以碳、氮、矽原子及乙烯基為共價橋樑所形成之七與五環熔合多電子平面分子：合成、鑑定及其共軛高分子於有機太陽能電池與有機場效電晶體之應用

Carbon, Nitrogen, Silicon and Ethylene-bridged Multifused Heptacyclic and Pentacyclic Electron-rich Arenes: Synthesis, Characterization and Their Conjugated Polymers for Organic Field-Effect Transistors and Photovoltaic Applications

吳忠憲(Jhong-Sian Wu)

指導教授 ： 許千樹

國立交通大學/理學院/應用化學系所/博士(2012年)

https://doi.org/10.6842/NCTU.2012.00312

摘要

在本論文中，我們將雙噻吩咔唑 (dithienocarbazole) 外圍噻吩的3號位置和中心咔唑的3與6號位置利用碳、氮、矽原子以及乙烯基為共價橋樑形成七環熔合多電子分子 (dithienocyclopenta-carbazole (DTCC)，dithienopyrrolo-carbazole (DTPC)， dithienosilolo-carbazole (DTSC) 與 dithienobenzo-carbazole (DTBC))，為了改善薄膜態下分子間的作用力，DTCC 的苯環側鏈被更具有柔軟性的正辛烷所取代而形成dithienocyclopenta-carbazole (DTCC-C8)，此外，以中心為芴 (fluorene) 的dithienocyclopenta-fluorene (DTCF) 也使用類似的方式來合成，在多環單體的合成上，以碳原子為價橋之 DTCC、DTCC-C8 與 DTCF 的關鍵合成步驟為 Friedel-Craft反應，而以乙烯基為價橋的DTBC 則主要是利用一步驟的多重Suzuki-Miyaura cross-coupling 來合成，另一方面，以矽與氮原子為價橋之 DTSC 與 DTPC 的關鍵合成步驟分別為 lithiation/nucleophilic addition 與一步驟的多重鈀催化 Buchwald–Hartwig 反應，此後，將這些新穎的多電子單體與缺電子受體 (benzothiadiazole (BT) 或 dithienylbenzothiadiazole (DTBT)) 一起共聚成新的給體-受體交錯型共軛高分子。
相較於非熔合高分子 poly(2,7-fluorene-alt-dithienylbenzothiadiazole) (PFDTBT) 與 poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT)，含有階梯狀平面分子 DTCF與 DTCC 之 poly(dithienocyclopenta-fluorene-alt-benzothiadiazole) (PDTCFBT) 與poly(dithienocyclopenta-carbazole-alt-benzothiadiazole) (PDTCCBT) 表現出較紅位移的光學吸收與較窄的光學能隙，將材料依照此結構ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al 製作成太陽能電池元件後，PDTCCBT 有較高的光電轉換效率3.7%，此外，修飾過側鏈的 DTCC-C8 其高分子 poly(dithienocyclopenta-carbazole-alt-benzothiadiazole) PDTCCBT-C8 表現出較強的分子間堆疊，因此其光學吸收較為紅位移，並且在元件方面也表現出較佳的效率 4.6% (開路電壓 0.74 V，短路電流 10.3 mA/cm2，填充因子 60.0%)，另一方面，由於在 DTSC 單體中的噻咯 (silole) 擁有拉電子的能力，所以導致了高分子 poly(dithienosilolo-carbazole-alt-benzothiadiazole) (PDTSCBT) 擁有較低的 HOMO 能階，反之，DTPC 擁有推電子能力的吡咯 (pyrrole)，其高分子poly(dithienopyrrolo-carbazole-alt-benzothiadiazole) (PDTPCBT) 的HOMO 能階則相對較高，而其光學能隙之大小順序為：PDTSCBT (1.83 eV) > PDTCCBT-C8 (1.64 eV) > PDTPCBT (1.50 eV)，這樣結果顯示出七環熔合多電子單體之推電子能力強弱為DTPC > DTCC-C8 > DTSC，太陽能電池元件方面，PDTSCBT 表現出最佳的光電轉換效率5.2%，並且擁有相當大的開路電壓0.82 V，我們也將單體 DTBC 與dithienylbenzothiadiazole 共聚成交錯型共軛高分子poly(dithienobenzo-carbazole-alt-dithienylbenzothiadiazole) (PDTBCDTBT)，其元件表現出相當高的5.5% 效率 (開路電壓 0.79V，短路電流 10.87 mA/cm2，填充因子 64.5%)，藉由將三氧化鉬 (molybdenum oxide，MoO3) 當做緩衝層，元件效率可以進一步的改進為6.2% (開路電壓 0.79V，短路電流 11.52 mA/cm2，填充因子 68.2%)，在五環熔合多電子單體方面，單一異構物且呈 angular 形狀的 anthradithiophene (aADT) 也被合成出來，此後，再與ditheniodiketopyrrolopyrrole 和 bithiophene 做共聚分別形成高分子poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) 與 poly(anthradithiophene-alt-bithiophene) (PaADTT)，有結晶性的 PaADTT 表現出高的電洞遷移率 (7.9 × 10-2 cm2V-1s-1) 與開關比 (1.1 × 107)，而以 PaADTDPP 為材料的太陽能電池元件則有3.66%的轉換效率，藉由添加添加劑1-chloronaphthalene (CN)，可以將效率更進一步的提升到4.24%，此光電轉換效率則是在以含有 anthradithiophene 的高分子之太陽能電池中最高效率的一個，最後，由於我們合成的多環單體都具有共平面且剛硬的特性，因此是相當適合用來製作成有機場效電晶體，PDTSCBT、PDTCCBT-C8 與PaADTDPP 分別表現出高的電洞遷移率0.073、0.110 與 0.073 cm2 V-1s-1。

