| Cadmium telluride(CdTe)is an important p-typical II-VI semiconductor material,which is used to the manufacture of solar cell devices more than 40 years.CdTe thin film is considered as a great promising candidate for photovoltaic applications,owing to its high optical absorption coeficient in the visible area,high theoretical conversion efficiency(33%),and a direct band-gap of approximately 1.45 eV at 300 K.To date,various methods are used to prepare CdTe thin films,including magnetron sputtering,close space sublimation(CSS),eletrochemical deposition and template-assisted approaches etc.Among the methods mentioned above,the eletrodeposition method is the most generally concerned due to its easily controlled,low-cost,and scalability for preparation of thin films.In this article,we successfully fabricate compact and uniform cadmium telluride(CdTe)films on flexible nickel foils using simple electrodeposition technique and sintering in a nitrogen atmosphere.Various test techniques,such as X-ray diffraction(XRD),energy-dispersive X-ray(EDS),scanning electron microscopy(SEM),ultraviolet-visible absorption spectroscopy and photoelectrochemical measurements are used to characterize the results.The effect of the concentration of sodium tartrate on the structures and properties of the deposited CdTe thin films are studied.The main work is as follows:(1)The electrodeposition of CdTe nanorod array thin film was performed at room temperature by a three electrode electrochemical cell in potentiostatic regime.The substrate(Ni),high purity graphite plate,and a saturated silver/silver chloride(Ag/AgCl)electrode are employed here as the working electrode,counter electrode,and reference electrode,respectively.In the solution what is used to synthesis CdTe nanorods,cadmium sulfate is used as the cadmium source,sodium telluride as the telluride source,and sulfuric acid is used to adjust the PH value of the solution.The dense uniform,good connectivity,and no perforated CdTe nanorod array thin film is prepared at fixed potential of-0.4 V for 1 h.(2)A moderate amount of sodium tartrate is added into an acidic solution as surfactant for CdTe thin film fabrication.The advantage of sodium tartrate as a surfactant is easily volatilized from the film during the annealing process because of its small molecular weight,which can prevent the carbon precipitation.The effects of surfactant sodium tartrate concentration on the structural,composition ratio,morphology,and optical and electrical properties of the deposited CdTe thin films are investigated under appropriate deposition potential and pH value.From the XRD results we can see that not only the growth of all samples preferentially orients along the(111)direction,but also the crystallinity of the films decreases gradually as the concentration of sodium tartrate increases.Meanwhile,we also find that the proportion of Cd and Te in CdTe film can be adjusted by adding different concentration of sodium tartrate.Instead,when the concentration of sodium tartrate in solution is low,CdTe film is rich in Te and becomes p-type conductive material.On the contrary,at higher sodium tartrate concentration,resulting Cd-rich n-type conductive material is produced.Furthermore,the increasement of sodium tartrate concentration will inhibit the growth rate of CdTe films and make it thinner.What is more,based on the analysis of optical and optoelectronic properties,we find that both the light absorption capacity and the short-circuit current of the film are significantly reduced by increasing concentration of sodium tartrate.We successfully capture the suitable sodium tartrate concentration that formed the CdTe film. |
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