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Dielectric Screening To Reduce Charge Transfer State Binding Energy in Organic Bulk Heterojunction Photovoltaics
journal contribution
posted on 2017-01-24, 00:00 authored by Sibel Leblebici, Jiye Lee, Alexander Weber-Bargioni, Biwu MaReaching high efficiencies
in organic photovoltaics is often limited
by dissociating charge transfer states at electron donor–acceptor
interfaces due to their large binding energies and rapid geminate
recombination. By adding a high-permittivity small molecule, camphoric
anhydride, at 20 wt % to a polymer–fullerene bulk heterojunction
photovoltaic device, we increased the film permittivity, reduced the
charge transfer state energy, and increased the power conversion efficiency
by 75%. At higher concentrations, the camphoric anhydride begins to
crystallize and phase separate from the bulk heterojunction, causing
the permittivity and power conversion efficiency to decrease. Adding
camphoric anhydride in low concentrations is an effective strategy
to increase permittivity and reduce recombination at the donor–acceptor
interface and as a result increase organic photovoltaic efficiency
in bulk heterojunction devices.