5,6-雙氟-2,1,3-苯并噻二唑與硒吩之高結晶性共軛高分子之合成與鑑定及其於有機太陽能電池之應用

Abstract

硒吩擁有許多優點，例如容易被極化以及容易形成醌型形式等性質使得含硒吩之高分子具有較窄能隙、易於獲取光子的能力以及高結晶性，這些性質使含硒吩之高分子在電晶體以及太陽能電池的領域中擁有相當優良的表現，但舊有合成含有枝狀碳鏈之硒吩的方法相當複雜且昂貴，因此在此研究中我們選用了另一條的路徑成功地簡化含枝狀碳鏈之硒吩的合成，並且設計合成三種FBT與硒吩共聚之高結晶性共軛高分子PFBT2Th2Se、PFBT2Se2Th及PFBT4Se。在此我們根據性質分析來討論硒吩的影響，而其結果顯示出FBT與硒吩之間的電荷轉移能力比噻吩來得強，進而使含硒吩之高分子的吸收範圍較為紅移，此外這三種含硒吩之高分子的吸光性質擁有隨溫度改變的特性，顯現出硒吩的帶入並不會對高分子的結晶行為造成影響，而這三種高分子在微差掃描卡計的結果中皆有相當明顯地熔點及結晶點，更證實了此三種高分子具有結晶行為。而為了更深入的探討主動層的形貌以及排列方式，我們使用了GIWAXD來測量，從其結果說明此三種高分子在與PC71BM混滲後皆呈現面朝上的排列，而此種排列有利於垂直方向的電荷傳遞，我們利用這些性質將之應用於反結構的有機高分子太陽能電池 (ITO/ZnO/Active layer/MoO3/Ag)，在元件表現上PFBT2Th2Se:PC71BM擁有0.68 V的開路電壓、69.1 %的填充係數以及很高的短路電流18.46 mA/cm2而得到8.68 %的光電轉換效率，在同樣的製程條件下PFBT2S2e2Th:PC71BM有0.66 V 的開路電壓、65.0 %的填充係數以及卓越的短路電流21.02 mA/cm2因此擁有超越9 %的效率，此外PFBT4Se:PC71BM也有0.62 V的開路電壓、63.6 %的填充係數以及最高的短路電流22.63 mA/cm2得到8.92 %的轉換效率，目前為止在文獻中只有極少數的材料可以達到超越20 mA/cm2的電流值，而22.63 mA/cm2更是目前最高的數據之一。

Selenophene has several advantages such as high polarizability and high quinoidal population which endow many selenophene-based materials with narrower optical bandgap, enhance light-harvesting ability and higher crystallinity. These beneficial properties lead to the improved charge carrier mobiliies in transistor devices or higher photocurrents in OPV devices. The traditional method to synthesize 3-alkyl selenophene is quite complicated and costly. We successfully design an efficient way to simplify the synthesis of selenophene. We utilize selenophene to synthesize three donor-acceptor copolymers consisting of 5,6-difluorobenzo[2,1,3]thiadiazole (FBT) and selenophene called PFBT2Th2Se, PFBT2Se2Th and PFBT4Se, respectively. Selenophene has higher intramolecular charge transfer ability with FBT than thiophene. Therefore, the polymers containing selenophene display more red-shifted absorption. The selenophene-containing polymers also show temperature-dependent absorption spectrum, indicating that the incorporation of selenophene does not affect the crystalline behavior of the polymers. Furthermore, the results from differential scanning calorimeter (DSC) confirm that these three polymers have crystalline behavior since it shows the obvious melting point upon heating and the clear crystallization point upon cooling. The combination of these characteristics enhances the charge transport efficiency. Hence, the devices which utilize these selenophene-containing polymers can obtain impressive current density (>20 mA/cm2). To gain a deeper insight into the nanoscale morphology and orientation of the photoactive layers, the grazing-incidence wide-angle X-ray diffraction (GIWAXD) was employed. The results suggest that the three polymers blended with PC71BM adopt face-on orientation which is beneficial for charge carrier transport in the vertical direction in the active layer. Organic photovoltaic devices are fabricared with inverted atchitecture (ITO/ZnO/Active layer/MoO3/Ag). The device using PFBT2Th2Se:PC71BM shows a PCE of 8.68 % with a Voc of 0.68 V, an FF of 69.1 %, and a high Jsc of 18.46 mA/cm2. Under similar conditions, the device using the PFBT2Se2Th:PC71BM blend presents a PCE of 9.02% with a Voc of 0.66 V, an FF of 65.0 %, and an impressive Jsc of 21.02 mA/cm2. Furthermore, the device with PFBT4Se displays a PCE of 8.92 % with a Voc of 0.62 V, FF of 63.6 %, and a superior Jsc of 22.63 mA/cm2 which represents one of the highest current densities from PSCs reported in the literature.