| 摘要: | 本研究利用超音波輔助化學水浴法搭配不同比例的鍍液成功製備出不同結晶形態的Ag-In-S薄膜，並對此材料進行物理性質及光電性質分析。實驗結果發現當[Ag]/[In]=1時為AgInS2 (Orthorhombic)晶形結構且表面則呈現塊狀樣貌;[Ag]/[In]=5時為AgIn5S8 (Cubic)晶形結構且表面呈現疊層片狀樣貌，薄膜的直接能隙在1.90 ~ 2.05 eV之間，各比例薄膜皆為n型半導體。開環電位法結果得知各薄膜的平帶電位(相對於SCE) 約在-1.09 ~ -1.23 V之間。光電性質量測結果顯示，使用犧牲試劑作為電解液，當[Ag]/[In]=3時具有最佳光電流值，在1.0 V偏壓下照射100 mW/cm2光強度的氙燈可產生1.45 mA/cm2的光電流，EIS分析結果獲得各比例的薄膜在無偏壓的條件下，皆具有相當大的表面態阻抗，隨著偏壓的增加，表面態阻抗大幅的下降且電容有增加的趨勢，使得載子能夠順利被表面態捕捉並穿透界面與電解液進行反應。最後於IMPS的分析結果中發現，隨著偏壓的增加，第一象限的半圓有隨之縮小的現象，搭配EIS的分析結論推測為半導體中少數載子與電解液的反應主導著第一象限半圓的變化，利用公式擬合得知薄膜的擴散係數、電子存活時間、表面態存活時間等係數，可以觀察到擴散係數與電子存活時間皆隨著偏壓的增加而增加，其中以[Ag]/[In]=3時具有最大的擴散係數與存活時間，利用此係數可計算出電子的擴散長度，其中[Ag]/[In]=3時有最佳的擴散長度，在1.0 V偏壓下具有1362 nm。;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. |
