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Keywords:

  • organic photovoltaic devices;
  • NIR absorption;
  • charge-transfer complexes;
  • organic heterojunctions

Abstract

Exploitation of energy from the near-infrared (NIR) region is one strategic approach for enhancing the performance of organic photovoltaic devices (OPVs). While effort has been mostly put toward developing materials with narrow energy gaps, here, a simple approach for harvesting NIR photons with wide-energy-gap materials by making use of their interactive charge-transfer complex (CTC) is shown. It is shown using photoemission studies that the interface between molybdenum (VI) oxide and 5,6,11,12-tetraphenylnaphthacene (MoO3/rubrene) possesses an abrupt discontinuity in the vacuum level (VL), resulting in significantly overlapped electron wavefunctions and CTC formation. The CTC induces an intermediate state within the original energy gap of rubrene with energy of ≈1.3 eV, suggesting the feasibility of a charge transfer (CT) exciton generated upon NIR excitation. This is confirmed by generation of electric power OPVs with an active layer of MoO3:rubrene composite under excitation with a NIR light source.