Revised hole injection mechanism of a thin LiF layer introduced between pentacene and an indium tin oxide anode

초록

Hole injection enhancement has been reported for organic thin-film transistors and light-emitting diodes at the indium tin oxide (ITO) anode side by introducing a LiF layer, which is usually used as an electron injection layer at the cathode side to reduce the electron injection barrier. We report a revised mechanism for the hole injection enhancement by studying a prototype interface of pentacene/LiF/ITO anode. Upon deposition of LiF on ITO, the work function of ITO decreases, and energy level realignment occurs between the pentacene and ITO. The hole injection barrier from the ITO to the pentacene highest occupied molecular orbital increases significantly with LiF insertion. Thus, the reduction in the hole injection barrier is not a critical factor for the hole injection enhancement. We suggest that a LiF insulating buffer layer enhances both injection barriers and tunneling through the barrier when a bias is applied. (C) 2010 American Institute of Physics. [doi:10.1063/1.3481092]

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