Design and Numerical Simulation on the Optical and Electrical Behavior of a ZnO:Al Nanowire Array a-Si pin Solar Cell
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Design and Numerical Simulation on the Optical and Electrical Behavior of a ZnO:Al Nanowire Array a-Si pin Solar Cell Chang-Wei Liu1, Zingway Pei1, Shu-Tong Chang1, Ren-Yui Ho1, Min-Wei Ho1, Yi-Chan Chen2, and Chi-Lin Chen2 1 Graduate Institute of Optoelectronic Engineering, National Chung Hsing University, Taichung, 40227, Taiwan 2 Photovoltaics Technology Center, Industrial Technology and Research Institute, Hsinchu, 310, Taiwan ABSTRACT One of the parameters that limit the efficiency of a thin film solar cell, especially the a-Si and the nc-Si solar cell is the cell thickness. Although thicker film can absorb most of the sun light, the optical generated carriers recombines through the numerous gap states in the film that obtains lower short circuit current and fill factor. This might indicate thinner a-si film can be used to eliminate the recombination. However, thinner a-Si film could not absorb enough sun light that also limit the short circuit current. In this works, we utilize nanowire structure to remove the dilemma between the light absorption and the carrier transport. The designed structure has ZnO:Al nanowire array on the substrate. The p-i-n a-Si solar cell structure is grown along the surface of each ZnO: Al nanowire sequentially. Under sunlight illumination, the light is absorbed in the axis direction of the nanowire. However, the carrier transport is along the radial direction of the solar cell. Therefore, the long nanowire can absorb most of the solar light. In the mean time, the thickness of the solar cell still is thin enough for photo-generated carrier transport. The dependence of short circuit current, open circuit voltage and fill factor to the length, diameter and density of ZnO:Al nanowires were simulated. INTRODUCTION In thin film solar cell, light management is essential for efficient absorption of incident light in thin absorber layer. A novel cell structure in order to separate the way of light absorption and carries transport is discussed in this work. Brendan et. al. first suggest this principle and simulate the electrical properties of planar and radial p-n nanorod solar cell with different materials like Si and GaAs [1]. The results suggest the ultimate efficiency for nanorod solar cell doesn’t exceed the limit of the planar solar cell. But, this efficiency can be achieved at thinner solar cell. However, for the most popular thin film solar cell, a-Si pin solar cell, this suggestion may not apply well since the carriers in the a-Si pin solar cell are separated by an internal field in stead of the diffusion in the Si p-n solar cell. Therefore, in our work, the thin film solar cell with amorphous silicon p-i-n layers grown on ZnO: Al nanowire array is simulated. In this simulation, an amorphous silicon material model is constructed in the commercial TCAD software to simulate a planar a-Si pin solar cell to verify the integrity of the simulation parameters. PARAMETERS SETTING OF PHYSICAL MODEL Through commercially available TCAD software such as Sentaurus Device [2], an 2D
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