矽基太陽能電池抗電位誘導衰變效應之研究

Abstract

在太陽能產業發展當中存在重要的品質與可靠度的問題，此問題將會導致太陽能模組整體發電的效率產生衰減，更嚴重的甚至將使整體太陽能模組失效。此問題稱為電位誘導引發的衰變現象(Potential Induced Degradation，PID)，又簡稱為PID效應。而本論文研究的主題則是研究此議題所發生的原因，藉由了解與分析它的成因再同時提出如何減緩和解決此議題。 本實驗研究分為兩個部分；第一，藉由調整矽基太陽能電池抗反射層(氮化矽薄膜)的成膜氣體流量比(SiH4:NH3)來觀察太陽能電池對於PID效應的影響與變化。而在文獻探討中也可以發現，當成膜氣體當中的SiH4比例增高時，將使得氮化矽薄膜緻密性與鍵結產生改變，此項特性將可阻滯外來的鈉金屬離子的遷移，將可提高矽基太陽能電池對於PID效應的抵抗。 第二，在矽基太陽能電池的製程當中，使用熱氧化法新增一氧化層於矽基板與抗反射層之間，使之形成Si/SiO2/SiNx結構，藉由TEM分析後，發現此項結構當中的氧化層厚度約為10nm。在進行氧化過程當中，在界面處將存在一表面的的固定正電荷(Fixed Oxide Charge)，此界面的正電荷將使得外來的鈉金屬離子在侵入太陽能電池時如同遇上一電荷屏障，並可有效阻滯金屬離子的移動，也因此可以提高矽基太陽能電池的對於PID效應的抵抗。

Potential induced degradation (PID) is an important reliability issue in the silicon-based solar energy technology. This problem greatly degrades the photoconversion efficiency of the solar cell module and, in the worst case, results in the overall failure of the solar cell system. This thesis discusses the causes of the PID effect and focuses modification methods alleviating the effect. The study is divided into two parts. First, we adjusted the gas flow ratio of the gas precursor (SiH4/NH3) to study the influence of the ratio on the film quality of the silicon nitride (SiNx) anti-reflection coating layer, which can alleviate the PID effect by retarding sodium ions from diffusing from the glass panel to the solar cell module. From the study, a high SiH4/NH3 flow rate ratio improves the chemical structure of the nitride film, resulting in a better performance in blocking the migration of foreign sodium ions and thus a improved resistance against the PID effect. In the second study, we modify the device structure of the Si-base solar cell by depositing a thermal silicon oxide layer between the Si wafer and the anti-reflection layer. forming a Si/ SiO2/ SiNx multilayer structure. The thickness of the oxide layer was about 10 nm according to TEM analysis. Because of the oxide layer, positive fixed oxide charges are present at the interface and forms a potential barrier retarding the invasion of external sodium metal ions from the solar cell packaging materials into the solar cell modules. As a consequence PID effect can be greatly reduced by the addition of the thermal oxide layer.