具有微腔结构的有机顶发射电致发光器件的光谱分析

摘要: 制做了具有微腔结构的蓝色和白色有机顶发射电致发光器件。利用TBADN:3%DSAPh和Alq3:DCJTB/TBADN:TBPe/Alq3:C545材料为发光层,在玻璃基片上,依次制备薄膜：Ag为阳极反射层, CuPc作为空穴注入层,NPB作为空穴传输层,ITO为光程调节层; Al/Ag作为半透明阴极,电极的透射率在30%左右。通过改变ITO层的厚度,TBADN:3%DSAPh器件获得了深蓝色发光光谱,色坐标为(0.141, 0.049),半高宽为17nm发光光谱,实现了窄带发射,Alq3:DCJTB/TBADN:TBPe/Alq3:C545器件得到了不同颜色（红、蓝、绿）的发光光谱,实现了对光谱的调节作用。文章对微腔顶发射器件的发射强度和发光光谱半高宽的结果进行了分析。     

Spectrum study of top-emitting organic light-emitting devices with micro-cavity structure

Blue and white top-emitting organic light-emitting devices OLEDs with cavity effect have been fabricated.TBADN:3%DSAPh and Alq3:DCJTB/TBADN:TBPe/Alq3:C545 were used as emitting materials of microcavity OLEDs.On a patterned glass substrate,silver was deposited as reflective anode,and copper phthalocyanine (CuPc)layer as HIL and 4'-bis[N-(1-Naphthyl)-N-phenyl-amino]biphenyl(NPB)layer as HTL were made.Al/Ag thin films were made as semi-transparent cathode with a transmittance of about 30%.By changing the thickness of indium tin oxide ITO,deep blue with Commission Internationale de L'Eclairage chromaticity coordinates(CIEx,y)of(0.141,0.049)was obtained on TBADN:3%DSAPh devices,and different color(red,blue and green)was obrained on Alq3:DCJTB/TBADN:TBPe/Alq3:C545 devices,full width at half maxima(FWHM)was only 17 nm.The spectral intensity and FWHM of emission in cavity devices have also been studied.     

Radiation simulations of top-emitting organic light-emitting devices with two- and three-microcavity structures

We demonstrate the simulation results of the radiation properties from top-emitting organic light-emitting devices (top-emitting OLEDs) with two- and three-microcavity structures based on the general electromagnetic theory. The parameters of the layer thickness and complex refractive index of each layer, the locations and density of the oscillating dipoles, and the emission photoluminescence spectrum are varied to optimize the device performance. In evaluating the deice performances, the output spectrum, the intensity distribution, and the viewing-angle characteristics of a top-emitting OLED are concerned. The simulation results are consistent with the Fabry-Perot cavity equation, which can be used as a guideline for designing a two-cavity top-emitting OLED. In such a design process, the dipole position is chosen first. Then the thicknesses of the whole organic layer, the semitransparent cathode, and the dielectric layer are adjusted for optimizing the device performance. In a three-cavity top-emitting OLED, not only the emission intensity and the viewing angle can be optimized at the same time, but also the emission wavelength can be independently tuned. Besides, the use of a three-cavity structure helps to narrow the spectral width and increase the color purity.     

Highly efficient electrophosphorescent polymer light-emitting devices

We report a high performance polymer electroluminescent device based on a bi-layer structure consisting of a hole transporting layer (poly(vinylcarbazole)) and an electron transporting layer poly(9,9-bis(octyl)-fluorene-2,7-diyl) (BOc-PF) doped with platinum(II)-2,8,12,17-tetraethyl-3,7,13,18-tetramethylporphyrin (PtOX). The devices show red electrophosphorescence with a peak emission at 656 nm and a full width at half maximum of 18 nm, consistent with exclusive emission from the PtOX dopants. BOc-PF emission is not observed at any bias. The required doping levels for these phosphorescence-based polymer light-emitting diodes (PLEDs) are significantly lower than for other reported phosphorescence-based PLEDs or organic light-emitting diodes (OLEDs). A doping level of 1% or more give an LED with exclusive PtOX emission, whereas related PLEDs or OLEDs doped with phosphorescent dopants require doping levels of >5% to achieve exclusive dye dopant emission. The device external efficiency was enhanced from 1% to 2.3% when doped with PtOX. The lower doping level in BOc-PF/PtOX based PLEDs decreases triplet–triplet annihilation in these devices, leading to quantum efficiency that is only weakly dependent on current density. The luminescence transient decay time for this device is 500 μs.     

