Effect of Oxygen‐Containing Functional Side Chains on the Electronic Properties and Photovoltaic Performances in a Thiophene–Thiazolothiazole Copolymer System

Abstract

ABSTRACTWe report the synthesis and characterization of new thiazolothiazole‐based semiconducting polymers with alkoxy and/or ester groups as the side chain. An introduction of the alkoxy groups raised the HOMO energy level of the polymers, whereas the introduction of the ester groups lowered the LUMO energy level. It is found that, interestingly, in the monomers the electronic effect of the ester group was more significant than that of the alkoxy groups, whereas in the polymers the effect of the alkoxy group was more significant. PTzBT‐oBOeHD with both the alkoxy and ester groups gave the most redshifted absorption spectrum compared to the polymers with the alkyl and alkoxy groups (PTzBT‐oBOHD) and with the alkyl and ester groups (PTzBT‐BOeHD). Solar cells using PTzBT‐oBOeHD gave the highest power conversion efficiencies of up to 4.5% with the highest short‐circuit current density (JSC) of 10.9 mA/cm2 among those with the newly synthesized polymers.