| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 102 === In our study, we have prepared Ag-In-S semiconductor thin film by ultrasonic chemical bath deposition. The effect of various molar ratio in solutions on the crystal, morphological and photoelectrochemical (PEC) properties of the samples was measured. According X-ray diffraction studies, it was found that when [Ag]/[In]=1 in the solution, AgInS2 was be prepared after annealed for 1h in a nitrogen environment at 400℃ in a quartz tube. However, the crystal structure will become polycrystalline AgIn5S8 gradually with increase [Ag]/[In] molar ratio. The film thickness、flat band potentials、energy band gaps of the samples were between 0.38 and 0.89 μm, -1.09 and -1.23 V vs. SCE, -1.90 and -2.05 eV, respectively. All films had appropriate absorption coefficient which upper than 105 cm-1. Under the visible light irradiation with intensity of 100mW/cm2, the photocurrent density can achieve 1.45 mA/cm2 when [Ag]/[In]=3 with applied potential of 1.0 V vs. SCE in the three-electrode system. Form EIS, the results show all of samples had surface state, with 1.0 V bias, surface state resistances will decrease quickly and capacitances will increase. Indicate the minority carriers can across the interface between thin film and electrolyte with applied potential. IMPS measurements show that first quadrant semicircle reduces with applied potential, and it can be attributed to the rate constant of minority carriers recombination with electrons or react with electrolyte. The simulation results exhibit thin film parameters, like: diffusion coefficient、electron lifetime、surface state lifetime, etc. Among these parameters, the electron lifetime has clear rise when applied bias. [Ag]/[In]=3 has longest electron lifetime, so according the function Ln=(Dnτn)1/2, the electron diffusion length can be calculated.
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