太陽能電池中電位誘發衰退現象之改善研究

Abstract

太陽能電池中電位誘發衰減現象將使得太陽能電池的效率隨使用時間而遞減，所以近年來業界不僅嚴格要求太陽能電池需通過抗電位誘發衰減驗證，同時也積極致力於以低成本的方法使太陽能電池具備抗電位誘發衰減能力。本論文主要研究矽太陽能電池中電位誘發衰減現象，並提出以簡易的製程方法改善矽太陽能電池中電位誘發衰減現象。我們不僅研究以不同PECVD機台製作SiNx抗反射層的抗電位誘發衰減的能力，同時對於無法製作出具抗電位誘發衰減的SiNx抗反射層的PECVD機台(業界熱門機種)，我們還提出在PECVD製程前增加退火步驟的改善方法，比較電位誘發衰減測試前與測試後，分析這些太陽能電池的電致發光影像及量測其效率，証明我們提出的簡易製程改善方式不僅可提高SiNx抗反射層抗電位誘發衰減的能力，且可通過抗電位誘發衰減驗證。為了了解退火步驟如何改善SiNx薄膜抗電位誘發衰減的能力，我們將樣品進行橢圓儀量測、化學蝕刻速率分析與紅外光光譜量測，最後，我們推論退火步驟將改變整層SiNx抗反射層結構，而不是只改變SiNx薄膜與SiO2界面，進而改善SiNx抗反射層，抗電位誘發衰減的能力。總之，我們提出簡易且低成本的製程方法，使得業界熱門使用PECVD機種可以製造出具抗電位誘發衰減的SiNx抗反射層。

Since potential induced degradation (PID) in solar cells will degrade the efficiency of solar cells for being operated a period of time, solar cell manufacturers not only have to fabricate PID-free solar cells, but also need to innovate cost-effective methods to fabricate PID-free solar cells. This thesis focuses on the studies of PID in silicon solar cells, and proposes an easy and cost-effective means to eliminate the PID of Si solar cells. We investigated the PID of Si solar cells with SiNx antireflection coating (ARC) layer coated by two types of PECVD equipment. Moreover, for the PECVD equipment (more popular types in manufacturers) that cannot produce the SiNx ARC films for PID-free solar cells, we propose a means to solve the PID issue by adding an annealing step prior to PECVD coating of SiNx. The results of electroluminescence (EL) images and efficiency measurements of solar cells after PID test show that our proposal can largely eliminate the PID in solar cells. Consequently, the solar cells are of PID free. To understand why additional annealing step can largely eliminate the PID of solar cells, the samples are characterized by ellipsometry, chemical wet etching, and Fourier transform infrared spectroscopy (FTIR). Based on the results, we deduced that the annealing will affect the properties of entire SiNx layer rather than that of the film near the SiNx/SiO2 interface. In conclusion, we proposed an easy and cost-effective method to fabricate SiNx film for PID-free solar cells by using the popular PECVD equipment in manufacturers.