具有不同氧化銦錫結構之寬能隙氮化鎵太陽能電池研究

Abstract

最近幾年，氮化鎵/氮化銦鎵化合物半導材料經常被廣泛討論，因為氮 化鎵/氮化銦鎵的能隙具有很寬的可調範圍，從 0.7 eV~3.4 eV，如此寬的 可調能隙在加上其本身為直接能隙，因此被認為最具有發展超高效率太陽 能電池的材料，理論上七個接面的氮化鎵/氮化銦鎵太陽能電池其轉換效率 可達 46%，短路電流為 8.33 mA/cm 2 開路電壓為 6.26 V，在聚光 500 倍 的條件下四接面的太陽能電池轉換效率高達 62%。 這次論文研究主要是製作抗反射奈米結構，此結構可應用在氧化銦錫 (Indium Tin Oxide, ITO)抗反射結構處理上，增加抗反射處理為在一段寬 廣的波段中得到較低的反射率，其在表面的仿生性奈米結構做到最密堆 積，對抗反射效果可以達到多向性抗反射與寬頻譜的抗反射效果。 我們成功利用了奈微米球微影術(Nanosphere lithography, NSL)製作 大面積氮化矽基的次波長抗反射層結構應用在氮化銦鎵三五族太陽能電池 上，並利用乾式非等向性反應式離子蝕刻的參數調整達到形貌控制的效果 進而比擬蛾眼結構，比傳統四分之一波長厚度的抗反射層更具有寬頻譜範 圍的抗反射能力，除了 500 nm~700 nm 為傳統單層抗反射層的優勢之外， 都可普遍使反射率大幅降低。由於在紫外光與近紅外光的抗反射特性，應 用在氮化銦鎵太陽能電池上，相較於沒有製作抗反射層以及傳統單層抗反 射層的太陽能電池元件，分別提升了 10.38%以及 5.29%的光電轉換效率。

Recently, indium gallium nitride materials(In x Ga 1−x N) have been extensively investigated for application in photovoltaic devices owing to their energy bandgaps lying between 0.7 and 3.4 eV. The properties of the wide bandgap range make it useful for the fabrication of high performance multi-junction solar cells. In theory, an efficiency of about 46% is achievable for a seven junctions with the photocurrent density was 8.33mA/cm 2 and the open-circuit voltage was 6.26V. And it will be reached 62% for 4 junctions tandem cell at concentration of 500x. The research focuses on the fabrication technology for structure of anti-reflection . The structure can be applied to anti-reflection ITO film. In order to get much lower reflective coefficient in a broad band, a nano structure made of thermoplastic was proposed . The pitch between the neighbor structures on the surface gets shorter, the effect of anti-reflection can become better. We have successfully fabricated large-scale SiNx-based sub-wavelength antireflective structures (SWS) for a InGaN solar cell employing the polystyrene nanosphere lithography. The sidewall profiles of sub- wavelength structures were controlled by adjusting anisotropic etching parameters to mimic moth-eye structures. Compare to the conventional single-layer anti-reflective coating (SL ARC) which shows suppressed reflectance in 500 nm~700 nm wavelengths, the SWS ARC shows a broadband spectral response of reflection characterisitcs. Both the reflectance spectroscopy and external quantum efficiency measurements confirm the improved optical absorption in the ultraviolet/blue and near-infrared wavelengths. Hence, the conversion efficiency of the InGaN solar cell is enhanced by 10.38% and 5.29% due to much improved current-matching.