以氮原子為共價橋樑所形成之五環多電子平面分子:合成、鑑定及其共軛高分子於有機太陽能電池之應用

Abstract

本篇論文中，我們合成了一個新穎的施體 (donor) 單體benzodi(pyrrolothiophene) (BDPT)，接著與四個受體 (acceptor) 2,1,3-benzothiadiazole (BT) 、1,4-diketopyrrolo[3,4-c]pyrrole (DPP) 、 N-ethylhexylthieno[3,4-c]pyrrole-4,6-dione (TPD-EH) 、N-octylthieno[3,4-c]pyrrole-4,6-dione (TPD-C8) 進行Stille coupling聚合反應，得到了四個交錯型共軛高分子，分別為PBDPTBT、PBDPTDPP、PBDPTTPD-EH以及PBDPTTPD-C8。 這四個共軛高分子皆有良好的熱穩定性，其熱裂解溫度 (Td) 在395〜430 oC之間；由於受體拉電子能力的不同，在電子、電化學、光學特性上皆有明顯的不同，我們可以發現隨著受體拉電子能力越強，其共軛高分子之能隙會越小，在吸收光譜也會越紅位移，在這四個共軛高分子中，以PBDPTDPP之光學能隙1.25 eV為最小，其次為PBDPTBT的1.52 eV，再來是PBDPTTPD-EH的1.77 eV以及PBDPTTPD-C8的1.79 eV，與受體拉電子能力 (electron withdrawing ability) DPP > BT > TPD相符合，在電化學方面此四個共軛高分子LUMO能階皆高於PC71BM之LUMO能階0.3 eV以上，使受光激發之激子 (exciton) 能夠順利在共軛高分子與PC71BM之介面進行拆解成電子電洞。 我們將這些共軛高分子材料運用於塊材異質接面 (bulk heterojunction，BHJ) 高分子太陽能電池中，其元件結構為:ITO/PEDOT:PSS/Polymer:PC71BM/Ca/Al。在這四個共軛高分子分別與PC71BM混摻製作元件後，以共軛高分子PBDPTTPD-EH混摻PC71BM (1:3,w/w) 製作之元件光電轉換效率最佳，其開路電壓 (Voc) 為0.75 V，短路電流 (Jsc) 為9.69 mA/cm2，填充因子 (FF) 為 51.2%，光電轉換效率 (PCE) 為3.72%。

We have designed and synthesized a nitrogen-bridged pentacyclic structure, benzodi(pyrrolothiophene) (BDPT). Its corresponding distannyl monomer Sn-BDPT was copolymerized with four different acceptors, 2,1,3-benzothiadiazole (BT), 1,4-diketopyrrolo[3,4-c]pyrrole (DPP), N-ethylhexylthieno[3,4-c]pyrrole-4,6-dione (TPD-EH), and N-octylthieno[3,4-c]pyrrole-4,6-dione (TPD-C8) by Stille coupling to afford four alternating conjugated copolymers, PBDPTBT, PBDPTDPP, PBDPTTPD-EH, PBDPTTPD-C8, respectively. These four conjugated copolymers exhibited good thermal stability with decomposition temperature (Td) ranging from 395 oC to 430 oC. The optical, electrochemical, and optoelectronic properties of the polymers varied significantly with respect to the electron-withdrawing ability of the acceptors. The optical band gap of these conjugated copolymers was estimated to be 1.25 eV, 1.52 eV, 1.77 eV, 1.79 eV for PBDPTDPP, PBDPTBT, PBDPTTPD-EH, PBDPTTPD-C8, respectively. This result indicates that the electron-withdrawing ability is in the order: DPP >BT >TPD. The LUMO energy levels of all the conjugated copolymer are higher than that of PC71BM, which assures that excitons can be efficiently dissociated at the interface between conjugated copolymers and PC71BM Bulk heterojunction (BHJ) solar cell devices were fabricated to evaluate these polymers with the configuration of ITO/PEDOT:PSS/Copolymer:PC71BM/Ca/Al. The device based on PBDPTTPD-EH:PC71BM (1:3, in wt%) exhibited a highest PCE of 3.72% with a Voc of 0.75 V, a Jsc of 9.69 mA/cm2, and a fill factor of 51.2%.