The influence of Back Surface Electric Field on HIT Solar Cells

本論文以電漿輔助化學氣相沉積系統(PECVD)製作n型異質接面(HIT)太陽電池，在背面n層採用不同濃度與能隙之雙n型氫化非晶矽層 ((n)a-Si:H/(n+)a-Si:H)的背表面電場層(BSF)結構，探討雙BSF層結構提升內建電場維持開路電壓及減少漏電流等對HIT太陽電池特性之影響。 以改變PH3流量的方式製作一系列不同光學能隙及活化能之n型 a-Si:H層。先以單一n型a-Si:H層作為HIT太陽電池之BSF層，探討不同光學能隙與濃度之單一BSF層對HIT太陽電池之影響。再以改變能隙配比與厚度配比兩種方式組合成雙BSF層，探討相對單一BSF層對HIT太陽電池之影響。 結果顯示，高PH3流量可降低n型 a-Si:H層光學能隙及活化能，有較高之內建電場使電池特性較佳。採用高能隙與i層接面及低能隙與Al金屬層接面的雙BSF結構之HIT太陽電池，其整體光電轉換效率，皆大於單BSF結構之HIT太陽電池。輕摻雜高能隙之BSF層較重摻雜層緻密，與本質層接觸後形成之介面缺陷較少使復合減小提高填充因子及開路電壓，而重摻雜低能隙之BSF層與Al金屬層接面接觸後有效降低串聯電阻使短度電流增加，進而提升光電轉換效率。適當的組合能隙與厚度配比可以優化HIT太陽電池的性能。The n-type heterojunction with intrinsic thin film (HIT) solar cells were prepared by plasma-enhanced chemical vapor deposition (PECVD). The double n-type layers with different bandgap and doping concentration of (n)a-Si:H/(n+)a-Si:H structure were fabricated at the back n-layer as the double back surface field (BSF) layers. We discuss the the characteristic of HIT solar in incressing the Vbi, mataining the Voc and decressing the leakage current. A set of the n-type a-Si:H layer is fabricated by changing the PH3 flow. First, the single n-type a-Si:H layer is used as the BSF layer in HIT solarcells. The effects of single BSF layers which have different optical energy gaps and concentrations on HIT solarcells were be investigated. Then change the bandgap ratio and thickness ratio in double BSF layer. Last discuss the effects of HIT solarcells in single and bouble BSF layer. The results show that the high PH3 flow can reduce the optical band gap and activation energy of n-type n-Si:H layer, and have higher built-in electric field to make the solarcell characteristics better. The high energy gap and i-layer interface and low energy gap and Al metal layer interface which are used in HIT solar cells with double-BSF structure, have higher photoelectric conversion efficiency than HIT solar cells with single BSF structure. The light doping BSF layer which has high bandgap is more dense than heavy doping. And the light doping BSF layer contact with intrinsic may decrease the interface defect. It can decrease the recombination and increase the F.F. and VOC. On the other hand, the heavy doping layer which has low bandgap contact with Al electrode may decrease the series resistance, so that the JSC will be increased and the photoelectric conversion efficiency will also be increased. Appropriate combination of energy gap and thickness ratio can optimize the performance of HIT solar cells.致謝 i 摘要 ii Abstract iii 目錄 v 表目錄 vii 圖目錄 ix 第一章 緒論 i 1.1前言 1 1.2 HIT太陽電池 2 1.3 研究動機目的 4 1.4 論文架構 6 第二章 文獻探討 7 第三章 研究方法 14 3.1 實驗流程 15 3.1.1 實驗設備 16 3.1.2基板清洗與表面粗糙化處理方式 19 3.1.3量測儀器 22 3.2 實驗參數設計 26 3.2.1 p型、本質、n型氫化非晶矽單層膜 26 3.2.2 ITO透明導電膜 31 3.2.3 p-i-n太陽電池 33 3.2.4 單層BSF結構之HIT太陽電池 33 3.2.5 雙層BSF結構之HIT太陽電池 34 第四章 結果與討論 37 4.1 矽基板之表面粗糙化 37 4.2 p型、本質、n型氫化非晶矽單層膜 38 4.2.1 p型氫化非晶矽薄膜之光學與電學特性分析 38 4.2.2 本質氫化非晶矽薄膜之光學與電學特性分析 41 4.2.3 n型氫化非晶矽薄膜之光學與電學特性分析 44 4.3銦錫氧化物透明導電薄膜( ITO) 47 4.4 p-i-n太陽電池 48 4.5單BSF結構之HIT太陽電池 49 4.6 雙BSF結構之HIT太陽電池 50 4.6.1 固定總厚度與能隙，改變厚度配比 50 4.6.2 固定總厚度與厚度配比，改變能隙配比 52 第五章 結論 54 第六章 未來工作 55 參考文獻 5