Investigation on the Performance of CIGS/TiO2 Heterojunction Using SCAPS Software for Highly Efficient Solar Cells

In this study, Cu (In, Ga) Se-2 (CIGS) material with the non-toxic titanium dioxide TiO2 as an n-type buffer layer and indium tin oxide as the window layer are numerically simulated using a solar cell capacitance simulation software package. This numerical analysis has been carried out with the aim of boosting the performances of CIGS/TiO2 solar cells by tuning the defect density and band gap energy of the ordered vacancy compound (OVC) layer and by using a Back-electron reflector (EBR) layer, namely Al2O3. Solar cell performance is investigated as a function of absorber thickness. It is found that there exists an optimal thickness. The effect of OVC compounds on the performance of the device structure are discussed leading to an optimal band gap energy and defect density of about 1.17 eV and 4.97 x 10(13) cm(-3), respectively. The matching solar cell conversion efficiency reached a maximum value of 12.38% by introducing the OVC layer. It is also shown that, in spite of a decrease in thickness, the external quantum efficiency (EQE) of ultrathin CIGS solar cells can be enhanced owing to the employment of EBR. The significant improvement of EQE, mainly in the near-infrared part of the solar spectrum, can be ascribed to the low parasitic absorption loss in the ultrathin CIGS layer (similar to 570 nm).