WO2014045219A1

WO2014045219A1 - Light source

Info

Publication number: WO2014045219A1
Application number: PCT/IB2013/058666
Authority: WO
Inventors: Georg Friedrich Gaertner; Stefan Peter Grabowski; Horst Greiner; Hans-Peter Loebl
Original assignee: Koninklijke Philips N.V.; Philips Deutschland Gmbh
Priority date: 2012-09-21
Filing date: 2013-09-19
Publication date: 2014-03-27

Abstract

The invention relates to a light source (1) with a light generating unit (2) like an organic light emitting diode and an outcoupling device (6) for coupling light out of the light generating unit. The outcoupling device comprises a first layer (3) with an outcoupling structure facing the light generating unit, a second layer (4) having a refractive index being smaller than the refractive index of the first layer, and a third layer (5) having a refractive index being similar to the refractive index of the second layer. The combination of the first layer with the outcoupling structure and the additional third layer leads to an increased outcoupling efficiency of the light generated by the light generating unit into surrounding air.

Description

Light source

FIELD OF THE INVENTION

The invention relates to a light source comprising a light generating unit and an outcoupling device for coupling light out of the light generating unit. The invention relates further to the outcoupling device.

BACKGROUND OF THE INVENTION

WO 2006/035341 Al discloses an illumination system comprising at least one organic light emitting diode (OLED) deposited on a rigid and translucent substrate. The OLED includes first and second electrodes for providing electrical power to the OLED. The substrate is arranged on a translucent waveguide. At a side facing away from the OLED the waveguide is provided with means for coupling out light emitted by the OLED, wherein in operation light generated by the OLED travels through the substrate and the waveguide and is emitted by the illumination system in a direction substantially normal to the waveguide.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an outcoupling device for coupling light out of a light generating unit like an OLED, which allows for an increased outcoupling efficiency. It is a further object of the present invention to provide a light source comprising the outcoupling device and the light generating unit.

In a first aspect of the present invention an outcoupling device for coupling light out of a light generating unit is presented, wherein the outcoupling device comprises:

a first layer for facing the light generating unit, the first layer having a first refractive index and an outcoupling structure,

a second layer having a second refractive index being smaller than the first refractive index, and

a third layer having a third refractive index being similar to the second refractive index, wherein the first, second and third layers are arranged such that the light to be coupled out of the light generating unit traverses the first, second and third layers in this sequence.

The combination of the first layer, which has the relatively high first refractive index and the outcoupling structure, and of the second and third layers, which have relatively small refractive indices, leads to an increased outcoupling efficiency.

The arrangement of the first, second and third layers such that the light to be coupled out of the light generating unit traverses the first, second and third layers in this sequence means that, before the light enters the second layer, it has traversed the first layer at least one time, and that, before the light enters the third layer, it has traversed the first layer and the second layer at least one time.

The outcoupling structure within the first layer can be, for instance, a scattering structure or another structure influencing the light generated by the light generating unit. The outcoupling structure can be an inner outcoupling structure within the first layer. The inner outcoupling structure within the first layer may be formed by scattering particles within the first layer. Moreover, the outcoupling structure can also be formed on a surface of the first layer facing the light generating unit and/or on a surface of the first layer facing the second layer, i.e. the outcoupling structure can also be formed by a structured interface between the first layer and the light generating unit or the first layer and the second layer, respectively.

The outcoupling structure preferentially comprises scattering elements like scattering particles within the first layer or hills and valleys on the respective interface, wherein the scattering elements may have dimensions in the order of the wavelength of the light generated by the light generating unit. In an embodiment the scattering elements have dimensions in the range of 0.2 to 4.0 micrometers. If the scattering elements are scattering particles within the first layer, the dimensions of the scattering elements are preferentially in the range of 0.2 to 1.5 micrometers, further preferred within the range of 0.2 to 0.7 micrometers. If the scattering elements are provided by a surface modulation on a surface of the first layer, the scattering elements have preferentially dimensions in the range 0.5 to 2.0 micrometers.

Two refractive indices, in particular, the second and third refractive indices, are preferentially regarded as being similar, if the difference between the refractive indices is smaller than 6 percent of the average of the two refractive indices over the visible wavelength range, i.e. over 400 to 780 nm, further preferred smaller than 3 percent of the average of the two refractive indices and, even further preferred, if the two refractive indices are equal, which is at least the case, if, for instance, the second and third layers are made of the same material.

In an embodiment the light generating unit is an OLED comprising an anode layer, a cathode layer and intermediate layers between the anode layer and the cathode layer, wherein the first refractive index is similar to a) an average of the refractive indices of the intermediate layers or b) an average of the refractive indices of the intermediate layers and the anode layer or c) the refractive index of the anode layer. If the refractive index of the anode layer is larger than the refractive index of the intermediate layers, it is preferred that the first refractive index is similar to the refractive index of the anode layer. These first refractive indices can lead to an increased efficiency of coupling light from the OLED into the first layer, which in turn can lead to a further increased total outcoupling efficiency. The intermediate layers are preferentially organic layers.

The materials of the three layers are transparent. The first layer can comprise at least one of glass, in particular, optical glass such as a float glass plate, transparent glass ceramics, transparent ceramics, also including transparent oxides, nitrides, carbides, fluorides, and transparent plastic, transparent synthetic, especially acrylic glass. Also the second and/or the third layer can comprise at least one of this list. In an embodiment, at least one of the first, second and third layers is a glass layer. For example, the second layer can be a float glass plate with a refractive index within the range 1.5 to 1.56 and the third layer can be a float glass plate with the same refractive index. Preferentially, between the second layer and the third layer an intermediate index matching glue or varnish is present. Instead of a glass plate, for example, a transparent plastic plate like a acrylic glass, especially plexiglass, plate can be used as the third layer.

The light generating unit preferentially comprises a light generation area, wherein the third layer has preferentially a thickness within the range of 5 to 30 percent of the square root of the light generation area. In particular, the third layer may have a thickness within the range of 3 to 30 mm. The second layer and the third layer may be integrated such that they form a single layer having a thickness within the range of, for instance, 4 to 35 mm. If the second and third layers, in particular, the single layer forming the second and third layers, comprise these dimensions, the outcoupling efficiency can be further increased.

The first layer may have a thickness within the range of 3 to 100 micrometers. The absorption of the first, second and third layers is preferentially smaller than 10 percent, further preferred smaller than 5 percent. It is preferred that a side surface of the third layer comprises a reflective coating. It is also preferred that a side surface of the third layer is tilted. For instance, the third layer can be formed as a truncated pyramid or a truncated cone, wherein the surface of the third layer having the larger diameter or the surface of the third layer having the smaller diameter may face the second layer. Also the reflective coating of the side surface and the tilting of the side surface can further improve the outcoupling efficiency.

In a preferred embodiment the outcoupling device is adapted to couple light out of several light generating units, wherein the third layer has a continuous extension for covering the several light generating units. Since the outcoupling device is dimensioned such that it couples light out of several light generating units, wherein the third layer is continuous between different light generating units, a relatively seamless tiled light source can be provided.

The third layer comprise a first surface directed towards the first layer and a second surface directed away from the first layer, wherein the second surface may comprise a semitransparent mirror coating. This coating can further increase the uniformity of the light emission. Moreover, it can give a mirror- like appearance of the second surface, which will in use be the outer surface of the outcoupling device, if the light generating units are switched off.

The third layer may comprise structures in intermediate regions between the light generating units for redirecting light more towards the second surface. This can further increase the efficiency of coupling the light out of the light generating unit.

The structures are preferentially formed in at least one of the first surface and the second surface of the third layer. The structures can be grooves. The grooves may be arranged in the intermediate regions such that they resemble a chocolate bar type geometry or reversed chocolate bar type geometry of the third layer.

The structures may have tilted surfaces, wherein the surfaces are preferentially tilted by a tilt angle within a range of 30 to 70 degrees, further preferred within a range of 45 to 60 degrees. The structures may have a triangular, hexagonal or rounded cross section. These shapes of the structures can further improve the outcoupling efficiency.

The structures may comprise a reflective coating. For instance, in an embodiment the inside of the preferred grooves is preferentially coated with a mirror layer like an aluminium layer or a silver layer. However, in another embodiment the grooves may not be coated with a mirror layer. Especially if the grooves are formed in the second surface, which is an outside surface directed away from the first layer, the grooves are not coated with a mirror layer, because through the surfaces of the grooves the light can leave the third layer to the outside.

It is preferred that the outcoupling device is adapted to allow the light generating units to be arranged in an arrangement, in which each light generating unit occupies a first area surrounded by a free second area, in which a light generating unit is not present, wherein a sum of the first area and the second area is similar to the product of a) the first area with b) the ratio of the outcoupling efficiency of the outcoupling device with the third layer to the outcoupling efficiency of the outcoupling device without the third layer. The sum of the first area and the second area is preferentially regarded as being similar to the product of the first area with the ratio of the respective outcoupling efficiencies, if the sum differs by less than 10 percent from the product. Such a configuration of the light generating units leads to a further increased uniformity of the light provided by the several light generating units. The light generating unit generates the light in the first area such that the first area may be regarded as being a light generation area, whereas the second surrounding area can be regarded as being a non-light generation area.

The light generating unit is preferentially an OLED, wherein the first layer of the outcoupling device can already be provided with an anode layer such that only the further layers of the OLED need to be deposited onto the anode layer for forming the OLED. In particular, a manufacturer may manufacture the outcoupling device with the anode layer, wherein the same or another manufacturer may then deposit the further layers of the OLED for producing a light source.

In a second aspect of the present invention a light source for providing light is presented, wherein the light source comprises a light generating unit for generating light and an outcoupling device for coupling light out of the light generating unit, according to the first aspect of the present invention.

In a preferred embodiment the light source comprises several light generating units, wherein the outcoupling device is adapted to couple light out of the several light generating units and wherein the third layer of the outcoupling device has a continuous extension for covering the several light generating units.

In a further embodiment the light source may comprise several light generating units and several outcoupling devices associated with the several light generating units for coupling light out of the several light generating units, wherein the several light generating units and the several outcoupling devices form a three-dimensional arrangement. In particular, at least one of the several light generating units in combination with at least one of the several outcoupling devices forms at least one side wall of the three-dimensional arrangement and at least one other of the several light generating units in combination with at least one other of the several outcoupling devices form a top part or a bottom part of the three-dimensional arrangement. For instance, a pair of a light generating unit and an outcoupling device can form a side wall of the three-dimensional arrangement and another pair of a light source and an outcoupling device can form a top part or a bottom part of the three-dimensional arrangement. Moreover, each side wall of the three-dimensional arrangement can be formed by a pair of a light generating unit and an outcoupling device and the top part or the bottom part of the three-dimensional arrangement can be formed by a further pair of a light generating unit and an outcoupling device. The side walls and the top or bottom part of the three-dimensional arrangement can be rectangular, in order to form, for instance, a cube-like arrangement. However, the side walls and the top or bottom part can also have another shape, in order to form other kinds of three-dimensional arrangements. For instance, the side walls can be rectangular and the top or bottom part can be a hexagon, or the side wall can be cylindrical and the top or bottom part can be circular, in order to form a cylindrical three-dimensional arrangement.

