新型角形萘并雙硒吩分子及其高分子之合成、分子性質與有機太陽能電池及電晶體之應用

Abstract

本論文成功地設計並合成出一種新穎的 4,9-雙烷基角形萘并雙硒吩分子 4,9-dialkyl angular-shaped α-naphthodiselenophenes (4,9-dialkyl α-aNDS)，可以利用有效且直接的方式，由兩邊硒吩 3 號位置都接上炔基碳鏈的烯類化合物，在鹼性條件下進行兩次 6π-電子環化，此反應具有良好的位向專一性，能夠將角形萘并雙硒吩的 4 和 9 號位置引入碳鏈，得到 4,9-dialkyl α-aNDS，最後，再分別進行錫化反應，可得到單體 2,7-distannyl-4,9-didodecyl angular-shaped α-naphthodiselenophene (Sn-α-aNDS-C12) 及 2,7-distannyl-4,9-bis(2-butyloctyl) angular-shaped α-naphthodiselenophene (Sn-α-aNDS-BO)。將單體分別與含有不同側鏈的 DTFBT-HD (5,6-difluoro-4,7-bis(4-(2-hexyldecyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole)、DTFBT-BO (4,7-bis(4-(2-butyloctyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole)、DPP-OD (2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione)、TT-C12 (4,4'-didodecyl-2,2'-bithiophene) 及 DTFBT-C12 (4,7-bis(4-dodecylthiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole)，在鈀金屬催化下，進行Stille 聚合反應，可以得到一系列交錯型低能隙高分子 PaNDSDTFBT-HD、PaNDSDTFBT-BO、PaNDSDPP-OD、PaNDSTT-C12 與 PaNDSDTFBT-C12，另外，本實驗室先前研究之 2,7-distannyl-4,9-didodecyl angular-shaped α-naphthodithiophene (Sn-α-aNDT-C12) 與 Br-DTFBT-HD 進行聚合反應後，還可得到 PaNDTDTFBT-HD，最後探討這六種共軛高分子之性質，並應用於有機太陽能電池及有機場效電晶體元件上。 此六種共軛高分子材料的分子量與溶解度都有很大的差異，可能是受到電子予體及受體的結構及側鏈所影響。α-aNDS 系列高分子之熱裂解溫度皆高於 400 oC，良好的熱穩定性利於元件製作及應用。而高分子的光學能隙值大小依序為：PaNDSDPP-OD (1.39 eV) < PaNDSDTFBT-HD (1.60 eV) < PaNDSDTFBT-C12 (1.64 eV) < PaNDSDTFBT-BO (1.66 eV) < PaNDTDTFBT-HD (1.68 eV) < PaNDSTT-C12 (2.08 eV)，明顯受到高分子內受體單元的拉電子效應所影響，且予體單體之光學能隙 α-aNDS-C12 (3.28 eV) 小於 α-aNDT-C12 (3.35 eV)，也應證了含有硒吩的材料會較易形成醌型結構，擁有較低的能隙值，造成吸收較紅移。而電化學能隙值的趨勢與光學能隙值相符，並且所有高分子之 HOMO 能階都低於 －5.3 eV，代表此六個材料在大氣下具有相當的穩定性。 本研究所合成的六種共軛高分子材料應用於 bottom-gate 與 bottom-contact 元件結構的有機場效電晶體 (organic field effect transistors, OFETs) 上，PaNDSDTFBT-HD 的電洞遷移率為 0.16 cm2 V-1 s-1，稍微高於 PaNDTDTFBT-HD 的 0.12 cm2 V-1 s-1，另外，高分子材料 PaNDSDPP-OD 應用於 OFET 元件，遷移率有 0.14 cm2 V-1 s-1，若改用 bottom-gate 與 top-contact 的方式，還能擁有 α-aNDS 系列高分子中最高的電洞遷移率 0.47 cm2 V-1 s-1。而應用於有機太陽能電池上，PaNDTDTFBT-HD 在加入添加劑 10 vol % 的硫化二苯基 (diphenyl sulfide, DPS) 後，能幫助高分子與碳球 PC71BM 均勻混合於溶液中，使相同分子間的聚集減少，並協助分子排列，而形成表面型態良好且膜厚適當的元件主動層，因此擁有不錯的開路電壓值 (Voc) 0.78 V、短路電流值 (Jsc) −12.21 mA/cm2 及填充因子 (FF) 62.7 %，所以得到此系列高分子最高的光電轉換效率 6 %，因此我們相信 α-aNDS 具有潛力成為有機半導體材料之重要單體，能夠成就高效率的高分子太陽能電池及有機場效電晶體。

