Synthesis, photophysical and photovoltaic properties of a new class of two-dimensional conjugated polymers containing donor-acceptor chromophores as pendant groups

Abstract

A new design for constructing two-dimensional conjugated copolymers with the D(1)A(D-2) repeating pattern (A: acceptor, D-1: donor 1, D-2: donor 2; molecules enclosed in parentheses are pendant groups.), is proposed. D-1 and A are employed to construct the linear main-conjugated polymer chain and D-2 is situated at the conjugated side chains connected to A. We designed and synthesized a series of D-1-A(D-2)-type copolymers, in which D-1 = diindeno[1,2-b: 2',1'-d]-thiophene (DIDT) or fluorene (F), A(D-2) = bis-[4-(dioctylamino)-phenyl] quinoxaline (DOAQX) or bis-[4-(dioctylamino)-phenyl] thieno[3,4-b]-pyrazine (DOATP), and D-2 = N,N-dioctylanilines. The resultant copolymers, PDIDTDOAQX, PFDOAQX, PDIDTDOATP and PFDOATP, possess at least two strong ICT absorptions, thus resulting in better light harvesting. Their optical and electronic properties were thoroughly investigated experimentally and computationally. Bulk heterojunction photovoltaic cells on the basis of ITO/PEDOT: PSS/polymer: PC71BM/Ca/Al configuration were fabricated and characterized. The photovoltaic performances of the devices incorporating these polymers follow the sequence: PDIDTDOAQX > PFDOAQX > PDIDTDOATP > PFDOATP, which is in good agreement with the magnitude of their hole-mobilities.