It shall be understood that the outcoupling device of the first aspect and the light source of the second aspect have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 shows schematically and exemplary an embodiment of a light source for providing light,

Fig. 2 shows schematically and exemplarily a light generating unit of the light source,

Figs. 3 to 5 show schematically and exemplarily further embodiments of a light source for providing light, Fig. 6 shows a graph exemplarily illustrating the dependence of the

outcoupling efficiency from the thickness of a third layer of a light source in accordance with Figure 1,

Fig. 7 shows a graph exemplarily illustrating a dependence of a luminous efficacy of a thickness of a third layer of a light source in accordance with the embodiment shown in Fig 1 ,

Fig. 8 shows schematically and exemplarily a bottom view of the light source shown in Figure 4, and

Figs. 9 to 12 illustrate schematically and exemplarily further embodiments of a light source for providing light.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows schematically and exemplary an embodiment of a light source for providing light. The light source 1 comprises a light generating unit 2 for generating light and an outcoupling device 6 for coupling light out of the light generating unit 2 into air.

The light generating unit 2 is schematically and exemplary shown in more detail in Figure 2. In this embodiment the light generating unit 2 is an OLED comprising a cathode layer 10, an anode layer 12 and intermediate layers 11 between the cathode layer 10 and the anode layer 12, wherein these layers form a stack of layers 8. In this embodiment the cathode layer 10 is a non-transparent metal layer, which comprises, for instance, aluminum or silver, and the anode layer 12 is an indium tin oxide (ITO) layer. The intermediate layers 11 can be, for example, two or more layers and include known organic layers, which are configured such that light is generated by the intermediate layers 11, if a voltage is applied to the cathode layer 10 and the anode layer 12 via a voltage source 7. The light generated within the intermediate layers 11 can leave the light generating unit 2 through the anode layer 12 in an outcoupling direction 13. The light source 1 shown in Figure 1 emits therefore the light 9, which has been coupled out into air, in the bottom direction. In another embodiment in addition the cathode layer 10 can be transparent such that the generated light can leave the OLED 2 also through the cathode layer 10. The OLED 2 can therefore be a bottom emitter as shown in Figure 1 , or a bottom and top emitter.

The outcoupling device 6 is adapted to couple light out of the light generating unit 2 into the surrounding, in particular into air, in the outcoupling direction 13. The outcoupling device 6 comprises a first layer 3 facing the light generating unit 2, in particular, contacting the anode layer 12 of the light generating unit 2, wherein the first layer 3 has a first refractive index and an inner outcoupling structure schematically indicated in Figure 1 by the stripes. The outcoupling device 6 further comprises a second layer 4 having a second refractive index being smaller than the first refractive index and a third layer 5 having a third refracting index being similar to the second refractive index, wherein the first, second and third layers 3, 4, 5 are arranged such that the light to be coupled out of the light generating unit 2 traverses the first, second and third layers 3, 4, 5 in this sequence for coupling the generated light out into air, wherein at interfaces between layers having different refractive indices the light may of course be partly reflected.

The second layer 4 of the outcoupling device 6 is preferentially a glass substrate, i.e. a glass plate like a float glass plate. The third layer 5 of the outcoupling device 6 is preferentially a highly transparent transparent glass plate, which may be polished. The first layer 3 has a first refractive index being similar to an average of the refractive indices of the intermediate layers 11, i.e. the first refractive index of the first layer 3 preferentially matches with the average of the refractive indices of the intermediate layers 11 of the light generating unit 2. In this embodiment the intermediate layers 11 have an average refractive index of about 1.8. The first refractive index of the first layer 3 is therefore also preferentially about 1.8. In other embodiments the first refractive index of the first layer 3 can have another value, wherein preferentially the first refractive index is equal to or larger than 1.7.

The first layer 3 is preferentially made of an inorganic material being transparent to light generated by the OLED 2. In particular, the inorganic material used for the first layer 3 does preferentially not absorb the light generated by the OLED 2.

The first layer can be made of silicon oxynitride, i.e. SiO_xN_y, with a refractive index of 1.8, silicon nitride with a refractive index of 1.9 or another suitable oxide with a refractive index being larger than 1.7. In other embodiments the first layer can also be made of another material having a relatively large refractive index, which is preferentially larger than 1.7, and being optically transparent for the light generated by the light generating unit.

The first layer comprises an inner outcoupling structure formed by scattering particles which may be, for instance, Si0₂, Ti0₂ or Nb₂0₅ particles. These particles may have a diameter within the range of 0.2 tol .5 micrometers and further preferred within the range of 0.2 to 0.7 micrometers. In particular, the scattering particles may have a diameter that corresponds to the wavelength of the light generated by the light generating unit 2.

The third layer 5 has a thickness within the range of 5 to 10 mm and the second layer 4 can have a smaller thickness between, for instance, 0.7 to 2.0 mm. The third layer 5 comprises tilted side surfaces 14, which may comprise a reflective coating. In this embodiment the third layer 5 is formed as a truncated pyramid or a truncated cone, wherein the second layer 4 is provided on the surface of the third layer 5, which has a smaller diameter than an opposing outer surface of the third layer 5 and which in Figure 1 forms a top surface. The third layer 5 can be regarded as being a flat low index extractor plate which together with the outcoupling structure in the first layer leads to a significant increase of the outcoupling efficiency.

Although in Figure 1 the second layer 4 and the third layer 5 are formed by two different glass elements, which are put together, in another embodiment the second layer and the third layer can also be integrated such that they form a single layer having a larger thickness, which may correspond to the sum of the thicknesses of the separate second and third layers 4, 5 of the outcoupling device 6. For instance, this single integrated layer, which may be used instead of the second and third layers 4, 5 exemplary and schematically shown in Figure 1 , may have a thickness within the range of 6 to 11 mm.

