Peter Juhasz

Charge injection and transport properties of an organic light-emitting diode

Summary The charge behavior of organic light emitting diode (OLED) is investigated by steady-state current–voltage technique and impedance spectroscopy at various temperatures to obtain activation energies of charge injection and transport processes. Good agreement of activation energies obtained by steady-state and frequency-domain was used to analyze their contributions to the charge injection and transport. We concluded that charge is injected into the OLED device mostly through the interfacial states at low voltage region, whereas the thermionic injection dominates in the high voltage region. This comparison of experimental techniques demonstrates their capabilities of identification of major bottleneck of charge injection and transport.

New phenanthrene-based organic semiconductor material for electronic devices

This work describes the thin-film fabrication technology and characterization of devices based on organic semiconductor 3,6-bis(5`-hexyl-2,2`-bithiophen-5-yl)phenanthrene (H2T36Phen). The surface morphology, optical, and electrical properties are investigated for thin organic films. It demonstrates that the solution-based depositions require different substrate surface treatment than the evaporation-based deposition.

Technology of conductive polymer PEDOT:PSS films

The structural, optical, and electrical properties of copolymer poly(3, 4-ethylenedioxythiophene):(styrenesulfonic acid) (PEDOT:PSS) thin films deposited from aqueous solution have been investigated. To increase the conductivity three different dopants have been used: dimethyl sulfoxide (DMSO), sorbitol, and ethylene glycol. Even though the dopants increase the conductivity by three orders, the surface morphology and optical properties do not change significantly. The discussion on secondary doping effect is carried out to explain the observations.

Determination of defect states in P3HT material for solar cell application

The defect states are investigated in ITO/P3HT/In organic diode structure by steady-state current-voltage technique and deep-level transient spectroscopy (DLTS) method. The temperature dependencies are used to evaluate charge transport activation energies. The activation energy of about 0.15 eV estimated from the current-voltage measurement as well as from the DLTS technique represents the dominant defect state in P3HT.

Ferroelectric polymer films for flexible memory devices

Here we demonstrate application of organic ferroelectric insulating material: copolymer vinylidene fluoride and trifluoroethylene P(VDF-TrFE) for organic memory devices. The metal-insulator-metal structures have been used to study the ferroelectric properties and represent the model applications for ferroelectric field-effect transistors (FeFETs) and ferroelectric random access memories (FRAM). The current-voltage and capacitance-voltage characteristics depicted ferroelectric switching phenomenon present in thin-film structures and polarization properties have been analysed. This work describes the MIM device fabrication technology as well as the evaluation of material properties: saturated polarization, maximum electric field intensity, critical electric field, and relative dielectric constant.