The interfacial electronic structures of molybdenum oxide (MoOx) deposited on fullerene (C-60) which could be used as a hole-injecting layer in inverted top-emitting organic light-emitting diodes (TE-OLEDs) were investigated by photoemission spectroscopy. The hole-injecting barrier height (Phi(h)(B)) at each interface investigated by an ultraviolet photoemission spectroscopy was reduced to from 1.4 to 0.1 eV as the thickness of MoOx (Theta(MoOx)) was increased from 0.1 to 5.0 nm on C-60. In these interface system, the sign of vacuum-level shift, highest occupied molecular orbital (HOMO)-level shift, and core-level shifts were all positive indicating that the interface mechanism is attributed to the work-function differences due to a band bending at these interfaces. Moreover, the near-edge X-ray absorption fine structure spectra at carbon K-edge did not show any structural modification as well as any chemical reaction at the MoOx-on-C-60 interfaces when Theta(MoOx) was changed on C-60. From these results, the inverted TE-OLED with C-60 (5.0 nm)/MoOx (5.0 nm) showed the power efficiency of 1.7 lm/W at a luminance of about 1000 cd/m(2) and the maximum luminance of about 76.000 cd/m(2) at the bias voltage of 11.0 V. It exhibited the highest performance among the inverted TE-OLEDs fabricated as a function of MoOx thickness from 0 to 5.0 nm. (C) 2013 Elsevier B.V. All rights reserved.