Figure 3 shows schematically and exemplary a further embodiment of a light source for providing light. In this embodiment the light source 101 comprises several light generating units 2 for generating light and an outcoupling device 106 for coupling light out of the light generating units 2. The light generating units 2 are similar to the light generating unit described above with reference to, for instance, Figure 2, wherein the voltage source for applying the voltage to the respective stack 8 of layers of the respective light generating unit 2 is not shown in Figure 3 for clarity reasons.

The outcoupling device 106 comprises a first layer 3 facing the light generating units 2. In particular, the first layer 3 comprises several first layer parts, wherein each first layer part is coupled to the respective light generating unit 2 and is similar to the first layer describe above with reference to Figure 1. The outcoupling device 106 further comprises a second layer 4 formed by several second layer parts assigned to the respective light generating unit 2, wherein each second layer part corresponds to the second layer described above with reference to Figure 1. Moreover, the outcoupling device 106 comprises a continuous third layer 105, which has a continuous extension for covering the several light generating units 2. Since the outcoupling device 106 is dimensioned such that it can couple light out of several light generating units 2, wherein the third layer 105 is continuous between the different light generating units 2, a relatively seamless tiled light source 101 can be provided.

The third layer 105 comprises a first surface 115 directed towards the light generating units 2 and a second surface 116 directed away from the light generating units 2, i.e. the first surface 115 is an inner surface and the second surface 16 is an outer surface. The third layer 105 comprises structures 117 in intermediate regions between the light generating units 2 for redirecting light more towards the second outer surface 116. These structures 117 further increase the efficiency of coupling the light out of the light generating units 2 into air. In this embodiment the structures 117 are formed on the inner first surface 115 and include grooves. The grooves are arranged in the intermediate regions such that they provide a chocolate bar or reversed chocolate bar appearance of the third layer 105.

The grooves have a triangular cross section such that the surfaces 118 of the grooves are tilted. The tilt angle of the surfaces 118 of the grooves is preferentially within a range of 30 to 70 degrees, further preferred within a range of 45 to 60 degrees. In other embodiments the grooves can also have another shape, for instance, they can have a hexagonal or rounded cross section. The tilt angle is preferentially defined with respect to the vertical direction, i.e. a direction being perpendicular to the layer structure and parallel to the outcoupling direction.

The structures in the third layer 105 for directing the light more to the second outer surface 116 also include outer tilted side faces 114, which may be shaped and tilted in accordance with the surfaces of the grooves in the intermediate regions between the light generating units 2. The tilted surfaces 114, 118 of the structures of the third layer 105 may comprise a reflective coating. In particular, the inside 118 of the grooves and the outer tilted surfaces 114 may be coated with a mirror layer. The light, which is coupled out into the air by using the outcoupling device 106, is indicated by arrows 109.

Figure 4 shows schematically and exemplary a further embodiment of a light source for providing light. The light source 201 disclosed in Figure 4 is similar to the light source 101 shown in Figure 3, except for the second and third layers of the outcoupling device 206. In this embodiment, the second and third layers are integrated such that they form a single layer 205 having a first surface 215 facing the several light generating units 2 and a second surface 216 directed away from the light generating units 2, wherein the layer 205 comprises structures 217 with surfaces 214, 218, which are similar to the structures described above with reference to Figure 3. In particular, also in this embodiment, tilted surfaces 214, 218 are provided with a reflective coating. The light, which is coupled out by using the outcoupling device 206, is indicated by the arrows 209 in Figure 4.

Figure 5 shows schematically and exemplary a further embodiment of a light source for providing light. The light source 301 shown in Figure 5 is similar to the light source described above with reference to Figure 3, except for the third layer 305 of the outcoupling device 306. Also the third layer 305 comprises structures 317 with surfaces 318, 314, wherein the structures 317 include grooves located in intermediate regions between the light generating units 2. However, in this embodiment, the structures 317 are provided on a second outer surface 317 being opposite to a first inner surface 315, which faces the light generating units 2. Moreover, the surfaces 314, 318 do preferentially not comprise a reflective coating, because in this embodiment the light generated by the light generating units 2 may also be outcoupled into air through the tilted surfaces 314, 318. The light, which has been generated by the light generating units 2 and coupled out into the air by using the outcoupling device 306, is indicated by the arrows 309.

If the light source comprises several light generating units 2, the outcoupling device can be adapted to allow the light generating units 2 to be arranged in an arrangement, in which each light generating unit 2 occupies a first area 119, 219, 319 surrounded by a free second area, in which a light generating unit 2 is not present, wherein a sum 120, 220, 320 of the first area 119, 219, 319 and the second area is similar to the product of a) the first area 119, 219, 319 and b) a ratio of the outcoupling efficiency of the outcoupling device with the third layer to the outcoupling efficiency of the outcoupling device without the third layer. In particular, if the thickness of the third layer, which may be regarded as being a flat extraction plate, is given, the outcoupling device and the light generating units are preferentially adapted such that the sum of the respective first area and the respective second area is similar to the product of the respective first area with the ratio of the outcoupling efficiency of the outcoupling device with the third layer having the given thickness to the outcoupling efficiency of the outcoupling device without the third layer. This condition may be described by following equation:

A, + Α_Ί = A, ,

1^{2 1} OE wo

wherein Α denotes the first area, A₂ denotes the second area, OE_w denotes the outcoupling efficiency with the third plate and OE_wo denotes the outcoupling efficiency without the third plate.

