Numerical Simulation Of Thin-Film Silicon Solar Cells

In this thesis, the performance of thin-film silicon solar cells was studied by using the AMPS-1D computer simulation tool which was developed by Pennsylvania State University. The performance of p-i-n a-Si:H solar cells, p-i-n nanocrystalline Si:H solar cells and nanocrystalline Si:H HIT solar cells was investigated in the following chapters. The major research can be briefed as follows:(1). The a-Si:H p-i-n single-junction solar cells were studied in this thesis. The results showed that the defect states in p/i interface seriously affect the cell performance. Therefore, a thin intrinsic a-SiC:H layer was needed to insert between p-type-doped a-SiC:H emitter and (i)a-Si on the illuminated side, which decrease the defect states so that the carrier recombination at the interface was reduced dramatically. The distribution of valence band offset could be altered by adjusting the buffer band gap, which leads to a change for the distribution of recombination rate. Best cell performance was obtained when the buffer band gap was adjusted to 2.00 eV. Meanwhile, the short-wavelength response was improved after setting the buffer layer. In addition, the cell performance could be further optimized by improving the quality of materials and selecting the appropriate mobility band gap in intrinsic absorption layer.(2). The structure of (p⁺)nc-SiC:H/(i)nc-Si:H/(n⁺)nc-Si:H p-i-n solar cells was designed. Firstly the thickness of i-layer of the cell is optimized. When the thickness of i-layer is 200 nm, the best performance of the cell is obtained. We could obtain the mathematical relationship between the nc-Si:H grain size and crystalline ratio and the relationship between the grain size and the optical band gap by fitting the experimental data. When the nanograin size of the intrinsic nc-Si:H layer increases, the optical absorption coefficient decreases, resulting in worse performance. In addition, the doping concentration of the window layer has a profound effect on the photovoltaic characteristics of the solar cells. Best results are obtained when the doping concentration is 3×10¹⁸ cm^-3.(3). The photovoltaic properties of nanocrystalline Si:H (nc-Si:H) heterojunction with intrinsic thin layer (HIT) solar cells with the structure of TCO/(p⁺)nc-Si:H/(i)a-Si:H/(n)c-Si/(i)a-Si:H/(n⁺)nc-Si:H/Al were studied. The results exhibit that work function of transparent conductive oxide (WTCO) electrode should be as high as possible to obtain high power output. Doping concentration and the thickness of (p⁺)nc-Si:H emitter should be optimized to yield better cell efficiency. Interface charge states can be reduced by depositing a high-quality intrinsic amorphous Si:H layer on (n)c-Si to get high performance cell. Open-circuit voltage and short-circuit current of the solar cell with back surface field can be remarkably improved.