新型六環平面梯狀分子二茚噻吩并噻吩與四環平面烷基化角形萘并雙噻吩之合成、鑑定與高分子太陽能電池之應用

Abstract

我們成功設計和合成一種含噻吩并噻吩與苯環之六環平面梯形共軛分子diindenothieno[3,2-b]thiophene (DITT)，此分子結構是利用橋頭碳原子將鄰近的噻吩與苯環以共價鍵之方式相連接，形成含有兩個環戊二烯之六環熔合平面梯狀分子。具有剛硬且平面之DITT經修飾後成為電子予體boronic-DITT分別與不同的電子受體dibromo-2,1,3-benzothiadiazole (Br-BT) 及dibromo-4,7-di(2-thienyl)-2,1,3-benzothiadiazole (Br-DTBT) 在鈀金屬催化下進行Suzuki 耦合聚合反應，即可成功合成出兩個交替行共軛高分子PDITTBT及PDITTDTBT。共軛高分子PDITTBT與PDITTDTBT在元件上平均達0.9 V之高VOC值，且PDITTDTBT元件效率可達到5.8%。此外，PDITTDTBT與雙加成富勒烯材料DMPCBA混摻之元件表現Voc可達到單層元件結構鮮少達到之高電壓值1.14 V，為一般P3HT與PCBM混摻之近兩倍 (Voc ≒ 0.6 V)。因此本研究提供一個可獲得高Voc卻不犧牲Jsc以提升電池效率之重要思路，對於低能隙高分子設計及製作高效率電池元件有指標性的進展。 接著我們成功開發出新式合成方法，可有效率地合成出四種烷基化角形萘并雙噻吩 (angular-shaped naphthodithiophene, aNDT) 之同分異構平面分子4,9--aNDT、5,10--aNDT、4,9--aNDT與5,10--aNDT，其結構中心為萘環與兩端噻吩相熔合。此方法可選擇性導入長碳鏈於萘環之內側或外側位置；並且烷基側鏈能夠使剛硬結構之aNDT溶於一般有機溶劑，大幅增加此類分子之應用性。此新型合成方法是利用低價鈦金屬進行之McMurry耦合去氧縮合反應與鈀金屬催化之Sonogashira耦合反應搭配，得到關鍵中間體dithienyl-ene-diyne。最後進行分子內6π電環反應，即可選擇性合成出四種擁有側鏈之烷基化四環平面分子aNDT。 並且本研究為首次以新型烷基化4,9--aNDT為電子給體 (aNDT-OD、aNDT-BO) 分別與不同的電子受體bis(5-bromo-4-octylthienyl)-4,7-di(2-thienyl)-2,1,3-benzothiadiazole (Br-DTBT)、bis(5-bromo-4-octylthienyl)-difluoro-benzothiadiazole (Br-DTFBT) 與dibromo-diketopyrrolopyrrole (DPP) 在鈀金屬催化下進行Stille聚合反應，成功合成出新型交替共軛高分子PaNDTDTBT、PaNDTDTFBT、PaNDTDPP-OD及PaNDTDPP-BO。其中PaNDTDTFBT與PC71BM混摻之異質接面太陽能電池可達光電轉換效率為6.86%，且PaNDTDPP-BO電洞遷移率為0.2 cm2/V−1s−1之高效率有機場效電晶體，證明aNDT類型之低能隙高分子為理想的有機半導體材料。 最後本研究進一步透過錫化之-aNDT-C12與-aNDT-C12電子予體分別與電子受體naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole (NT) 共聚得到兩個互為結構異構的D-A共聚高分子PNDTDTNT與PNDTDTNT。我們發現-aNDT與-aNDT的分子幾何形狀對於高分子的立體構型與固態堆疊扮演著關鍵角色進而影響各種物理性質，本研究經由系統性微觀的分析以理解高分子巨觀物理特性與元件表現。透過理論計算可以了解PNDTDTNT擁有較PNDTDTNT更加的平面特性而且高分子主鏈也更為直線型，因此，由2D-WAXD之分析證實PNDTDTNT在固態下可以自組裝型成較多的規則性π堆疊與層間堆疊。同時在吸收光譜中也可觀察到PNDTDTNT之吸收範圍較PNDTDTNT紅移，這是由於PNDTDTNT較強的分子間作用力與較佳的有效共軛系統所致。最終，亦由於PNDTDTNT較高程度的規性堆疊結構使其表現出較 PNDTDTNT優異的OFET電洞遷移率0.214 cm2 V−1 s−1。此外更值得一提的事， PαNDTDTNT:PC71BM所混參的異質接面太陽能電池可達到8.01%優異的效率。

