Study Of Synthesis And Properties Of CdTe Thin Films

With the continued growth of energy consumption and environmental issues such as increasingly serious haze, the solar energy of China is abundant and widely distributed and the Chinese government will develop and apply new energy as a national strategic emerging industries. Photovoltaic power system is a typical representative of the new energy, of which the core part is the solar cells. Cadmium telluride material is an ideal material for solar cells. Among the synthesis methods for CdTe thin film, electrodeposition is easily controlled, adjustable and advantagous compared with others. TeO2 as tellurium source is used in the conventional methods for electrochemically synthesis of CdTe thin films. Moreover, the concentration ratios of Cd (II) and Te (IV) is greater than 10. In this thesis, the use of water-soluble salt Na2TeO3 as tellurium source instead of the usually used TeO2 for CdTe electrodeposited onto flexible metal Mo substrate is explored.CdTe thin films have been deposited onto the Mo foil from aqueous acidic bath via electrodeposition method with water-soluble Na2TeO3. X-ray diffraction and X-ray photoelectron spectroscopy studies indicate that the CdTe thin films are crystallized in zinc-blende symmetry. The effect of tellurite concentration on the morphology of the deposited thin film with the concentration ratios of Cd(II) and Te(IV) equal to 2 and 4 is investigated. In such case, the lower tellurite concentration added into the bath brings the higher Cd:Te molar ratios in the as-grown thin film, which is composed of the grain and relatively smooth. The Cd:Te molar ratios in the annealed films are both stoichiometric at different tellurite concentrations. In addition, the reduction of tellurite concentration leads to the porous thin film and weakens the crystallinity of thin film. The island growth model is used to interpret the growth mechanism of CdTe preliminarily according to the CV curve and observations. The bandgap of the CdTe thin films is assigned to be 1.49 eV from the UV-vis spectroscopy measurement at the different concentrations, which is considered to serve as a promising candidate for the heterojunction solar cells.