Organic electroluminescent element

• US 9,112,174 B2
• Filed: 08/09/2012
• Issued: 08/18/2015
• Est. Priority Date: 08/12/2011
• Status: Expired due to Fees

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Yamae, Kazuyuki
• Primary Examiner(s): Geyer, Scott B
• Assistant Examiner(s): MUSTAPHA, ABDULFATTAH B
• Application Number:
  US14/238,368
• Publication Number:
  US 20140191226A1
• Time in Patent Office: 1,104 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H10K 2102/351 Thickness
• CPC Class Codes: H10K 50/125 specially adapted for multicolour light emission, e.g. for emitting white light
• CPC Class Codes: H10K 50/131 with spacer layers between the electroluminescent layers
• CPC Class Codes: H10K 50/19 Tandem OLEDs
• CPC Class Codes: H10K 50/852 comprising a resonant cavity structure, e.g. Bragg reflector pair

Abstract

An organic electroluminescent element having a structure in which a plurality of light-emitting layers stacked between a first electrode with light reflectivity and a second electrode with optical transparency while one or more interlayers with a light transmissive property are interposed between the plurality of light-emitting layers. A first interlayer is formed as the interlayer closest to the first electrode. A first light-emitting unit is formed between the first electrode and the first interlayer to include a first light-emitting layer which has a first light-emitting source, and a second light-emitting unit is formed on a side of the first interlayer close to the second electrode to include a second light-emitting layer which has a second light-emitting source. The first interlayer is a semi-transmissive layer which has both of optical transparency and light reflectivity and has a total light absorption ratio of 10% or less.

Claims

1. An organic electroluminescent element with a structure in which a plurality of light-emitting layers are stacked between a first electrode with light reflectivity and a second electrode with optical transparency while one or more interlayers with a light transmissive property are interposed between the plurality of light-emitting layers,

wherein:

the one or more interlayers includes a first interlayer closest to the first electrode;

a first light-emitting unit is formed between the first electrode and the first interlayer to include a first light-emitting layer which is one of the plurality of light-emitting layers and has a first light-emitting source;

a second light-emitting unit is formed on a side of the first interlayer close to the second electrode to include a second light-emitting layer which is one of the plurality of light-emitting layers and has a second light-emitting source; and

the first interlayer is a semi-transmissive layer which has both of optical transparency and light reflectivity and has a total light absorption ratio of 10% or less,

wherein

the organic electroluminescent element has a characteristic which satisfies relations of;

0.9*X≦

D1(λ

1)≦

1.1*X;

0.1*Y≦

D3(λ

2)≦

2.0*Y; and

0.8*Z≦

D1(λ

1)+D2(λ

1)≦

1.2*Z,

wherein;

λ

1 represents a weighted-averaged emission wavelength of the first light-emitting source;

λ

2 represents a weighted-averaged emission wavelength of the second light-emitting source;

D1(λ

1) represents an optical path length defined as a product of a refractive index at the wavelength λ

1 and a thickness with regard to a medium situated between the first light-emitting source and the first electrode;

D2(λ

1) represents an optical path length defined as a product of a refractive index at the wavelength λ

1 and a thickness with regard to a medium situated between the first light-emitting source and the semi-transmissive layer;

D3(λ

2) represents an optical path length defined as a product of a refractive index at the wavelength λ

2 and a thickness with regard to a medium situated between the second light-emitting source and the semi-transmissive layer; and

X, Y, and Z satisfy equations of X=φ

1(λ

1)*(λ

1/4π

)+λ

1*l/2, Y=(φ

2(λ

2)*(λ

2/4π

)+λ

2*m/2, and Z=φ

1(λ

1)+φ

2(λ

1)*(λ

1/4π

)+λ

1*n/2, respectively,

wherein;

l, m, and n are integers of 0 or more, respectively;

φ

1 represents a phase shift expressed by a following formula (1) which occurs at the first electrode;

φ

₂ represents a phase shift expressed by the following formula (1) which occurs at the semi-transmissive layer;

φ

₁(λ

₁) represents a phase shift of light emitted from the first light-emitting source which arises from reflection at the first electrode;

φ

₂(λ

₁) represents a phase shift of light emitted from the first light-emitting source which arises from reflection at the semi-transmissive layer;

φ

₂(λ

₂) represents a phase shift of light emitted from the second light-emitting source which arises from reflection at the semi-transmissive layer; and

the formula (1) is;

2. The organic electroluminescent element as set forth in claim 1, wherein the semi-transmissive layer has a total light reflectance of 10% or more but less than 50%.

3. The organic electroluminescent element as set forth in claim 1, wherein the semi-transmissive layer contains Ag or an alloy of Ag as a main component.

4. The organic electroluminescent element as set forth in claim 1, wherein l is not less than 1 in the equation for X.

5. The organic electroluminescent element as set forth in claim 1, wherein l, m, and n are not less than 1, respectively in the equations for X, Y, and Z.

6. The organic electroluminescent element as set forth in claim 1, further comprising a light diffusion layer on an outcoupling face of the second electrode.

7. The organic electroluminescent element as set forth in claim 6, wherein

an optical path length D_d(λ

₁) between a face of the light diffusion layer close to an outcoupling side and the semi-transmissive layer at the wavelength λ

₁ is ten times or more as long as an emission wavelength λ

₁ of the first light-emitting unit.

8. The organic electroluminescent element as set forth in claim 6, further comprising a substrate with optical transparency on the outcoupling face of the second electrode,

wherein

the substrate has a refractive index of 1.55 or more.