickness in blue region. The influence of buffer layer thickness was investigated and it was found that most of the photo-generated carriers are collected by a thinner CdS layer. A significant decrease in current density, open circuit voltage and conversion efficiency occurred with increasing buffer layer thickness. This behavior was attributed to a decrease in the number of collected carriers due to the recombination of electron-hole pairs proceeded from the absorbed photons in the CdS bulk for large thickness. As a result, efficiencies around 27% were obtained through optimization while that of baseline structure was 25%. Our results have shown that the suggested structures both produce higher efficiencies than that of baseline structure and may lead to produce more efficient CIGS-based thin film solar cells.