title: Direct observation of photoinduced bound charge-pair states at an organic-inorganic semiconductor interface.
abstract: It is generally considered that photoinduced charge transfer at the organic-inorganic interfaces in hybrid photovoltaic devices immediately results in a pair of free charge carriers. We extend a novel interface-selective ultrafast "optical pump-push photocurrent probe" technique to study hybrid photovoltaic systems and observe bound electron-hole pair states at the organic-inorganic interface formed between electron-accepting zinc oxide and electron-donating conjugated polymers. We estimate that ∼50% of photogenerated charges stay bound and later recombine, thus hindering the photovoltaic performance of polymer/ZnO cells. We further demonstrate that interface modification with a fullerene derivative decreases the fraction of bound charges to ∼25%, which substantially improves the device efficiency.
authors.affiliation: Cavendish laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Yana
authors.initials: Y
authors.lastname: Vaynzof
authors.forename: Artem A
authors.initials: AA
authors.lastname: Bakulin
authors.forename: Simon
authors.initials: S
authors.lastname: Gélinas
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend