Investigation of effective local contact Al2O3 rear passivation for high-efficiency thin CIGS solar cells

Abstract

Copper indium gallium selenide (Cu(In,Ga)Se2; CIGS) solar cells with small thicknesses active layer have limits to show high efficiency owing to high carrier recombination and low reflection at the electrode/active layer interface. A passivation layer applied to the rear of the CIGS solar cell is regarded as one of the solutions. However, depending on the thickness of the passivation layer, the surface morphology of the thin CIGS absorber layer can be changed, affecting light absorption and photovoltaic properties. In this study, the optical electrical performances of CIGS solar cells with a thin enough layer of the local contact aluminum oxide (Al2O3) (LC-Al2O3) rear passivation were analyzed and demonstrated. The thin passivation layer with tens of nanometers resulted in higher increased efficiency because of improved open circuit voltage and short circuit current density. In addition, from the experiment, the optimal thickness of the thin passivation layer was derived. Too thin a layer causes a degradation of the performance, providing the surface scattering and parasitic resistance. Our results can be used to develop guidelines for designing high-performance CIGS solar cells with optimized passivation layers.