氟取代電子予體小分子有機太陽能電池材料的設計、合成與鑑定

Abstract

在本論文中，我們合成出一系列由不同氟數量以及位置修飾的 DTDCPB 衍生物作為小分子型太陽能電池。DTDCPB 為具有不對稱的予體-受體-受體 (D-A-A) 結構的化合物，在先前的報導中，其元件可以達到8.2% 高效率。氟為電負度最大的元素且為最小的拉電子基團。將氟引入我們的材料中，氟取代 DTDCPB 衍生物的最高佔有軌域和最低未佔有軌域的能階會降低，而能隙的差距會變大。低的最高佔有軌域有利於使我們能做到蒸鍍型小分子最高的開路電壓 1.02 V。根據氟原子在電子予體端取代的位置 (氟在苯並噻二唑的鄰位或間位)，會影響其在光物理性質中的波長和消光係數。我們發現了氟的修飾會對光電壓以及光電流產生比較權衡的影響。藉由精密的調整電子予體和電子受體的濃度和材層的厚度，以 DTDCPB-Fm–C70 為系統的蒸鍍型塊材異質結構太陽能電池，其效率可達到6.12%，開路電壓為 0.93 V，以及短路電流為 10.50 mA/cm−2。 最後的部分，我們藉由改變分子的結構來調整能階，以取得更好的光子接收。因為噻吩基團多電子的特性以及具有較多比例的醌型結構，使先前報導過的 DTDCTB 分子有非常優異的短路電流 14.8 mA/cm2。我們藉由引入含氟的噻吩得到新材料 DTDCTB-DF 在元件的表現中，相較於 DTDCTB 有較好的開路電壓。藉由最佳化混摻的結果DTDCTB-DF-C70，可以獲得5.3% 的高效率，開路電壓為 0.96 V，以及短路電流為 11.5 mA/cm−2。

In this work, a novel family of DTDCPB series with various numberous and positions of fluorine substitution have been synthesized as donor materials for small-molecule organic solar cells. The compound DTDCPB has an unsymmetrical donor−acceptor−acceptor (D-A-A) framework, which gave a remarkable PCE of 8.2%, is reported. Fluorine is the most electronegative element and the smallest electron-withdrawing group. Introduction of fluorine to our materials, the fluorinated DTDCPB derivatives exhibited decreased LUMO and HOMO energy levels, but with large band gap. The low-lying HOMO feature is beneficial to achieve reasonable highest Voc of 1.02 V for vapor-deposited small molecule OSCs. The substituted positions of fluorine on the donor unit (the fluorine ortho- or meta- to the) would affect the absorption wavelength and the extinction coefficient in their optical properties. We found there is a trade-off between the photovoltage and the photocurrent due to the modification of fluorine. By fine-tuning the layer thicknesses and the donor:acceptor blended ratio in the bulk heterojunction layer, vacuum-deposited hybrid bulk heterojunction devices, based on Fm–C70 gave a PCE of 6.12% along with Voc of 0.93 V, Jsc of 10.5 mA/cm2. Furthermore, we changed different backbone structure to adust molecular energy level for better light harvesting. The compound DTDCTB has a wonderful Jsc of 14.8 mA/cm2, because of the electron-rich and fortified quinoidal characters of thiophene. The new material DTDCTB-DF, with fluorinated thiophene, can improve the device performance as compared to DTDCTB. With an optimized blend ratio of DTDCTB-DF-C70, a high PCE of 5.3% was obtained, with Voc of 0.96 V, Jsc of 11.5 mA/cm2.