We have successfully designed, synthesized and characterized a novel ladder-type multifused diindenothieno[3,2-b]thiophene (DITT) unit in which two outer phenylene subunits are covalently fastened to the central thieno[3,2-b]thiophene. The rigid and coplanar DITT building block was used as an electron donor unit and copolymerized with electron-deficient acceptors, dibromobenzothiadiazole (BT) and dibromo- dithienylbenzothiadiazole (DTBT), to tune the electronic band gaps of the copolymers for a better light harvesting ability. Moreover, these copolymers provide a deep-lying highest occupied molecular orbital (HOMO) level for obtaining polymer solar cells with a high open-circuit voltage (Voc). PDITTDTBT/PC71BM device exhibited a high Voc of 0.92 V, a Jsc of 10.71 mA/cm2 and an impressive power conversion efficiency (PCE) of 5.8% due to the much deep-lying HOMO energy level and appropriate light absorption of PDITTDTBT. This research provides a guideline of molecular engineering to obtain high Voc without sacrificing Jsc. More importantly, the PDITTDTBT blended with a bis-adduct C60 DMPCBA resulted in an extra high Voc of 1.14 V, which is almost double than the average Voc (ca. 0.6 V) derived from the P3HT/PCBM-based devices. On the other hand, although the tetracyclic angular-shaped naphthodithiophenes (aNDTs) derivatives are an emergent building block for constructing promising semiconductor conjugated polymers, the absence of aliphatic side chains as solubilizing groups on the aNDTs greatly restricted their further application toward polymer synthesis. To create a new class of aNDT-based polymers for widespread applications in solution-processable OFETs and PSCs, side-chain engineering of the aNDT-based structures plays a pivotal role in improving solubility and optimizing electronic/steric properties associated with the resultant solar cell characteristics. We describe a new strategy to synthesize 4,9- and 5,10-dialkylated -aNDTs as well as 4,9- and 5,10-dialkylated β-aNDTs. Four isomeric precursors with different dithienyl-ene-diyne arrangements undergo base-induced double 6-cyclization to construct the central naphthalene cores, leading to the formation of the regiospecific products. These 2,7-distannylated dialkylated aNDT-based monomers can be used for Stille cross-coupling to produce promising conjugated materials for various optoelectronic applications. For the first time, the corresponding 2,7-stannylated-4,9-dialkylated aNDT monomers were polymerized with FBT and DPP acceptors to make two new PaNDTDTFBT and PaNDTDPP donor-acceptor copolymers. The photovoltaic devices based on the PaNDTDTFBT:PC71BM blend not only showed a promising PCE of 6.52% with conventional configuration but achieved a higher PCE of 6.86% with inverted configuration. Moreover, PaNDTDPP with strong intermolecular interaction achieved a high FET hole mobility of 0.202 cm2V−1s−1. Moreover, the distannylated -aNDT and -aNDT monomers were copolymerized with the Br-DTNT monomer by the Stille coupling to furnish two isomeric copolymers, PNDTDTNT and PNDTDTNT, respectively. The geometric shape and coplanarity of the isomeric -aNDT and -aNDT segments in the polymers play a decisive role in determining their macroscopic device performance. Theoretical calculations showed that PNDTDTNT possesses more linear polymeric backbone and higher coplanarity than PNDTDTNT. The less curved conjugated main chain facilitates stronger intermolecular - interactions, resulting in more red-shifted absorption spectra of PNDTDTNT in both solution and thin film compared to the PNDTDTNT counterpart. 2D-WAXD analysis revealed that PNDTDTNT has more ordered π-stacking and lamellar stacking than PNDTDTNT as a result of the lesser curvature of the PNDTDTNT backbone. Consistently, PNDTDTNT exhibited a greater OFET hole mobility of 0.214 cm2V−1s−1 than PNDTDTNT with a mobility of 0.038 cm2V−1s−1. More significantly, the solar cell device incorporating the PNDTDTNT:PC71BM blend delivered a superior efficiency of 8.01% that outperformed the PNDTDTNT:PC71BM-based device with a moderate PCE of 3.6%.