N型矽晶圓太陽能電池三維模擬

Abstract

在本篇論文中，著重在研究n型矽基板太陽能電池的光電特性之模擬。為了有效降低研究成本與最佳化各式太陽能電池，透過模擬得知結果是有效的方法。模擬可應用在不同材料、結構、表面鈍化、光學抗反射層、表面紋理結構。從最早期數值計算，一維模擬(ex. PC1D)，二維模擬已經發展成熟，但是有些特性因為其二維特性而無法被討論。三維模擬可以提供更廣泛的結構測試與光電特性研究。在光性方面，模擬紋理均一性與隨機位置，並反映在反射率上。在電性方面，三維模擬不同之寄生串聯電阻與金屬柵線。 在第二章中，用實際太陽能電池的光電特性，驗證二維維模擬的準確性並提出各項模擬所需之參數。同時，不同入光角度造成的電性與光性影響也被提出來討論在三、四章中，從三維光學模擬可得知製作出擁有紋理結構擁有隨機位置與均一大小可得到最好的反射率。而從電性模擬中，最佳化不同材料、厚度、接觸電阻、寬度、金屬主柵線與副柵線與其連接圖形，模擬三種不同形狀副柵線(三角形、多段式、一般長方形)的填充因子。

Modeling of photovoltaic devices has become more and more important and helpful not only to predict the performance of new devices but also to provide ideas and guidelines to industry without manufacture. The goal of this thesis is to provide an analysis of solar cells to the numerical simulation using state-of-the-art TCAD simulator featuring the capability to handle 2-D and 3-D geometries. The electrical and optical simulation of wafer based n-type Silicon solar cell is done by two-dimensional simulation. Firstly, the optical properties are analyzed by raytracing method. To calibrate the reflectance, some new optical models are introduced. Secondly, we simulate the electrical properties of solar cells. Other than Jsc, Voc, fill factor (FF) and efficiency, we also look into external quantum efficiency (EQE) and reflectance of the simulated cell with reference to fabricated cell. Finally, the angular effects on optical and electrical simulations are reported. We look into the optical and electrical issue by 3D simulations. In optical part, non-uniformity and random position issue of solar cells are discussed. The random position fills the skyline of textures. This enhances the light trapping ability of the solar cell and decreases the reflectance. However, non-uniformity of textures makes space between textures. It let light escape from texture surface leading higher reflectance. The electrical properties are discussed. The series resistance from metal grid is simulated. The simulation optimizes the thickness of metal grid and resistivity of different material. The width of busbar for planar solar cells is simulated. The different materials of metal grids, contact resistance, and height of metal grids are investigated to optimize the structure of the grid on the top of cells. The 3D simulation is used to optimize the size and shape of the finger on the top of the cells. The tradeoff between short circuit Jsc to favor small grid area and the FF to favor large grid area leads to an optimum value of finger width about ~20 μm, with silver (14.7nΩ-m), contact resistance (1mΩ-cm2), and height of metal grids (30-40 μm). To reduce the I2R drop of the finger, triangle and multi-segments are considered. Given the same metal area, the short circuit current and the open circuit voltage of the different finger design are similar. The resistive loss of triangle and multi-segment fingers are smaller than rectangular (conventional) fingers. The FFs of multi-segment, and triangular fingers are larger than the those of rectangular fingers for the same shadow area. The multi-segment fingers have comparable FF with triangular fingers.