We report the reduction of contact resistivity between Au and pentacene by O2 plasma treatment. Contact resistance dramatically reduced from 5.65to0.22MΩcm by the treatment. O2 plasma treatment transformed Au to AuOx, increasing the surface energy from 45.1to71.5mJ∕m2. Molecular adsorption geometry of pentacene on AuOx changed from a planar structure to an upright type, improving crystallinity and molecular packing. Thus, defects and traps at the interface were reduced, decreasing the contact resistance between Au and pentacene.
We report the enhancement of the electron injection by inserting a 1-nm-thick magnesium oxide (MgO) buffer layer between Al cathode and tris (8-hydroxyquinoline) aluminum in an inverted top-emitting organic light-emitting diode (OLED). The turn-on voltage of OLEDs decreased from 10 to 6 V and the luminance increased about 61% as the MgO interfacial layer was employed. The MgO interfacial layer played a role in reducing the energy barrier of electron injection, leading to the reduction of the turn-on voltage and the enhancement of luminance.
The effect of oxygen plasma treatment on enhancement of hole mobility was demonstrated using pentacene organic thin-film transistors (OTFTs) with bottom-contact Au electrodes. Linear field-effect mobility increased from 3.2×10−2to7.4×10−2cm2∕Vs as the Au electrodes were treated with O2 plasma. Secondary electron emission spectra revealed that the work function of oxygen plasma-treated Au is 0.5eV higher than that of untreated Au. This led to a reduced hole injection barrier at the interface of Au with pentacene, increasing the field-effect mobility of OTFTs.
Pentacene was in situ deposited on both bare-Au and O 2 plasma-treated Au ͑O 2 -Au͒. The band structure at the interface of Au with pentacene was quantitatively determined using ultraviolet photoelectron spectroscopy. The work function of Au increased from 4.65 to 5.28 eV as the Au surface was treated with O 2 plasma. The corresponding interface dipoles were −0.30 eV for bare Au and −0.71 eV for O 2 -Au, respectively. Thus the hole injection barrier at the interface reduced from 0.45 to 0.15 eV by the O 2 plasma before the deposition of pentacene, leading to an increase of the linear field-effect mobility of thin-film transistors.A high work function metal is essential to obtain good ohmic contact with p-type organic semiconductor pentacene ͑PEN͒ through the small hole injection barrier at the interface of metal contact with PEN. Gold ͑Au͒ is a typical material used as a source ͑S͒ and drain ͑D͒ electrode for pentacene-based organic thin-film transistors ͑OTFTs͒ due to its chemical inertness and high work function. 1,2 However, when PEN is deposited on Au, the vacuum level shifts downward at the interface, making a barrier for holes with the barrier heights ͑⌽ BH ͒ of 0.85 eV at the Au/PEN interface. 3 It was reported that the contact resistance between Au and PEN could be reduced by O 2 plasma treatment on Au electrode prior to PEN deposition. 4 The surface of Au was transformed into AuO x ͑Au-O bond formation͒ when the Au surface was exposed to O 2 plasma. Enhanced crystallinity of PEN deposited on O 2 plasmatreated Au was observed. In addition, the oxygen chemisorption at the surface of Au increases the work function via electron transfer from gold to chemisorbed oxygen. 5 Thus it was considered that O 2 plasma treatment may reduce the ⌽ BH at the Au/PEN interface. However, the effect of O 2 plasma on the interface barrier height between Au and PEN has not been reported yet. Because the metal/ organic contact properties is a determining factor of device performances in bottom-contact ͑BC͒ OTFTs, it is important to understand the band structure between O 2 plasma-treated Au and PEN.In this paper, we report the effect of O 2 plasma treatment on hole injection barrier at the interface of PEN with Au film. The band structure at the interface was investigated using synchrotron radiation photoemission spectroscopy ͑SRPES͒ and ultraviolet photoelectron spectroscopy ͑UPS͒ with in situ deposition of PEN on both the untreated Au ͑bare Au͒ and the treated one ͑O 2 -Au͒. From these, the effect of O 2 plasma treatment on the reduction of hole injection barrier in BC OTFT is discussed.High conducting ͑ϳ5 ⍀ cm͒ n-type Si with thermally grown SiO 2 ͑300 nm thick͒ was used as the starting substrates, which functioned as the gate electrode and the gate insulator, respectively. Cr/Au ͑3/50 nm͒ films were used as S-D electrodes of OTFTs. Details of device fabrication process can be found elsewhere. 6 Electrical properties were measured using an HP-4156A semiconductor parameter analyzer in an air ambient at room temperature with r...
We report how treatment of nickel (Ni) with O(2) plasma affects the polarity of Ni surface, crystallinity of pentacene film on the Ni, and electrical properties of pentacene organic thin-film transistors (OTFTs) that use Ni as source-drain electrodes. The polar component of surface energy in Ni surface increased from 8.1 to 43.3 mJ/m(2) after O(2)-plasma treatment for 10 s. From X-ray photoelectron spectra and secondary electron emission spectra, we found that NiO(x) was formed on the O(2)-plasma-treated Ni surface and the work function of O(2)-plasma-treated Ni was 0.85 eV higher than that of untreated Ni. X-ray diffraction and atomic force microscopy measurements showed that pentacene molecules are well aligned as a thin-film and grains grow much larger on O(2)-plasma-treated Ni than on untreated Ni. This change in the growth mode is attributed to the reduction of interaction energy between pentacene and Ni due to formation of oxide at the Ni/pentacene interface. Thus, O(2)-plasma treatment promoted the growth of well-ordered pentacene film and lowered both the hole injection barrier and the contact resistance between Ni and pentacene by forming NiO(x), enhancing the electrical property of bottom-contact OTFTs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.