Modeling of a-Si:H Solar Cells on V-Grooved Glass Substrates
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MODELING OF A-Si:H SOLAR CELLS ON V-GROOVED GLASS SUBSTRATES G. TAO, M. ZEMAN, AND J.W. METSELAAR Delft University of Technology, P.O.Box 5031, 2600 GA Delft, The Netherlands ABSTRACT We present the results of a series of numerical study of a-Si:H solar cells on different Vgrooved substrates. The light absorption profiles were calculated by taking into account the V-groove inner reflection and the reflection at the glass/air interface. These profiles were used for modeling the performance of solar cells with the 1-D Amorphous Semiconductor Analysis (ASA) computer package, which has been developed in our laboratory. The J-V characteristics under AM1.5 and the external quantum efficiency are simulated for Vgrooves with different tilt-angles (0 degree for flat substrate). Results show that effective light trapping occurs for V-grooves with tilt-angle larger than 21 degrees. INTRODUCTION There is not much room left for improving the material quality in order to improve the stability and the conversion efficiency of a-Si:H cells. However, significant improvement can be achieved through the solar cell design (external improvement). Recently, a-Si:H solar cells deposited on V-grooved glass substrates have drawn attention [1, 2, 3]. Because every facet in this structure (fig 1) is relatively smooth, such cells are expected to have a good electrical performance. It is also believed that these cells may suffer less from light induced degradation because thinner intrinsic layer can be used. However, there is still lack of systematic study for such V-grooved cells. To evaluate the performance of the V-grooved a-Si:H solar cells, we have carried out a series of optical and electrical simulations. MODELING The ASA (Amorphous Semiconductor Analysis)[4], which has been developed at the Delft University, was used to simulate the behaviour of the amorphous silicon solar cells. The GENPRO program is used to calculate the generation rate profiles in illuminated multi-layered structures. The generation rate profiles for monochromatic illumination as well as for AM1.5 illumination for the solar cells with flat substrates were calculated by GENPRO using the experimental optical data for separate layers in the solar cell. The light enters the solar cell through the p-layer. The generation rate profiles for the solar cells with V-grooved substrate were adapted from those for flat substrate solar cells by taking into account the inner-reflection of light at the V-groove facet and the glass/air interface. The cells used in our simulation and their model parameters We simulated both homojunction and heterojunction single p-i-n solar cells on Vgrooved glass substrate with different tilt-angles. The modeled heterojunction solar cells consist of an a-SiC:H p-layer, an a-Si:H intrinsic layer, and an a-Si:H n-layer. The standard parameters of the layers, which were used in simulations, are given in Table I. For the homojunction cells, we took the same values as those for heterojunction cells, except that the p layer has the same band-gap (1.79eV),
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