以氮原子為共價橋樑形成施體受體互為熔合之平面分子 : 合成、鑑定及其共軛高分子於太陽能電池之應用

Abstract

本研究的設計：利用共價鍵的連結方法將施體與受體相互熔合，形成新穎D-A平面結構。在此平面結構內，受體與施體間的光致分子內電荷轉移 (ICT) 將會增加。據我們所知，目前施體與受體互為熔合的共軛高分子於太陽能電池的應用尚未有過。 以dithienobenzothiadiazole (DTBT)或dithienoquinoxaline (DTQX)作為設計構想，設計出兩個施體-受體相互熔合的單體。BT和QX利用氮原子作為共價橋梁連接兩側噻吩的3號位置，形成兩個吡咯，命名為dithienopyrrolebenzothiadiazole (簡稱為TPBTPT) 和dithienopyrrolequinoxaline (簡稱為TPQXPT) 。 將TPBTPT與TPQXPT分別與芴、咔唑和CPDT進行Suzuki coupling與Stille coupling聚合反應，形成六個交錯型 (alternating) 共軛高分子：PFTPBTPT、PCTPBTPT、PCPDTTPBTPT、PFTPQXPT、PCTPQXPT和PCPDTTPQXPT。 本實驗材料之元件採用混摻異質接面結構製作：ITO/PEDOT:PSS/Copolymer:PC71BM/Ca/Al，因為芴和咔唑系列之共軛高分子的HOMO能階較低，故此類材料元件表現較佳。PFTPQXPT的PCE為3.4%，為本研究元件表現最之佳材料，其FF為54.64%，Jsc為8.62 mA/cm2，Voc為0.72 V。

In this research, we attempt to design new coplanar D-A interfused structures where electron-rich (donor) and electron-deficient (acceptor) units are covalently locked and conformationally rigidified. Electronic interaction between the donor and the acceptor unit in such a coplanar structure may be enhanced. To our knowledge, utilization of this molecular strategy to design a conjugated polymer for the photovoltaic applications has not been well explored. On the structural basis of DTBT and DTQX unit, we have designed two donor-acceptor fused dithienopyrrolebenzothiadiazole (denoted as TPBTPT) and dithienopyrrolequinoxaline (denoted as TPQXPT) structures in which the 3-positon of two outer thiophenes are covalently tied with the central benzothiadiazole and quinoxaline cores, respectively, by a nitrogen bridge, forming two pyrrole rings embedded in a multi-fused pentacyclic structure. The two monomers were copolymerized with fluorene, carbazole and CPDT units by Suzuki or Stille coupling to afford six alternating conjugated copolymers, PFTPBTPT, PCTPBTPT, PCPDTTPBTPT, PFTPQXPT, PCTPQXPT and PCPDTTPQXPT, respectively. Bulk heterojunction devices based on the configuration of ITO/PEDOT”PSS/copolymer:PC71BM/Ca/Al are fabricated to evaluate these materials. In general, fluorene and carbazole-based copolymers exhibited the better device performance due to their lower-lying HOMO energy levels. The PFTPQXPT-based device showed the best power conversion efficiency of 3.4% with a Jsc of 8.62 mA/cm2, a Voc of 0.72 V and a FF of 0.56.