Influence of Bulk Defect Density on the Efficiency of CIGS Based Photovoltaic Cell/Solar Cell

In CIGS-based thin-films, bulk defects are believed to represent disturbances either in a regular, periodical arrangement within the atoms or within the crystalline media which influence sheet resistivity. In this study, first a resistivity measurements were carried out on CIGS thin films using the Van Der Pauw technique. Then, a comparison between two Van Der Pauw four-point measurement configurations (aligned and square) were done which showed that the square configuration was the most appropriate configuration that can be recommended to measure thin film sheet resistance of CIGS films. Finally, a numerical simulation using SCAPS-1D software was used to study the influence of bulk defect density in a CIGS films as an absorber layer in a model photocell. Using the simulated data, three operating zones for the model photocell were identified depending based on the concentration of its bulk defect density. The influence of bulk defects on thickness, band gap and doping were then analyzed. It was revealed that when the bulk defect density was less than 5×1013 cm-3 for an absorber of thickness in the order of over 3 μm, a band gap between 1.3 eV-1.4 eV and acceptor density of 1016 cm-3were the optimal operating conditions for the model photocell. It was concluded that the CICS layer used as an absorber can be improved if its bulk defect density is tuned to optimal levels.