Transparent-cathode for top-emission organic light-emitting diodes

Abstract

A transparent-charge-injection layer consisting of LiF/Al/Al-doped SiO has been developed as (i) a cathode for top-emitting organic light-emitting diodes and as (ii) a buffer layer against damages induced by energetic ions generated during deposition of other functional thin films by sputtering, or plasma-enhanced chemical vapor deposition. A luminance of 1900 cd/m2 and a current efficiency of 4 cd/A have been achieved in a simple testing device structure of indium tin oxide (ITO) N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (60 nm)/Alq3 (40 nm)/LiF (0.5 nm)/Al (3 nm)/Al-doped SiO (30 nm). A minimum thickness of 30 nm of Al-doped SiO is also found to protect organic layers from ITO sputtering damage.

Ca/Ag bilayer cathode for transparent white organic light-emitting devices

“…A LiF/Al/Ag semitransparent cathode, entirely deposited using a thermal evaporation, was proposed by Hung et al [7]. Subsequently, several thin semitransparent cathodes of LiF/Al/Al:SiO [8], LiF/Al/Ag [9,10], LiF/Mg:Ag [11], Sm/ Au [12], Yb:Ag, and Yb:Au and Yb/Au [13], Ca or Mg metal, capped with either Al or Ag [14,15] have been studied. Recently, we had demonstrated a low sheet resistance (12 V/sq) and high transparent (over 70% in the visible region) Ca (10 nm)/Ag (10 nm) bilayer semitransparent cathodes [16,17].…”

Carbon nanotube sheets as electrodes in organic light-emitting diodes

“…Finally, the fabrication of top emitting devices using ITO anodes is limited as the ITO deposition process often damages the underlying organic semiconducting layers. 7 Thin and flexible carbon nanotubes sheets exhibiting excellent optical transparencies ͑40%-90%͒ and electrical conductivities ͑ϳ1 ϫ 10 4 S cm −1 ͒ have recently been fabricated using a room temperature deposition technique. 8 Their intrinsic work function ͑4.5-5.1 eV͒ 9,10 is similar to that of ITO ͑4.4-4.9 eV͒ 11 and can be tailored through both n-type and p-type charge transfer doping, 12 allowing, in principle, double-sided charge injection in transparent OLEDs.…”

Recent Developments in Top‐Emitting Organic Light‐Emitting Diodes

“…temperatures required. As a result, more people would like to utilize metals (e.g., Al and/or Ag; [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Ca; [ 49 , 50 ] Ca/Mg; [50][51][52] Ca/Ag; [ 11 , 53-59 ] Mg:Ag; [ 60 , 61 ] Sm [ 62 ] , Sm/Ag, or Sm/Au; [63][64][65][66][67] Yb/Au or Ag; [68][69][70] Au; [ 49 ] and Al/SiO:Al [ 71 ] ) as the TEOLED cathode, even though the T of even thin metal layers is much lower than that of TCO. Furthermore, the effects from the microcavities that exist in TEOLEDs infl uence certain emission characteristics, such as the emissive wavelength, the electroluminescent (EL) spectra, and the viewing angle.…”

“…The emissive material Alq 3 covered wide EL spectra with the peak wavelength of 528 nm. Han [ 71 ] and Cao [ 46 ] reported an Alq 3 -based adjustable color emission from bluish green to red (500 to 680 nm) by merely changing the ITO fi lm thickness between the two refl ective layers. Using the same method, Hsu [ 11 ] and Cao [ 46 ] also accurately calculated the cavity lengths corresponding to FWHM is much stronger than that of the effective cavity,…”