For instance, in an illustrative example the first area Α can be 11.4 cm² and for a given thickness of the third layer of, for example, 10.7 mm the outcoupling efficiency OE_w may be 90.5 percent. Moreover, the outcoupling efficiency OE_wo without the third layer may be 65 percent. In accordance with above mentioned equation, these values lead to a second area A₂ of 4.5 cm² , which amounts to 40 percent of the OLED area. If in this example the first area Α_λ is rectangular with a first side length of 3.8 cm and a second side length of 3.0 cm and if it is assumed that the distance between a side of the first area and an outer side of the second area in a direction perpendicular to the side of the first area is always the same, i.e. independently of which side of the first area is considered, this distance is 0.6 cm.

The light generating units are preferentially arranged in a rectangular regular pattern such that for each light generating unit the first area is larger than the second area. Moreover, the first areas of the different light generating units are preferentially similar and also the second areas of the different light generating units are preferentially similar. The second area surrounding a first area is preferentially defined by the half distance between neighboring light generating units, in particular between the stacks of layers 8.

In the embodiments described above with reference to Figures 3 to 5, the second outer surface 116, 216, 316 of the third layer 105, 205, 305 can comprise a semitransparent mirror coating. This coating can further increase the uniformity of the light emission. Moreover, it can give a mirror- like appearance of the second outer surface, if the light generating units are switched off. It should be noted that preferentially the reflective coating provided on the surfaces 118, 114, 218, 214 of the structures shown in Figures 3 and 4 reflects the light generated by the light generating units preferentially substantially completely, whereas the semitransparent coating, which may be provided on the outer second surface of the third layer, is preferentially adapted to allow the generated light to pass through, especially diffusely.

It should be noted that in Figures 1 to 5 the dimensions are not to scale. For instance, the second layer will generally be much thinner in relation to the thickness of the third layer than shown in, for instance, Figures 1, 3 and 5. For instance, the thickness of the second layer may be smaller than 1 mm, whereas the thickness of the third layer may be, for instance, 30 mm. Moreover, the thickness of the third layer 205 shown in Figure 4 may be similar to or larger than the sum of the thicknesses of the second layer and the third layer shown in Figure 3 or shown in Figure 5.

The preparation of medium to large area, in particular small molecule, OLEDs, especially of the layer structure consisting of organic materials, is generally carried out by thermal evaporation in vacuum on a light transmitting substrate like float glass. A typical OLED structure, especially a monochrome one, consists of a thin transparent anode, intermediate layers formed by a hole transport layer, a light emission zone, an electron transport layer and a cathode layer. Unfortunately typically about 50 percent of the light generated remains in the OLED layer stack because of guided modes, about 25 percent remain in the substrate and only 20 to 25 percent are coupled into air and can be used for lighting applications.

The outcoupling efficiency into air can be increased by, for instance, a factor of two, if an intermediate layer with high refractive index, i.e. the first layer, with internal outcoupling is used in combination with a flat and rather thin macro extractor, i.e. the third layer, having a relatively low refractive index and being, for instance, a glass plate with a thickness between 5 to 10 mm on the second layer, which may also be a glass plate having a relatively low refractive index. By using this configuration, wherein an intermediate index matching glue or varnish may be present between the second and third layers, can improve the outcoupling efficiency, to, for instance, 75 to 85 percent for large area light sources, i.e. light sources covering an area of about 10 cm². For small area light sources, i.e., for instance, for light sources covering an area of 20 mm², the outcoupling efficiency may be even larger.

The outcoupling efficiency is preferentially defined as the ratio of a) the luminous efficacy of the respective light source comprising the light generating unit and the respective outcoupling device to b) the luminous efficacy of the light generating unit with the first and second layers, but without the third layer, wherein the light generating unit with the second layer only is arranged on a half sphere macro extractor, which allows the entire light within the second layer to be extracted into the surrounding air. The diameter of the half sphere macro extractor is preferentially at least two times larger than a lateral dimension of the light generating unit, which may be a square OLED. The outcoupling efficiency can also be determined in another way. For instance, instead of measuring the luminous efficacy the luminous flux can be directly used for determining the outcoupling efficiency.

In an exemplary embodiment the luminous efficacy of a warm wide OLED could be increased from 35 lm/W to 80 lm/W by using the first layer having the internal outcoupling structure and the third layer being, in this example, an extra glass plate having a thickness of 5 mm. If the glass plate forming the third layer has a thickness of 10 mm, the luminous efficacy can be further increased to, for instance, 89 lm/W.

Figure 6 shows exemplarily the outcoupling efficiency OE in percent depending on the total thickness of the second and third layers. The outcoupling efficiency has been measured for two large area OLEDs on an outcoupling device comprising first, second and third layers for forming a first light source and a second light source,

respectively, wherein the first layer of the first light source does not comprise an outcoupling structure and the first layer of the second light source comprises an outcoupling structure. The stack of layers of the first OLED covers an area of 10.7 cm² and the stack of layers of the second OLED covers an area of 11.4 cm². The first and second OLEDs are hybrid warm white OLEDs. In Figure 6 the squares and circles indicate measured outcoupling efficiencies for the first and second light sources, wherein the line 20 represents a fit to the circles and the line 21 represents a fit to the squares. The measurements have been performed in an integrating sphere.

It can be seen in Figure 6 that with increasing total thickness of the second and third layers the outcoupling efficiency increases, wherein the outcoupling efficiency of the second light source indicated by the line 20 is larger than the outcoupling efficiency of the first light source indicated by the line 21. Thus, due to the combination of a) the outcoupling structure of the first layer and b) the third layer the outcoupling efficiency can be increased in comparison to just using the third layer.

Figure 7 shows schematically and exemplarily the luminous efficacy depending on the total thickness of the second and third layers of third and fourth light sources, respectively. The third light source comprises a large area OLED occupying an area of 10.7 cm² and an outcoupling device comprising first, second and third layers and the fourth light source comprises a large area OLED with an outcoupling device comprising first, second and third layers, wherein the OLED of the fourth light source occupies an area of 11.4 cm². Both OLEDs are stacked hybrid white OLEDs. The first layer of the third light source does not comprise an outcoupling structure and the first layer of the fourth light source comprises an outcoupling structure.

