Research Progresses on High Efficiency Amorphous and Microcrystalline Silicon-Based Thin Film Solar Cells
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1245-A21-03
Research Progresses on High Efficiency Amorphous and Microcrystalline Silicon-Based Thin Film Solar Cells Ying Zhao, Xiaodan Zhang, Guofu Hou, Huizhi Ren, Hong Ge, Xinliang Chen, Xinhua Geng The Institute of Photoelectronic Thin Film Devices and Technology, Nankai University, 300071, Tianjin, China ABSTRACT This paper reviews our research progresses of hydrogenated amorphous silicon (a-Si:H) and microcrystalline (μc-Si:H) based thin film solar cells. It coves the three areas of high efficiency, low cost process, and large-area proto-type multi-chamber system design and solar module deposition. With an innovative VHF power profiling technique, we have effectively controlled the crystalline evolution and made uniform μc-Si:H materials along the growth direction, which was used as the intrinsic layers of pin solar cells. We attained a 9.36% efficiency with a μc-Si:H single-junction cell structure. We have successfully resolved the cross-contamination issue in a single-chamber system and demonstrated the feasibility of using single-chamber process for manufacturing. We designed and built a large-area multi-chamber VHF system, which is used for depositing a-Si:H/μc-Si:H micromorph tandem modules on 0.79-m2 glass substrates. Preliminary module efficiency has exceeded 8%. INTRODUCTION Amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) tandem (micromorph) solar cells with an a-Si:H top cell and a μc-Si:H bottom cell technology has been gradually transferred from research laboratories to manufactures [1,2]. The a-Si:H/μc-Si:H micromorph structure has the advantage of higher efficiency and better stability than the cells with pure a-Si:H and amorphous silicon germanium alloy (a-SiGe:H). However, On the way towards real mass production, several technical issues need to be resolved. Among the hurdles, high efficiency, large-area uniformity, and reduction of manufacturing cost are the three major areas for further studied. Our group has focused on these three areas. In this paper, we review our progress made in the last a few years. EXPERIMENT All μc-Si:H films and μc-Si:H single-junction solar cells with a small area of 0.25 cm2 were deposited in a cluster-tool system with a background pressure of 5×10-6Pa. The intrinsic μc-Si:H layers were deposited with plasma enhanced chemical vapor deposition (PECVD) with a very high frequency (60 MHz ) excitation. The solar cells were deposited on SnO2 or Al doped ZnO coated glass substrates with a pin structure, where the μc-Si:H p-layer and a-Si:H n-layer were deposited with VHF (60MHz) and RF (13.56MHz), respectively. The a-Si:H top cells were deposited on the μc-Si:H single-junction bottom cells in a seven-chamber in-line PECVD system
with the excitation frequency of 13.56 Hz. Chemically etched Al doped ZnO layers were also used to enhance the light trapping. Intrinsic μc-Si:H films were deposited on Eagle-2000 glass substrates for material characterization. Raman spectroscopy was used to measure the crystallinity. The crystalline volume fraction (XC) was
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