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A23.2.1

High Efficiency Solar Cells with Intrinsic Microcrystalline Silicon Absorbers Deposited at High Rates by VHF-PECVD Yaohua Mai1, 2, Stefan Klein1, Reinhard Carius1, Xinhua Geng2, Friedhelm Finger1 1 IPV, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany, 2 Institute of Photoelectronics, Nankai University, Tianjin 300071, P. R. China. ABSTRACT Intrinsic microcrystalline silicon (µc-Si:H ) was prepared at high deposition rates (RD) by very high frequency plasma-enhanced chemical vapor deposition (PECVD) working at high-pressure high-power (hphP). The material has similar electrical and optical properties as µc-Si:H material deposited at low rates by low-pressure low-power PECVD, apart from a more pronounced structure in-homogeneity along the growth axis for material deposited on glass substrates. With optimized deposition conditions high efficiency solar cells can be grown with deposition rates of up to 15 Å/s without deterioration of the performance as a function of RD. A high conversion efficiency of 9.8 % was obtained for a single junction µc-Si:H p-i-n solar cell at a deposition rate of RD = 11 Å/s. INTRODUCTION In an attempt to lower the production cost and enlarge the market share of thin film silicon based solar cells, high rate growth of hydrogenated microcrystalline silicon (µc-Si:H) has become one of the hot topics. For the plasma-enhanced chemical vapour deposition (PECVD), very high frequency (VHF) [1-3] and high-pressure high-power (hphP) [4, 5] have been successfully developed for high rate deposition of µc-Si:H with high material qualities. Also, combination of the two methods, VHF-hphP, has been explored [6-8]. In this paper, we present the systematic investigation on the structural, electrical, and optical properties of µc-Si:H material deposited with VHF-hphP and at high deposition rate (RD) and their influences on the resulting solar cells. The µc-Si:H material and solar cells deposited at high RD are compared with a reference series deposited under conventional low-pressure low-power (lplP) conditions. EXPERIMENTAL DETAILS All films and solar cells were fabricated in a multi-chamber system [9] by PECVD with discharge excitation frequency at 94.7 MHz. Substrate size is 10×10 cm2. The gas supply is a simple cross-flow geometry, i.e. no gas showerhead arrangement. As high efficiency µc-Si:H solar cells are always found close to the transition from highly crystalline to the amorphous growth [2, 5, 8, 9], different structure phase compositions covering the entire crystallinity range were obtained for the material by the variation of silane concentration, defined as the flow rate ratio of processing gases, SC = [SiH4]/([SiH4]+[H2]). For the SC series of hphP films presented in

A23.2.2

this paper, working pressure (pdepo) of 2.1 hPa, discharge power (PVHF) of 60 W, and total flow rate (Fltotal) of 100 sccm were used. If not otherwise stated, the deposition parameters of intrinsic layers in the hphP solar cells are the same as for the hphP film series. Under lplP conditions, pdepo=0.25 hPa,