Numerical investigation of ultrathin CIGS solar cells featuring SiO₂/GaAs double rear passivation

In this work, we propose a modified GaAs/SiO₂ based Double Rear Passivation (DRP) structure for CIGS solar cells. DRP essentially comprises two distinct mechanisms for reducing recombination at the solar cell's rear. One component of the DRP is the incorporation of SiO₂ at the end of the structure. Silicon dioxide served as our passivation material. When deposited on Molybdenum, the SiO₂ coating generates a consistent fixed charge. This SiO₂ back passivation layer, along with its inherent fixed charge, is essential for preventing minority carrier (particularly electron) recombination. The fixed charge in this region produces an electrical barrier that minimizes back surface recombination by attracting holes while redirecting electrons away from the interface. The second component of the DRP is GaAs, which, due to its larger bandgap compared to the absorber, can generate an auxiliary field at the rear of the structure. Consequently, the resultant field from these two layers reduces recombination at the cell's rear. In this study for a CIGS solar cell, we incorporated CIS as a second absorber, and we achieved a 25.9% efficiency with 0.4 μm absorber thickness, which represents a significant improvement for ultra-thin cells.