Researchers from the University of Santiago de Compostela in Spain and Ghent University in Belgium have published a paper titled 'Efficiency improvement of ultrathin CIGS solar cells' in TIB Open Publishing. The study focuses on optimizing rear-passivation parameters (cell pitch, opening width, and interface trap density) in ultrathin CIGS solar cells using TCAD tools. It highlights the impact of rear passivation on conversion efficiency and device reliability. Calibration of the device considered all material properties and interface defects. Simulations revealed that changes in absorber thickness and doping concentration enhance cell performance, while traps at the rear u-CIGS/Al₂O₃ interface hinder efficiency by increasing carrier recombination. Introducing a negative fixed charge density in the rear passivation layer minimizes this effect, reducing recombination and improving performance. The optimized ultrathin CIGS solar cell achieved 15% efficiency with a cell pitch of 1.5 µm and an opening width of 300 nm at a fixed bandgap.