Direct Measurement of Acceptor Group Localization on Donor-Acceptor Polymers Using Resonant Auger Spectroscopy

Abstract

We use near edge X-ray absorption fine structure (NEXAFS) and resonant Auger spectroscopy combined with density functional theory (DFT) to investigate the electronic structure of the LUMO of two similar donor/acceptor-type polymers, PCPDTBT and PCDTBT, which are of interest for organic photovoltaic applications. We find the resonant Auger results to be independent of film morphology and likely dominated by localized structure rather than extended chain interactions. We show that the degree of excited state localization onto the benzothiadiazole acceptor group in each polymer is similar, suggesting that that the differences in IQE between these two polymers are not explained by the electronic structure of the LUMO.