G. Z. Ran

A top-emission organic light-emitting diode with a silicon anode and an Sm/Au cathode

A top-emission organic light-emitting diode (TEOLED) with a p-type silicon anode and a semitransparent samarium/gold cathode has been constructed and studied. With a structure of Al∕p-Si∕SiOx∕N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine(NPB)∕Tris-(8-hydroxyquinoline)aluminum(Alq)∕LiF∕Al, we have found that compared to indium-tin-oxide, the p-Si anode enhances the unbalance between electron- and hole-injection, which is a disadvantage factor for the light-emitting efficiency of the TEOLED. Selecting p-Si wafers with suitable electric resistivities and inserting an ultrathin low temperature grown SiOx layer of about 1.5nm between the anode and NPB can effectively restrict hole-injection. Moreover, a low work function Sm∕Au cathode was used to enhance electron-injection. The electroluminescence efficiency of the TEOLED depends on the thickness of the Sm layer in the cathode. A current efficiency of 0.55cd∕A and a power efficiency of 0.07lm∕W have been reached.

An effect of Si nanoparticles on enhancing Er3+ electroluminescence in Si-rich SiO2:Er films

Er-doped Si-rich SiO2 (SRSO:Er) films have been deposited on n(+)-Si substrates by the magnetron sputtering technique, and both photoluminescence (PL) and electroluminescence (EL) at 1.54 mum have been observed from the films at room temperature. Dependence of pi, and EL intensities on the excess-Si content and annealing temperature has been studied. It is found that proper Si content and annealing temperature can evidently enhance EL intensity. An SRSO:Er film with 20% excess Si (area ratio of the Si target to the whole target) had more intense EL than a SiO2:Er film without excess Si, both annealed at 800 degreesC, by a factor of 5. This fact clearly demonstrates that energy coupling between Si nanometer particles and Er3+ ions also exists in the EL process as well as in the PL process. Experimental results also indicate that crystallization is not a prerequisite for NSPs enhancing luminescence in SRSO:Er films. The PL and EL spectra of the SRSO:Er films have much broader full widths at half maximum (FWHM, similar to 60 nm) than those of the other Er-doped materials reported. This wide FWHM can perhaps be used in wavelength division multiplexing in optical communication in future

Room temperature Er3+ 1.54 µm electroluminescence from Si-rich erbium silicate deposited by magnetron sputtering

Si-rich erbium silicate (SRES) films were deposited on p-type Si substrates by the magnetron sputtering technique and then annealed at 850 and 1000 °C in N2. Rutherford backscattering spectroscopy and Raman spectroscopy indicate that erbium silicates and Si excess, both in the amorphous phase, coexist in the SRES films. Photoluminescence excitation measurement indicates the sensitization effect of Si excess by an energy transfer process in the SRES film. The current–voltage characteristics show apparent improvement of carrier injection and transport in the SRES device (indium tin oxide (ITO)/SRES/p-Si) due to the Si excess in the SRES film. Room temperature Er3+ 1.54 µm electroluminescence from the SRES device (ITO/SRES/p-Si) has been measured and studied by comparison with the erbium silicate device (ITO/erbium silicate/p-Si) and Er-doped Si-rich Si oxide (Er : SRO) device (ITO/Er : SRO/p-Si).

Passivated p-type silicon: Hole injection tunable anode material for organic light emission

We find that hole injection can be enhanced simply by selecting a lower-resistivity p-Si anode to match an electron injection enhancement for organic light emitting diodes with ultrathin-SiO2-layer-passivated p-Si anode (Si-OLED). For a Si-OLED with ordinary AlQ electron transport layer, the optimized resistivity of the p-Si anode is 40Ωcm; for that with n-doped Bphen electron transport layer, it decreases to 5Ωcm. Correspondingly, the maximum power efficiency increases from 0.3to1.9lm∕W, even higher than that of an indium tin oxide control device (1.4lm∕W). This passivated p-type silicon is a hole injection tunable anode material for OLED.

Improving charge-injection balance and cathode transmittance of top-emitting organic light-emitting device with p-type silicon anode

Both charge-injection balance and high transmittance for the cathode are important to achieve high electroluminescence (EL) efficiency for a top-emitting organic light-emitting device (TEOLED) fabricated on silicon substrate. In this letter, by optimizing the electrical resistivity of the p-type silicon chip used as the anode and applying a Yb/Au double layer cathode with high electron-injection property and high transmittance, the TEOLED with a configuration of p-type silicon/thermal grown SiO2/NPB/Alq(3)/Yb/Au exhibits a higher EL efficiency than those of the TEOLEDs each with a Si chip as the anode reported previously. Its current efficiency is almost equal to that of a TEOLED with the same configuration except for an indium tin oxide anode. (c) 2005 American Institute of Physics.

Top-emission Si-based phosphor organic light emitting diode with Au doped ultrathin n-Si film anode and bottom Al mirror

We report a highly efficient top-emission Si-based phosphor organic light emitting diode (PhOLED) with an ultrathin polycrystalline n-Si:Au film anode and a bottom Al mirror. This anode is formed by magnetron sputtering followed by Ni induced crystallization and then Au diffusion. By optimizing the thickness of the n-Si:Au film anode, the Au diffusion temperature, and the other parameters of the PhOLED, the highest current and power efficiencies of the n-Si:Au film anode PhOLED reached 85±9 cd/A and 80±8 lm/W, respectively, corresponding to an external quantum efficiency of 21±2% and a power conversion efficiency of 15±2%, respectively, which are about 60% and 110% higher than those of the indium tin oxide anode counterpart and 70% and 50% higher than those of the bulk n+-Si:Au anode counterpart, respectively.

Role of the dielectric capping layer in enhancement of light outcoupling for semitransparent metal-cathode organic light-emitting devices

We study theoretically the effects of the dielectric capping layer on the light outcoupling efficiency for semitransparent metal-cathode organic light-emitting devices. The outcoupling enhancement is co-determined by the improved transmission, the reduced (or improved) reflection, and the reduced absorption, as well as the suppressed surface plasmon polaritons. For some metals such as aluminium, the outcoupling efficiency can be enhanced largely by capping, but it can hardly be enhanced for some metals such as ytterbium. As a practical cathode, the Ag(15 nm)/TeO2(24 nm) combination achieves an outcoupling efficiency of 21.5%, competitive with bottom-emission devices.

Room-temperature 1.54-μm electroluminescence from Er-doped Si-rich SiO2 films deposited on p-Si by magnetron sputtering

Abstract Er-doped Si-rich SiO 2 (SRSO:Er) films with excess silicon contents of 0, 10, 20 and 30% were deposited on p-Si substrates using the magnetron sputtering technique, and then Au/SRSO:Er/p-Si light-emitting diodes (LEDs) were fabricated after the SRSO:Er/p-Si samples were annealed separately at 600, 700, 800, 900 and 1000 °C. Room temperature 1.54-μm electroluminescence (EL) from the Au/SRSO:Er/p-Si LEDs was observed when the forward bias was above 4 V. It was found that excess silicon with a proper content in a SRSO:Er film annealed at a suitable temperature can evidently enhance EL intensity of the LED made of the film. The optimum annealing temperatures for enhancing EL intensity were 900, 900, 800 and 700 °C for the SRSO:Er films containing 0, 10, 20 and 30% excess silicon, respectively. The 1.54-μm EL intensity of the Au/SRSO:Er/p-Si LED made of a SRSO:Er film with 20% excess silicon being annealed at 800 °C was the most intense.

Combination of passivated Si anode with phosphor doped organic to realize highly efficient Si-based electroluminescence

Silicon light source plays a key role in silicon optoelectronics, but its realization is an extremely challenging task. Although there are longterm intensive efforts to this topic, the power conversion efficiency (PCE) of the silicon-based electroluminescence is still no more than 1%. In this present report, a highly efficient silicon light source has been achieved. The device structure is p-Si (5 Omegacm)/ SiO2(approximately 2 nm)/ NPB / CBP: (ppy)(2)Ir(acac) / Bphen /Bphen: Cs2CO3 / Sm / Au. The SiO2 passivated Si is the anode having a suitably high hole-injection ability, and CBP: (ppy)(2)Ir(acac) is a highly efficient phosphor doped organic material. The device turn-on voltage is 3.2 V. The maximum luminance efficiency and maximum luminous power efficiency reach 69 cd/A and 62 lm/W, respectively, corresponding to a maximum PCE of 12% and an external quantum efficiency of 17%.

Light extraction efficiency of a top-emission organic light-emitting diode with an Yb/Au double-layer cathode and an opaque Si anode

We have computed the transmittances of four types of cathode--Yb/Au, Al/Au, Yb/Ag, and Al/Ag double layers--and the light extraction efficiencies of the top-emission organic light-emitting diodes with these cathodes, respectively, based on the characteristic matrix method and the dissipation spectrum model. Computations show that the Yb/Au cathode has a markedly higher transmittance than the other three types of cathode when the Yb and Au thicknesses in the Yb/Au cathode are, respectively, equal to the Al (or Yb) and Au (or Ag) thicknesses in the other three types of cathode. The power lost to the Yb/Au cathode due to the surface plasmon polaritons is the lowest, and hence the device with the Yb/Au cathode has the highest extraction efficiency. The transmittances for the four cathodes are also measured experimentally.