開發新型梯形茚基雙噻吩并噻吩、茚基雙硒吩與蒽并雙硒吩分子: 合成、性質鑑定及高分子太陽能電池之應用

Abstract

我們設計並且合成一種新的七環分子indacenodithieno[3,2-b]thiophene arene (IDTT)，其分子的特色是外側之兩個噻吩並噻吩(thieno[3,2-b]thiophene (TT))之3號位置與中心之苯基，用一個橋樑碳原子以共價鍵來連結，形成一個包含兩個環戊二烯(cyclopentadienyl)之新穎七環結構。並與電子受體4,7-dibromo-2,1,3-benzothiadiazole (BT)、 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole (FBT) 與1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD) 進行Stille聚合反應，得到三個給體−受體交錯型高分子: PIDTTBT、PIDTTFBT 與 PIDTTTPD。此結構單體 IDTT相較我們之前已發表的高分子 PDITTBT 單體 DITT 而言包含較多的並噻吩，使得高分子有良好的共平面，提昇電洞的傳輸能力，以及增強固態吸光之能力。我們將高分子製作成正結構太陽能電池原件上( ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al )，最後其元件效率可分別達到3.8% , 4.2% 及 4.3%。 本論文第一次成功利用分子內Friedel−Crafts環化方法合成出苯環−硒吩以碳原子為架橋的多環分子indacenodiselenophene (IDS)，並且引入不同側鏈 4 - 己基苯基團 alkyl/4 - 辛氧苯基團alkoxy 在sp3的碳價橋上有不同側鏈是，可得到兩種單體 IDS-OC8與IDS-C6，共聚交錯型高分子: PIDSBT-OC8、PIDSBT-C6、PIDSFBT-OC8、 PIDSFBT-C6 與 PIDSTPD-C6。高分子在光學與電化學性質方面並無太大差異，而在元件表現上PIDSBT-C6 與 PIDSFBT-C6 的光電轉換效率較優於 PIDSBT-OC8 與 PIDSFBT-OC8 (3.8% 與 3.9% vs 2.6% 與 1.9%)。在含有氟原子的電子受體有較低的 HOMO 能階使得電壓值較高之外，電流質也有很大的提升。 而 PIDSFBT-C6 與 PIDSTPD-C6 在有機場效電晶體上的表現也有較好的電動遷移率，所以這證明了側鏈4 - 己基苯基團在 IDS 這系統上較優於4 - 辛氧苯基團。而在理論計算我們也發現4 - 辛氧苯基團辛氧基與苯環是成平面狀，而4 - 己基苯基團己基則超出與苯環平面。分子之間不同的排列進而影響效率。PIDSBT-C6 有最好的電動遷移率 8.0 × 10−2 cm2 V−1 s−1 而 PIDSTPD-C6 在有加入 5％ 氯奈下有最佳的光電效率 4.6％。 而最後利用6π電子環化方法合成出多環分子angular-anthradiselenophene(aADS)，並與分子受體DPP、DTFBT進行Stille聚合反應可得一系列交錯型高分子，PaADSDTFBT-C4、PaADSDTFBT-C8、PaADSDTFBT-C20 與 PaADSDPP。在電化學性質方面，PaADSDTFBT-C4、PaADSDTFBT-C8、PaADSDTFBT-C20並無太大差異；但是在光學方面，PaADSDTFBT-C4、PaADSDTFBT-C8 較PaADSDTFBT-C20 吸收較為紅位移，我們認為直鏈高分子在固態下有較好的排列；而在有機場效電晶體高分子 PaADSDTFBT-C4、PaADSDTFBT-C8也有不錯的電洞遷移率(1.0 × 10-2 cm2 V-1s-1與 2.7× 10-2 cm2 V-1s-1)，而在太陽能電池元件上，PaADSDTFBT-C4與 PaADSDTFBT-C8的光電轉換效率較優於PaADSDTFBT-C20 (3.5% 與 4.4% vs 0.3%)，原因在於電流值與填充因子有很大的提升；所以從數據得知，在aADS系統中含有直鏈高分子 PaADSDTFBT-C4與 PaADSDTFBT-C8在分子的排列、有機場效電晶體與太陽能電池上的結果都優於支鏈高分子 PaADSDTFBT-C20。

