1 research outputs found
Thioalkyl-Substituted Benzothiadiazole Acceptors: Copolymerization with Carbazole Affords Polymers with Large Stokes Shifts and High Solar Cell Voltages
Copolymers of carbazole and 4,7-bisÂ(2-thienyl)-2,1,3-benzothiadiazole
(dTBT) incorporating thioalkyl (−SR) and alkoxy (−OR)
solubilizing groups on the 2,1,3-benzothiazdiazole (BT) unit are synthesized
and compared. The introduction of −SR and −OR groups
onto the BT unit of the polymer was found to have different effects
on the electronic properties of the polymers as well as the conformation
of the polymer backbone. Large conformational changes between the
ground state (GS) and excited state (ES) geometries of the polymers
with −SR groups led to very large Stokes shifts of up to 224
nm. The polymer with −OR groups was found to have approximately
double the photovoltaic efficiency at ∼4% compared to the polymers
with −SR groups (PCE ∼ 2%). However, polymers with −SR
groups were found to give very high open circuit voltages (<i>V</i><sub>OC</sub>) of over 1 V. Changing the −SR chain
length from ethyl to dodecyl was found to have little influence on
the solar cell performance of the polymer or the magnitude of the
Stokes shift