關鍵字

共軛高分子 ； 高分子太陽能電池 ； 場效電晶體

並列摘要

In this research, the 3-positions of the two outer thiophenes of dithienocarbazole unit are covalently fastened to the 3,6-positions of the central 2,7-carbazole cores by carbon, nitrogen, silicon and ethylene bridges, leading to a new class of multifused heptacyclic units dithienocyclopenta-carbazole (DTCC), dithienopyrrolo-carbazole (DTPC), dithienosilolo-carbazole (DTSC) and dithienobenzo-carbazole (DTBC), respectively. To improve the intermolecular interactions in solid state, the original 4-octoxyphenyl side chains on the DTCC unit are replaced with the more flexible octyl groups to furnish a dithienocyclopenta-carbazole (DTCC-C8) unit. Structurally analogous to DTCC, carbon-bridged dithienocyclopenta-fluorene (DTCF) has also been synthesized but using fluorene as the central core. Friedel-Craft cyclization is the key step for the synthesis of carbon-bridged DTCC, DTCC-C8 and DTCF units, while a one-pot benzannulation via multiple Suzuki-coupling is utilized to efficiently synthesize ethylene-bridge DTBC. Silicon-bridge DTSC and nitrogen-bridged DTPC units were also successfully constructed by lithiation/nucleophilic addition and one-pot double palladium-catalyzed amination via Buchwald–Hartwig reaction, respectively. These newly designed electron-rich monomers were copolymerized with benzothiadiazole (BT) or dithienylbenzothiadiazole (DTBT) units to afford a range of new donor-acceptor alternating copolymers.
Compared to nonfused poly(2,7-fluorene-alt-dithienylbenzothiadiazole) (PFDTBT) and poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT), poly(dithienocyclopenta-fluorene-alt-benzothiadiazole) (PDTCFBT) and poly(dithienocyclopenta-carbazole-alt-benzothiadiazole) (PDTCCBT) containing ladder-type heptacyclic structures (DTCF and DTCC) with forced planarity exhibited red-shift absorption spectra and narrow band gaps. By fabricating conventional device with ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al configuration, PDTCCBT exhibit a higher power conversion efficiency of 3.7%. Due to the side chains modification of DTCC-C8 unit to induce stronger interchain interactions, poly(dithienocyclopenta-carbazole-alt-benzothiadiazole) PDTCCBT-C8 exhibited more red-shift absorption and higher efficiency of 4.6% (Voc = 0.74 V，Jsc = 10.3 mA/cm2，FF = 60.0%) than PDTCCBT. On the other hand, the silole units in DTSC possess electron-accepting ability that lowers the highest occupied molecular orbital (HOMO) energy levels of poly(dithienosilolo-carbazole-alt-benzothiadiazole) (PDTSCBT), whereas stronger electron-donating ability of the pyrrole moiety in DTPC increases the HOMO energy levels of poly(dithienopyrrolo-carbazole-alt-benzothiadiazole) (PDTPCBT). The optical band gaps are in the following order: PDTSCBT (1.83 eV) > PDTCCBT-C8 (1.64 eV) > PDTPCBT (1.50 eV). This result indicates that the donor strength of the heptacyclic arenes is in the order: DTPC > DTCC-C8 > DTSC. The bulk heterojunction photovoltaic device using PDTSCBT as the p-type material delivered a promising efficiency of 5.2% with an enhanced Voc of 0.82 V. For DTBC, the photovoltaic device based on the poly(dithienobenzo-carbazole-alt-dithienylbenzothiadiazole) (PDTBCDTBT) possessing highly rigid and coplanar structure exhibited an PCE of 5.50% (Voc of 0.79 V, a Jsc of 10.87 mA/cm2, a FF of 64.5%). By using MoO3 as a buffer layer, the performance of the device was further improved to a high PCE of 6.2% with a Voc of 0.79 V, a Jsc of 11.52 mA/cm2, a FF of 68.2%. For the pentacyclic arene, an isomerically pure anti-anthradithiophene (aADT) arranged in an angular shape was developed. This newly designed 2,8-stannylated aADT monomer is copolymerized with a ditheniodiketopyrrolopyrrole unit and a bithiophene unit, respectively, to furnish poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) and thiophene-rich poly(anthradithiophene-alt-bithiophene) (PaADTT). PaADTT with crystalline nature achieve a high FET mobility of 7.9 × 10-2 cm2V-1s-1 with an on-off ratio of 1.1 × 107. The photovoltaic device based on the PaADTDPP exhibit a PCE of 3.66%. By adding 1.5 vol.% 1-chloronaphthalene (CN) as a processing additive, the PCE can be improved to 4.24%. The efficiency is the best one among these devices based on the polymers containing anthradithiophene. Finally, in view of the coplanar geometries and rigid structures of these ladder-type arenes, it is highly desirable to utilize these polymers for organic field-effect transistors (OFETs). PDTSCBT, PDTCCBT-C8 and PaADTDPP exhibited the high hole mobilities 0.073, 0.110 and 0.073 cm2 V-1s-1, respectively.

並列關鍵字

conjugated polymers ； polymer solar cells ； field effect transistors

參考文獻

2. MRS Bull. 2008, 33, 297.

3. Energy Policy 2005, 33, 1099.

7. McCreery, R. Chem. Mater. 2004, 16, 4477.

8. Tang, C. W. Appl. Phys. Lett. 1986, 48, 183.

14. The Concise Columbia Electronic Encyclopaedia, Third Edition, Figure 2.1