High Deposition Rate of Microcrystalline Silicon for n-i-p Solar Cell by Using VHF PECVD Method
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0974-CC10-31
High Deposition Rate of Microcrystalline Silicon for n-i-p Solar Cell by Using VHF PECVD Method Jun-Chin Liu1, Chin-jeng Huang1, Techi Wong2, Jian-Shu Wu1, Yih-Rong Luo1, and Chi-Lin Chen1 1 ITRI, Hsinchu, 310, Taiwan 2 PVTC, ITRI, Hsinchu, 310, Taiwan
Abstract P doped, intrinsic, and n doped microcrystalline silicon (μc-Si) thin films were successfully synthesized on 10×10 cm2 transparent conductive oxide (TCO) /glass substrate by using a Very High Frequency Plasma Enhanced Chemical Vapor Deposition (VHF-PECVD, 80MHz) single chamber system. The crystal fraction of p and n type μc-Si:H with a thickness of 100nm was over 70% and 80%, respectively. Intrinsic μc-Si:H was deposited at a substrate temperature of 250℃ with a high deposition rate over 1 nm/s. The optimum cell initial efficiency of μc-Si:H single junction solar cell had been achieved 7.03 % so far. The a-Si/μc-Si tandem solar cell with an efficiency up to 10.9% had been done.
1. Introduction During this year, due to the feed-stock shortage problem, the market of Si wafer solar cell grows slowly. Therefore, Si thin film solar cell had attracted many attentions. Especially, Applied Materials and Oerlikon were announced to provide the turn-key solution of a-Si thin film solar cell in 2007. Although, the efficiency degradation of a-Si thin film solar cell was a much concern issue under light illumination. However, a-Si/μc-Si tandem solar cell could not only enlarge the spectrum range of absorption but also eliminate the a-Si thickness to reduce the light degradation degree. Due to the absorption coefficient ofμc-Si is lower than a-Si, so the thickness of µc-Si must be
larger than 1μm to absorb light. Hence, the deposition rate of μc-Si thin film become a big challenge to increase the throughput in the future. Many deposited methods could be achieved a high deposition rate, including of ECR, Micro Wave and Very High Frequency PECVD. The uniformity of thin film was mainly limited by standing wave in large glass substrate. Therefore, VHF PECVD is considered an easy way to manufacture Si thin film at higher deposition rate and have the less ion bombardment effect on Si thin film. In present article, Si thin films were deposited in a VHF PECVD system. In addition to use a barrier layer, reducing series resistance and the carrier recombination in the solar cell would be the critical issues.
2. Experiment This experiment was executed at a capacitance type VHF (80MHz) PECVD system, which was shown as Figure 1. It was just composed of one main chamber and the p, i, and n doped layers of solar cell must be deposited sequential in one chamber. Substrate temperature was set at 250℃. The distance of electron gap was holds at
2cm. Reacting gases were fed in from the shower head, which used as the top cathode. Substrate of 10×10 cm2 glass was positioned on the susceptor, which was used as the anode electrode. The experimental parameters were including of SiH4/H2 flow ratio, pressure, and VHF power density. Film structure was investigated by SEM and Small a
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