Energy level diagrams of optimized ambipolar organic thin film transistors used pentacene and C60

摘要

The interface electronic structure of pentacene and C60 layer was investigated in detail by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitudes of measured interface dipole were 0.11 eV and 0.07 eV for the C60 deposited on pentacene (C60/pentacene) and the pentacene deposited on C60(pentacene/C60), respectively. The obtained C 1s spectra on pentacene/C60 and C60/pentacene indicate no significant chemical bonds existing at the interface. The offsets of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) at the C60-pentacene interface were 1.29 eV and 0.89 eV for C60/pentacene/Au while it were 1.5 eV and 1.1 eV for pentacene/C60/Au. This resulted in that the HOMO and LUMO offset depend on the deposition order of the organic layers. We fabricated the ambipolar OTFTs used the favorable structure of pentacene and C60, and obtained the field effect mobilities were 0.017 cm2/Vs and 0.007 cm2/Vs for p-channel and n-channel operations.