Effective hole-injection layer for non-doped inverted top-emitting organic light-emitting devices

Non-doped inverted top-emitting organic light-emitting diode with high efficiency is demonstrated through employing an effective hole-injection layer composed of MoO_x. One reason for high efficiency lies on the energy-level matching between MoO_x and hole-transport, and another is due to the Ohmic contact formed between MoO_x and Ag. Both of them lead to an improvement of the hole-injection capability from Ag top anode. Moreover, the symmetrical current of “hole-only” device with MoO_x shows better hole-injection capability, which is independent of the deposition sequence. The optimized device with MoO_x hole-injection layer exhibits maximum current efficiency of 3.7 cd/A at a raised luminance level of 14,900 cd/m² and a maximum luminance of 47,000 cd/m² under 18 V.     

Optimizing structure for constructing a highly efficient inverted top-emitting organic light-emitting diode with stable electroluminescent spectra

We demonstrate a highly efficient inverted top-emitting organic light-emitting diode （TOLED） having stable electroluminescent spectra and color coordination with variation of viewing angles by simply tuning the reso- nance wavelength corresponding to the free emission of the emitter. Using a doped fluorescent emitting system, the inverted TOLED exhibits an enhanced maximum current efficiency of 19 cd/A and a power efficiency of 17 lm/W, which are much higher than those （11 cd/A and 5 lm/W） of the counterpart with normal structure, although both TOLEDs behave with similar stable electroluminescent spectra characteristics. The results indicate that we provide a simple and effective method of constructing an excellent inverted TOLED for potentially practical applications.     

Metal-anode-dependent spectra and efficiency in blue top-emitting organic light-emitting devices

In this study, the blue top-emitting organic light-emitting devices (TEOLEDs) with different metal anodes are fabricated. The effect of different anode materials on the spectra and efficiency of blue TEOLEDs is studied. We demonstrate that Al is a more suitable anode material for blue TEOLEDs due to its larger phase shift on reflectance (PSR) than the other common metal materials, such as Ag and Au. The influence of light outcoupling layer (LOL) on the transmittance and PSR of cathode is also investigated to obtain the optimum condition for devices. Angle-independent electroluminescence (EL) spectra are obtained in blue TEOLEDs for each metal anode but the device with Al anode possesses higher efficiency and much thicker organic layers, which is beneficial to the lifetime of the device. These results offer a practicable platform for the realization of TEOLEDs based full-color displays and lightings.     

Highly efficient single-layer organic light-emitting devices using cationic iridium complex as host

Highly efficient single-layer organic light-emitting devices (OLEDs) based on blended cationic Ir complexes as emitting layer have been demonstrated using narrow band gap cationic Ir complex [Ir(Meppy)₂(pybm)](PF₆) (C1) as guest and wide band gap cationic Ir complex [Ir(dfppy)₂(tzpy-cn)](PF₆) (C2) as host. As compared with single cationic Ir complex emitting layer, these host–guest systems exhibit highly enhanced efficiencies, with maximum luminous efficiency of 25.7 cd/A, external quantum efficiency of 8.6%, which are nearly 3-folds of those of pure C1-based device. Compared with a multilayer host-free device containing C1 as emitting layer and TPBI as electron-transporting and hole-blocking layer, the above single-layer devices also show 2-folds enhancement efficiencies. The high efficiencies achieved in these host–guest systems are among the highest values reported for ionic Ir complexes-based solid-state light-emitting devices. In addition, a white-similar emission with CIE of (0.36, 0.47) has also been achieved with luminous efficiency of 4.2 cd/A as the C1 concentration is 0.1 wt.%. The results demonstrate that the ionic Ir complexes-based host–guest system provides a new approach to achieve highly efficient OLEDs upon single-layer device structure and solution-processing technique.     

Highly efficient ITO-free organic light-emitting diodes employing a roughened ultra-thin silver electrode

We investigated an efficient organic light-emitting diodes (OLEDs) using an ultra-thin silver (Ag) anode, whereas Ag was deposited on a roughened glass substrate by laser patterning method. The thin-film property of this roughened silver anode exhibited an optical transmittance of more than 65% in visible light at 532 nm and a low electrical sheet resistance of 3.2 Ω/sq, which is superior to standard indium-tin-oxide (ITO) glass. Therefore, we report an ITO-free, exciplex-forming phosphorescent OLED showing Lambertian emission with a luminance of 128,000 cd/m² at 8 V, and maximum current efficiency of 92.3 cd/A (external quantum efficiency of ∼24.5%) at 100 cd/m². We also observed the improvement in hole-injection efficiency at the interface of the Ag anode/di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane due to the modification in the worfunction of roughened Ag anode from 4.6 to 5.4 eV.     

High efficiency green phosphorescent top-emitting organic light-emitting diode with ultrathin non-doped emissive layer

Ultrathin non-doped emissive layer (EML) has been employed in green phosphorescent top-emitting organic light-emitting diodes (TOLEDs) to take full advantages of the cavity standing wave condition in a microcavity structure. Much higher out-coupling efficiency has been observed compared to conventional doped EML with relatively wide emission zone. A further investigation on dual ultrathin non-doped EMLs separated by a special bi-layer structure demonstrates better charge carrier balance and improved efficiency. The resulting device exhibits a high efficiency of 125.0 cd/A at a luminance of 1000 cd/m² and maintains to 110.9 cd/A at 10,000 cd/m².     

Highly efficient green phosphorescent organic light emitting diodes with simple structure

A series of simple structures is investigated for realization of the highly efficient green phosphorescent organic light emitting diodes with relatively low voltage operation. All the devices were fabricated with mixed host system by using 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB) which were known to be hole and electron type host materials due to their great hole and electron mobilities [μ_h(TAPC): 1 × 10^?2 cm²/V s and μ_e(TpPyPB): 7.9 × 10^?3 cm²/V s] [1]. The optimized device with thin TAPC (5–10 nm) as an anode buffer layer showed relatively high current and power efficiency with low roll-off characteristic up to 10,000 cd/m². The performances of the devices; with buffer layer were compared to those of simple devices with single layer and three layers. Very interestingly, the double layer device with TAPC buffer layer showed better current and power efficiency behavior compared to that of three layer device with both hole and electron buffer layers (TAPC, TpPyPB, respectively).     

通过引入电子阻挡层的高效率的有机磷光白光器件

以CBP作为母体材料,绿色磷光染料Ir(ppy)3作为敏化剂,以荧光染料rubrene作为受主,制备了结构为ITO/2T-NATA(25 nm)/ NPBX (25-d nm)/ CBP:5%Ir(ppy)3:0.5%Rubrene(8 nm)/NPBX(d nm)/DPVBi(30 nm)/TPBi(20 nm)/Alq(10 nm)/LiF(1 nm)/Al的白光器件.在器件中,敏化剂Ir(ppy)3、荧光染料rubrene的浓度分别为5.0 wt%和0.5 wt%,发光层的厚度选择8 nm,通过调整两层NPBX的厚度来改善器件的性能,得到了比较理想的白光发射.当d的厚度为10 nm 时,器件在7 V的电压下最大电流效率达到11.2 cd/A,在17 V的电压下其最大亮度达到28 170 cd/m2,色坐标为(0.37,0.42),处于白光区.     

High-performance inverted top-emitting green electrophosphorescent organic light-emitting diodes with a modified top Ag anode

Green electrophosphorescent inverted top-emitting organic light-emitting diodes with a Ag/1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) anode are demonstrated. A high current efficacy of 124.7 cd/A is achieved at a luminance of 100 cd/m² when an optical outcoupling layer of N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl-4,4′-diamine (α-NPD) is deposited on the anode. The devices have a low turn-on voltage of 3.0 V and exhibit low current efficacy roll-off through luminance values up to 10,000 cd/m². The angle dependent spectra show deviation from Lambertian emission and color change with viewing angle. Hole-dominated devices with Ag/HAT-CN electrodes show current densities up to three orders of magnitude higher than devices without HAT-CN.     

Highly efficient full-fluorescence organic light-emitting diodes with exciplex cohosts

Full-fluorescence organic light-emitting diodes (FOLEDs) with low cost and high efficiency are imperious demands for commercial process in flat panel display and lighting products. We fabricated a series of FOLEDs employing C545T and DCJTB as doped dyes and different exciplex blends as cohosts. The results proved that reverse intersystem crossing (RISC) efficiency of exciplex cohost has a significant effect on the device performance. Devices with TAPC:PIM-TRZ as cohost which possessed the highest RISC efficiency showed the best results. The green FOLEDs exhibited the maximum external quantum efficiencies (EQEs) approaching to 20%, the red FOLEDs exhibited EQEs over 10% and all the EQE roll-offs are less than 10% at 1000 cd m⁻², which are among the best reported results so far, suggesting these exciplex cohosts are promising for FOLEDs.     

High-performance green phosphorescent top-emitting organic light-emitting diodes based on FDTD optical simulation

We have successfully applied finite-difference time-domain (FDTD) method in top-emitting organic light-emitting diodes (TOLEDs) for structure optimization, demonstrating good agreement with experimental data. A mixed host with both hole transport and electron transport materials is employed for the green phosphorescent emitter to avoid charge accumulation and broaden the recombination zone. The resulting TOLEDs exhibit ultra-high efficiencies, low current efficiency roll-off, and a highly saturated color, as well as hardly detectable spectrum shift with viewing angles. In particular, a current efficiency of 127.0 cd/A at a luminance of 1000 cd/m² is obtained, and maintains to 116.3 cd/A at 10,000 cd/m².     

Highly efficient and foldable top-emission organic light-emitting diodes based on Ag-nanoparticles modified graphite electrode

Top-emission flexible organic light-emitting devices (TE-FOLEDs) are highly suitable for next generation display due to their numerous assets including top-emitting configuration and mechanical flexibility. One major challenge in TE-FOLEDs is to prepare a deformable and reflective bottom electrode capable of effective carrier injection. In this paper, a new strategy for efficient and foldable TE-FOLEDs is demonstrated. It is based on a highly conductive Ag-nanoparticles (Ag-NPs) modified graphite that is used as a flexible bottom electrode. The good reflectance to full-color emission (>59% over the whole visible wavelength range), ultralow sheet resistance (<5 Ω/sq), and high tolerance to mechanical bending (almost unchanged in resistance after bending 1000 times with an angle of ±90°) of the modified graphite synergistically constitute a breakthrough in the domain of TE-FOLEDs. The maximum current efficiencies reach 15.0, 50.2, 16.8 cd/A for red, green, blue emissions, respectively. Colorimetric gamut increased by 99.6% compared to bottom emission structure with the corresponding Commission Internationale de L'Eclairage (CIE) coordinates of the red/green/blue (R/G/B) devices. In particular, the TE-FOLEDs incorporating highly flexible graphite electrodes offer great mechanical durability and the initial brightness of 5000 cd/m can be maintained over 90% after bending for 1000 bending cycles. This approach is expected to open a new avenue for developing foldable displays.     

Highly efficient solution-processable europium-complex based organic light-emitting diodes

The development of solution-processable europium-complex based organic light-emitting diodes (OLED) has been limited by their low efficiency. In this paper, we show that it is possible to produce a highly efficient, solution-processable, europium-complex based OLED with an external quantum efficiency of 4.3% at a brightness of 100 Cd/m² using off-the-shelf materials and without any specific optical design for improved light extraction. This is achieved by optimizing the device structure and the host matrix used. To our knowledge, this is the highest efficiency reported for solution-processable europium-complex based OLED devices, and the efficiency roll-off has been reduced compared with other reported europium-complex based devices. Our approach should be applicable to a wide range of solution-processable lanthanide complexes.     

Highly efficient solution-processed small-molecule white organic light-emitting diodes

Solution-processed small-molecule white organic light-emitting diodes (WOLEDs) were fabricated with a co-host of hole-transporter 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TCTA) and electron-transporter 2,7-Bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13). By doping 15 wt% FIrpic or F₃Irpic and 0.5 wt% Ir(MDQ)₂(acac) in to the TCTA/SPPO13 host, highly efficient white OLEDs have been achieved which exhibit nearly identical emission spectra at different luminance. The F₃Irpic and Ir(MDQ)₂(acac)-based WOLED shows maximum efficiencies of 40.9 cd/A, 36.7 lm/W and 16.9%, and even high efficiencies of 30.1 cd/A and 12.3% at the practical luminance of 1000 cd/m², which are among the highest efficiencies of the solution-processed small-molecule WOLEDs. These results demonstrate a convenient way to realize solution-processed WOLEDs with high efficiency and high spectral stability through full small-molecule materials system.     

Polymer encapsulation of flexible top-emitting organic light-emitting devices with improved light extraction by integrating a microstructure

An improved efficiency from an encapsulated flexible top-emitting organic light-emitting device (FTOLED) has been demonstrated by integrating a microstructure onto the polymer encapsulation film. Soft-nanoimprint lithography is employed to integrate the microstructure onto the polymer surface, which enables large area fabrication with high quality, low cost, and repeatable use of the poly(dimethylsiloxane) mold. The light extraction of the FTOLEDs has been improved by integrating the microstructure with two-dimensional tapered micropillars array on the polymer encapsulation film, which can suppress the reflection by enhancing the critical angle of total reflection owing to its gradually changed refractive index. Moreover, the microstructured surface exhibits a hydrophobic property owing to its high contact angle, which results in a self-cleaning ability to protect the FTOLEDs from being polluted by water droplets and dust particles in practical applications.     

Stacked inverted top-emitting green electrophosphorescent organic light-emitting diodes on glass and flexible glass substrates

Stacked inverted top-emitting green electrophosphorescent organic light-emitting diodes (OLEDs) are demonstrated on glass and flexible glass substrates. A single-unit OLED is shown to have a current efficacy of 46.8 cd/A at a luminance of 1215 cd/m². When two of these OLEDs are stacked, the double-unit OLED exhibits a current efficacy more than twice that of the single-unit OLED, with a current efficacy of 97.8 cd/A at a luminance of 1119 cd/m². With the addition of an optical outcoupling layer of N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (α-NPD) on top of the semitransparent gold anode, the double-unit stacked OLED achieves a maximum current efficacy of 205 cd/A at a luminance of 103 cd/m², maintaining a high current efficacy of 200 cd/A at a luminance of 1011 cd/m². These stacked inverted OLED combine the advantages of inverted OLEDs with the benefits of having a stacked architecture.