Novel high band gap pendant-borylated carbazole polymers with deep HOMO levels through direct ⁺N=B^- interaction for organic photovoltaics

In this communication, we investigate the direct and still conjugated intramolecular ⁺N=B^- interactions in novel high band gap borylated carbazole containing polymers, namely, poly(3,6-(N-di(2,4,6-trimethyl)-phenylboryl-carbazole)-alt- 4,8-di(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b: 4,5-b'] dithiophene) (P(3,6-BCBDT)) and poly(3,6-(N-di(2,4,6-trimethyl)phenylboryl-carbazole)-alt-3,3 '''- didodecyl-2,2': 5',2 '': 5 '',2 '''-quaterthiophene) (P(3,6-BCQT)), which result in ambipolarity, high electron affinity, and deep HOMO levels. The quasi-donor-acceptor nature of the two polymers was confirmed by UV-Vis absorption, electro-chemical property studies, and computer modelling. Band gaps of 2.07 eV for P(3,6-BCBDT) and 2.23 eV for P(3,6-BCQT) were obtained. P(3,6-BCQT) afforded a power conversion efficiency of 1.44%, with a J_sc of 4.82 mA cm^-2, a V_oc of 0.79 V and a FF of 37%, and P(3,6-BCBDT) performed better with an efficiency of 3.82%, with a J_sc of 8.31 mA cm^-2, a V-oc of 1.0 V based on its low lying HOMO level, and a FF of 45%.