Charge transfer excitons at ZnMgO/P3HT heterojunctions: Relation to photovoltaic performance

Formation of hybrid charge transfer excitons (HCTE), i.e., coulombically bound charge pairs residing at inorganic/organic interfaces is verified in prototypical ZnMgO/poly(3-hexylthiophene) (P3HT) planar heterojunctions. Radiative recombination of HCTE generates electroluminescence (EL) in the near infrared spectral region. Via the Mg content, the energy offset ΔEIO between the ZnMgO conduction band minimum and the P3HT highest occupied molecular orbital is systematically tuned. Both, the EL emission maximum as well as the open circuit voltage VOC, scale linearly with ΔEIO, showing the clear correlation between the HCTE transition energy and the VOC at inorganic/organic semiconductor heterojunctions.