Abstract:The authors report the enhancement of hole injection using an RhOx layer between indium tin oxide anodes and 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The operation voltage of OLEDs at 700cd∕m2 decreased from 13 to 10 V as the Rh layer changed to RhOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.2 eV as the Rh layer transformed into RhOx. Thus, the hole injection energy … Show more
“…To achieve a high quantum yield with a long device lifetime, it is crucial that charge injection and transport be balanced and that the recombination zone be spread out in space. Four strategies have been reported in the literature: (i) using a low-work-function metal as the cathode, such as Ca or Ba capped with Al or Ag; − (ii) adding an injection, a buffer, and/or a charge-transport layer; − (iii) physically blending an emissive material with a charge-transporting material; − and (iv) chemically modifying an emissive material with charge-transporting moieties. − Of the four strategies, chemical modification appears to be the most versatile and, hence, has been the most intensively pursued. Low-molar-mass evaporable materials have been constructed by bonding electron- or hole-conducting moieties to light-emitting conjugated molecules through π-conjugation, inevitably affecting individual functionalities.…”
Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron-or hole-conducting core were designed for tunable charge injection and transport properties. Representative glassy-isotropic and glassy-liquid-crystalline (i.e., noncrystalline solid) materials were synthesized and characterized; they were found to exhibit a glass transition temperature and a clearing point close to 140 and 250°C, respectively; an orientational order parameter of 0.75; a photoluminescence quantum yield up to 51%; and HOMO and LUMO energy levels intermediate between those of blue-emitting oligofluorenes and the ITO and Mg/Ag electrodes commonly used in organic light-emitting diodes, OLEDs. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.
“…To achieve a high quantum yield with a long device lifetime, it is crucial that charge injection and transport be balanced and that the recombination zone be spread out in space. Four strategies have been reported in the literature: (i) using a low-work-function metal as the cathode, such as Ca or Ba capped with Al or Ag; − (ii) adding an injection, a buffer, and/or a charge-transport layer; − (iii) physically blending an emissive material with a charge-transporting material; − and (iv) chemically modifying an emissive material with charge-transporting moieties. − Of the four strategies, chemical modification appears to be the most versatile and, hence, has been the most intensively pursued. Low-molar-mass evaporable materials have been constructed by bonding electron- or hole-conducting moieties to light-emitting conjugated molecules through π-conjugation, inevitably affecting individual functionalities.…”
Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron-or hole-conducting core were designed for tunable charge injection and transport properties. Representative glassy-isotropic and glassy-liquid-crystalline (i.e., noncrystalline solid) materials were synthesized and characterized; they were found to exhibit a glass transition temperature and a clearing point close to 140 and 250°C, respectively; an orientational order parameter of 0.75; a photoluminescence quantum yield up to 51%; and HOMO and LUMO energy levels intermediate between those of blue-emitting oligofluorenes and the ITO and Mg/Ag electrodes commonly used in organic light-emitting diodes, OLEDs. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.
“…This shift therefore would be due to the intrinsically higher work function of SnO x as compared to ITO (~0.1–0.2 eV) 21 . The density of dipoles is increased at the surface by isolated SnO x NPs and their interactions decrease the effect of the surface dipole moment 12,15,45,46 .Figure 2( a ) Schematic band diagram of PHOLED devices showing the hole injection lowering effect of the SnO x NPs. ( b ) Current-density voltage (J–V) curves for hole only devices based on TAPC with and without SnO x NPs (device A and B).…”
Blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated with tin oxide (SnOx) nano-particles (NPs) deposited at the ITO anode to improve their electrical and optical performances. SnOx NPs helped ITO to increase the work function enhancing hole injection capability. Charge balance of the device was achieved using p- and n-type mixed host materials in emissive layer and the devices’ luminance and maximum external quantum efficiency (EQE) increased about nearly 30%. Tuning the work function using solution processed NPs allows rapid optimization of device efficiency.
“…The lower limit of the temperature range was determined by the GC detector sensitivity. There are many possible reasons for the change in yield, including current saturation, oxidation-state-dependent changes in the Rh thin film, adsorbate-induced changes at the metal interface, interfacial effects at the metal−semiconductor interface (especially in GaN), and, particularly in the case of the TiO x -based devices, barrier height change or other effects due to the oxidation and reduction of the supporting semiconductor . Despite this, it is notable that the reaction rate and chemicurrent remain proportional at low temperatures for both the TiO x and the GaN-based catalytic nanodiodes in both CO oxidation and the NO/CO reaction.…”
Ultra-thin-film 5 nm Rh/TiO x and Rh/GaN catalytic metal-semiconductor Schottky nanodiodes were fabricated using dc magnetron reactive sputtering, rapid thermal annealing, and electron beam evaporation. The diode barrier heights were characterized in different gas mixtures using current-voltage measurements. Barrier heights were found to vary with the local gas composition for Rh/TiO x nanodiodes but did not vary with gas composition for Rh/GaN nanodiodes. The nanodiodes were also studied during the oxidation of CO by O 2 and during the oxidation of CO by NO using chemicurrent measurements and gas chromatography. The hot electron chemicurrent was determined from the current in situ during reaction and the thermoelectric current measured in oxidizing conditions. Similar activation energies were measured from both the chemicurrent and gas chromatography, which indicates a correlation between hot electron chemicurrent and catalytic activity.
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