Deposition of P-Type Nanocrystalline Silicon Using High Pressure in a VHF-PECVD Single Chamber System
- PDF / 199,797 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 66 Downloads / 200 Views
Deposition of P-Type Nanocrystalline Silicon Using High Pressure in a VHF-PECVD Single Chamber System Xiaodan Zhang, Guanghong Wang, Xinxia Zheng, Shengzhi Xu, Changchun Wei, Jian Sun, Xinhua Geng, Shaozhen Xiong and Ying Zhao Institute of Photo-electronic Thin Film Devices and Technology of Nankai University, Weijin Road 94#, Nankai District, Tianjin 300071, P.R.China ABSTRACT In this article, we present a study of boron-doped hydrogenated nanocrystalline silicon (nc-Si: H) films by very high frequency-plasma enhanced chemical vapor deposition (VHF-PECVD) using high deposition pressure. Electrical, structural and optical properties of the films were investigated. Dark conductivity as high as 2.75S/cm of p-type nc-Si: H prepared at 2.5Torr pressure has been achieved at a deposition rate of 1.75Å/s for 25nm thin film. By controlling boron and phosphorus contamination, single junction nc-Si: H solar cells incorporated p-layers prepared under high pressure and low pressure, respectively, were deposited. It has been proven that nanocrystalline silicon solar cells with incorporation of p layer prepared at high pressure has resulted in enhanced open circuit voltage, short circuit current density and subsequently high conversion efficiency. Through the optimization of the bottom solar cell and application of ZnO/Al back reflector, 10.59% initial conversion efficiency of micromorph tandem solar cell (1.027cm2) with an open circuit voltage of 1.3864V, has been fabricated, where the bottom solar cell using a high pressure p layer was deposited in a single chamber. INTRODUCTION Plasma-enhanced chemical vapour deposition (PECVD) of p-i-n type solar cells in a single plasma reactor offers advantages of low cost compared to multi-chamber processes which use separate reactors for fabrication of the p-, i- and n-layers, respectively [1]. In addition, to further reduce costs to industry, it is essential that solar cells be deposited at high rate by high deposition pressure and the same, small electrode distance. In general, nc-Si: H p-layers are prepared by very high frequency-plasma enhanced chemical vapor deposition (VHF-PECVD) at low pressure or RF deposition at low or high pressure, respectively [2-5]. No further information on the fabrication and structural properties of nc-Si: H p-layers prepared by VHF-PECVD deposition at high pressure have been reported so far. Conditions for a better p-layer suitable for p-i-n type solar cell application are quite stringent. It must have low absorption, high conductivity, and sufficient crystallinity to promote the nucleation and homogeneous growth of the subsequent nanocrystalline intrinsic layer at the p/i interface [6]. In this study, dark conductivity, crystallinity, surface morphology as well as absorption coefficient of p-type nc-Si: H had been investigated varying deposition pressure and thickness as well as the performance of these films in single junction and micromorph solar cells.
393
EXPERIMENT The nc-Si: H films were deposited using a capacitively coupled ultrahigh vacuum (U
Data Loading...
