| Chalcopyrite CuIn1-xGaxSe2(CIGS) thin-film solar cells has advantages of high photoelectric conversion efficiency, low cost and good stability etc., which is one of the most promising thin film solar cells, But the multilayer film production process is complex, including molybdenum (Mo) back electrode layer, CIGS optical absorbing layer, CdS buffer layer, intrinsic ZnO (i-ZnO) window layer and ZnAlO (AZO) film, any one layer of poor quality will affect the photoelectric properties of the solar cells, so the process control is very important, This paper focuses on the CIGS absorption layer and Cd-free buffer layer preparation process control research.CIGS thin film is the core material of solar cells. In this paper, a kind of simple, controllable technology of the CIGS film fabrication is studied, First, sputter about1micron Mo electrodes on the substrate of the soda-lime glass, and then use dual chamber multi-target magnetron sputtering deposition system, by alternately DC sputtering CuGa target (atomic ratio is3:1; purity is99.999%) and pure In target (purity is99.999%), select a different stack method to prepare precursor film of CIGS on Mo electrode layer; and then, place precursor film into a special vacuum furnace to do selenium annealing by different heating mode to obtain quaternary compounds of CIGS semiconductor nanometer thin films. Based on the characterization of the films (SEM、AFM、XPS、XRD), the effect of precursor film lamination and selenizing heating method to the performance of CIGS thin film is analyzed, preparation conditions are optimizatized:In/CuGa/In multiple precursor film is pretreated when heat20minutes at250℃and then keep30minutes selenizing temperature of560℃, poly crystalline CIGS thin-film can be prepared with dense chalcopyrite structure, thin film particle diameter is about1μm, have good crystalline quality, film thickness is2μm, square resistance is0.11Ω/□. Between the wavelength of500-1100nm, film has good absorption to the visible and near infrared.The buffer layer is located on the CIGS absorbing layer and transparent conductive window layer, buffer the band gap difference of these two layers. The traditional buffer layer of CdS is harmful to person, and the band gap is narrow resulting in the loss of the short wave of Sunlight. Traditional CdS chemical bath preparation methods are wet technology which destroyed the vacuum after sputtering selenization or co-evaporation and dry manufacturing process, so the development of dry technology of cadmium free (Cd-free) buffer layer has the vital significance. In CIGS cells, the buffer layer material is very thin, the atomic layer deposition method is the best choice, this paper adopts atomic layer deposition of ZnO(ALD-ZnO)to replace CdS to be a buffer layer, it is soft deposition which is no use plasma, so it can avoid the damage of CIGS film when we prepared ZnO film using magnetron sputtering method. ALD technique can easily avoid the only liquid phase chemical bath (CBD) technology of the existing CIGS process, ALD equipment can joint with other vacuum process of the existing production lines seamlessly, the substrate is rarely exposed in the atmosphere; ALD-ZnO also enhances the quantum efficiency of the short wave and near infrared range, it has industrial application value.This paper studies the relationship between film thickness and zinc source (DEZn) pulse time; the film roughness degree and zinc source pulse time; temperature and the quality of the films; the thickness per growth cycle and carrying the DEZn gas flow; the optical properties of ZnO thin films with different zinc sources pulse, et al; the optimum technological conditions are obtained in our experimental range:DEZn pulse time is0.1seconds,DEZn cleaning time is3seconds; H2O pulse time is0.1seconds, H2O cleaning time is4seconds, carrying gas is high purity N2, carrying DEZn gas flow rate is150sccm, carrying H2O gas flow rate is200sccm, substrate temperature is250℃deposition vacuum is20hPa, thin film growth200cycle.Zinc oxide thin film which thickness of only56.8nm was deposited on soda-lime glass by the means of atomic layer deposition method, the sample surface morphology and phase are analyzed in the use of field emission scanning electron microscopy、AFM and X-ray diffraction (XRD)、XPS, it shows that the obtained ZnO nano-particles are of hexagonal fiber zinc structure, the particle’s diameter is between30nm and60nm; transmittance of the thin film Between the wavelength of400-900nm (in the visible region) is90%or more; and use zinc oxide thin film of atomic layer deposition method as the buffer layer of CIGS solar cell, the TEM shows the zinc oxide layer covers the CIGS thin film densely, and the photoelectric conversion efficiency of the cell is higher, which can totally replace the toxic CdS as the buffer layer, the technology of advanced and environmental protection, simple and controllable, will help the Cd-free CIGS solar cell industrialization.The structure of Glass/Mo/CIGS/ALD-ZnO/i-ZnO/n-ZnO:Al Cd-Free CIGS solar cells is prepared. The open circuit voltage of the cell is Voc-0.46V, Jsc (short circuit current density)=13.8mA/cm2, FF (fill factor)=0.59, the photoelectric conversion efficiency without antireflection coating reaches3.84%. |
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