The Properties Of Silver Sulfide Thin Films Prepared By Electro-deposition

Monoclinic structure of silver sulfide is an important group of binary II-VIsemiconductor compounds with band gap of1.1eV. And it has a high absorptioncoefficient(α＞104cm-1). Ag2S is a potential photoelectric conversion material,suitable for the absorber layer very much, these advantages have attracted widespreadattention. Furthermore, Ag2S is a kind of promising PV material because the elementsAg and S are friendly to the environment. The Ag2S thin films were prepared bycathodic constant-potential electro-deposition method. The structure and morphologyof the deposited films were investigated, respectedly.First, the rough range of experimental parameters such as the ratio of ionconcentration Ag+and S2O32-(Ag+/S2O32-), the deposition potential (E) and thesolution pH value(pH)were determined by investigating the cyclic voltammograms ofthe transparent indium tin oxide (ITO) coated electrodes in the solution of silvernitrate (AgNO3), sodium thiosulfate（Na2S2O3）and their mixtures, respectively. Theeffect of deposition potential, pH and annealing on the structure, morphology andother properties of the Ag2S thin films were studied by XRD analysis, scanningelectron microscopy and so on. The experiment paramaters were as follows: Ag+/S2O32=1/5; E=-0.23V~-0.28V (vs.SCE); pH=2.5; the deposition time lasting for1.5h.The samples obtained under the above conditions were analysed by XRD, XPS，SEM, AFM analysis. The results show that: the deposited films are monoclinic Ag2Swith the relative deviation of cell parameters within1.04%. The estimated cellparameters of the Ag2S films deposited at E=-0.25V are closest to those of thestandard sample. The intensity of XRD peaks changes with the pH value means thatacidity in the solution has some influence on the crystallization of films, and the peakof (-104) is strongest at pH=2.5. After annealing, the crystallization of the films hasbeen improved. The XPS spectrum shows that the oxidation state of Ag is+1, and thereduction state of S is-2in the stoichiometric films, and the atomic ratio of Ag and Sis nearly2. The SEM pictures show that films are unifirm with better compactness athigher deposition potential, but there are some aggregation when the potential up to-0.28V. The AFM images show that the RMS roughness is58.4nm, the average grainsize of the film is259nm at the optimal parameter. We have explored the optimal technical parameters of preparing Ag2S thin filmswith good quality, which will lay the base on the development of thin film solar cells.