Studies On Preparation And Properties Of CdTe Thin Film Deposited By Close Spaced Sublimation(CSS) Method

An overview is given on study of deposition conditions and doping characteristic of the CdTe thin films in this thesis. A Glass/ITO/CdS/CdTe/Cu thin film solar cell is also prepared in the thesis.We review recent development of photovoltaic materials all over the world, and set forth the principle,structure and efficiency of solar cell. We also review recent development of CdTe based polycrystalline thin film solar cells, and given an overview of the properties of CdTe thin films prepared by different deposition techniques.Then we narrate three common samples deposition methods and the structure principle of instrument .We also introduce the structure,electrical and optical properties of CdTe samples and analysis principle and relating instrument.The CdTe films doped Te are deposited onto glass substrate by Close Spaced Sublimation .The X-ray diffraction data indicate the pure CdTe films are polycrystalline zinc-blende structure with grain orientation predominantly along(111) direction.The electrical properties of CdTe films are investigated by Hall effect measurement using the Van der pauw method. Pure CdTe films have high electrical resistivity and are slightly p-type, due to the formation of Cd vacancies in the CdTe lattice acting as acceptor centers. The sheet resistivity of films are about 1010?/?.The sheet hole concentration is 105-6/cm2 and the Hall mobility is about hundreds cm2/v.s.The structural and electrical properties of CdTe films doped Te are markedly different from pure CdTe films. The second structure-hexagonal Te is found. The X-ray diffraction peak intensity shows the proportion of this structure is small. The lattice constants of the films increase and the diffraction peaks shift to low direction. The sheet resistivity dramatically decreases to 106?/?.The sheet hole concentration increases about 109/cm2 order of magnitude and the Hall mobility increases too. Te doping changes CdTe thin films into good p-type semiconductor and improves electrical properties of the films.CdTe films deposited by close space sublimation have better appearance and larger grain than the films deposited by RF-sputtering and vacuum thermal evaporation. The X-ray diffraction analysis shows films prepared by RF and VE have scattering peaks, however the peak intensity of pure CdTe films prepared by CSS method is higher than ahead both.CdS films and CdTe films are deposited on Glass/ITO substrate by CSS technique one after another, then a Cu film is deposited by RF-sputtering as metal back electrode, so at last a Glass/ITO/CdS/CdTe/Cu film solar cell is produced. When inputting light intensity is 70mw/cm2,cell area is 1×1cm2, the I-V curve of the cell shows open circuit voltage,short circuit electric current,filling factor and conversion efficiency is: VOC=180mV, ISC= 20mA, FF=0.62 and η=3.2% respectively。...