多層化金屬濺鍍預製層開發大面積CIGS太陽能電池

Abstract

本實驗使用先濺鍍金屬預製層後硒化(post selenization)退火的方式製作銅銦鎵硒太陽能電池。首先鈉玻璃基板上會先濺鍍一層400nm的鉬背電極，鍍製鉬金屬時採用兩層結構的濺鍍方法—第一層高製程壓力低瓦數濺鍍;第二層低製程壓力高瓦數濺鍍，如此可以得到附著力佳且高品質的背電極，電阻率為2.4x10-5Ω-cm. 金屬預製層的製作從常見的銅鎵和銦雙層結構(a)修改為多層堆疊的金屬預製層(b)，主要是因為金屬預製層製作會影響硒化處理後的吸收層品質。另外，由於銅、銦、鎵、硒元素的擴散能力不同，因此可以藉由濺鍍銅鎵和銦靶材的順序調整吸收層的能帶結構，示意結構如下 Mo/CuGa/In (a)  Mo/CuGa/In/CuGa/In/CuGa/In/CuGa/In/CuGa/In (b) 一般而言CIGS太陽能電池的鎵元素在硒化後會集中在吸收層底部形成單梯度的能帶結構，靠近背電極之吸收層能帶增大使得電子被複合機率降低，也就是增加了少數載子的收集，但是能帶的增大會減少低能量(長波長)光子的吸收也就是降低了電子-電洞對的產生，這一消一漲會達平衡，單梯度能帶結構之轉換效率可達18.8%。另外，若是CIGS薄膜表面鎵元素濃度提高形成雙梯度能隙的結構能更進一步的提升元件轉換效率。基於這個概念，多層的金屬預制層調整成 Mo/CuGa/In/In/ CuGa/ In/In/ CuGa/ In/ CuGa/ CuGa (c) 這種金屬預制層結構(c)就是要使鎵元素在吸收層表面與底部濃度高以提升能帶，實驗結果指出，多層化的金屬預製層不僅提升吸收層表面品質更能輕微調整元素的分佈，這些對銅銦鎵硒太陽能電池效率的提升有相當大的幫助。

The bi-layer structure of molybdenum back contact was deposited under higher working pressure and lower working pressure respectively. The one depositing at higher working pressure had good adhesion, and the other had low resistivity. Mo film with bi-layer structure had a low resistivity 2.4x10-5Ω-cm. Commonly method of precursor preparation was sputter-deposition bilayer stucture Mo/CuGa/In (a) precursor by selenization., however, the bilayer precursor after selenization were rough of morphology. Therefore, the following stack was uncompletly covered. Multi-layer stacked-precursors, however , substituted that due to smooth surface of CIGS . Mo/CuGa/In/CuGa/In/CuGa/In/CuGa/In/CuGa/In (b), There was immediately following an idea about Ga profile, which was induced by changing the Ga concentration on the surface/bottom of CIGS film. CIGS by selenization normally introduced back surface field(BSF) , which is located at the backside between CIGS film and Mo back due to MoSe2 layer formed. On the other hand, a single grading band gap was established in CIGS cells, which attached previous world record efficiency 18.8%. It increased the collection efficiency of minor carriers, electron, but reduced the absorption of low energy photons resulting from broaden band gap at the backside of CIGS. Moreover, a lot of studies indicated that double grading was a promising profile to further increase the device performance. In this study, Ga profile fabrication was to potentiate double-grading energy band gap of CIGS. Mo/CuGa/In/In/ CuGa/ In/In/ CuGa/ In/ CuGa/ CuGa (c) Additionally, the prospective idea, multi-precursor stacked, was a favorable method for improving cell efficiency.