Efficient electron transport in 4,4′-bis[N-(1-napthyl)-N-phenyl- amino] biphenyl and the applications in white organic light emitting devices

The electron transport capability of 4,4′-bis[N-(1-napthyl)-N-phenyl- amino] biphenyl (α-NPD) was investigated by fundamental physical measurements named as current-voltage (I-V) electrical property evaluation and displacement current measurement (DCM). In electron-dominated devices, the I-V characteristics of α-NPD were similar as that of (8-hydroxyquinolino) aluminum (Alq₃) owing to their same order of electron mobilities. The interface of Al/LiF and α-NPD was proven to be an Ohmic contact through the evaluation of I-V characteristics at low bias regime (<3 V). And an electron injection barrier, 0.21 eV, at Al/LiF/α-NPD was obtained by extrapolating the temperature dependent I-V curves. The electron transport behavior in α-NPD film was further confirmed by DCM evaluations. Furthermore, an efficient white organic light emission device was successfully fabricated by using α-NPD as hole transport layer and electron transport layer, respectively.