原子層沉積技術與奈米結構應用在矽晶太陽能電池抗反射層之研究

Abstract

本研究利用水熱法合成超長氧化鋅奈米陣列作為抗反射層，應用在太陽能電 池上。在水熱法製備中，我們探討分析不同前驅物濃度對奈米陣列之形貌與性質 的影響，包括結構、發光頻譜與反射率。從光學性質分析可以得知氧化鋅奈米柱 內部存在有大量的缺陷。因此我們利用熱處理來降低缺陷密度，使入射太陽光在 穿越抗反射層時不會被氧化鋅奈米陣列吸收。此外，我們進一步將抗反射層應用 在矽晶太陽能電池上，發現在熱處理前因為氧化鋅內部缺陷較多，使入射太陽光 在穿透氧化鋅奈米陣列的過程中被吸收，因此太陽能電池的效率較低；在經過熱 處理後因為缺陷被消除，而使得效率上升。另一方面，我們也觀察到合成氧化鋅 奈米陣列的化學原料濃度對抗反射層的形貌與結構有顯著的影響；在適當的化學 原料濃度時，太陽能電池的效率可達 17.83%。我們並利用原子層沉積技術在氧 化鋅奈米陣列上均勻的鍍上一層具有高包覆度的氧化鋁薄膜可作為氧化鋅的抗 腐蝕保護層，並提供額外的折射率梯度，使入射太陽光在進入矽晶片時會有更少 的反射率。同時我們利用時域有限差分(FDTD)模擬與實驗同時探討具有不同厚 度的氧化鋁薄膜會對反射率之影響，結果不論是實驗或模擬都顯示在氧化鋁薄膜 的厚度為 12nm 時，會有最低的反射率。最後，在最佳化氧化鋅奈米陣列抗反射 結構之後，矽晶太陽能電池的效率可以從無反射層的 9.08%提升到 18.28%。

In this thesis, we used a hydrothermal method to synthesize ultra-long ZnO nanorods array (NRA), which was utilized as the effective anti-reflective structure for enhancing the performance of silicon solar cells.We investigated the effect of precursor concentration on the characteristics of broadband anti-reflection as well as the efficiency of silicon solar cells. After the thermal treatment, a significant change in the photoluminescence spectra from ZnO NRA was observed. The deep-level emission was suppressed due to the removal of the intrinsic defect by the thermal treatment. Therefore, the sunlight can pass through the anti-reflective structure rather than be absorbed by the ZnO NRA. Finally, atomic layer deposition was used to deposit highly conformal Al 2 O 3 layer on the surface of ZnO NRA to further reduce reflectance and provide effective protection of the chemically fragile ZnO NRA from harmful environments. The thickness of the Al 2 O 3 layer for minimum reflectance was examined experimentally, which is in good agreement with the result obtained from the finite-different time-domain (FTDT) simulation. . Under the optimal precursor concentration and the thickness of conformal Al 2 O 3 layer, the efficiency of silicon solar cells could be greatly improved from 9.08% to 18.28% by using the ZnO NRA as the anti-reflective structure. The result indicates that the ZnO/Al 2 O 3 core-shell NRA is a very promising anti-reflective structure for effective enhancement of the performance of solar cells and other photonic devices.