Preparation Of Copper Indium Gallium Selenide Thin Film Solar Cells By Co-sputtering Of CuIn And CuGa Targets

In recent years,the demand for energy is growing due to the rapid development of economic.However,the limited fossil energy reserves restrict the development of human society and economy.Development and utilization of green and renewable energy is an effective way to solve the human energy crisis and environmental problems.Solar energy has received widespread attention because of its pollution-free and inexhaustible nature.Photovoltage is an important and direct way for mankind to use solar energy.Thin filming is an inevitable trend in the development of solar cells from the point of view of reducing material costs,integration of photovoltaic buildings and large-scale applications.Chalcopyrite phase CIGS thin film solar cells has become the focus of thin film solar cells because of its high light absorption coefficient,adjustable band width,low light resistance,high conversion efficiency and so on.At present,CIGS solar cells fabricated by co-evaporation technology have achieved the highest efficiency up to 22.6%in the lab.However,co-evaporation technology seems unsuitable for large-scale practical application due to its complicated preparation process,high production costs and diffuculty in large-area continuous production.In contrast,magnetron sputtering has the advantage of industrial compatibility,better reproducibility and convenience of continuous large-scale production.Therefore,double-target magnetron sputtering technique is employed here to fabricate high quality CIGS absorber layers with less secondary phases.Through this way,the composition of the CIGS absorber layers can also be precisely modulated by regulating the two independent magnetron sputtering targets.The effects of working pressure and sputtering power on the structure,composition and photoelectric properties of the CIGS absorber layer were studied in detail.The complete CIGS solar cells device was fabricated.Finally,the influence of post-selenization conditions on the performance of the device was studied systematicaly and the post-sintering process were optimized and improved.Benefited from the optimized selenization,the photoelectric conversion efficiency of the device was improved from 8.92%to 11.19%.Specifically,three parts of the research work were arried out listed as follows:1.Influences of working pressure on the CIGS absorber layerThe Cu/In/Ga precursor films were firstly deposited by using the Cu_0.2In_0.8 and Cu_0.8Ga_0.2double-target co-sputtering,High quality CIGS absorber layer can be fabricated by post seleniztion of the prepared Cu/In/Ga precursor films.The influences of working pressure on the composition,morphology and photoelectric properties of the CIGS absorber layer were investigated systematically by a series of characterization methods.The results showed that,p-type CIGS thin films can be easily fabricated by increasing the working pressure.However,the film's compactness and contact with the substrate is getting worse.The results of XRD and Raman showed that the diffraction peak of Cu₁₁In₉ alloy phase located at the diffraction angle of 42.5°when the working pressure is 0.2 Pa.Pure CIGS films with chalcopyrite phase were fromed at other conditions.The strong?112?peak indicated a preferred orientation along the?112?plane of the absorbers.Under the working pressure of 0.8 Pa,the CIGS absorber layer with good crystallinity was obtained.2.Effects of sputtering power on CIGS absorber layer:The effects of sputtering powers of CuIn and CuGa alloy target on the film composition,morphology and photoelectric properties of the CIGS absorber layer was systematically investigated.Solar cell devices based on a series of absorber films were fabricated.The results showed that the surface morphology of the prepared film is smooth and densely packed under the condition of 90 W for CuIn target is and 20 W for CuGa target.The crystallinity is perfect and no secondary phases could be observed.Based on the CIGS absorber layer,the photoelectric conversion efficiency of 8.92%was achieved with a J_sc of 38.21 mA/cm²,a V_oc of 424 mV,and a FF of 55.09%.3.Improvement and optimization of post-selenization processThe effects of selenization temperature on the composition,crystallinity and device performances of the CIGS films were systematically studied.The results showed that the stoichiometry of the CIGS absorptive layer is exact and the crystallinity is perfect.The photoelectric conversion efficiency can reach9.92%.On this basis,the alloying pre-treatment was conducted to further improve the degree of its alloying and component uniformity.The CIGS absorber layer prepared by alloying and selenization at 560oC has a reasonable composition and good crystallinity.The photoelectric conversion efficiency improved to 11.19%with a J_sc of 40.357 mA/cm²,a V_oc of 456 mV and a FF of 60.82%.