薄膜矽太陽能電池元件特性退化之模擬研究

Abstract

n-i-p型薄膜矽太陽能電池為太陽能電池發展的一支，其擁有運用較少材料以降低成本優勢，但單薄的吸收矽層厚度造成對太陽光頻譜吸收的不足，故發展出許多光捕捉機制，以改善光電轉換效率。如在矽層底端堆疊鋁金屬層作為背板反射層，以及在矽層與摻鋁氧化鋅間介面堆疊週期性的光柵結構，以增加其光吸收率。 為了使太陽能電池元件最好的表現，必須同時考量其光性與電性。許多文獻指出，在實際製程上，光柵結構太陽能電池其短路電流密度高於平面結構，以及開路電壓與填充因子低於平面結構現象出現，因此，光性與電性並非同時受光柵影響而得到提升。影響電性退化有許多可能原因，在本篇論文，將探究摻雜輪廓、摻雜輪廓中的載子復合週期、矽層與摻鋁氧化層間接面復合速度，利用2D與3D模擬各種光柵結構薄膜矽太陽能電池元件。 研究結果顯示，利用”perfect”摻雜輪廓可以抑制大幅度的電性退化，矽層與摻鋁氧化層間接面復合速度則為光柵結構薄膜矽太陽能電池電性退化的主因，其短路電流密度高於平面結構，而開路電壓與填充因子較平面結構來的低。

The n-i-p type thin film silicon solar cell uses less material and thus has lower cost advantage, but it is too thin to absorb the solar photons of the entire spectrum completely. There are light trapping techniques to improve its efficiency. For example, incorporating silver (Ag) layer under silicon (Si) as a back reflector and incorporating periodic gratings at interfaces between Si and aluminum doped Zinc Oxide (AZO) can enhance the absorption. In order to optimize device performance, it is necessary to use coupled optical and electrical modeling. It has been reported that short circuit current density (JSC) in solar cell with gratings is higher than the planar baseline. However, values of open circuit voltage (VOC) and fill factor (FF) in solar cell with gratings are usually worse than the planar baseline. Therefore, the absorption and electrical properties in solar cell with gratings are not definitely positive correlation. There are many factors leading to the electrical degradation. In this paper, we discuss about doping profile, carrier recombination lifetime in doping region, and surface recombination velocity at the interface between Si and AZO. The solar cells with gratings are simulated to investigate the electrical degradation by two-dimensional (2D) and three-dimensional (3D) simulation. In our results, electrical degradation is suppressed for solar cells with gratings and “perfect” type doping profile. It is demonstrated that the surface recombination at AZO and Si interfaces will lead to electrical degradation which is caused by grating structure. The JSC of solar cell with surface recombination is higher than the planar baseline but its VOC and FF are lower than the planar baseline.