Band edge emission enhanced organic light emitting diode with a localized emitter
A light emitting photonic crystal having an organic light emitting diode and methods of making the same are disclosed. An organic light emitting diode disposed within a photonic structure having a band-gap, or stop-band, allows the photonic structure to emit light at wavelengths occurring at the edges of the band-gap. Photonic crystal structures that provide this function may include materials having a refractive index that varies.
1. A light emitting device comprising a single light emitting photonic crystal having an organic electroluminescent emitter material disposed within the single photonic crystal, wherein
the organic electroluminescent emitter material has a free space emission spectrum that at least in part overlaps a stop-band of the photonic crystal, wherein
the photonic crystal emits light at a wavelength corresponding to an edge of the stop-band that the organic electroluminescent emitter material overlaps, and wherein the organic electroluminescent emitter material comprises an organic light emitting material localized in a zone having less than 10% of an optical thickness of the photonic crystal.
2. The light emitting device of claim 1 wherein the photonic crystal further comprises a stack of layers of varying refractive index.
3. The light emitting device of claim 2 wherein a layer of the stack of layers of varying refractive index comprises the organic electroluminescent emitter material.
4. The light emitting device of claim 3 wherein the layer of the stack of layers of varying refractive index comprising the organic electroluminescent emitter material is a layer of lower index of refraction materials.
5. The light emitting device of claim 2 wherein the stack of layers has a periodic modulation, measured in optical thickness, of refractive index with a period of modulation of λ/2 wherein λ equals the central wavelength of the photonic crystal stop-band.
6. The light emitting device of claim 2 wherein the stack of layers of varying refractive index comprised by the single light emitting photonic crystal comprises at least one pair of layers of materials with different refractive indices that, in turn, comprises a first layer of material with a higher refractive index and a second layer of a material with a lower refractive index, wherein the total optical thicknesses of the two layers combined equals λ/2, wherein λ equals the central wavelength of the photonic crystal stop-band.
7. The light emitting device of claim 5 wherein the period of the refractive index modulation through the stack of layers is disrupted by insertion of a layer of constant refractive index having an optical thickness equal to 3λ/4 wherein λ is the central wavelength of the stop-band of the photonic crystal.
8. The light emitting device of claim 3 wherein the layer comprising the organic electroluminescent emitter material further comprises additional organic materials each having a low index of refraction respective to an adjacent layer, wherein the additional organic materials are at least one of a charge transport material, a charge injection material, or a charge blocking material.
9. The light emitting device of claim 1 wherein the device is configured to emit light from only one surface.
10. The light emitting device of claim 9 wherein a metallic reflector is formed on a surface opposite the only one surface that emits light.
11. The single light emitting photonic crystal of claim 3 wherein a greater number of alternating layers of high index of refraction materials and low index of refraction materials are disposed upon a first side of the layer of the stack of layers of varying refractive index that comprises the organic electroluminescent emitter material than the lesser number of alternating layers of high index of refraction materials and low index of refraction materials disposed on the other side of the layer of the stack of layers of varying refractive index that comprises the organic electroluminescent emitter material that is opposite the first side.
12. The light emitting device of claim 3 wherein the layer of the stack of layers of varying refractive index comprising the organic electroluminescent emitter material is a layer of higher index of refraction materials.
13. The light emitting device of claim 3 wherein the layer of the stack of layers of varying refractive index that comprises the organic electroluminescent emitter material has an optical thickness of one quarter of a central wavelength of the band-gap.
14. The light emitting device of claim 7 wherein the layer of the stack of layers of varying refractive index that comprises the organic electroluminescent emitter material has an optical thickness equal to 3λ/4 wherein λ is the central wavelength of the stop-band of the photonic crystal.
15. The light emitting device of claim 1 wherein the molecules of the organic electroluminescent emitter material are spatially oriented to maximize stimulated emission parallel to the axis of transmission of the emitted light.
16. A light emitting device comprising a single light emitting photonic crystal having an organic electroluminescent emitter material disposed within the single photonic crystal, wherein
the organic electroluminescent emitter material has a free space emission spectrum that at least in part overlaps a stop-band of the photonic crystal, wherein
the photonic crystal emits light at a wavelength corresponding to an edge of the stop-band that the organic electroluminescent emitter material overlaps, wherein the edge of the stop-band occurs at a wavelength at which measured radiance of free space luminescent light emission by the organic electroluminescent emitter material is greater than one-quarter of the peak radiance of the free space luminescent emission spectrum of the emitter material.
17. The light emitting device of claim 16 wherein the photonic crystal further comprises a stack of layers of varying refractive index.
18. The light emitting device of claim 17 wherein a layer of the stack of layers of varying refractive index comprises the organic electroluminescent emitter material.
19. The light emitting device of claim 16 wherein the device is configured to emit light from only one surface, and further a metallic reflector is formed on a surface opposite the only one surface that emits light.
20. The light emitting device of claim 16 wherein the molecules of the organic electroluminescent emitter material are spatially oriented to maximize stimulated emission parallel to the axis of transmission of the emitted light.