Study On CdTe And Related Compound Polycrystalline Thin Films As Well As CdTe Solar Cell

In the present the study and application of thin film solar cells are the focus in the photovoltaic field. The polycrystalline thin film CdTe solar cell is one of the thin film solar cells which are mainly investigated. Some important problems about CdTe solar cells are not completely understood which result from their basic characteristics - polycrystalline thin films, compound semiconductor, heterojunction devices. This thesis has deeply investigated the several important steps to prepare CdTe solar cells, which include the deposition and post heat treatment of polycrystalline CdTe thin films (base layer), preparation of back contact layers, post heat treatment processing of CdS polycrystalline thin films, and device physics. The high efficient CdTe solar cells have been successfully prepared on the basis of detailed investigation of single layers. The main factors to limit conversion efficiency of CdTe solar cells are analyzed after the device characteristics were measured. The main creative results are achieved as follows,1. Developing the method characterizing CdTe thin film quality and optimizing the processing of preparation and post heat treatment for CdTe thin films by Close-Spaced Sublimation (CSS) in the cheap mixture atmosphere of argon and oxygen. The preferred-orientation extents were studied quantitatively with the texture coefficient on the function ofsubstrate, substrate temperature, and oxygen concentration. The optic and electrical properties of the single CdTe layer deposited on glass substrate by CSS were investigated on the function of processing of preparation and post heat treatment. Some results which have never before been reported before by other researchers are achieved.2. For the first time the mechanism of abnormal conductivity dependence on temperature are systematically explained from the perspective of phase transition, after the structure, optic and electrical properties of ZnTe:Cu polycrystalline thin films have been investigated on the function of copper concentration and temperature. According to the research results the post heat treatment processing of back contact layers was optimized for CdTe polycrystalline thin films.3 The post heat treat processing of CdS polycrystalline thin films are optimized after the structure, optic and electrical properties, surface characteristic have been investigated on the function of atmosphere, time, temperature. Firstly, CdS films are annealing at 380"C for 30 minutes in the atmosphere of N2+CdCl2 to achieve the proper feimi energy level; secondly, the films are treated at 380癈 for 10 minutes in the hydrogen atmosphere to clean the surface.4 The CdS/CdTe solar cells are prepared on the basis of above research results. The performances of solar cells were studied on the function of annealing temperature, substrate temperature, oxygen concentration for CdTe thin films, and the configuration, copper concentration, post heat treat processing for ZnTe/ZnTe:Cu back contact layers. The domestic record of conversion efficiency for polycrystalline thin films solar cells was continually created. In the present the highest conversion efficiency reaches 13.4%. And individual parameter of pefformance, filling factor and open voltage reach respectively 73.1%, 860mV. This approaches the advanced world level.5. The dependence of CdS/CdTe solar cells performance is simulatedon the function of CdTe thin film characteristics, .the performance of CdSTe interface layer in the CdS/CdTe, configuration of ZnTe(ZnTe:Cu) back contact layer, and back contact barriers. The similar investigations have never been reported by other researchers. These supply the important evidences to design structure of CdTe solar .cells. Then the new structure of high efficiency CdTe solar cells is presented as TCO (ZnO:F, CdSn04)/window layer (ZnS^ ZnSe)/CdTe(l-2um)/ZnTe (ZnTe:Cu)/Au.