Ultrathin Cu(In,Ga)Se2 solar cells : enhanced absorption by nanotextured functional back contacts

Ultrathin Cu(In,Ga)Se2 solar cell conversion efficiencies are limited by incomplete absorption of the solar spectrum. In this study, we experimentally investigate a light management strategy to enhance the performance of ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells through the implementation of a functional back contact with SiO2 nanostructure scatterers and a planar gold reflector. External quantum efficiency (EQE) and current–voltage measurements reveal significant improvements in short-circuit current density (Jsc), with a notable increase from 21.6 mA cm−2 to 27 mA cm−2 with a 25% increase for 300 nm CIGSe absorbers when transitioning from conventional molybdenum back contacts to functional back contacts with 500 nm SiO2 scatterers. This enhancement is attributed to a light trapping effect. Also, backside nanostructures imprint a height profile into all layers on top, which provides strongly suppressed front reflection. However, these gains are partially offset by reductions in open-circuit voltage (Voc) and fill factor (FF) possibly due to shunt pathways introduced by the nanotextured architecture. The highest power conversion efficiency of 12.9% was achieved with a 500 nm CIGSe absorber and 500 nm SiO2 scatterers, representing a 1.8% absolute efficiency gain over the reference Mo-based design. Optical simulations corroborate the experimental EQE trends, highlighting the role of nanostructure geometry in optimizing light absorption. Our findings demonstrate that carefully engineered light management structures can mitigate absorption losses in ultrathin CIGSe solar cells, providing the way for high-efficiency, cost-effective photovoltaic devices.