近年來替代能源的需求日益漸增，染料敏化太陽能電池因具有高光電轉換效率、低製作成本與低污染的特色而備受矚目。自二十年前開始，許多科學家投入開發高效率的染料，如釕金屬錯合物染料、紫質染料與有機化合物染料，卻因缺乏系統性與整合性的開發策略，使得效率只有些微的提升。
在本研究中，我利用密度泛函理論(DFT)與時間相依密度泛函理論(TD-DFT)，進行有機染料分子的光電性質分析，並藉由系統性的計算，提出針對有機染料的設計策略。在我的設計當中，有機染料分子主要由不同的電子予體(donor)與電子受體(acceptor)所構成，同時利用共軛分子(π-linker)與固著基團(anchoring group)修飾分子以調整紫外可見光譜的位置與強度。首先，為了要增強分子內電荷轉移的程度，在設計分子時，選擇推電子能力強的予體和拉電子能力強的受體之組合，並從結果中發現染料分子的光電性質主要受到電子受體的影響。因此我們能藉由改變電子受體的強度設計染料的光電性質。從結果得知，MPBA-T-CDM*CN 、MPBA-T-TP*CN與MPBA-T-CDT*CN為我們設計的染料中最具有潛力者，此三種染料皆具有很高的莫耳消光係數(molar extinction coefficient)，且波長分布在400 ~ 800奈米。除了探討有機染料的光電性質，本研究亦利用Vienna Ab-initio Simulation Package (VASP) 將染料分子吸附在二氧化鈦半導體表面上，利用態密度分析討論其電子耦合與電子注入的現象。而結果顯示我所設計的染料皆具有良好的電子耦合，使得電子能順利的注入至半導體表面。綜合染料分子的光電性質與其吸附至表面後的結果，再一次的說明此設計能大幅提升有機染料太陽能電池的效率。

Dye sensitized solar cells (DSSCs) have attracted considerable interest and been treated as promising alternative energy due to the high photon-to-current conversion efficiency, easy production and cost-effective properties. There are many efforts have been made to develop the efficient sensitizers, which are based on either metal or metal free organic complexes. But the lack of systematic and comprehensive developments results in little improvement in overall efficiency.
In this contribution, we have designed a series of metal free dye-sensitizers and studied their optoelectronic properties using the DFT and TDDFT methods. The designed sensitizers are based on different combinations of electron -donating (D) and -withdrawing (A) units, incorporating a π-linker and an anchoring group to modify the electronic structures and tune the UV-Vis absorption. First, we considered oligomers composed by strong donor and strong acceptor to have higher degree of intra-molecular charge transfer. The calculations show acceptor plays more important role in optoelectronic properties of D-A systems and donor has minor influence which is able to change the overall spectra slightly. Therefore, we design the optoelectronic properties of metal-free sensitizers via changing the strength of acceptor. Then, MPBA-T-CDM*CN, MPBA-T-TP*CN and MPBA-T-CDT*CN are the most potential sensitizers we have already designed owing to their high molar extinction coefficients and absorption in 400~800 nm. In addition to analyzing the optoelectronic properties of designed sensitizers, we simulate the adsorption of promising sensitizers onto TiO¬¬2 semiconductor surface. Also, we use density of states analyses to discuss the electron coupling between surface and sensitizer. According to the calculation, all of the designed dyes reveal good electron coupling and electrons can efficiently inject to the TiO2 surface. In brief, the efficient sensitizers not only have appropriate optoelectronic properties but also can inject electrons to surface effectively. Therefore, we believe these sensitizers can improve the overall efficiency intensely.

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