臺灣博碩士論文加值系統

本論文希望藉由半導體量子點取代傳統光電化學太陽電池中昂貴的釕錯合物染料，並提升其光電性能。傳統染料僅可吸收特定波長的太陽光，不若量子點可藉由調整粒徑大小，即改變其吸收之能隙寬（energy gap）。故可以此特性製造高效率之量子點敏化太陽電池（quantum dot sensitized solar cells, QDSSC）取代傳統染料敏化太陽電池（dye-sensitized solar cells, DSSC）。
在QDSSC中，量子點的能隙寬將決定何種光子如何將電子由價帶激發至傳導帶，而量子點的最高佔據分子軌道（highest occupied molecular orbital, HOMO）與最低未佔據分子軌道（lowest unoccupied molecular orbital, LUMO），將密切影響電子由量子點注入金屬氧化物半導體的難易，以及電子注入後回流的情形。本研究利用第一原理計算，建立分子尺度的CdSe原子團與奈米尺度的銳鈦礦TiO2（101）表面模型，以時間獨立（time independent）與時間相依（time dependent）的密度泛函理論（density functional theory, DFT），搭配B3LYP（Becke, three-parameter, Lee-Yang-Parr）與PBE（Perdew-Burke-Ernzerhof ）兩種不同的交換相關泛函，來計算CdSe原子團的能隙寬、電子軌道與態密度分布（density of states, DOS）。並且分析CdSe原子團在己烷中的溶劑效應，CdSe原子團在TiO2表面的最穩定吸附結構，以及吸附前後CdSe原子團能隙寬的影響。
在實驗部分，使用紫外可見光度計（UV/VIS spectrophotometer）測量CdSe量子點之紫外可見吸收光譜。同時比對實驗與計算結果，發現皆符合量子尺寸效應，亦即藉由縮小CdSe量子點的粒徑，即可增加CdSe量子點的能隙寬。綜合的計算結果可知，可藉由混合多種粒徑的CdSe量子點，達到增加QDSSC中太陽光的吸收率；本論文並且提出CdSe量子點吸附於TiO2上時，電子轉移之適當鍵結模式，藉此可再提升電子注入TiO2之效率。

This research intends to use the semiconductor quantum dots to replace those expensive ruthenium dyes in the traditional photoelectrochemical solar cells. By varying the quantum dot sizes, there is a potential to expand the absorption spectrum to cover all ranges of the sunshine, without changing materials. Under proper nano-structure design, the quantum dot sensitized solar cells (QDSSC) may have higher quantum efficiency than the dye-sensitized solar cells (DSSC).
The energy gaps of variable sized quantum dots (QDs) dominate how the electrons are excited from the valence band to the conduction band by variable frequencies of input photons. The positions of both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) determines the ability of electron injection to the metal oxide semiconductors. Based on first principles calculation, the molecular structures of (CdSe)n (n=1~16) clusters and the anatase TiO2 (101) surface have been configured and optimized. Both time independent and time dependent density functional theory (DFT), which chose B3LYP (Becke, 3-parameter, Lee-Yang-Parr) and PBE (Perdew-Burke-Ernzerhof) exchange correlation functionals, are employed. Photoelectric properties, such as: electron orbitals, density of states (DOS), HOMO and LUMO (and resultant band gaps) are predicted. They are used to study the solvent effect of CdSe clusters in cyclohexane, binding energy between the CdSe cluster and the TiO2 surface, and the energy spectrum shift after adhesion.
An UV/VIS spectrophotometer was used to measure the absorption spectra of variable sized CdSe quantum dots. The band gaps calculated from the experiment are close to the predictions from the quantum simulation. It is concluded that we can enhance the sunlight absorption by mixing different diameters of CdSe clusters, and a more suitable bonding structure between the CdSe clusters and the TiO2 surface is proposed to promote the electron injection efficiency.

摘要 I
英文摘要 II
致謝 III
目錄 IV
表目錄 VI
圖目錄 VII
第一章 緒論 - 1 -
1.1前言 - 1 -
1.2研究動機與目的 - 2 -
1.3量子點敏化太陽電池 - 3 -
1.4文獻回顧 - 6 -
第二章 計算量子力學理論 - 9 -
2.1第一原理計算 - 9 -
2.2 Born-Oppenheimer近似 - 10 -
2.3多電子系統 - 12 -
2.4密度泛函理論 - 14 -
2.4.1 Hohenberg-Kohn原理 - 15 -
2.4.2 Kohn-Sham系統 - 18 -
2.4.3 交換相關泛函 - 19 -
2.4.4 基底函數集合 - 21 -
2.4.5 贗勢與超軟贗勢 - 23 -
2.4.6自洽場計算 - 26 -
2.5時間相依密度泛函理論 - 27 -
2.5.1擴展Runge-Gross定理 - 28 -
2.5.2時間相依Kohn-Sham方程式 - 32 -
2.5.3線性響應定理 - 33-
2.6紫外可見分光光度計原理 - 35 -
第三章 系統模型建構與實驗方法 - 37 -
3.1計算與實驗流程 - 37 -
3.2計算參數設定 - 38 -
3.2.1 G09計算設定 - 38 -
3.2.2 PWscf計算設定 - 40 -
3.2.3 實驗參數設定 - 42-
第四章 計算與實驗結果討論 - 44 -
4.1幾何結構最佳化 - 44 -
4.2 (CdSe)n光電性質分析 - 47 -
4.3 TiO2（101）表面吸附 - 55 -
4.4 CdSe量子點紫外可見光光譜實驗結果 - 61 -
第五章 結論與未來工作建議 - 63 -
5.1結論 - 63 -
5.2 未來工作建議 - 64 -
參考文獻 - 66 -

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