| In this study, energy shortage, environment pollution and the present situation ofphotovoltaic industry development are discussed, and the copper indium gallium selenide(CIGS) thin film solar cells are introduced. It gives a brief introduction on CIGS thin filmbattery, working principle and performance parameters, the parameters of preparation ofCIGS thin film. The experiments are carried out with magnetron sputtering method, in avacuum plating system to prepare CIGS thin film absorption layer, buffer layer cadmiumsulfide (CdS) thin film and the window layer (ZnO) thin film on soda lime glass. Throughrelated testing equipment, for example, X-ray detector (XRD), scanning electron microscope(SEM). Detailed experiment is carried out to study the impact of different substratetemperature, heat treated temperature and the electric power on CIGS thin film surfacemorphology and crystallization. The results are shown as following:Magnetron sputtering of CIGS thin film absorption layer. The process parameters are listhere: target distance from the substrate10cm, the bottom vacuum is4.0x10-4pa, the gaspressure is5.5x10-1, the argon gas flow is31standard ml/min (SCCM), sputtering power is125w, prepares of CIGS thin film respectively in different process parameters on glasssubstrate, with sputtering film thickness to2microns. Then the CIGS thin film samples areheat treated with argon protective atmosphere. By XRD spectrum detection analysis, the peakpositions of CIGS thin film are consistent with standard card. It shows from the results thatthe CIGS thin film has chalcopyrite crystal structure.Sputter CIGS thin film with different substrate temperatures. In the process of thin filmgrowth, substrate temperature is one of the important conditions. It has apparent influence onthe thin film growth for membrane structure characteristics. The electric power is125w,without annealing, experiment sets different substrate temperature, and as the substratetemperature increase, the film surface topography becomes rough. When temperature is lowthan300℃, the film surface is relatively uniform and smooth. When temperature is above400℃, the thin film has more internal defects, rough surface, and even has crack. Whensubstrate temperature is below200℃, the CIGS thin film has amorphous structure; As thesubstrate temperature increase, the diffraction peak of (112) gradually increases, and thecrystallization of the thin film is more and more obvious.Different annealing temperatures have influence on CIGS thin film. Annealing treatmentmakes the material re-crystallizing, and this process can improve the film properties, such ascrystallization, phase composition, the optical and electrical properties. The sputteringparameters are: electric power125w, room temperature, and then taken out and put in theargon gas protection atmosphere with different annealing temperature60min. It shows fromdiffraction peaks of the CIGS thin film that annealing treatment samples are improvedobviously than untreated one, the intensity of CIGS crystal peak becomes much stronger. CIGS thin film has chalcopyrite crystal structure with our laboratory preparation process.With the increase of annealing temperature, the diffraction peaks increase first and thenbecome weak. When the substrate temperature is400℃, the diffraction peak of crystal of(112) is the strongest. At this temperature, the atoms on the surface of thin film have highersurface diffusion ability, and can occupy effective lattice position, decrease surface energyand make the crystal structure growing easily. The CIGS thin film sputtered at roomtemperature and after heat treatment, on the other hand, appears broken bubble on surface,and makes the film surface morphology damage. The bubbles are from InSe phase.Different substrate temperature sputtering CIGS thin film after400℃annealing. Aftertesting analysis, CIGS thin film surface have more bubbles when the substrate temperature istoo low or the substrate temperature is too high. When the substrate temperature is400℃,the surface of CIGS thin film shows less bubbles, flat, dense, continuity, the ideal state ofCIGS thin film. When the substrate temperature is increased, CIGS thin film appears InSephase, and enhances the randomness of growth crystal. When sputtering on soda lime glasssubstrate with temperature400℃and after400℃annealing, CIGS thin film has structureof chalcopyrite, which conforms to the stoichiometric ratio, and the film has high crystallinityand gets high surface quality.Different powers sputter deposition CIGS thin film. Sputtering power has effect on CIGSthin film crystallization, morphology, phase structure, preferred orientation of grain size, andetc. Sputtering CIGS thin film at room temperature, and without annealing treatment, changesthe condition of power system. With the increase of sputtering power, the intensity of (112)diffraction peaks increase first, and then decrease. When power increases to a certain extent,the (112) crystal priority growth is restrained, the random orientation is strengthened. Whenthe sputtering power is165w, CIGS thin films appear the strongest (112) preferredorientation, but the reason of CIGS thin film the preferred orientation of crystallization andspecific influence on the properties of thin film solar cells is still in study.Magnetron sputtering of cadmium sulfide (CdS) thin film. CdS thin film plays importantrole in CIGS thin film batteries as buffer layer. To study the mechanism of CdS thin film asbuffer layer is indispensable. Experiment mainly focuses on the effect of annealing on CdSthin films. CdS thin film at2θ=26.7degrees has the strongest peak, corresponding to thesix-party phase (002) surface or cubic phase (111), suitable for using in the CIGS thin filmsolar cells. Annealing at400℃makes CdS lattice grow up, and grain become uniform. Itreduces the film lattice defects, increasing the density of the film, flatness, and improves theperformance of the film.Magnetron sputtering of zinc oxide (ZnO) thin film. The layer of the ZnO thin film is thewindow layer of CIGS solar cells. In the experiment, ZnO thin film is prepared on glasssubstrate with DC,300℃sputtering parameter, and then annealing at different temperature.The thin film has compact structure, good crystallinity, and the (002) crystal peak of ZnO can be observed apparently. |
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