Abstract
We investigate the optical absorption in a thin Cu(In,Ga)Se(2) solar cell with a Lambertian white paint beneath a transparent back contact. Although this configuration has been proposed more than 30 years ago, it turns out that rigorous simulation of Maxwell's equations demand powerful numerical calculations. This type of approach is time consuming and does not provide a physical insight in the absorption mechanisms. Here, we use the radiative transfer equation to deal with multiple scattering of the diffuse part of the light. The collimated part is treated accounting for wave effects. Our model is in good agreement with optical measurements.
Highlights
Copper indium gallium diselenide (CIGS) is one of the most promising thin film solar cell technologies [1]
In a thin film with a thickness on the order of 0.5 μm or less, the thickness of the absorber layer is smaller than the absorption depth of light; optical management is of crucial importance
A transparent conductive oxide (TCO) is needed between the absorber and the white paint for charge carrier extraction
Summary
Copper indium gallium diselenide (CIGS) is one of the most promising thin film solar cell technologies [1]. Reducing the amount of indium by thinning the absorber layer in solar cells is of main interest. The typical thickness of CIGS in commercial cells is about 2–2.5 μm. For this thickness, most of the light in the visible range is absorbed in a single pass due to the high absorption coefficient. In a thin film with a thickness on the order of 0.5 μm or less, the thickness of the absorber layer is smaller than the absorption depth of light; optical management is of crucial importance. With current technology, reducing the thickness of CIGS results in increased parasitic losses in the Mo back contact. It was proposed to replace the back contact by a more reflective material such as silver or gold [2,3,4]
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