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Silicon nanowires solar cell Xiaobing Xie, Xiangbo Zeng, Wenjie Yao, Ping Yang, Shiyong Liu, Wenbo Peng, Chao Wang, Xingwang Zhang, Hongliang Zhu, Zhanguo Wang Key Laboratory of Semiconductor Material Science, Institute of Semiconductors,Chinese Academy of Sciences, East Qinghua road 35A, Haidian District ,Beijing 100083, China ABSTRACT We made an amorphous-silicon (a-Si) solar cell with a nanowire-array structure on stainless steel(SS) by plasma enhanced chemical vapor (PECVD) deposition. This nanowire structure has an n-type Si nanowire array in which a-Si intrinsic layer and p type layer are sequentially grown on the surface of the nanowire. The highest open-circuit voltage (Voc) and short-circuit current density (Jsc) for AM 1.5 illumination were 620 mV and 13.4 mA/cm2, respectively at a maximum power conversion efficiency of 3.57%. INTRODUCTION Recently there has been significant interest in the photovoltaic properties of silicon nanowires (SiNWS) [1-6] for the development of high efficiency and low-cost solar cells. Radical junction nanowires based photovoltaic structures, in particular, provide potential advantages of more efficient charge collection[7,8] and natural anti-reflective structure that allows light trapping and thus enhanced absorption.[9-11]. A radial p-n junction structure made of rods array exhibited improving photo-generated carrier collection for material with short minority carrier diffusion lengths[12] theoretically. SiNWs solar cells based on such a radial p-n junction structure have been reported. experimentally [2, 4, 13]. However, much effort is still needed to improve SiNWS cells with performances exceeding to that of the existing crystalline silicon photovoltaic technology. In this work, we reported radial n-i-p structure SiNWs solar cells on stainless steel by PECVD. EXPERIMENT

SiNWS solar cell fabrication begins with first cleaning the SS substrates using standard solvents, followed by sputter deposition of a 10-nm-thick Indium Tin Oxides (ITO ) film. Following form of nanoscaled indium droplets by hydrogen plasma treatment[14 ], catalytic CVD employing the vapor-liquid-solid VLS growth mechanism[15] is used to grow n-type Si nanowires. The nSiNWs array was subsequently coated with conformal a-Si:H i-layer (~300 nm) and p-layer (~20 nm) deposited in situ to create the radial n-i-p structure. After a-Si:H layers deposition, the array was sputter coated with a 300-nm-thick ITO layer acting as electrical contact. The detail deposition parameters of each layer are summarized in Table 1. The cell performance was characterized by photocurrent density-voltage measurement under xeon solar simulator ( 100mW/cm2, calibrated by a standard silicon solar cell) at room temperature.

Table1．Deposition parameters for SiNWS solar cell Substrate temperature (0C) Pressure ( Pa) Power (mW/cm2) Gas (sccm)

H treatment 400

n-SiNWS 400

i layer 150

P layer 70

200 100

200 50

133 50

500 100

SiH4:H2：PH3 6：60：0.06

SiH4:H2 6：60

SiH4:H2：B2H6 1：100：0.03

H2 flow 60

Figure 1(a )shows SEM image of n-Si