Fabrication and development of doping-free amorphous silicon based thin film solar cells using molybdenum oxide and lithium flouride

Abstract

This thesis discusses about the “doping-free” structured a-Si:H based solar cells. In the conventional tructured a-Si:H based solar cells, the doping is used in the p-type window layer and the n-type back contact ayer. Starting from the replacement of the p- and n-layer, respectively, several methods are adopted in order o improve the efficiency of the solar cells. Finally, using MoO3 window layer and LiF/Al back contact together, he “doping-free” structured amorphous Si based solar cells are implemented. In chapter 1, a social and economic background of photovoltaic is reviewed. Also, advantages and imits of the amorphous silicon based thin film solar cell are mentioned. From this background, fundamental tudies of other researchers’ are introduced. Furthermore, the motivation of this work subjected “doping-free” solar cell is appealed. The “doping-free” scheme is cost effective, safe and environmentally not harmful, and easily adoptable for various substrates. In chapter 2, the fabrication and measurement systems for the amorphous Si based thin-films and the solar cells using those films are explained. In chapter 3, it is discussed about the effect of UV irradiation on MoO3 window layer. Using UVtreated MoO3 film as a window layer of the cell, the Voc is increased. It was confirmed from UV photoelectron spectroscopy measurements that the UV irradiation increased the work-function of the MoO3 window layer, resulting in drastically increasing the open circuit voltage of the cell by 52 mV (about 7 %) for the optimized UV treatment time of 60 minutes. The best conversion efficiency of 6.11 % was obtained. The cell performance improvement is due to the enhanced Voc by the UV treatment on the window layer. In chapter 4, a MIS Schottky structure for glass/SnO2:F/n-MoO3/SiOx insulator/i-a-Si:H/n-a-Si:H/Al solar cell structure is proposed. It is investigated about the effect of the thickness of the SiOx insulator. The Voc was enhanced in the cells with a 0.9-nm-thick...