以分子建構含石墨烯電極之高分子太陽能電池之界面與形態( I )

Abstract

本計畫目前3個主要之創新(i)合成新穎予體-受體共軛高分子供有機太陽能電池使用(ii)以添加劑調整主動層之型態使得元件最佳化(iii)製成石墨烯陽極並置入有機太陽能電池元件。(i)我們合成一個新的共軛高分子，PDTTTPD，此高分子結合2,5-di-(thiophen-2-yl)thieno[3,2-b]thiophene與thieno[3,4-c]pyrrole-4,6-dione兩個單元，並展現出高度的結晶性與良好的熱穩定度。光伏元件以高分子PDTTTPD與[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)在1:1混合重量比的條件下製作，光電轉換效率達5.1％。( Chem. Commun., 2011, 47, 5064； IF=5.7)我們成功合成新的共軛高分子，PBDTBO，係由benzo[1,2-b:4,5- b’]dithiophene(BDT)與5,6-bis(octyloxy)benzo[c][1,2,5]-oxadiazole (BO)兩單元所組成。此高分子具有良好溶解度，同時最高電子填滿軌域(HOMO)位於較低能階。光伏元件以高分子PBDBO與PC61BM在混合重量比1:1的條件下製作，光電轉換效率達5.7%。(Chem. Commun., 2011, 47, 8877； IF=5.7)我們利用施蒂勒反應(Stille coupling)聚合法合成一系列具有結晶性的低能系共軛高分子--- PTHBO，PBTTBO，PTTTBO。此系列高分子利用多電子基團Thiophene(TH), 2,2-bithiophene(BT), thieno[3,2-b]thiophene(TT)與缺電子基團2,1,3-benzooxadiazole(BO)進行共聚而得。所有高分子對碳球的能階偏移(energy offsets)足夠進行有效的電荷轉移，同時最高電子填滿軌域(HOMO)也都具有較低的能階(-5.7eV)。所有高分子均呈現良好的熱穩定性，高度結晶性及寬廣的吸收光譜。因此這些高分子與碳球形成的塊狀光伏元件，其開路電壓(Voc)可達1.02V。此外以PTTTBO與PC61BM混合(1:1, w/w)，並利用添加劑1,8-二碘辛烷(DIO, 0.5 vol%)製成之光伏元件，在AM1.5G的模擬光源下轉換效率達5.3%。(Macromolecules, 2011, 44, 9115； IF=5.7)。(ii)我們證實以PBTTTPD/PC71BM(1:1.5, w/w)為主動層的光伏元件，在旋轉塗佈的過程中可藉由選擇適當鏈長的添加劑(1,6-二碘己烷, DIH)，使元件由5%轉換效率增加達到7.3%，整體增幅45%。同時我們藉由同步輻射的掠角入射X光進行小角與廣角散射實驗(GIWAXS/GIWAXS)，並結合穿透式電子顯微鏡分析，證實添加劑DIH不僅促進高分子結晶性(在薄膜平行方向(in-plane)與薄膜垂直方向(out-of-plane)，分別增加3.6與2.4倍)，也可以降低PC71BM聚集物的平均大小，從150nm減至30nm。(Adv. Mater., 2011, 23, 3315； IF=10.8)(iii)我們以一層接著一層的方法，將tetracyanoquinodimethane(TCNQ)置於層與層的石墨烯之間當成p型參雜，製作一多層的石墨烯薄膜作為太陽能電池之陽極。我們以此多層石墨烯/TCNQ薄膜構成之陽極製作P3HT/PC61BM的光伏元件，並進行特性量測。結果發現利用三層石墨烯夾兩層TCNQ構成之陽極所製作的光伏元件具有最佳光電轉換效率(2.58%)。此石墨烯薄膜製成之陽極因高電導率與穿透度在次世代軟性元件中具有相當高的吸引力。(ACS Nano accepted； DOI: 10.1021/nn301721q； IF= 9.8)

In this report, there are three major breakthroughs: (i) synthesized novel donor-acceptor conjugated polymers We prepared a new conjugated polymer, PDTTTPD exhibits high crystallinity and excellent thermal stability. A device incorporating PDTTTPD and PC71BM exhibited a power conversion efficiency of 5.1%. We synthesis a new conjugated polymer, PBDTBO, exhibits a deep HOMO energy level of -5.27 eV and excellent solubility. A device incorporating PBDTBO and PC61BM exhibited a power conversion efficiency of 5.7%. We have used Stille coupling polymerization to synthesize a series of new crystalline lowband gap conjugated polymers—PTHBO, PBTTBO, and PTTTBO. In particular, the photovoltaic device comprising the PTTTBO/ PC61BM blend system and DIO as an additive exhibited a value of Voc of 0.85 V, a Jsc of 11.6 mA cm2 and a promising PCE of 5.3%. (ii) polymer/fullerene morphology optimization using additivesWe demonstrate that the PCE of a device incorporating a PBTTPD/PC71BM film as the active layer can be improved from 5% to 7.3% after incorporating DIH during solution processing. We also elucidated the precise active layer morphology with simultaneous synchrotron GIWAXS/GIWAXS and TEM and found that the additive DIH not only induced higher polymer crystallinity, but also decreased the average size of the aggregated fractal-like PC71BM clusters to 30 nm by removing their grain boundaries. (iii) the development of graphene anodes for polymer solar cells We report a layer-by-layer molecular doping process on graphene for forming sandwiched graphene/ TCNQ/graphene stacked films for polymer solar cell anodes, where the TCNQ molecules were securely embedded in between two graphene layers. P3HT/PCBM bulk heterojunction polymer solar cells based on these multilayered graphene/TCNQ anodes are fabricated and characterized. The P3HT/PCBM device with an anode structure composed of two TCNQ layers sandwiched by three CVD graphene layers shows the optimum PCE (2.58%).