We have developed a useful synthetic strategy to successfully prepare 4,9-dialkyl angular-shaped α-naphthodiselenophenes (4,9-dialkyl α-aNDS) molecules where the angular geometry of the fused selenophenes and the position of two aliphatic chains on the central naphthalene core can be regiospecifically controlled. The diselenophenyl-ene-diyne precursor underwent base-induced double 6π-cyclization to construct the central naphthalene moieties with the alkyl chains specifically at the 4,9-positions. The 4,9-dialkyl α-aNDS were doubly lithiated by n-butyllithium followed by treatment with trimethyltin chloride, yielding 2,7-distannyl-4,9-didodecyl angular-shaped α-naphthodiselenophene (Sn-α-aNDS-C12) and 2,7-distannyl-4,9-bis(2-butyloctyl) angular-shaped α-naphthodiselenophene (Sn-α-aNDS-BO) monomers, respectively. Two monomers were copolymerized with DTFBT-HD (5,6-difluoro-4,7-bis(4-(2-hexyldecyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole), DTFBT-BO (4,7-bis(4-(2-butyloctyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole), DPP-OD (2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione), TT-C12 (4,4'-didodecyl-2,2'-bithiophene), and DTFBT-C12 (4,7-bis(4-dodecylthiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole) monomers by the Stille coupling to give PaNDSDTFBT-HD, PaNDSDTFBT-BO, PaNDSDPP-OD, PaNDSTT-C12, and PaNDSDTFBT-C12, respectively. For comparison, a thiophene-based analogue, 2,7-distannyl-4,9-didodecyl angular-shaped α-naphthodithiophene (Sn-α-aNDT-C12) monomer, was copolymerized with DTFBT-HD monomer to afford PaNDTDTFBT-HD. The differences of the donor-acceptor structures play a key role in determining electronic/steric and intermolecular/intramolecular properties associated with the device characteristics. The α-aNDS-based copolymers showed good thermal stability with high decomposition temperatures (Td) over 400 oC. The optical band gaps (Eg opt) of polymers and monomers are in the following order: PaNDSDPP-OD (1.39 eV) < PaNDSDTFBT-HD (1.60 eV) < PaNDSDTFBT-C12 (1.64 eV) < PaNDSDTFBT-BO (1.66 eV) < PaNDTDTFBT-HD (1.68 eV) < PaNDSTT-C12 (2.08 eV), and α-aNDS-C12 (3.28 eV) < α-aNDT-C12 (3.35 eV). The tendency of Eg opt showed that the electron-withdrawing ability of the acceptors influences the band gap of copolymers. Selenium-based materials have the more quinoidal character and less tendency of twisting than sulfur-based materials, resulting in a smaller band gap and more red-shifted absorbance. The organic field effect transistor (OFET) mobilities of the copolymers were measured by the devices with a bottom-gate/bottom-contact configuration. The hole mobilities of the PaNDSDTFBT-HD, PaNDTDTFBT-HD and PaNDSDPP-OD device were estimated to be 0.16, 0.12 and 0.14 cm2 V-1 s-1, respectively. Moreover, the PaNDSDPP-OD device with a bottom-gate/top-contact configuration possesses a highest hole mobility up to 0.47 cm2 V-1 s-1, which is attributed to the strong intermolecular interaction of the polymer associated with the rigid and coplanar structure of the α-aNDS and DPP units. The bulk heterojunction solar cell using PaNDSDTFBT-HD:PC71BM blend with 10 vol % diphenyl sulfide (DPS) as the additive delivered a Voc of 0.78 V, a Jsc of −12.21 mA/cm2, an FF of 62.7%, and a high power conversion efficiency (PCE) of 6.00% in the inverted architecture. These preliminary results demonstrated that the α-aNDS is a promising building block to construct new generation of materials for high-performance solar cell and transistor applications.