CN100502089C - Method for improving organic electroluminescence device color purity using photon crystal heterojunction - Google Patents

Abstract

A heterojunction (HJ) area of photon crystal is setup in ITO layer on output light path of organic electroluminescence (OEL) device. HJ is composed of n pieces of multilayer films, which are prepared by using self-assembly technique, of Nano microsphere photon crystal of SiO2, and where n is natural number (2<=n<=5). Position of photon forbidden band in each multilayer film of HJ can be adjusted by method of selecting Nano microspheres in different diameters. Adjusting frequency range of reflected light of the multilayer films makes these films allow light within frequency range needed to pass through, and reflect light out of the frequency range so as to raise color purity of OEL device. Comparing with methods including adding filter, using structure of micro cavity, and preparing distributed Bragg reflector, the disclosed method possesses advantages of simple structure, lower cost, and reduced waste of light energy caused by light absorption, and effect of planar optical waveguide.

Description

Utilize photon crystal heterojunction to improve the method for organic electroluminescence device color color purity

Technical field

The present invention relates to a kind of method that improves organic electroluminescence device color color purity, it will be applied to: 1) organic electroluminescence device.2) inorganic electroluminescence device of emission spectrum broad.

Background technology

In organic electroluminescence device, the emission spectrum broad of organic material commonly used, half-peak breadth is generally 50-100nm.Owing to the minimizing along with the half range value of luminescent spectrum of the visual sense efficient of human eye increases, the colorimetric purity that therefore improves organic electroluminescence device is very meaningful.In order to improve the colorimetric purity of display device, generally be to adopt the method for adding filter, unwanted light absorption is fallen, this has caused certain luminous energy waste; Another technology is to utilize micro-cavity structure, strengthens certain wavelengths by optimizing light emitting layer thickness, and this needs the accurately thickness of control luminescent layer, and also requires the thickness of red-green-blue luminescent layer to have nothing in common with each other in full-color display spare; Another technology is that the output at light prepares distributed Bragg reflector to select ejected wave long, and this needs expensive vacuum coating equipment, complex process, and cost is higher.

Summary of the invention

The technical problem to be solved in the present invention is to overcome luminous energy waste and the cost problem of higher that exists in the prior art, a method that improves organic electroluminescence device color color purity has been proposed, a photon crystal heterojunction structure is set in the ITO layer on output light path, this heterojunction is made up of n photon crystal multi-layer film, and n is natural number and 2≤n≤5; Each multilayer film is separately with the emergent light reflected back luminescent layer of certain frequency scope, and allows the light of particular frequency range to pass through.Regulate the light that the catoptrical frequency range of these photon crystal multi-layer films makes them can both allow to be in the required frequency range and pass through, and reflection is in the emergent light outside this frequency range.The luminous energy of having avoided like this utilizing filter to bring when improving the emergent light colorimetric purity is wasted.Owing to the introducing of this heterostructure, destroyed the Planar Optical Waveguide Structures of luminescent device simultaneously, can reduce emergent light effectively because the optical energy loss that the planar optical waveguide effect is brought.

Technical scheme of the present invention:

Utilize photon crystal heterojunction to improve the step of the method for organic electroluminescence device color color purity:

Step 1 is utilized

Method prepares the dispersed nano SiO of n kind (n is natural number and 2≤n≤5) diameter ₂Microballoon requires relative standard deviation σ＜5% of microballoon size on monodispersity; Following principle is followed in the selection of these microsphere diameter sizes:

If require the centre wavelength of n frequency range of the emergent light that no thoroughfare to be respectively λ ₁, λ ₂, λ ₃... λ _n, (n is natural number and 2≤n≤5), then

${0.816D}_n=\frac{{\mathrm{\&lambda;}}_n}{{2n}_{\mathrm{eff}}}$

D wherein _nBe a kind of required SiO wherein ₂Diameter of micro ball, effective refractive index n _Eff=1.347.

Above-mentioned

Method derives from document

, W, Fink A, Bohn E, J.Colloid interface Sci.26 (1968) 62. disclosed methods.

Step 2, the preparation of electroluminescent device anode: the sheet glass that cleans up is dry in baking oven, on sheet glass, utilize self-assembling technique n (n is natural number and the 2≤n≤5) SiO that successively grow then ₂The microballoon photon crystal multi-layer film forms photon crystal heterojunction, and the number of plies single in n multilayer film is between 8～20 layers; The ITO layer of applying electronic beam evaporation or magnetron sputtering technique continued growth 50～200nm thickness on photon crystal heterojunction again;

Prepare each SiO ₂In the time of the microballoon photon crystal multi-layer film, the number of plies is less than 8 layers can not provide tangible forbidden photon band, and the number of plies then can increase the preparation of devices difficulty more than 20 layers.

Above-mentioned self-assembling technique derives from document Peng Jiang, Gordana N.Ostojic, Roxana Narat, Daniel M Mittlemanand Vicki.L.Colvin, Adv.Mater, 13 (2001) 389. disclosed methods

Step 3, the preparation of electroluminescent device luminescent layer and cathode electrode: application vacuum evaporation method or spin coating method prepare luminescent layer on the ITO layer, luminescent layer is an individual layer, or comprise the multilayer of luminescent layer, hole transmission layer and electron transfer layer, or comprise the only multilayer of one of luminescent layer, hole transmission layer and electron transfer layer; Evaporating Al electrode then.