The circles and the triangles indicate measured values, wherein the line 22 is an interpolation line representing the fourth light source and the line 23 is an interpolation line representing the third light source. As can be seen in Figure 7, with increasing total thickness of the second and third layers the luminous efficacy increases, wherein for the fourth light source comprising the first layer with the outcoupling structure the luminous efficacy is significantly larger than the luminous efficacy measured for the third light source comprising the first layer without the outcoupling structure.

For the exemplary measurements shown in Figures 6 and 7, the configuration schematically and exemplarily indicated in Figure 1 has been used.

The third layer can regarded as being a flat macro extractor having the form of, for instance, a flat truncated pyramid, for instance, as schematically and exemplarily shown in Figure 1. This flat truncated pyramid may also be used turned around by 180 degrees. Also round flat macro extractors in the form of truncated cones may be used as third layer.

Several OLEDs, in particular, several large area OLEDs, can be assembled to a larger area combined OLED with a suitably structured flat macro extractor, in order to achieve a seamless tiled light source, in particular, as exemplary described above with reference to Figures 3 to 5. In particular, as shown in Figure 3, the light source an comprise OLEDs 2 on an intermediate layer 3 with internal outcoupling, which comprises the relatively high first refractive index, on a base 4, which has the relatively low second refractive index, on a flat macro extractor plate 105 with grooves below the non active border area with electrical connections (not shown in Figure 3), wherein the grooves have a triangular cross section and are oriented to the inside. Preferentially the inside of the grooves is coated with a mirror layer. The intermediate layer with the internal outcoupling is the first layer, the base with the relatively low second refractive index is the second layer and the flat macro extractor plate is the third layer. Moreover, corresponding to Figure 4, in another embodiment, the flat macro extractor plate and the base can be integrated into a single element 205, wherein on top of this single element 205, which forms an integrated second and third layer, the first layer 3 with the outcoupling can be provided, wherein on this first layer 3 with the outcoupling a structured ITO layer of the OLEDs can be provided. Thus, in this embodiment, the single layer 205 with the first layer 3 and the structured ITO layer can be used as a substrate for OLED deposition. Furthermore, in accordance with Figure 5, the grooves can be oriented to the outside of the light source, wherein in this case, the inside of the grooves is preferentially not coated with a mirror layer, because the light can also escape from the tilted sides.

Figure 8 shows schematically and exemplarily a bottom view of the light source 201 schematically and exemplarily shown in Figure 4. In Figure 8 it can be seen that the light generating units 2 with the outcoupling device 206 comprising the structures 217 form a two-dimensional arrangement having a chocolate bar like appearance. In another embodiment such a two-dimensional arrangement can also be obtained by arranging several of the combinations of light generating units 2 and outcoupling devices 6, as schematically and exemplarily shown in Figure 1, side by side. Several combinations of light generating units 2 and outcoupling devices 6 can also be arranged such that they form a three- dimensional arrangement as will be described in the following with reference to Figures 9 to 12. Figure 9 shows schematically and exemplarily a light source 401 comprising several light generating units 2 and several outcoupling devices 6 associated with the several light generating units 2 for coupling light out of the several light generating units 2, wherein the several light generating units 2 and the several out coupling devices 6 form a three- dimensional arrangement. The light generating units 2 and the outcoupling devices 6 can be similar to the light generating unit and the outcoupling device described above with reference to, for instance, Figure 1. However, in this embodiment a first combination of a light generating unit 2 and an outcoupling device 6 is hexagonally shaped for forming a top part 430 and several second pairs of light generating units 2 and outcoupling devices 6 are rectangularly shaped for forming side walls 431 of the three-dimensional arrangement.

Optionally, also the bottom part of the three-dimensional arrangement can be formed by a pair of a light generating unit 2 and an outcoupling device 6, which are hexagonally shaped. But, preferentially the bottom side remains open for a base mount and for electrical feedthroughs. Figure 10 schematically and exemplarily illustrates the side walls 431 and the top part 430 of the light source 401 in a virtually unfolded view.

In the embodiment shown in Figures 9 and 10 a six-sided OLED luminaire with flat extractor plates and a hexagon top OLED is provided. In another embodiment the three-dimensional arrangement can have another shape. For instance, as illustrated in Figure 11, which schematically and exemplarily shows a virtually unfolded view of a further light source 501, also the top part 530 can be rectangularly shaped and formed by a combination of a rectangularly shaped light generating unit 2 and a rectangularly shaped outcoupling device 6. Since also the side walls 531 are made of rectangularly shaped combinations of outcoupling devices 6 and light generating units 2, the entire three-dimensional arrangement is rectangular. In particular, the light source 501 is a four-sided luminaire with four rectangular sides formed by rectangular light generating units and outcoupling devices, wherein the outcoupling devices have a diameter being larger than the diameter of the light generating units, and with a square top plate formed by a further combination of a light generating unit and an outcoupling device, wherein also regarding the top plate the diameter of the outcoupling device is larger than the diameter of the light generating unit.

