含4，4’-二烷基-3，3’-二腈基二噻吩共軛高分子之合成及其在有機光伏電池之應用

Abstract

本研究經由Stille coupling反應聚合出一系列主鏈含有4，4’-二烷基-3，3’-二腈基二噻吩之π共軛高分子，PBTCNOc-T，PBTCNOc-2T，PBTCNOc-TT，PBTCNHx-DTTT 及 PBTCNOc-DTTT,藉由導入不同共軛長度的電子予體到主鏈之中，這些電子予體分別為噻吩、二噻吩、噻吩[3，2-b]並噻吩、3，6-二辛基-2, 5-二噻吩基噻吩[3，2-b]並噻吩，其中3，6-二辛基-2, 5-二噻吩基噻吩[3，2-b]並噻吩可看作是二噻吩及噻吩[3，2-b]並噻吩的混合結構，此電子予體結構中的辛基在製作溼式製程有機太陽能電池元件的過程中可以幫助其溶解度。 從實驗結果來看，不同共軛長度的電子予體會影響共軛高分子間的堆疊並影響其能階的變化。從吸收光譜圖來看，PBTCNHx-DTTT 及 PBTCNOc-DTTT這兩組高分子在薄膜狀態下的吸收與其在溶液狀態下的吸收相比有著顯著的紅位移。推測是這兩組高分子側鏈所在的位置及分布較容易促使高分子主鏈上的堆疊。這五組高分子由於含有腈基，這類強拉電子的官能基在上面，所以高分子的HOMO (最高佔據分子軌域)能階，受到腈基的影響，有被拉深的效果。隨著電子予體推電子能力的不同，對高分子的HOMO能階的深淺有著很大的影響。選用PBTCNHx-DTTT，及PBTCNOc-DTTT這兩組來做元件是由於這兩組高分子有較長的吸收波長，對可見光能夠有效的利用。而從元件的光伏特性表現來看，在高分子的共軛系統中導入腈基是讓元件的開路電壓提高至0.82 V的主因。 元件結構為ITO/ZnO/PBTCNOc-DTTT:PC61BM ( w/w = 1:1)/MoO3/Ag之反式異質接面之有機光伏電池可達到光電轉換效率為2.74 %，開路電壓為0.82 V，短路電流為6.97 mA/cm2，填充因子為0.48。而我們實驗室使用P3HT:PC61BM ( w/w = 1:1)以相同的元件結構所做成的反式有機太陽能電池座位對照，其光電轉化效率可達3.68 %，開路電壓為0.57 V，短路電流為11.17 mA/cm2，填充因子為0.58。

We have synthesized and characterized aseries ofnew-conjugateddonor-acceptor (D-A) copolymers (PBTCNOc-T,PBTCNOc-2T,PBTCNOc-TT,PBTCNHx-DTTT and PBTCNOc-DTTT) bearing dicyanobithiophene unit(BTCN) as the electron acceptorwith various thiophene-based unit as the electron donorvia Stille coupling reaction. The electron donors of these copolymers arethiophene (T),2，2’-bithiophene (2T),thieno-[3,2-b]thiophene (TT) and3, 6-dioctyl-2, 5-di(thiophen-2-yl)thieno[3, 2-b]thienothiophene (DTTT),respectively. The electron donor, DTTT can be considered as a hybrid form of 2T and TT, and the two n-octyl side chains on the thienothiophene unit provide the sufficient solubility of PBTCNHx-DTTT and PBTCNOc-DTTT necessary for the solution fabricationof organic photovoltaics. Experiment evidences indicate that different electron donor moiety affects the stacking of the copolymers and hence their energy levels.A pronounced red-shifted UV-visible absorption band was observed for the thin films sample of PBTCNHx-DTTT and PBTCNOc-DTTT when compared with that of solution samples. This is attributed to the appropriate location and distribution of the alkyl side chains that affects the main chain stacking of these copolymers. All copolymers studied herein containing cyano (CN) substituents, strong withdrawing functional groups. The HOMO energy levelof these copolymers are all deepened IV compared with that of poly(3-hexyl)thiophene (P3HT). Such deepened HOMO energy level are beneficial to the increasing open-circuit voltage (VOC) of the device. The power conversion efficiency (PCE) of inverted bulk-heterojunction organic photovoltaics(OPVs)based on ITO/ZnO/PBTCNOc-DTTT:PC61BM (w/w= 1:1)/MoO3/Agis2.74%. AVOCof 0.82V,short-circuit currentdensity (Jsc)of 6.97 mA/cm2, and fill factor (FF) of0.48,have been achieved. Aninvertedbulk-heterojunction OPVs based on ITO/ZnO/ P3HT:PC61BM ( w/w = 1:1)/MoO3/Ag wasalsofabricated tocomparewith aforementioned device of PBTCNOc-DTTT. It has a PCE of 3.68%, a VOCof 0.57V, Jsc of 11.17 mA/cm2, and (FF) of 0.58.