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The impact of via etching on triple junction solar cell performance has been investigated for through cell via contact architectures. Triple junction solar cells with standard top and back contacts have been fabricated and vias have been etched through the subcells to investigate the new geometry proposed. The external quantum efficiency, the open-circuit voltage (Voc), the fill factor (FF), and the ideality factor have been measured and compared to those of standard triple junction solar cells without vias. In this way, we evaluate the losses attributable to via etching. Small performance losses from via integration are observed, but performance can be partially restored with an ammonium sulfide passivation treatment. Furthermore, the results show that the Voc losses are almost absent at the high sun concentration that the new architecture is designed for. The source of the performance degradation is correlated with a larger total surface recombination at the edges of the device. The passivation treatment allows an effective surface passivation of the via holes.

Novel architectures for light trapping in ultrathin Cu(In,Ga)Se2 (CIGS) solar cells are proposed and numerically investigated. They are composed of a flat CIGS layer with nanostructured back mirrors made of highly reflective metals. Multi-resonant absorption is obtained for two different patterns of nanostructured mirrors. It leads to a dramatic increase in the short-circuit current predicted for solar cells with very thin CIGS layers. We analyze the resonance phenomena and the density of photogenerated carriers in the absorber. We discuss the impact of the material used for the buffer layer (CdS and ZnS) and the back mirror (Mo, Cu, Au, and Ag). We investigate various CIGS thicknesses from 100 to 500 nm, and we compare our numerical results with experimental data taken from the literature. We predict a short-circuit current of Jsc = 33.6 mA/cm2 for a realistic solar cell made of a 200-nm-thick CIGS absorber with a copper nanostructured mirror. It opens a way toward ultrathin CIGS solar cells with potential conversion efficiencies up to 20%.