運用理論計算探討富勒烯與新穎非富勒烯小分子受體材料之分子改質與光電性質的關聯性

Exploration of The Relationship between Molecular Modification and Photoelectric Properties of The Fullerene and Non-Fullerene Small Molecule Acceptor by Using Theoretical Calculations

朱博亞(PO-YA CHU)

指導教授 ： 黃慶怡

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201804256

摘要

本研究選擇新穎非富勒烯小分子IDT受體材料IDTT-DCI、IDTT-ID、IDTT-NTz與IDTT-BT為研究對象，並採用量子力學方法來探討在末端基上引入不同的取代基對光電性質之影響。選用的取代基有硝基(-NO2)、氰基(-CN)、羧酸基(-COOH)、氟基(-F)、乙炔基(-ethyne)、乙烯基(-ethene)、甲基(-CH3)、醇基(-OH)與一級胺基(-NH2)。首先對未引入取代基之受體材料進行幾何最佳化並針對其構型進行一系列分析，包括其主鏈平面性、主鏈與末端基之扭轉角與側鏈結構的分析。接著引入末端取代基與未改質之受體材料進行構型參數的比較，結果發現引入末端取代基因體積小且位置遠離易扭轉之結構使結構變化不大，與眾多文獻之論點相同。進一步我們利用Zindo方法模擬材料之UV-vis吸收光譜以及吸光性質，發現IDTT-DCI與IDTT-ID兩材料因LUMO能階之電子軌域分佈集中於主鏈上，在末端基上沒有大量之電子分佈，使取代基引入對其光吸收強度的變化不大，有趣的是所有末端基的引入對其吸收強度皆有微幅增加的現象；而IDTT-NTz與IDTT-BT兩材料因LUMO能階之電子軌域分佈集中於末端基之苯環上，使取代基之引入對其吸光強度的變化非常大，發現到拉電子能力越強之取代基引入將使吸收強度越增加，原因為LUMO電子軌域將越往取代基上分佈，進而使吸收強度有大幅度地增加。而在四種材料中取代基的引入，隨著拉電子能力的減弱，對能階皆有逐漸提升的現象；而取代基若具有π電子，對能隙有縮小的幫助，進而使吸收位置有紅位移的現象。此外，將傳統富勒烯與新穎IDT衍生物一同比較後，發現到傳統富勒烯其碳球具有高度對稱性，使躍遷偶極距低落，導致在長波長的躍遷沒有吸收的現象，且在短波長之吸收也不大；新穎非富勒烯材料則因共軛平面結構不僅讓π電子共軛性好，在取代基的引入也使長波長之躍遷偶極距增加。最後取代基的引入將使能階有所變化，所以我們將IDT系列衍生物與電子予體材料進行能階的匹配給予最適合之受體材料組合，其中IDTT-DCI-ethene與PBDB-T匹配不論是Voc值、吸收位置與光捕獲效率皆有優化的現象。此外P3HT與IDTT-BT-OH匹配後理論Voc可達1.41eV；PTB7-Th與IDTT-ID-COOH可達1.39eV;PffBT4T-2OD與IDTT-ID-NO2可達1.33eV；PBDB-T與IDTT-ID-ethene可達1.39eV。

關鍵字

非富勒烯小分子受體 ； 取代基改質 ； 量子力學 ； 光電性質 ； 紫外-可見光吸收光譜

並列摘要

In this study, novel non-fullerene small molecule IDT receptor materials IDTT-DCI, IDTT-ID, IDTT-NTz and IDTT-BT were selected as the research objects, and quantum mechanical simulation method was used to investigate the effect on photoelectric properties by introducing different substitutions on the terminal groups. The selected substituents are nitro (-NO2), cyano (-CN), carboxylic acid (-COOH), fluoro (-F), ethynyl (-ethyne), vinyl (-ethene), methyl. (-CH3), an alcohol group (-OH) and a primary amine group (-NH2). The unmodified acceptor material was first geometrically optimized and undergoing a series of analyses for its conformation, including its main chain planarity, the torsion angle between the main chain and the terminal group, and the side chain structure. Subsequent introduction of the terminal-substituent and the unmodified acceptor material was carried out to compare the conformation parameters. As a result, it was found that introducing the terminal-substituted with a small volume and its modified position away from the structure,which is easy to twist makes the structure hardly change, which matches the results of many literatures. Furthermore, we used the Zindo method to simulate the UV-vis absorption spectrum and the light absorption properties of the materials. It was found that the isodensity representations of the LUMO of the IDTT-DCI and IDTT-ID materials is concentrated on the main chain. The distribution of electrons makes the change of the light absorption intensity little, and it is interesting that the introduction of all terminal groups has a slight increase in the absorption intensity; while the electrons distribution of the LUMO of IDTT-NTz and IDTT-BT materials is concentrated on the benzene ring of the terminal group, makes the introduction of the substituent extremely changes the absorption intensity of the substituent. It is found that the stronger the electron-withdrawing ability, the more the absorption is introduced. Because the LUMO electronic orbital distributing over the substituents increases the absorption intensity. In the introduction of the substituents in the four materials, as the ability to withdraw electrons weakens, the energy level is gradually increased. If the substituent has π bond, the band gap is shrinking, and the absorption position has a red-shift phenomenon. In addition, the traditional fullerenes were also compared with the novel IDT derivatives, and it was found that the carbon sphere structure of the fullerenes has a high degree of symmetry, which makes the transition dipole moment very low, resulting in no absorption at long wavelength transitions and absorption at short wavelengths; novel non-fullerene materials not only make the π-electron conjugate better due to its conjugated planar structure, but also increase the long-wavelength transition dipole moment by the introduction of the substituent. The introduction of the terminal substituent will change the energy level, so we will match the IDT series of derivatives with the electron donor material to give the most suitable acceptor material combination. We found that in the combination of IDTT-DCI-ethene and PBDB-T, not only the Voc and the light capture efficiency are optimized, but also has a significantly increase in red-shift. In addition, the theoretical Voc of P3HT and IDTT-BT-OH can reach 1.41eV; PTB7-Th and IDTT-ID-COOH can reach 1.39eV; PffBT4T-2OD and IDTT-ID-NO2 can reach. 1.33eV; PBDB-T and IDTT-ID-ethene can reach 1.39eV.

並列關鍵字

non-fullerene small molecule acceptor ； substituent modification ； quantum mechanics ； photoelectric properties ； UV-vis spectrum

參考文獻

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