The technique effect that the present invention compares with prior art:

In the prior art, the technology of improving organic electroluminescence device color color purity mainly contains: add colour filter, utilize micro-cavity structure or prepare distributed Bragg reflector at the output of light.The present invention compares with above-mentioned these technology, and cost is lower, and technology is simple relatively, has avoided the luminous energy that light absorption brought waste.Simultaneously, the introducing of photon crystal multi-layer film has destroyed the Planar Optical Waveguide Structures of luminescent device, reduces emergent light effectively because the optical energy loss that the planar optical waveguide effect is brought.

Principle of the present invention and foundation:

In photonic crystal, refractive index is periodically variable, and its cycle size is in the optical wavelength magnitude.When light is propagated in photonic crystal, owing to be subjected to the influence of periodically scattering, forbidden photon band can appear, frequency drops on photon in the forbidden photon band and will be reflected by photonic crystal and can not pass through.Utilize the SiO of self-assembling technique preparation ₂The Nano microsphere photon crystal film, the method that can pass through selection different-diameter microballoon is regulated the position of forbidden photon band, thus change is forbidden and is allowed by the light frequency scope.Pass through by regulating the light that the catoptrical frequency range of these photon crystal multi-layer films makes them can both allow to be in the required frequency range in the photon crystal heterojunction, and reflect the colorimetric purity that the emergent light that is in outside this frequency range just can improve organic electroluminescence device.

Description of drawings

Fig. 1 contains the organic electroluminescence device structure chart of photon crystal heterojunction

1 is glass substrate among Fig. 1; 2 is the ITO layer; 3 is photon crystal heterojunction; 4 is luminescent layer; 5 is metal electrode.

Fig. 2 luminescent material is ALq ₃The emission spectrum of simple organic electroluminescence device

PC1 and PC2 are＜111 in Fig. 3 photon crystal heterojunction〉optical transmission property on the direction, wherein SiO among the PC1 ₂Diameter of micro ball D ₁=266nm, SiO among the PC2 ₂Diameter of micro ball D ₂=285nm

Fig. 4 prepares ALq behind the photon crystal heterojunction ₃The emission spectrum of electroluminescent device

Embodiment

Utilize photon crystal heterojunction to improve the method for organic electroluminescence device color color purity:

Improving luminescent layer with the preparation photon crystal heterojunction is ALq ₃The colorimetric purity of organic electroluminescence device be example, ALq ₃Be a kind of green light material commonly used, but its emission spectrum is longer in the hangover of long wave direction, has influenced the colorimetric purity of luminescent device.

Step 1 is utilized

Two kinds of dispersed nano SiO of method preparation ₂Microballoon, its diameter is respectively D ₁=266nm, D ₂=285nm requires relative standard deviation σ＜5% of two kinds of microsphere diameter sizes on monodispersity.

Step 2, the preparation of electroluminescent device anode: the sheet glass that cleans up is dry in baking oven, utilize self-assembling technique 16 layers of multilayer film PC1 that is made up of for the 285nm microballoon diameter of growth earlier then on sheet glass, 16 layers of multilayer film PC2 that is made up of for the 266nm microballoon diameter of continued growth form photon crystal heterojunction again; Use the ITO layer of magnetron sputtering technique continued growth 50～200nm thickness on photon crystal heterojunction again; Fig. 3 be in the photon crystal heterojunction that calculates PC1 and PC2＜111 optical transmission property on the direction, with λ ₀=627nm is a centre wavelength, width Delta λ ≈ 50nm and λ ₀=585nm is a centre wavelength, and the transmitance of the light in two scopes of width Delta λ ≈ 50nm is all less than 50%.

Step 3, the preparation of electroluminescent device luminescent layer and negative electrode: on the ITO layer, use vacuum evaporation method and prepare ALq ₃Luminescent layer, evaporating Al electrode then.To simple ALq ₃Emission spectrum of organic electroluminescence device (Fig. 2) and preparation have the ALq of photon crystal heterojunction ₃The result of calculation of organic electroluminescence device emission spectrum (Fig. 4) shows, because with λ ₀=627nm is a centre wavelength, width Delta λ ≈ 50nm and λ ₀=585nm is a centre wavelength, and the transmitance of the light in two scopes of width Delta λ ≈ 50nm is all less than 50%, and the colorimetric purity of luminescent device has brought up to 60.1% from 54.8%.

Claims (1)

1. utilize photon crystal heterojunction to improve the method for organic electroluminescence device color color purity, it is characterized in that, use the anode that following step prepares organic electroluminescence device:

Step 1 is utilized

Method prepares the dispersed nano SiO of n kind diameter ₂Microballoon, n are natural number and 2≤n≤5, require relative standard deviation σ＜5% of microballoon size on monodispersity; Following principle is followed in the selection of microsphere diameter:

If require the centre wavelength of n frequency range of the emergent light that no thoroughfare to be respectively λ ₁, λ ₂, λ ₃... λ _n, n is natural number and 2≤n≤5, then:

${0.816D}_n=\frac{{\mathrm{\&lambda;}}_n}{{2n}_{\mathrm{eff}}}$

D wherein _nBe a kind of required SiO wherein ₂Diameter of micro ball, effective refractive index n _Eff=1.347;

Step 2, the preparation of electroluminescent device anode: the sheet glass that cleans up is dry in baking oven, on sheet glass, utilize self-assembling technique n the SiO that successively grow then ₂The microballoon photon crystal multi-layer film forms photon crystal heterojunction, and n is natural number and 2≤n≤5, and the number of plies single in n multilayer film is between 8～20 layers; The ITO layer of applying electronic beam evaporation or magnetron sputtering technique continued growth 50～200nm thickness on photon crystal heterojunction again.

Images