Observation of space-charge-limited current due to charge generation at interface of molybdenum dioxide and organic layer

Current density-voltage characteristics of hole-only devices are influenced by thicknesses of molybdenum dioxide (MoO2) and molybdenum trioxide (MoO3) as buffer layers. A space-charge-limited current of N,N-'-diphenyl-N,N-'-bis(1-naphthyl)-1,1(')-biphenyl-4,4(')-diamine (alpha-NPD) is observed in a wide range of MoO2 thicknesses from 0.25 to 10 nm and at a specific MoO3 thickness of 0.75 nm. Charge transfer characteristics at interfaces of MoO2/alpha-NPD and MoO3/alpha-NPD are investigated from changes in fluorescence intensity of alpha-NPD. Reasons of the improved device characteristics are discussed in terms of interfacial charge generation composed of charged transfer and charge separation.