氧化鋅奈米柱抗反射層應用於無鎘銅銦鎵硒薄膜太陽能電池之製備與分析

Abstract

銅銦鎵硒是深具潛力的薄膜太陽能電池材料，目前最佳轉換效率為瑞士聯邦材料測試與開發研究所發表的百分之二十點四。然而銅銦鎵硒薄膜太陽能電池傳統緩衝層材料為硫化鎘，其中鎘的成份對環境有相當的毒害，因此本論文以硫化鋅作為緩衝層的替代材料。在另一方面，增進太陽能電池轉換效率最直接的方法就是抗反射層的應用，而因設計上的限制，傳統抗反射層無法達到全波段抗反射的效果，因此本論文以氧化鋅奈米柱作為抗反射層，利用其漸進折射率的特性進而改善太陽能電池的轉換效率。 對於硫化鋅緩衝層，我們漸進式的改善化學水浴法的沈積條件，包括沈積啟始點以及反應溶液混合次序，根據硫化鋅於化學水浴法中的成長機制，儘可能增強異質成核反應並壓制同質成核反應，得到厚度大約為100奈米以及1.44鋅與硫的化學當量比之硫化鋅薄膜。 對於氧化鋅奈米柱抗反射層，我們研究氧化鋅奈米結構的高度與光學特性的關係，發現雖然隨著奈米柱高度增加表面反射而降低，但穿透也隨之降低，進而提出吸收效應的存在。經過分析後提出沈積時間介於8-14分鐘為奈米柱對於增進太陽能電池效率的最佳區間。 最後我們將硫化鋅薄膜作為緩衝層製作元件並搭配氧化鋅奈米柱為抗反射層，經過太陽能電池電壓與電流特性分析後，得到成長時間為11分鐘的氧化鋅奈米柱使得元件效率與短路電流分別得到8.3%和7.56%的相對增益值。

The Copper Indium Gallium Diselenide (CIGS) is the most promising material for solar cell application. Until now, the best conversion efficiency reaches 20.4% by EMPA, Swiss. However, the traditional buffer material is cadmium sulfide (CdS), the cadmium is toxic for environment. Thus the zinc sulfide (ZnS) was adopted for the alternative material for buffer layer in this thesis. On the other hand, the direct manner improved the conversion efficiency is application of anti-reflection layer. However, the traditional anti-reflection layer unable to reach broad-band anti-reflection due to the limitation of design. Thus, zinc oxide nanorod (ZnO NR) with graded refraction index was adopted for the anti-refleciton layer, and further improve the conversion efficiency of solar cell. For the ZnS buffer layer, we improved the deposition conditions consisted of initial point of deposition and mixed order of reactant and according to the growth mechanism in the chemical bath deposition, enhance the heterogeneous and suppress the homogeneous nucleation as possible to acquire the ZnS thin film with 100-nm-thick and 1.44-Zn/S ratio. For ZnO NR antireflection layer, we study the relationship between the height of ZnO NR and optical properties. We found the surface reflectance was reduced via the increase of height of ZnO NR but the transmittance was decreased accordingly. The absorption effect was proposed. After analyzing, the most promising period of ZnO NR growth for improvement of efficiency was between 8 and 14 minutes. Finally, we used ZnS as buffer layer and ZnO NR as anti-reflection layer for fabrication of CIGS solar cells. After analyzing the current-voltage characteristics, the CIGS solar cell with NR deposited for 11 minutes acquired the relative gains of conversion efficiency and short-circuit are 8.3% and 7.56%, respectively.