Strong interface p-doping and band bending in C60 on MoOx

The electronic energy level evolution of fullerene (C60) on molybdenum oxide (MoOx)/conducting indium tin oxide (ITO) interfaces has been investigated with ultra-violet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES) and atomic force microscopy (AFM). It was found that the thermally evaporated MoOx inter-layer substantially increased the surface workfunction. This increased surface workfunction strongly attract electrons towards the MoOx layer at the C60/MoOx interface, resulting in strong inversion of C60. Energy levels of C60 relax gradually as the thickness of C60 increases. An exceptionally long (>400 Å) band bending is observed during this relaxation in C60. Such a long band bending has not been reported so far, for the organic/insulator (MoOx) interface. The effect of air exposed MoOx inter-layer between ITO and C60 has also been investigated. After air exposure of MoOx almost no band bending was observed and the electronic energy levels of C60 remained more or less flat.

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► Exotic properties of C60, a crucial material for OPV and OTFT.
► Very strong p-doping of C60.
► Large band bending of over 400 Å is observed in C60.
► Helpful in the device fabrication of strongly n-type behaving semiconductor.
► MoOx exposure to air affect the electronic energy levels and the device performance.