Improving Thin-Film Crystalline Silicon Solar Cell Efficiency with Back Surface Field and Blaze Gratings
| Autor: | Shin-Yi Wu, 吳信毅 |
|---|---|
| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 In this thesis, we use package softwares to develop numerical simulations of solar cells. The built numerical models evaluate the photon absorption based on wave optics and carrier transport behavior based on semiconductor physics. Based on the established model, we improve the efficiency of thin-film crystalline (TF-cSi) solar cells with the incorporation of back surface field (BSF) and optimized blaze grating structures. First, we use finite element method (FEM) and a program called PC1D based on semiconductor physics to calculate the energy level distribution and carrier transport in solar cells. According to general geometric optics, photon-generated current and cell efficiency can be obtained by these programs. In the simulation, the application of BSF significantly increases the efficiency of TF-cSi solar cells. Moreover, the cell with BSF and efficient light-confinement mechanism has the maximal efficiency while the cell thickness is shorter than the diffusion length of carriers. Therein, the optimal thickness of cSi solar cells can be obtained. In addition, the cell with BSF has the maximal carrier collection efficiency in a wide wavelength range when cell thickness is thinner. Hence, short-circuit current density can be enhanced. The open-circuit voltage of devices is also increased due to the decreasing of saturation current density when reducing the cell thickness. Next, we use FEM and rigorous couple-wave analysis (RCWA) method based on wave optics to calculate the photon absorption of silicon layer. With these simulation tools, we try to enhance the photon absorption by efficient light-trapping structure. For this light-trapping structure, blaze grating is used at the back surface. It is known that blaze grating has larger diffraction efficiency for high order diffraction, which results in larger equivalent optical path length in the silicon layer. Therefore, the photon absorption of devices is enhanced. In addition, we simulate a solar cell with a light-trapping structure which has been proposed in the literature and compare this structure with ours. According to the results, our structure has larger cell efficiency enhancement. Since the diffraction angle and efficiency of the reflective light depend on the grating period and the geometric form of gratings, respectively, it is feasible to enhance the absorption in the long wavelength range by varying the structural parameters of blaze gratings. With the introduction of $J-V$ characteristic of an ideal solar cell and reasonable physical parameters, the photon absorption is converted into the cell efficiency. With our calculation, the optimized structural parameters of blaze grating is obtained, and the photon absorption enhancement and the efficiency enhancement between cells with and without blaze grating are calculated and compared. Furthermore, the blaze grating greatly enhances the light-trapping ability of the TF-cSi solar cells and shows a significantly improvement of the photon absorption in the long wavelength range. Finally, we use a program to develop the simulation that combines wave optics and carrier transport. We calculate the cell efficiency and the photon-generated current in TF-cSi solar cells with blaze grating. Then, we consider the case including both the optimized blaze grating and BSF and calculate the efficiency enhancement of these devices. In our simulation, both BSF and blaze grating can significantly improve the efficiency of TF-cSi solar cells. In addition, BSF and blaze grating mainly enhance the open-circuit voltage and short-circuit current density, respectively. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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