The Study of Optical and Electrical Properties of a-SiC:H for Multi-junction Si Thin Film Solar Cell
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1245-A07-11
The study of Optical and Electrical Properties of a-SiC:H for Multi-junction Si Thin Film Solar Cell.
J.H. Shim, W.K. Yoon, S.T. Hwang, S.W. Ahn, and H.M. Lee LG Electronics Inc., 16 Woomyeon-dong, Seocho-gu, Seoul, Korea
ABSTRACT Studies have shown that wide band gap material is required to investigate for multijunction applications. Here, we address proper deposition condition for a-SiC:H film adopting various deposition conditions. Those conditions were realized to single layers and cells to analyze their electrical and optical properties. In high power high pressure regime, we observed that the defect density get much lowered to the similar level of a-Si:H film with high H2 dilution. Solar cells fabricated with the optimized condition show high efficiency and lower LID effect with only 13 % reduction indicating that a-SiC:H is promising materials for multi-junction solar cells. INTRODUCTION For the Si based thin film solar cell, tandem structured solar cell has been studied to utilize solar spectrum more effectively for the higher efficiency solar cells. Many theoretical simulations show high efficiencies with tandem solar cells, there are still discrepancy between simulations and realized cells due to the material limitations, such as low optical absorption and high defect density [1,2] Yunaz et al.[3] had simulated multi-junction cells and showed that wide bandgap (Eg) materials are needed as a top cell to make solar cell with efficiency higher than 20%. Then also mentioned that one of the promising candidate materials with wide Eg is hydrogenated amorphous silicon carbide (a-SiC:H) [3]. Whereas, a good quality a-SiC:H film with low defect densitty has not been reported till now due to its microstructural disorder reducing photoelectronic quality significantly with incorporated carbon content [4,5]. The researchers have tried to make a-SiC:H film with increase of an excitation frequency or high hydrogen dilution ratio of the reactive gases (R ratio), for the better incorporation of the carbon atom into a-Si:H matrix to obtain higher Eg suppressing the defect states. Whereas, the increase of an excitation frequency from RF(13.65MHz) to VHF(60, 70 MHz) or microwave there were no clear relations observed between deposition condition and film quality [5,6,7,8] The a-SiC:H film quality was enhanced with the increase of hydrogen dilution ratio to silane (SiH4) gas. In Fourier transformed infrared spectroscopy (FT-IR), although there are still controversial to understand the origin of the distribution of the peaks near at 2000 cm1 [9,10,11], many experimental results supported that the peaks near 2000 cm-1 possesses two stretching modes with the monohydride configuration of Si-H bonding at 1980-2030 cm-1 and the dihydride configuration of Si-H2 at 2060-2160 cm-1 [12,13]. The latter mode is regarded as mostly related to the defect states which will affect the light induced degradation (LID) known as the Staebler-Wronski effect. In this work, we focused our research on the reduction of defect states in t
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