Optical modeling of light trapping structure in thin film Si solar cells

Optical modeling of light trapping structure in thin film Si solar cells
Issue Date
19th International Photovoltaic Science and Engineering Conference and Exhibition
Efficient light trapping capability in active materials is essential in order to maximize the cell performance in thin film Si solar cells, and formation of light trapping structure such as etching and pattering is routinely adopted in these solar cells. In this study, an optical modeling study was performed on thin film Si solar cells by supposing the so-called ‘superstrate’ scheme; Glass-TCO-Si-TCO/metal back contact. As a TCO layer and metal reflector layer, aluminum-doped ZnO thin films and Ag were assumed, respectively, and their relevant optical constants obtained in our laboratory were used. As active layer, either hydrogenated amorphous (a-Si:H) or microcrystalline (c-Si:H) silicon whose optical properties were obtained from literature were used. In the simulation, ray-tracing simulation method was adopted, and total reflections from the structure were derived as a parameter of determining the optical efficiency. In the modeling, an angular distribution function (ADF) given by Gaussian scattering model was applied for the treatment of the diffused ray from textured TCO structure. Comparative model structures with/without TCO texturing were performed, and the effects of patterned glass substrate with patterning shapes of triangular or circular for two-dimensional pattern and pyramidal, semi-spherical for three-dimensional pattern were also analyzed. It is shown that the patterning of the glass which has been utilized in crystalline Si solar cells can be still very powerful technique for the enhancement of optical efficiency even in thin film Si solar cells. Furthermore, it will be pointed out that the combination of the TCO texturing and the glass patterning can amplify the light trapping efficiency in thin film Si solar cells.
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