Study On The Preparation And Performance Of W-Ti Diffusion Barrier For Flexible Cigs Solar Cell On Stainless Steel Foil

CuIn1-xGaxSe2?CIGS?solar cell has attracted a great deal of attention for its broad development prospects.Compared with the glass-substrate CIGS solar cell,flexible CIGS solar cell is of many advantages of being curled,lightweight,and being manufactured by roll-to-roll process.In this work,a Tungsten-Titanium?W-Ti?layer has been used as the Fe diffusion barrier in the CIGS solar cell on stainless steel foil?SSF?,and the effectiveness of the method has been verified;A Cu-Ga layer was applied to enhance the adhesion among related different layers in the CIGS solar cells and between layer and SSF substrate.The influences of the Cu-Ga layer and H₂ Se concentration mixed working gases in annealing on CIGS solar cells have been investigated.The main research work in this study includes as follows: W-Ti layers were prepared by magnetron sputtering method.The influences of working gas pressure,sputtering current,thickness of the layer,and substrate surface states on the properties of W-Ti layers such as sputtering rate,phase structure,and grain size were examined.The process parameters for fabricating the W-Ti layer were optimized;Rutherford Backscattering Spectrometry?RBS?was used to analyze the Fe distribution in the W-Ti layer annealed at different temperatures.The diffusion constant and the activation energy of the Fe diffusing in the W-Ti layer were calculated based on Fick's Second Law;The diffusion mechanisms were deduced by the comparison of the activation energy and the Fe diffusion distance of W-Ti layers with different thickness.The lifespans of the CIGS solar cell were predicted for the different thicknesses using the diffusion constant and the activation energy based on Fick's Second Law.CIGS solar cells` on SSF were fabricated with a CuGa layer to enhance the adhesion between Mo back contact and the CIGS absorber.The influences of the CuGa layer and H₂ Se concentration on CIGS solar cells were studied.The results show that the phase structure of W-Ti is influenced by working gas pressure,and the grain size of W-Ti layer grows with the increase of thickness.The diffusion constant of Fe in W-Ti with the thickness of 400 nm is estimated to be 3.4×10-16 m2/s.The activation energy of Fe diffusing in W-Ti layer is 43 k J/mol.In addition,the leading Fe diffusion mechanism in the W-Ti layer is the grain boundary diffusion.The anti-diffusion capacity of W-Ti as the Fe diffusion barrier can be enhanced by a large margin with the increase of the thickness.A W-Ti layer prepared at carrier gas pressure 0.7 Pa,sputtering current 1.5 A can block Fe from diffusing into a CIGS solar cell efficiently.A Cu-Ga layer can enhance the adhesion between Mo back contact and the CIGS absorber without degrading the performance of the CIGS film.A 5 vol% H₂ Se atmosphere can both ensure the large grain size of CIGS film and the adhesion of the CIGS solar cell.The highest conversion efficiency of 5.4% has achieved in the work for the CIGS solar cell on the SSF prepared with the W-Ti diffusion barrier,the Cu Ga layer and annealed under 5 vol% H₂ Se atmosphere.