設計ITO/TiO2光子晶體基板達成非晶矽太陽電池的吸收提升

Abstract

我們藉由設計光子晶體結構來提升反射與達到光誘捕效果，以提升非晶矽薄膜太陽能電池主動區的光學吸收路徑，增加吸收效率。在這篇文章中，我們建立光子晶體在非晶矽太陽能電池中的模擬模型，分別位於背光面作為背反射器；以及位於主動區的入光面作為光子晶體基板，再經由嚴格耦合波分析（RCWA）法計算並分析模擬結果。 在主動區背光面的光子晶體結構，我們選擇材料ITO（折射率約2.01）和a-Si（折射率約4.25）以六角最密堆積交互排列。經優化後，兩種不同的ITO結構——孔洞與柱狀，分別提高了吸收效率2.89％與3.26％。而利用最佳化結構有效增加長波長區吸收的特性，可以達到減少主動區厚度節省材料的效果。 在主動區入光面的光子晶體結構，由於ITO/a-Si光子晶體結構會造成能量損失，因此我們選用TiO2（折射率約2.49）取代a-Si。ITO/TiO2光子晶體結構優化後，孔洞結構提升吸收約16.97％；柱狀結構提升約18.93％。在短長波區，此結構減少了反射，並在長波長區提供光散射增加吸收長度。最後，我們模擬光子晶體基板的光學特性。反射和穿透頻譜顯示，光子晶體基板在入射光由正向到大角度的變化下，都有助於減少反射、增加穿透來提升主動區的吸收。

We demonstrate a flatted photonic crystal (PhC) structure to serve both function of reflection and light trapping effect in a-Si thin film solar cells. In this work, we build a model in simulation of PhC structures in different side of solar cells, rear and front, which is calculated by rigorous coupled-wave analysis (RCWA) method. In rear side of cell, we chose materials of ITO (n=2.01) and a-Si (n=4.25) to for construction of hexagonal hole and rod array. The optimum structure enhance absorption at about 3.26% by hole and about 2.89% by rod. In other hand, optimized PhC structures can reduce thickness of active layer at about 35% by enhance optical path length in long wavelength region. In front side, we replace a-Si by TiO2 (n=2.49) to avoid energy loss brought by a-Si in PhC structures. The optimized ITO/TiO2 PhC structure enhance at about 18.93% by hole and at about 16.97% by rod. The ITO/TiO2 PhC structures at front side provide anti-reflective effect in short wavelength region and light scattering effect in long wavelength region. Finally, we simulated optical properties of two substrates possess the same dimension of the front PhC structures. The reflectance and transmittance spectrum show that the PhC substrates contribute more absorption in active layer at large angles of incident light.