Numerical modeling of the effect of multiple incoherent layers in Cu(In,Ga)Se 2 solar cells based on the equispaced thickness averaging method.

We investigate the effect of multiple incoherent layers on the optical characteristics of Cu(In,Ga)Se2 (CIGS) solar cells, based on the equispaced thickness averaging method (ETAM). The studied multiple incoherent layers consist of a glass cover layer, surface flattening layer, and transparent conducting layer, whose respective thicknesses are larger than the coherence length of sunlight (∼0.6  μm). An independent equispaced thickness is added to each incoherent layer and the coherent simulation results, obtained by the finite element method, are averaged over a combination of the equispaced thicknesses. By applying the proposed method, we calculated the reflectance spectra in planar and surface-textured CIGS solar cells. Considering the planar structure, the calculation results based on the ETAM are in good agreement with the exact analytical solution based on the generalized transfer matrix method. The statistical deviation from the exact solution was calculated with respect to the number of the equispaced thicknesses in each incoherent layer. When only four equispaced thicknesses are used, the calculated deviation from the exact solution rapidly decreases to 1% for planar and 10% for surface-textured CIGS solar cells, which demonstrates that the effect of the multiple incoherent layers can be efficiently calculated based on the ETAM in thin-film solar cells.