本論文利用硫化鎘量子點（CdS quantum dots）作為染料敏化太陽能電池（Dye-sensitized Solar Cells, DSSCs）的光敏化劑，並研究CdS量子點的沈積製程對電池效率的影響。在CdS量子點的合成方面，在微乳化系統中成功合成出4-6nm大小且分散均一的粒子。而在CdS量子點的沈積方面，利用原子力顯微鏡觀察發現在TiO2薄膜上事先利用帶有硫醇官能基的矽氧烷分子作表面修飾後，能使CdS量子點有效且完整的覆蓋在TiO2薄膜表面，形成量子點的自組裝單分子層（self-assembly quantum dot monolayers），之後再利用化學浴沈積法（Chemical Bath Deposition, CBD）持續沈積CdS量子點，並研究CBD層數對電池的短路電流（short-circuit current）、開路電壓（open-circuit potential）以及效率的影響。實驗結果發現在5次的CBD製程後，可得到最高的短路電流（3.44mA/cm2）、開路電壓（657mV）以及1.35%的電池效率。此效率值已超越目前文獻中量子點敏化太陽能電池的最高紀錄。在不照光的環境下，經量測電流電壓曲線發現CdS量子點的自組裝單分子層薄膜具有一能障（energy barrier）能抑制激發電子回到量子點的基態能階與電解質中，降低電子電洞再結合的機率，故能得到最佳效率。另外也對TiO2薄膜厚度作關於吸收光譜、穿透度以及電性的分析，發現在此系統中，厚度為5.51μm的TiO2薄膜能得到最高短路電流與最高效率。

In this study, cadmium sulfide quantum dots (CdS QDs) were used as a sensitizer of dye-sensitized Solar Cells (DSSCs). The effect of assembly technique of CdS QDs on the cell efficiency was studied in this work.
We successfully synthesized uniform dispersed CdS QDs of 4-6nm in diameter by a microemulsion process. A self-assembly monolayer was first formed on TiO2 surface, which leaves a pending thiol group for anchoring the CdS QDs. The assembly of the QDs on the SAM-modified TiO2 surface was confirmed by the analysis of atomic force microscopy. After forming the “self-assembly QD monolayer”, CdS QDs were further deposited by chemical bath deposition (CBD) and the cell efficiency was studied as function of the CBD layers. The result showed that the highest short-circuit current(3.44mA/cm2), open-circuit potential(657mV), and highest cell efficiency(1.35%), appeared at 5 layers of CBD coating. According to the current-voltage characteristic measured in dark space, we found the existence of an energy barrier due to the self-assembly QD monolayers, which plays a role to inhibit the recombination effect of excited electrons to the holes in CdS QDs and to the electrolyte. Therefore we conclude that the high efficiency of the solar cell is attributed to the effect of self-assembly QD monolayers in reducing the probability of electron-hole pair recombination. In addition to the above studies, the optimum thickness of TiO2 film was also studied and a thickness of 5.51μm was found to perform best in the DSSCs.

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