- 學位論文
A Density Functional Theory Study of the Electronic Transition of Squaraine-Derived Dye Sensitizer in Solution and Adsorbed on TiO2 Cluster
A Density Functional Theory Study of the Electronic Transition of Squaraine-Derived Dye Sensitizer in Solution and Adsorbed on TiO2 Cluster
摘要
Squaraine (SQ) 染料因在遠紅光/近紅外光區具有很強的吸光能力而備受矚目，其光譜特性與太陽光光譜吻合程度高，對太陽光的利用率好，是應用於太陽能電池的理想染料。本研究使用電子密度泛函理論 (Density Functional Theory, DFT) 以及time dependent的電子密度泛函理論(TD-DFT) 計算七個非對稱SQ染料分子，探討染料分子在溶劑中，以及吸附於銳鈦礦相 (TiO2)38 cluster (101)面兩種狀態下的分子結構、光學性質及與電荷轉移性質，並進一步分析染料吸附於(TiO2)38的系統，在被光激發後，電子重新分布的情形。在計算結果中，SQ染料的LUMO能階高於(TiO2)38 conduction band者，在激發後行direct electron injection 機制；而LUMO能階低於(TiO2)38 conduction band者，以及在激發後，電子密度流動方向遠離anchoring 端者，則行indirect electron injection 機制。有兩個吸收帶的SQ染料 (JD10及YR6)，同時進行direct 及indirect electron injection：較低能量的吸收帶[(SQ) →*(SQ) transition] 行indirect electron injection 機制，較高能量的吸收帶，則在激發後行direct electron injection 機制。 最後，我們將計算出的電荷轉移量與電池裝置測得的短路電流密度產生關聯。本計算研究使我們對SQ染料吸附在TiO2時，被光激發後所產生的電荷轉移現象有更詳盡的了解。
並列摘要
Squaraine (SQ) dyes are well-known for their intense absorption in the red/near-IR spectral regions, which closely match the spectral response of the sun light. Thus, the SQ dye seems to be promising for light absorption in the red/near-IR spectral region. In this study, we employ density functional theory (DFT) as well as time dependent DFT to investigate the structural, optical and electron transfer properties of seven SQ-derived dyes in solution and adsorbed on a (TiO2)38 cluster with an anatase (101) surface, as a model for the corresponding DSCs. We calculate the absorption spectra of dye-(TiO2)38 systems and analyze the redistribution of electron density of their excited states upon photo-excitation. Our study shows the SQ dyes with their LUMO energies higher than the edge of (TiO2)38 conduction band follow direct electron injection mechanism upon excitation; on the other hand, the electron injection of SQ dyes upon excitation follow indirect electron injection mechanism when their LUMO energies are lower than the edge of (TiO2)38 conduction band or their directions of electron transfer is away from the anchoring side. SQ dyes owning two intense absorption bands (e.g. JD10 and YR6) follow both direct and indirect electron injection mechanisms. Interestingly, The JD10 and YR6 follow indirect electron injection mechanism when their most intense and low-energy bands [(SQ) →*(SQ) transition] are excited; on the other hand, JD10 and YR6 follow direct electron injection mechanism when less intense and high-energy bands are excited. Finally, we rationalize and correlate our calculated quantities of electron transfer of SQ-derived dyes with their experimental observed short-circuit currents. Our calculations provide a better understanding on the electron transfer mechanisms of SQ-derived dyes adsorbed on TiO2 upon photo-excitation.