利用Stille連結聚合法合成含咔唑側鏈之低能隙電子施體/受體導電高分子及其特性研究與應用

Abstract

近幾年來利用導電高分子/奈米顆粒混成系統來製作太陽能電池受到工業界及學術機關的高度興趣。因為高分子太陽能電池擁有價格低廉，並且可利用捲式塗佈技術進行大面積加工，使得這項研究受到極大的重視。目前由P3HT/PCBM混成系統做成的太陽能電池元件效率為4%。為了使效率超越P3HT/PCBM混成的太陽能電池元件，一個擁有適當光學能隙的導電高分子是重要的材料性質。在本篇碩士論文中，利用Stille 連結聚合法來製備一個含良好電洞傳導性質咔唑為側鏈的高分子,其主鏈是由quinoxaline/thiophene交錯行成的導電高分子，並且我們發現這樣的高分子對於一般有機溶劑仍然保有優秀的溶解性質。在化學合成過程中我們利用NMR，FT-IR和GPC等儀器來判定單體及高分子PCPQT的化學結構。此次合成出的新型高分子PCPQT是由交錯的電子施體thiophene單元和電子受體quinoxaline單元聚合而成。由電子施體和電子受體所形成的交錯型導電高分子，因為在其主鏈會形成電荷傳導現象，所以會在光學性質上有著我們希望的良好的性質。PCPQT 高分子可以溶解在多種有機溶劑中，如四氫扶喃。另外我們也發現隨著分子量的增加，在紫外光-可見光吸收光譜中會有從530nm紅移到630nm的現象。在X射線衍射分析實驗中我們發現聚合度分佈大的PCPQT高分子沒有晶體規則性，而純化過後聚合度分佈較小的PCPQT會有(100)面的晶體規則結構。在循環伏安法的電化學測試中，可以發現此高分子擁有比P3HT更低的HOMO能階，大約是5.5eV。目前，經由台灣大學凝態科學研究中心王立義老師的指導下，由其實驗室劉虹葳同學利用PCPQT/PCBM混成系統製作而成的太陽能電池元件已經達到0.4%的電力轉換效率。初步的研究發現PCPQT有著約 的電洞傳導率。最顯著的特色是PCPQT/PCBM混成系統的太陽能電池元件擁有比P3HT/PCBM混成系統還要高的開路電壓約0.75V。

Solar cells based on conducting polymer/nanoparticle hybrid system have recently attracted an ever increasing attention both in academics and industries due especially to their potential to be used in low cost, large area, and roll-to-roll production. To further enhance the power conversion efficiency of 4% achieved from solar cells made of regioregular poly(3-hexyl thiophene)/[6,6]-phenyl C61 butyric acid methyl ester (P3HT/PCBM), new conducting polymers with optimized band energy levels are demonstrated to be one of the key material properties. In this master thesis work, I synthesized a highly soluble quinoxaline/thiophene alternating conducting polymer with hole transport moiety of carbazole as side chain using Stille coupling polymerization method. Various analytical techniques including H-NMR, C13-NMR, FTIR and GPC confirmed a successful synthesis of the constituent monomers [2,5-bis (trimethylstannyl) thiophene and 3-(4-(5,8-dibromo-2-(4-(9-butyl-9H-carbazol-3-yl) phenyl)quinoxalin-3-yl) phenyl)-9 -butyl-9H-carbazole(7)] and the resulting alternating conducting polymer PCPQT. The new conducting polymer PCPQT consists of alternating electron-donating thiophene unit and electron-accepting quinoxaline unit and shows interesting optical properties because of the formation of a charge-transferred (CT) electronic structure along the polymer chain. The polymer is soluble in organic solvents such as tetrahydrofuran and showed an increase in UV-VIS peak from 530nm to 630nm with increasing molecular weight. Powder X-ray diffraction analysis confirms that polydispersed PCPQT exhibits no crystalline order while monodispersed PCPQT shows a crystalline order plane of (100). The CT copolymers are electrochemically active in both oxidation and reduction regions and the cyclic voltammetry measurements show that the HOMO level of the CT polymer is ~5.5eV which is significantly lower than that of P3HT. Preliminary measurements have revealed hole mobilities of about of the pure material and a power conversion efficiency (PCE) up to 0.4% based on the solar cell consisted of PCPQT/PCBM hybrid system under AM 1.5 simulated sun light (100mW/cm2). Notably, the solar cell device made from PCPQT/PCBM exhibits a higher (~0.75V) than that of the conventional P3HT/PCBM one due mainly to the lower HOMO level of PCPQT. Further improvements are anticipated through a rational design of new low band gap quinoxiline/thiophene CT type conducting polymers.