The Preparation And Properties Of Gradient AZO Thin Films

Currently,crystalline silicon(c-Si)solar cells still play a vital role in photovoltaic industry.To improve the photoelectric transformation efficiency,the surface passivation of c-Si solar cells is necessary.This paper designs a gradient AZO thin film by combining the merits of Al2O3 and AZO.The Al concentration presents gradient change from the surface of the AZO thin film to the interface of AZO/c-Si.Higher concentration of Al at the AZO/c-Si interface is beneficial to the silicon substrate passivation,and lower concentration of Al at the surface of the AZO thin film can improve the photoelectric properties.Gradient AZO thin films were deposited by atomic layer deposition(ALD),and structure,topography,electrical,optical and passivation properties of gradient AZO thin films were investigated by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM),Hall measurement,UV-visible spectrophotometer and quasi-steady state photoconductance(QSSPC)technique.The effects of technological condition on the properties of gradient AZO films were studied.The results showed that the as-prepared gradient AZO thin films had the hexagonal wurtzite structure.The growth temperature had great effect on orientation,grain size and crystallinity of films,which greatly influenced the photoelectricity properties of films.While growth temperature had little influence on passivation properties.With the increased of growth temperature,the crystal quality of gradient AZO thin films increased first and then decreased,and resistivity decreased first and then increased.The average transmittance of all the gradient AZO films exceeding 80% were obtained in the visible region.When the growth temperature was 150°C,the gradient AZO film had an optimal passivation performance.The effects of Al concentration gradient on the properties of gradient AZO films were studied.The results showed that the Al concentration gradient had great impact on photoelectric and passivation properties of films.With increasing Al concentration gradient,we observed diminished crystallinity and amorphous tendency of gradient AZO thin films,which caused the deterioration of the electrical conductive properties of films.The average transmittance of all the gradient AZO films could be more than 80% in the visible region.In addition,as-deposited gradient AZO thin films demonstrated excellent passivation properties.The effects of annealing on the passivation properties of gradient AZO films were studied.The results showed that annealing treatment had a significant effect on passivation properties of films.The maximum minority carrier lifetime(120.6?s)was obtained at 0.71%/nm Al concentration gradient.Annealing treatment enhanced the minority carrier lifetime about 9.2 times than as-deposited(13.2?s).The minority carrier lifetime had also achieved great improvement by optimizing the annealing temperature.When annealing temperature was 500°C,the minority carrier lifetime was raised to 135.7?s,and surface recombination velocity(191.3cm/s)was decreased an order of magnitude than un-coated Si wafer(5854.8cm/s).Gradient AZO thin films have the excellent performance of photoelectric and passivation synchronously.Therefore,we believe that it has great prospects as surface passivation layer for silicon solar cell.