Abstract:The two-step process including the deposition of the metal precursors followed by heating the metal precursors in a vacuum environment of Se overpressure was employed for the preparation of Cu(In,Ga)Se 2 (CIGS) films. The CIGS films selenized at the relatively high Se flow rate of 25 Å/s exhibited improved surface morphologies. The correlations among the two-step process parameters, film properties, and cell performance were studied. With the given selenization conditions, the efficiency of 12.5% for the fabricated CIGS solar cells was achieved. The features of co-evaporation processes including the single-stage, bi-layer, and three-stage process were discussed. The characteristics of the co-evaporated CIGS solar cells were presented. Not only the surface morphologies but also the grading bandgap structures were crucial to the improvement of the open-circuit voltage of the CIGS solar cells. Efficiencies of over 17% for the co-evaporated CIGS solar cells have been achieved. Furthermore, the critical factors and the mechanisms governing the performance of the CIGS solar cells were addressed.
The CuIn 1-x Ga x Se 2 (CIGS) films are prepared by the selenization process including the deposition of the metal precursors followed by heating the metal precursors in a Se overpressure. The impacts of Se deposition rates on the morphology, grain growth, and atomic ratios of the resulting CIGS films are investigated. The CIGS films prepared at the high Se flow rate exhibit the improved surface morphology. The CIGS films prepare by slenization process with Se vapor are made into solar cells. The best active-area efficiency of 11.9% for the CIGS solar cells fabricated with the given selenization conditions is achieved.
We deposited zinc-based films with various ammonia (ammonium hydroxide; NH4OH) and selenourea concentrations, at the bath temperature of 80 °C, on soda-lime glass substrates using the chemical bath deposition (CBD) process. We analyzed the results using X-ray photoelectron spectroscopy (XPS), which showed binding energies of zinc, selenium, and oxygen. The as-deposited films, containing zinc selenide, zinc oxide, and zinc hydroxide, were also verified. The films prepared in this investigation can be referred to a zinc compound, characterized as Zn(Se,OH). A conformal coverage of the Zn(Se,OH) films, with the smooth surface morphologies, was obtained by optimizing the ammonia or selenourea concentrations in the deposition solutions. The Zn(Se,OH) films had a preferred (111) orientation, corresponding to a cubic crystal structure. The bandgap energies of the as-deposited Zn(Se,OH) films were determined from the optical absorption data, suggesting a dependence of the bandgap energies on the atomic percentages of ZnSe, Zn(OH)2 and ZnO in the films. The same variation tendency of the compositions and the bandgap energies for the films, deposited with an increment in the ammonia or selenourea concentrations was achieved, attributing to the facilitation of ZnSe formation. These results show that the compositions, and therefore the bandgap energies, can be controlled by the ammonia concentrations, or selenourea concentrations.
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