Figure 12 shows schematically and exemplarily a further embodiment of a light source. In this embodiment the light source 601 comprises light generating units 2 and outcoupling devices 6 forming a cylindrical three-dimensional arrangement, wherein the light generating unit 2 forming a part of the side wall 631 of the light source 601 is an OLED on a foil and the outcoupling device 6 of the side wall 631 is cylindrically formed. For instance, the several layers of the outcoupling device 6 can be formed by several cylindrical elements forming the first, second and third layers of the outcoupling device 6, wherein these cylindrical elements are put together. Moreover, also in this embodiment the second and third layers can be integrated such that they form a single layer, wherein in this case the outcoupling device 6 can be formed by a first circular layer, which faces the light generating unit 2, which has a first refractive index and which has an outcoupling structure, and a second cylindrical layer having integrated the second and third layers. The light source 601 further comprises a circular top part 630 formed by a circular light generating unit 2 and a circular outcoupling device 6. Also this circular outcoupling device 6 comprises the first to third layers, wherein the second and third layers may be integrated in a single layer. Moreover, also in this embodiment the outcoupling device 6 of the top part 630 preferentially has a diameter being larger than the diameter of the circular light generating unit 2 of the top part 630.

In an embodiment, the side wall 631 of the light source 601 may be formed by a three-dimensionally shaped transparent extraction envelope, which may be attached via an index matching fluid, varnish or glue to a three-dimensionally shaped light generating unit 2 being, in this embodiment, a three-dimensionally shaped OLED on a foil. The foil may be adapted to form the first layer of the outcoupling device 6 and the extraction envelope may form integrated second and third layers of the outcoupling device 6. The extracting envelope may be a Plexiglas or glass cylinder forming the integrated second and third layers and having a thickness, which may be similar to the thickness described above with respect to the second and third layers.

The first, second and third layers can also be formed in another way. For instance, the second layer can be provided on an inner surface of a Plexiglas or glass cylinder forming the third layer, wherein a further layer having an outcoupling structure can be provided on the second layer for forming the first layer.

Above described light sources like the light source described above with reference to Figure 5 may comprise transparent extraction plates or extraction envelopes, which may have a groove structure at an outer surface, which can lead to a seamless or structured tiling of several light generating units. Several light generating units can be assembled in a plane or can be combined to a three-dimensional luminaire. Instead of seamless tiling also a structural effect of the borders can be used as a decorative effect.

Regarding the three-dimensional light sources, i.e. regarding the three- dimensional arrangements of the light generating units and outcoupling devices, the side emission can be useful and a redirection of this emission may not be needed. This can further improve the outcoupling efficiency.

The light sources described above with reference to Figures 9 to 12 comprise several combinations of light generating units 2 and outcoupling devices 6, wherein in Figures 9 to 11 each of these combinations can be regarded as forming a tile of the respective light source. These tiles can be attached to each other by attaching the corresponding side faces of the respective outcoupling devices to each other by using an attaching means like a glue. The respective contacts can be, for instance, index matched, and they can be transparent for using a side emission. However, they can also comprise two-sided mirrors. For example, contact sides of truncated pyramids can be attached to each other with an intermediate two- sided mirror.

Although in the embodiments described above with reference to Figures 9 to 12 each side wall, top part or bottom part is formed of a single combination of a light generating unit and an outcoupling device, in other embodiments a side wall, a top part or a bottom part may also comprise several combinations of light generating units and

outcoupling devices. For instance, the side wall of a light source can consist of a flat arrangement of tiles, wherein each tile comprises a combination of a light generating unit and an outcoupling device.

Although Figures 9 to 12 show several variants of lantern type luminaires, in other embodiments the light sources can also form other lantern type luminaires. In particular, light sources can be provided having another geometrical shape, in particular, another regular geometrical shape. For instance, triangles, hexagons or other flat elements can be arranged in a three-dimensional polyhedron shape. Moreover, the light sources can have the shape of a cube, a tetrahedron, a dodecahedron consisting of pentagon surfaces, an icosahedron or suitable combinations thereof, for instance, a combination of a tetrahedron with an icosahedron, wherein two triangular sides of these two hedrons, which have the same dimensions, can be attached to each other. Also stellations can be formed. Instead of regular polyhedrons with regular side areas of the same type and dimensions, also irregular, especially convex polyhedron can be formed. Generally one side of the light source is open for a base mount or a top mount, respectively, and for electrical feedthroughs.

The tilt angle of the sides of the grooves and the width of the cross section of the grooves, in particular, of the triangular cross section of the grooves, can be chosen such that a seamless tiling of combined large area OLEDs can be achieved. Preferentially, the tilt angles of the sides of the grooves range from 30 to 70 degrees, further preferred from 45 to 60 degrees.

Although, in the cross sectional views shown in Figures 3 to 5, only three light generating units are shown, in other embodiments the light source can of course comprise less or more light generating units in a certain direction of the preferably two-dimensional arrangement of the light generating units forming the respective light source.

The third layer is preferentially a rectangular layer, i.e. in a top view it is preferentially rectangular. However, the third layer can also have another shape, for instance, it can be circular, triangular, hexagonal, et cetera.

Although in above described embodiments certain dimensions of the different layers are mentioned, in other embodiments the layers can also have other dimensions. For instance, if the light generating unit is a rectangular OLED occupying an area of 3 times 3 cm², the thickness of the third layer can be in the range of 5 to 15 mm or in the range of 5 to 10 mm. If the OLED occupies an area of 13 times 13 cm², the third layer can have a thickness in the range of 15 to 30 mm or in the range of 15 to 25 mm. The second layer can be relatively thin, for instance, it can have a thickness between 0.7 and 2.0 mm.

Although in some above described embodiments the sides of the grooves have a reflective coating, in other embodiments instead of or in addition to the reflective coating the sides can also be adapted to scatter the light, for instance, by roughening the sides.

Although in above described embodiments comprising several light generating units the outcoupling device is preferentially adapted such that a seamless tiling can be provided, the outcoupling device may also be adapted such that spatial structures, in particular, structures between the light generating units, are visible. For instance, the light source comprising several light generating units and the outcoupling device can be configured such that the above described chocolate bar type geometry or reversed chocolate bar type geometry of the third layer is visible.

