Pentacene Orientation on Source/Drain Electrodes and Its Effect on Charge Carrier Transport at Pentacene/Electrode Interface, Investigated Using In Situ Ultraviolet Photoemission Spectroscopy and Device Characteristics

Abstract

The valence band structures and ionization energies of pentacene layers grown on poly (3,4-ethylenedioxythiophene) polymerized with poly (4-styrenesulfonate) (PEDOT:PSS) and Au electrodes were characterized using in situ ultraviolet photoemission spectroscopy. The pentacene layers grown on Au films consist of amorphous phase and round oval grains regardless of the pentacene deposition temperature, whereas the pentacene deposited on PEDOT:PSS films showed highly distinctive ordered structures depending on the deposition conditions. The pentacene layer (thickness: 30 nm) grown on PEDOT:PSS at room temperature (RT) showed a highly crystalline thin film phase (001) and typical terrace-like structure, but that grown on PEDOT:PSS at 100°C consists of a weakly oriented thin film/bulk mixed phase with a disordered grain structure. However, irrespective of the molecular ordering structure, the pentacene layers grown on PEDOT:PSS films showed nearly the same hole-injection barriers (0.40 ∼ 0.45 eV) at both interface (10 nm) and bulk regions (30 nm). On the basis of the correlation between the molecular ordering and device characteristics, we conclude that the carrier transport at pentacene/electrode interface relies more on the hole-injection barrier than on the ordering of the pentacene layer grown on the electrode.

Temperature-dependent orientation study of the initial growth of pentacene on amorphous SiO 2 by molecular dynamics simulations

“…The other theoretical confirmations of our results can be found in the recently literature: Yun and co-workers investigated the molecular structure of pentacene grown on PEDOT:PSS using in situ ultraviolet photoemission spectroscopy (UPS) [29]. The results indicated that the pentacene layer grown at room temperature shows a highly crystalline thin film phase with typical terrace-like structure, but that grown at 373K consists of a weakly oriented thin film/bulk mixed phase with a disordered structure.…”

Solution-processed n-type fullerene field-effect transistors prepared using CVD-grown graphene electrodes: improving performance with thermal annealing

“…The changes in the vacuum level shift and F E.B with T A were attributed to the crystalline morphologies of the C 60 films deposited on graphene and annealed at different T A values. 46 These results demonstrated that carrier injection could be facilitated in OFETs by reducing the electron injection barrier from graphene to C 60 after thermal annealing at high T A .…”

In-Depth Investigation of the Correlation between Organic Semiconductor Orientation and Energy-Level Alignment Using In Situ Photoelectron Spectroscopy

“…However, the magnitude of the DPs in the PEN/PE structure was higher than those in the other structures because of the standing orientation of the PEN molecules on the PE electrode. 14,24 As a result, the PEN layer grown on the PE electrode over a deposition time of 18 min had an IP value of 4.79 eV, which was lower than those of the PEN layers formed on the Au (5.09 eV) and MWPE (5.06 eV) electrodes. Similar to the PEN layer, the layers of DBTTT and DNTT, which also have shape anisotropy, exhibited orientationdependent IP changes.…”

“…The density of states (DOS) close to and far from the Fermi energy (E F ) were attributed to the π and σ bands, respectively. 14,25,26 As shown in SI Figure S6(a) and (b), the UPS spectra of the PEN films grown on the PE, Au, and MWPE electrodes differed in terms of the sec. cutoff positions, indicating different electronic configurations.…”

“…The hole-injection barrier (E h ) is determined by the difference between the HOMO level of the OSC layer (E HOMO ) and the electrode work function (Φ electrode ), that is, E h = E HOMO(organic) − Φ electrode . 14,18 In some cases where the OSC layer is too thin, when the valence band structures of OSC and Au electrode appear together, the E h values were determined after subtracting and the valence band of the OSC appear together because the thickness of the OSC is thin, the EB value is determined by considering the valence band structure of Au itself.…”