Abstract
In general, the optical and electrical characteristics of Cu(In,Ga)Se2 (CIGS) solar cells have been studied under the condition that sunlight is normally incident from the air to the CIGS solar cell having no thick front encapsulation layers. To obtain the calculation results in a realistic module application, we calculate the optical and current–voltage (J–V) characteristics of surface-textured CIGS solar cells by simultaneously considering the thick front encapsulation layers and oblique sunlight incidence. Using the proposed angle-dependent equispaced thickness averaging method (ADETAM), we incoherently model two successive front encapsulation layers of a cover glass layer and an ethylene vinyl acetate (EVA) layer, whose respective thicknesses are greater than the coherence length of sunlight (~0.6 μm). The angular dependences of reflectance spectrum and J–V curves are calculated and compared in a surface-textured CIGS solar cell with and without the inclusion of the two front encapsulation layers. We show that the optical absorption improvement of the surface-textured CIGS solar cell over the planar CIGS solar cell can be over-predicted when the thick front encapsulation layers are not considered in the optical modeling.
Highlights
Thin-film solar cells have been greatly studied as one of the promising alternatives to traditional silicon-based solar cells due to their potential to low cost and high efficiency [1]
The numerical methods of the rigorous coupled wave analysis (RCWA) [16], the finite-difference time-domain (FDTD) [17,18], and the finite element method (FEM) [19,20,21] should be used, where wave equations are directly solved in a small mesh or grid for optical modeling
The spectral irradiance of sunlight is assumed to follow the air mass (AM) 1.5 sunlight with a total power of S0 = 100 mW/cm2, which is shown in inset of Figure 2a
Summary
Thin-film solar cells have been greatly studied as one of the promising alternatives to traditional silicon-based solar cells due to their potential to low cost and high efficiency [1]. Light absorption efficiency of planar thin-film solar cells can be improved by use of surface-textured structures, of which absorption characteristics cannot be calculated based on the above-mentioned analytical methods applied to planar structures In this case, the numerical methods of the rigorous coupled wave analysis (RCWA) [16], the finite-difference time-domain (FDTD) [17,18], and the finite element method (FEM) [19,20,21] should be used, where wave equations are directly solved in a small mesh or grid for optical modeling. In a realistic module configuration, millimeter thick front encapsulant and cover glass layers, which can provide a higher mechanical durability and operational stability, are deposited on the top contact layer These front optically-incoherent encapsulation layers will affect the light absorption and power conversion efficiencies of surface-textured thin-film solar cell, which has to be considered to obtain the accurate optical modeling results.
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