Modelling of high-efficiency substrate CIGS solar cells with ultra-thin absorber layer

Abstract

Solar cells based on Cu(In,Ga)Se2 (CIGS) are very promising thin-film solar cells due to their high absorption coefficient and appropriate optical band gap. In this work, a model of substrate thin-film solar cell of structure ZnO:Al/CdS/CIGS/Mo/glass has been established to estimate the cell parameter of ultra-thin absorber layer. The quantitative assessment of the optical losses due to reflection at interfaces and absorption in window layer (ZnO:Al) and buffer layer (CdS) as well as the recombination losses at front and rear surface of CIGS layer has been studied. The optical losses are carried out based on the optical constants of the used materials, and the recombination losses are carried out in terms of the parameters of the absorber layer. The effect of antireflection coating and reflectivity from metal electrode on the short-circuit current density and hence on the cell efficiency has been studied. It has been shown that the optical losses can prevent 30% of the incident photons from reaching the absorber layer at 150 nm thickness for each of the ZnO:Al and CdS layers. The antireflection coating of 100 nm thickness is capable of increasing JSC by 8%. High efficiency of 19.56% has been obtained at 1 µm thickness of CIGS layer under certain parameters of the used materials, and this efficiency can reach 20.22% at 100% reflectivity from the back contact.