Although in above described embodiments the first layer comprises an inner outcoupling structure, alternatively or in addition the first layer can also comprise an outcoupling structure on the surface facing the light generating unit and/or on the surface facing the second layer. Thus, the interfaces between the first layer and the light generating unit and/or the first layer and the second layer can be structured for providing the outcoupling structure. Although in the above described embodiments the light generating unit is an OLED, the light generating unit can also be another kind of light generating means. For instance, the light generating unit can also be an inorganic light emitting diode.

Although in above described embodiments the outcoupling device is optically connected with the light generating unit, in other embodiments the outcoupling device can also be a separate device, which may already comprise an anode layer, in particular, an ITO layer, on the first layer, wherein this separate outcoupling device can be provided to an OLED producer, which provides the OLED layers on the outcoupling device for producing a light source comprising the OLED and the outcoupling device.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.

The invention relates to a light source with a light generating unit like an organic light emitting diode and an outcoupling device for coupling light out of the light generating unit. The outcoupling device comprises a first layer with an outcoupling structure facing the light generating unit, a second layer having a refractive index being smaller than the refractive index of the first layer, and a third layer having a refractive index being similar to the refractive index of the second layer. The combination of the first layer with the outcoupling structure and the additional third layer leads to an increased outcoupling efficiency of the light generated by the light generating unit into surrounding air.

Claims

CLAIMS:

1. An outcoupling device for coupling light out of a light generating unit (2), the outcoupling device (6; 106; 206; 306) comprising:

a first layer (3) for facing the light generating unit, the first layer having a first refractive index and an outcoupling structure,

a second layer (4; 205) having a second refractive index being smaller than the first refractive index, and

a third layer (5; 105; 205; 305) having a third refractive index being similar to the second refractive index,

wherein the first, second and third layers are arranged such that the light to be coupled out of the light generating unit (2) traverses the first, second and third layers in this sequence.

2. The outcoupling device as defined in claim 1, wherein the light generating unit (2) is an organic light emitting diode comprising an anode layer (12), a cathode layer (10) and intermediate layers (11) between the anode layer (12) and the cathode layer (10), wherein the first refractive index is similar to a) an average of the refractive indices of the

intermediate layers (11) or b) an average of the refractive indices of the intermediate layers

(11) and the anode layer (12) or c) the refractive index of the anode layer (12).

3. The outcoupling device as defined in claim 1, wherein the light generating unit (2) comprises a light generation area and wherein the third layer (5; 105; 305) has a thickness being within the range of 5 to 30 percent of the square root of the light generation area.

4. The outcoupling device as defined in claim 1, wherein the third layer (5; 105; 305) has a thickness within the range of 3 to 30 mm.

5. The outcoupling device as defined in claim 1, wherein the second layer and the third layer are integrated such that they form a single layer (205) having a thickness within the range of 4 to 35 mm.

6. The outcou ling device as defined in claim 1, wherein the outcou ling device (106; 206; 306) is adapted to couple light out of several light generating units (2), wherein the third layer (105; 205; 305) has a continuous extension for covering the several light generating units (2).

7. The outcoupling device as defined in claim 6, wherein the third layer (105; 205; 305) comprises a first surface (115; 215; 315) directed towards the first layer (3) and a second surface (116; 216; 316) directed away from the first layer (3), wherein the third layer (105; 205; 305) comprises structures (117; 217; 317) in intermediate regions between the light generating units (2) for redirecting light more towards the second surface (116; 216; 316).

8. The outcoupling device as defined in claim 7, wherein the structures (117; 217; 317) have tilted surfaces (118; 218; 318), wherein the surfaces (118; 218; 318) are tilted by a tilt angle within a range of 30 to 70 degrees.

9. The outcoupling device as defined in claim 7, wherein the structures (117; 217; 317) have a triangular, hexagonal or rounded cross section.

10. The outcoupling device as defined in claim 7, wherein the structures (117; 217) comprise a reflective coating.

11. The outcoupling device as defined in claim 6, wherein the outcoupling device (106; 206; 306) is adapted to allow the light generating units (2) to be arranged in an arrangement, in which each light generating unit (2) occupies a first area (119; 219; 319) surrounded by a free second area, in which a light generating unit (2) is not present, wherein a sum (120; 220; 320) of the first area (119; 219; 319) and the second area is similar to the product of a) the first area (119; 219; 319) with b) the ratio of the outcoupling efficiency of the outcoupling device (6; 106; 206; 306) with the third layer (105; 205; 305) to the outcoupling efficiency of the outcoupling device (6; 106; 206; 306) without the third layer (105; 205; 305).

12. A light source for providing light, the light source (1; 101; 201; 301; 401; 501; 601) comprising:

a light generating unit (2) for generating light,

an outcoupling device (6; 106; 206; 306) for coupling light out of the light generating unit (2) as defined in claim 1.

13. The light source as defined in claim 14, wherein the light source (1; 101; 201; 301) comprises several light generating units (2), wherein the outcoupling device (6; 106; 206; 306) is adapted to couple light out of the several light generating units (2), wherein the third layer (105; 205; 305) of the outcoupling device (6; 106; 206; 306) has a continuous extension for covering the several light generating units (2).

14. The light source as defined in claim 12, wherein the light source comprises several light generating units (2) and several outcoupling devices (6) associated with the several light generating units (2) for coupling light out of the several light generating units (2), wherein the several light generating units (2) and the several outcoupling devices (6) form a three-dimensional arrangement.

15. The light source as defined in claim 14, wherein at least one of the several light generating units (2) in combination with at least one of the several outcoupling devices (6) form at least one side wall of the three-dimensional arrangement and at least one other of the several light generating units (2) in combination with at least one other of the several outcoupling devices (6) form a top part or bottom part of the three-dimensional arrangement.