In the first part, we have developed a new multifused indacenodithieno[3,2-b]thiophene arene (IDTT) unit where the central phenylene is covalently fastened with the two outer thieno[3,2-b]thiophene (TT) rings, forming two cyclopentadiene rings embedded in a heptacyclic structure. This rigid and coplanar IDTT building block was copolymerized with electron-deficient acceptors, 4,7-dibromo-2,1,3-benzothiadiazole (BT), 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole (FBT) and 1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD) via Stille polymerization, respectively. Because the higher content of the thienothiophene moieties in the fully coplanar IDTT structure facilitates π-electron delocalization, these new polymers show much improved light-harvesting abilities and enhanced charge mobilities compared to PDITTBT copolymer using hexacyclic diindenothieno[3,2-b]thiophene (DITT) as the donor moiety. The device using PIDTTBT:PC71BM (1:4, w/ w) exhibited a decent power conversion efficiency (PCE) of 3.8%. Meanwhile, the solar cell using PIDTTFBT:PC71BM (1:4 in wt %) blend exhibited a greater Voc value of 0.9 V and a larger Jsc of 10.08 mA/cm2, improving the PCE to 4.2%. The enhanced Voc was attributed to the lower-lying of HOMO energy level of PIDTTFBT as a result of fluorine withdrawing effect on the BT unit. A highest PCE of 4.3% was achieved for the device incorporating PIDTTTPD:PC71BM (1:4 in wt %) blend. In the second part, a pentacyclic indacenodiselenophene (IDS) arene was synthesized via intramolecular Friedel-Craft cyclization of the selenophene moieties. This IDS framework was used as a model system to investigate the alkyl/alkoxy side-chain effect by preparing IDS-OC8 and IDS-C6, where the side chains on the sp3 carbon in the cyclopentadienyl ring are 4-octyloxyphenyl groups and 4-hexylphenyl groups, respectively. The Sn-IDS-OC8 and Sn-IDS-C6 monomers were copolymerized with to afford five new IDS−based donor−acceptor alternating copolymers, PIDSBT-OC8, PIDSBT−C6, PIDSFBT-OC8, PIDSFBT-C6, and PIDSTPD-C6. Despite the fact that the octyloxy and hexyl side chains play a negligible role in the optical and electrochemical properties of the resulting polymers, the solar cell performance is highly associated with the side chains of the polymers. Under similar device fabrication conditions, the PIDSBT-C6 and PIDSFBT-C6-based devices showed much improved efficiencies than the corresponding PIDSBT-OC8, and PIDSFBT-OC8-based devices (2.6% and 1.9% vs 3.8% and 3.9%). The improvement is mainly the result of much enhanced Jsc values. Consistently, PIDSBT-C6 and PIDSFBT-C6 exhibited much higher FET hole mobilites than the corresponding PIDSBT-OC8, and PIDSFBT-OC8. These results clearly revealed that the 4-hexylphenyl group was a more suitable side chain than the 4-octyloxyphenyl group in the IDS system, and the side-chain dependent mobility of the polymers was the dominating factor to determine the photocurrents and efficiencies of PSCs. PIDSBT−C6 exhibited a high hole mobility of 0.08 cm2 V−1 s−1 and PIDSTPD-C6:PC71BM (1:4 in wt %)-based solar cell with 5 v% chloronaphthalene (CN) delivered a highest PCE of 4.6%. This work not only disclosed a new selenophene-containing ladder-type IDS structure and its copolymers, but also provided useful insights into the alkyl/alkoxy side-chain effect for future design of conjugated polymers. Donor-acceptor copolymers incorporating selenophene units have emerged as promising photoactive materials because of the selenophene’s unique nature to improve light-harvesting ability, photo-stability, and charge mobility of the polymers. In the third part of this thesis, a new angular-anthradiselenophene (aADS) was developed. These aADS monomers were copolymerized with dithienyl-5,6-difluoro-2,1,3-benzothiadiazole (DTFBT) and dithienyldiketopyrrolopyrrole (DPP) to afford four new aADS -based donor-acceptor alternating copolymers, PaADSDTFBT-C4,PaADSDTFBT-C8,PaADSDTFBT-C20 and PaADSDPP. The branch and linear side chains have negligible impact on the optical and electrochemical properties of the resulting polymers due to the fact that the side chains have no direct conjugation with the polymeric backbones. However, this side-chain structural variation might dramatically affect the molecular packing of the polymers, leading to different device performances. Under similar device fabrication conditions, the PaADSDTFBT-C4 and PaADSDTFBT-C8 devices showed much higher efficiencies than the corresponding PaADSDTFBT-C20 devices (4.4% and 3.9% vs. 0.3%). The improvement is mainly a result of much enhanced Jsc values. PaADSDTFBT-C8 exhibited a highest hole mobility of 2.7 × 10-2 cm2 V-1 s-1 and PaADSDTFBT-C4:PC71BM (1:2 in wt%)-based device exhibited a highest Voc of 0.84 V, a Jsc of 8.19 mA/cm2, a FF of 66%, and a highest PCE of 4.4%.