Acceptor-acceptor-type conjugated polymer for use in n-type organic thin-film transistors and thermoelectric devices

摘要

The development of n-type conjugated polymers (CPs) forming an acceptor-acceptor (A-A)-type structure are quite challenging due to the synthetic limitation of imposing a functional group on the electron deficient aromatic structure. The diketopyrrolopyrroles (DPP) structure exhibits n-type characteristics; however, the extended it-structure enables stannylation at the terminal position. The stannylated DPP is beneficial for making n-type CPs, but its use in the development of n-type CPs and their application in n-type organic thin-film transistors and organic thermoelectric devices have been not extensively studied. In the present study, we synthesized the A-A-type conjugated polymer, poly [((2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo [3,4-c]pyrrole-l,4-dione)-5,5'-diyl)-alt-((2,7-bis(2-ethylhexyl)benzo [lmn] [3,8]phenanthroline-l,3,6,8(2H,7H)-tetraone)-4,9-diy1))] (PDPP-NDI), by Stille coupling of distannylated DPP and dibrominated naphthalene diimide (NDI). The alternating copolymerizadon of DPP and NDI moieties led to a low-lying LUMO energy level of -4.4 eV, suitable for electron transport. The n-type organic thin-film transistors were fabricated with PDPP-NDI, and a substantial average electron mobility of 3.78 × 10~(-2) cm~2 V~(-1) s~(-1) was obtained after thermal annealing. The n-type organic thermoelectric devices were developed via n-doping, and PDPP-NDI exhibited n-type thermoelectric properties, with an average power factor of 1.82 × 10~(-3) μW m~(-1) K~(-2).