Efficient photogeneration of free charge carriers has long been recognized as one of the paramount challenges in organic photovoltaic devices. The low dielectric constant organic semiconductors fall short to reduce strong Coulombic interaction of tightly bound exciton and hence lead to a loss mechanism in OPVs due to charge-carrier recombination. To circumvent this problem, we adopt a strategy to enhance the dielectric constant of organic semiconductors by incorporating triethyleneglycol (TEG) side-chains. We report the synthesis of three new semiconducting copolymers by combining thiophene substituted diketopyrrolopyrrole (TDPP) monomer with three other monomeric units with varying electron-donating strength: benzodithiophene (BBT-3TEG-TDPP), TDPP (TDPP-3TEG-TDPP), and naphthalene diimide (P(gNDI-TDPP). 3TEG-BBT and P(gNDI-TDPP) showed the highest dielectric constants (~ 5) at 1MHz frequency suggesting an efficient contribution of dipolar polarization from TEG side-chains. Furthermore, transient absorption spectroscopy studies show low exciton diffusion length as observed in donor-acceptor type conjugated polymers. Our results suggest that utilizing the polar side-chains enhances the dielectric constant in a frequency regime of MHz. However, it is not sufficient to reduce the Coulombic interaction between hole and electron in excitonic solar cells.

Rational design of donor-acceptor based semiconducting copolymers with high dielectric constants

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.