含光吸收側鏈之5,6-雙氟-2,1,3-苯并噻二唑與吡咯并吡咯二酮之共軛高分子之合成及應用

Abstract

本研究致力於研究低能隙共軛高分子材料，並將其應用於有機半導體元件，如有機場效電晶體 (OFETs) 與有機薄膜高分子太陽能電池 (OPVs)。 第一部分將不同的吸光基團導入低能隙高分子側鏈中，由於UV吸收對於太陽能電池元件效率中的短路電流有所影響，故在此研究中，我們將以合成全光譜吸收的共軛高分子材料作為主軸，在高分子側鏈上添加吸光基團，從UV吸收達成全光譜吸收為目標，合成出多種不同類型的random copolymers，進而去探討其材料特性以及有機薄膜太陽能電池元件效率。我們將紫質衍生物與PTh4FBT高分子主練結合，期望利用紫質能帶的吸光，可解決低能隙高分子中藍光區吸光不足之問題。而以紫質衍生物為側鏈的共軛高分子PTh4FBT-Por-Py增加了藍光區的吸收，其PCE值達到了8.0%。而另一紫質衍生物為側鏈的共軛高分子PTh4FBT-DiPor-Py，增加了藍光區與紅光區的吸收，由於紫質衍生物過於龐大，使得高分子結構排列不易，PCE值為2.23%。而PTh4FBT-Por-Py在與不同高分子搭配所製成的三元混摻高分子太陽能電池，與PTB7(7.1%)搭配可以有效的提升PCE值(8.2)。而與PTB7-Th(8.1%)搭配，其 PCE 值有在進一步的提升(9.0%)。 第二部份，用Perylene這個較小結構的吸藍光材料作為側鏈的共軛高分子PTh4FBT-Pery-1與PTh4FBT-Pery-2，吸藍光材料perylene有助於加強藍光區吸收，使得藍光區域波峰上升，擴大吸光範圍，PTh4FBT-Pery-1其PCE值為5.00 %，而提升高分子中perylene的比例，其高分子PTh4FBT-Pery-2有更好的PCE值(5.33 %)。 第三部份我們成功的合成出三種以3,6-bis(2-bromothieno-[3,2-b]thiophen-5-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]-pyrrole-1,4-(2H,5H)-dione (Br-TTDPP)為電子受體，與三種不同的電子予體bithiophene (BT), di(2-thienyl)ethene (TVT), di(selenophene-2-yl)ethene (SVS) 所共聚出的TTDPP-BT、TTDPP-TVT以及TTDPP-SVS。在XRD分析中， TTDPP-SVS的π-π stacking距離最大，且TTDPP-SVS的lamellar方向的間距是三種高分子中最小的，此外，TTDPP-BT的遷移率為0.0882 cm2V-1S-1， TTDPP-TVT的遷移率為0.0945 cm2V-1S-1，而 TTDPP-SVS有最低的起始電壓 (Vth) 為-3.6 V與最高的遷移率為0.196 cm2V-1S-1。

This research is aimed to enhance the performances of low band gap (LBG) polymer in the optoelectronic applications, such as organic field-effect transistors (OFETs) and organic polymer photovoltaics (OPVs).

First part, we introduce the different light harvesting groups in the polymer chains. Broadening the absorptions has the potential to increase the short-circuit current. In this study, we synthesized different random copolymers by introducing the light harvesting groups in the side chains to enhance the light absorption. Moreover, we investigated the characteristics and the power conversion efficiency.The porphyrin side chain units were introduced to the PTh4FBT polymers to increase the absorption in blue-light region. PTh4FBT-Por-Py not only enhance the absorption of blue-light region, but also had the high PCE value of 8.0%. In comparison with PTh4FBT-Por-Py, PTh4FBT-DiPor-Py had much more enormous side chains. The gigantic side chains destroyed the stacking of the polymers. Though PTh4FBT-DiPor-Py increased the absorption of blue-light region and red-light region, but got low PCE value of 2.3%. Ternary organic solar cells are emerging as a promising strategy to enhance device power conversion efficiency by broadening the range of light absorption through the incorporation of additional light-absorbing components. When we blended PTh4FBT-Por-Py with PTB7, the PCE value could enhance from 7.1% to 8.2%. Moreover, the PCE value of blending with PTB7-Th grew from 8.1% to 9.0%.

Next, we used the perylene as smaller side shains in PTh4FBT to synthesized PTh4FBT-Pery-1 and PTh4FBT-Pery-2. The side chains of perylene could contribute to promote the absorption blue-light region. In comparison with PTh4FBT-Pery-1, PTh4FBT-Pery-2 had more proportion of perylene. When we enhanced the ratio of perylene, the much more blue-light could be absorbed. Thus, the PCE value of PTh4FBT-Pery-2 was higher than PTh4FBT-Pery-1.

In the third part, the new donor-acceptor (D-A) conjugate polymers based on 3,6-bis(2-bromothieno-[3,2-b]thiophen-5-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]-pyrrole-1,4-(2H,5H)-dione (Br-TTDPP) combined with three different electron-donating monomers bithiophene (BT), di(2-thienyl)ethene (TVT), di(selenophene-2-yl)ethene (SVS) were synthesized. The optical band gap, electrochemical properties and organic field-effect transistors (OFETs) device performance of TTDPP-based polymers were systematically investigated. X-ray diffraction (XRD) was used to evaluate the molecular packing of TTDPP-based polymers. Among three polymers, TTDPP-SVS showed the smallest d-spacing and largest distance of 0.372 for π-π stacking. In paticular, a OTFT having a TTDPP-SVS active layer showed the highest hole mobility of 0.196 cm2 V-1 s-1, the lowest threshold voltage down to -3.6 V, and the highest Ion/Ioff ratio of 6.5×104. This indicate that π-extened SVS significantly improves charge transport properties.