Preparation And Properties Of Key Materials For Cu(In_1-xAl_x)Se₂ Thin Film Solar Cells

Energy and environmental issue has become a hot topic in current society.Solar energy,as a kind of clean energy source,is an inevitable trend in the future development.Cu(In1-xAlx)Se2(CIAS)thin film solar cells have very important research significance with low costs,high conversion efficiency,and wide band gap of absorption layer which can be adjusted.The key structures of CIAS solar cell are absorption layer and buffer layer.In this paper,the CIAS absorption layers were prepared by vacuum evaporation method,CBD was used to prepared buffer layer ZnS which is environmentally friendly and nontoxic.In the end,SLG/ITO/CIAS/ZnS multilayer films were prepared by the addition of the back electrode.CIAS absorption layers were deposited on SLG with high purity elemental copper,indium,aluminum and selenium in their stoichiometric proportion.The effects of the distance between substrate and evaporation source,the stage’s speed and annealing temperature were studied to determine the optimum process parameters.CIAS absorption layers were prepared with these parameters,the effects of different copper atoms ratio Cu/(In+Al)and aluminum atoms ratio Al/(In+Al)on the properties of the films were studied.The results showed when the distance between substrate and evaporation source was 60mm,the stage’s speed was 30r/min,500 ℃ annealing for one hour under an atmosphere of argon,copper atoms ratio was about 1 and aluminum atoms ratio varied from 0.1 to 0.4,the thin films’ thicknesses were 1-2 pm with well-distributed,compact surface which had the typical structure of chalcopyrite preferential growth along the(112)orientation,and the electrical properties were good,too.ZnS buffer layers were deposited on SLG with ZnSO4·7H2O,SC(NH2)2 and NH3·H2O,ZnS films were tested and analyzed before and after annealing.Results showed that the atomic ratios of Zn and S were beyond 1:1·before and after annealing,the greater value happened after annealing.Annealing improved the uniformity and compactness of the films,and the phase was not changed.The film thicknesses were increased;the transmittance and the band gap were decreased.ITO was used as a back electrode to prepare SLG/ITO/CIAS multilayers,the multilayers had well-distributed,compact surface and typical structure of chalcopyrite preferential growth along the(112)orientation.When x=0.14,0.24 and 0.38 in Cu(In1-xAlx)Se2 films,Eg=1.15eV,1.18eV and 1.60eV.The absorption coefficient of multilayers was 104-6×104cm-1 near the band gap.ZnS was deposited on SLG/ITO/CIAS multilayers.Cross-sectional SEM showed that there was a better adhesion in the multilayers,the thicknesses of CIAS absorption layers were 1-1.5μm,and ZnS has infiltrated into the CIAS absorption layer of a certain depth.