Enhancing Cu(In, Ga)Se2 Solar Cell Efficiency with Vertically Channel-Stacked WSe2 Rear Passivation Layers

The performance of Cu(In,Ga)Se₂ (CIGS) solar cells was significantly improved by introducing a layered WSe₂ thin film as a rear passivation layer in the back contact region. A vertically aligned stacking channel of the WSe₂ thin film was obtained by converting a WO_x thin film using a plasma-assisted selenization process. With the insertion of the WSe₂ layer, we observed a notable accumulation of Ga at the rear side of the CIGS absorber layer, facilitated by the vertically channel-stacked WSe₂ thin film. Increased open-circuit voltage is attributed to the reconstruction of the band alignment due to the modified Ga concentration profile, effectively mitigating electron flowing toward back contact and recombination within the back contact region of the CIGS solar cell. Furthermore, a favorable conductivity along the channels of the vertically channel-stacked WSe₂ thin film and a steeper [Ga]/([Ga] + [In]) (GGI) gradient provide significant enhancements in short-circuit current density. The solar energy conversion efficiency of the CIGS solar cell, fabricated via a sequential process with elemental Se vapor, was boosted from 15.08% to 17.06%. The remarkable enhancement highlights the potential of employing two-dimensional materials as passivation layers in photovoltaic applications.