Tuning molecular energy levels and band gap of two-dimensional benzo[1,2-b:4,5-b '] dithiophene and quinoxaline bearing polymers

Yasa, Mustafa
Goker, Seza
Udum, Yasemin
Toppare, Levent Kamil
Two novel donor-acceptor (D-A)-type two-dimensional (2-D) polymers of PBDTSeQ (P1) and PBDTFQ (P2) were synthesized and characterized where 4,8-bis[5-(2-ethylhexyl) thiophen-2-yl] benzo[1,2-b:4,5-b'] dithiophene (BDT) was used as the donor unit. 2,3-Bis(3,4-bis(octyloxy)phenyI)-5,8-dibromoquinoxaline was used as the acceptor moiety and selenophene and furan were utilized as n bridges. Optoelectronic properties of the polymers were examined by electrochemical and spectroelectrochemical characterizations. In cyclic voltammetry (CV) studies, both polymers were found to be ambipolar. In anodic region, oxidation potentials were observed as 1.45 V and 1.15 V for P1 and P2 respectively, while reduction potentials were 0.65 V and 0.92 V. In cathodic region, redox potentials were found to be -1.36 V/-1.32 V and -2.0 V/-1.51 V for P1 and -1.45 V/-1.05 V and -2.15 V/-1.45 V for P2. Both polymers showed good solubility in common solvents. The synthesized polymers were used as photoactive layers in solar cell devices. P1-based device (ITO/PEDOT:PSS/P1:PC71BM (1:3, w/w)/LiF/Al) provided the best performance with a PCE of 4.04%, a V-OC of 0.67 V, a Jsc of 13.94 mA/cm(2), and a FF of 43.3%.