Efficiency improvement of ultrathin CIGS solar cells

• New strategies to enhance ultrathin Cu(In 1-x Ga x )Se 2 (u-CIGS) solar cell efficiencies. • Optimization of cell pitch sizes/opening widths for rear-passivated u-CIGS cells. • Effects of surface passivation with Al 2 O 3 on the performance of ultra-thin u-CIGS cells. • Demonstration that the proposed u-CIGS structure offers 15% efficiency. In this paper we present an optimization of rear-passivation parameters (cell pitch, opening width, and interface trap density) in u-CIGS solar cell using TCAD tools. The proposed investigation exhibits a significantly enhanced in understanding the beneficial effect of the rear passivation in ultrathin cell on conversion efficiency and reliability compared to existing solutions in the literature. Firstly, the device was calibrated according to the fabricated model taking in to account all material properties and defects at interfaces and within the bulk of the cells. Additional simulations demonstrate notable enhancements in cell performance due to changes in absorber thickness and doping concentration. However, traps were identified at rear u-CIGS/Al 2 O 3 interface as a key factor degrading conversion efficiency by promoting carrier recombination. Mitigating this mechanism is essential for improving device performance. Incorporating a negative fixed charge density in the rear passivation layer offers a promising solution, providing effective field-effect passivation to minimize minority carrier recombination at the rear surface. The proposed u-CIGS solar cell device achieves an impressive efficiency of 15 % using a cell pitch of 1.5 µm and opening width of 300 nm with a fixed bandgap.