以定光電流量測之吸收係數分析矽薄膜缺陷密度之研究

Analyzing the defect density of silicon thin film from optical absorption

張庭維(Ting-wei Chang)

指導教授 ： 李正中 ； 陳昇暉

國立中央大學/理學院/光電科學研究所/碩士(2010年)

摘要

石化燃料具有耗竭性與污染性等問題，矽薄膜太陽能電池作為未來
的替代性可再生能源之一，目前仍有轉換效率不高以及劣化嚴重等瓶
頸。為了提高電池轉換效率以及可靠性，矽薄膜缺陷密度量測扮演著
很重要的角色，定光電流量測法為簡易且方便之測量法，可量測具有
低缺陷密度之樣品。本文使用定光電流量測法量測非晶矽薄膜，為了
更為準確的分析缺陷密度，本研究基於非晶能態分佈理論，並使用擬
合吸收係數曲線法計算出缺陷密度。
對於微晶矽缺陷密度分析上，本研究引入等效介質理論並結合非晶
矽吸收係數的計算，成功的解釋微晶矽吸收係數隨結晶率的變化，且
可擬合出定光電流量測出之微晶矽吸收曲線之形貌，進而計算出微晶
矽薄膜裡含有的懸浮鍵密度。
此外，實驗證明使用定光電流量測出之a (1.4eV )與a (0.9eV )之間比值，可用來評定微晶矽薄膜太陽能電池本質層之品質，而經由本研究提出的分析方法，可證明a (1.4eV )與a (0.9eV )分別正比於結晶率與懸浮鍵密度。

關鍵字

缺陷密度 ； 矽薄膜 ； 吸收係數

並列摘要

There is on hand the issue of the environmental impact of conventional energy sources. As the result, silicon thin film solar cells become one of alternative sources of energy. But it still needed to be improved by different
methods. The dangling-bond has been studied in the past years as an important measure to optimize the quality of silicon thin film solar cell.
Dangling-bond is the main defect in a-Si:H and μc-Si:H, influencing the carrier transport and therefore are crucial for photovoltaic devices. Constant photocurrent measurements was known to be sensitive for evaluating the
bulk defect density from optical absorption. We calculated the inter-band absorption form the model of density of state in a-Si. Thus the defect density could be determined from the absorption coefficient by curve fitting
For μc-Si:H, which exists a large variety of structure compositions ofamorphous silicon and crystalline silicon grains. The absorption in μc-Si:H
is influenced not only by the amount of defects but also by the crystallization volume fraction. We calculate the absorption spectral of microcrystalline silicon by applying the effective-medium theory. The results explain successfully that absorption coefficient at 1.4eV was
proportional to the crystallization volume fraction and absorption coefficient at 0.9eV was proportional to the dangling bound concentration of microcrystalline silicon. The defect density in amorphous phase could be determined from the absorption coefficient by curve fitting.
By dividing the absorption coefficient at 1.4eV with the value at 0.9eV, we used the factor to judge quality of μc-Si:H and predict PV device performance by multiplying Voc with Isc when using this layer as its intrinsic layer. The results show a good relationship between the quality
factor and the product of open-circuit voltage and short-circuit current.

並列關鍵字

absorption coefficient ； defect density ； silicon thin film

參考文獻

[1] L. Raniero, N. Martins, P. Canhola, S. Zhang, S. Pereira, I. Ferreira, E.

Fortunato, R. Martins, Sol Energ Mat Sol C 87/1-4 (2005) 349.

[3] R.C. Chittick, J.M. Alexander, M.E. Sterling, J. Electrochem. Soc 116

[4] W.E. Spear, P.G. LeComber, Solid State Communications 17 (1975)

[6] Staebler, Wronski, Appl. Phys. Lett. 31 (1977) 292.