Abstract:
Presented an organic light-emitting device (OLED) that includes at least one active region, at least one organic layer, a first glass plate on which the at least one active region is applied, and a second glass plate. The active region is disposed between the first and the second glass plates. The first and second glass plates are at least partially transparent in the near infrared spectral range. The OLED further includes a bonding material that includes a solder glass and is disposed between the first and second glass plates. The bonding material forms at least one frame that surrounds the active region and mechanically connects the first glass plate with the second glass plate and seals the active region. The bonding material absorbs near infrared radiation. The OLED further includes spacer particles that have a mean diameter that maintains a height between the first and second glass plates.

Description:
CROSS-REFERENCE APPLICATION 
     This patent application is a continuation of application Ser. No. 11/141,476, filed May 31, 2005 now abandoned, which claims the priority of U.S. provisional patent application Ser. No. 60/627,905, filed Nov. 15, 2004. The disclosure content of both application Ser. Nos. 11/141,476 and 60/627,905 are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to organic light-emitting devices such as light-emitting diodes (OLEDs). 
     BACKGROUND OF THE INVENTION 
     Organic devices such as OLED-devices contain at least one active organic layer on a substrate sandwiched between two electrodes. To protect the active organic layer and other functional parts of the device, a cap is bonded to the substrate with the help of a bonding material. Usually the cap is bonded to the substrate using polymeric adhesives, for example epoxy adhesives, as bonding material. The bonding material fixes the cap on the substrate and acts as a barrier to harmful atmospheric gases such as oxygen and moisture. After mounting the cap on the substrate, the adhesive has to be cured. Many commonly used adhesives can be cured by heat treatment, for example on a hot plate or in an oven. However, heat treatment can damage the active organic layer or other functional parts of the device and can therefore adversely affect the performance of the device. To avoid damaging of the device during the heat treatment, the curing temperatures are generally adjusted to the temperature tolerance of the active organic layer or other functional parts of the device and not only to the curing properties of the bonding material. On the one hand, this can lead to enhanced permeation rates for harmful atmospheric gases of the cured bonding material and on the other hand, limits the number of bonding materials suited for sealing the device. Particularly, higher curing temperatures can allow the use of bonding materials with lower permeation rates for gases like oxygen and moisture. 
     In U.S. Pat. No. 6,692,610, a method of fabricating devices such as OLED-devices is disclosed. The method includes applying an adhesive on a cap or substrate. The adhesive is partially cured to initiate the cross-linking process while remaining in the liquid phase. The cap is then mounted onto the substrate and the adhesive is cured to encapsulate the device. By partially curing the adhesive prior to mounting the cap, the curing of the adhesive can be achieved without prolonged exposure to UV-radiation or high temperatures, which can adversely impact the device. 
     However, this method requires a further process step which makes the production of devices more complicated and expensive. Furthermore, the above-mentioned U.S. Pat. No. 6,692,610 does not disclose an alternative to the heat treatment, which would allow the use of bonding material with improved barrier properties. 
     SUMMARY OF THE INVENTION 
     According to one aspect, the invention involves an organic light-emitting device. The organic light-emitting device includes at least one active region that includes at least one organic layer, a first glass plate on which the at least one active region is applied, and a second glass plate. The at least one active region is disposed between the first and the second glass plates. The first and the second glass plates are at least partially transparent in the near infrared spectral range. The organic light-emitting device further includes a bonding material that includes a solder glass and is disposed between the first and the second glass plates. The bonding material forms at least one frame that surrounds the at least one active region and mechanically connects the first glass plate with the second glass plate and seals the at least one active region. The bonding material absorbs near infrared radiation. The organic light-emitting device further includes spacer particles that have a mean diameter that maintains a height between the first and the second glass plates. 
     In one embodiment, the spacer particles are selectively disposed in areas without the at least one active region. In another embodiment, the spacer particles include a non-conductive material. In still another embodiment, the second glass plate includes a coating on a side facing the first glass plate, and the coating includes the spacer particles. In yet another embodiment, a thickness of the coating excluding the spacer particles is smaller than the mean diameter of the spacer particles. In another embodiment, the spacer particles are disposed on the first glass plate and are covered by the organic layer. In still another embodiment, the spacer particles are disposed on the first glass plate in an area atop the at least one active region. 
     According to another aspect, the invention involves an organic light-emitting device. The organic light-emitting device includes at least one active region comprising at least one organic layer, a first glass plate on which the at least one active region is applied, and a second glass plate. The at least one active region is disposed between the first and the second glass plates. The first and the second glass plates are at least partially transparent in the near infrared spectral range. The organic light-emitting device further includes a bonding material that includes a solder glass and is disposed between the first and the second glass plates. The bonding material forms at least one frame that surrounds the at least one active region and mechanically connects the first glass plate with the second glass plate and seals the at least one active region. The bonding material absorbs near infrared radiation. The organic light-emitting device further includes at least one getter material which binds harmful atmospheric gases and is disposed between the first and the second glass plates and within the frame. 
     In one embodiment, the getter material includes an alkaline earth metal. In another embodiment, the said getter material forms a layer that covers the at least one active region. In still another embodiment, the getter material includes Barium. In yet another embodiment, the getter material forms a ring and is disposed in an area between the at least one active region and the bonding material. In another embodiment, the getter material has a height equal to the height between the first and the second glass plates. In still another embodiment, the organic light-emitting device further includes a protective layer disposed between the getter material and the first glass plate. In another embodiment, the ring of the getter material includes a plurality of getter patches separated by channels. In yet another embodiment, the protective layer includes an insulating material. 
     According to still another aspect, the invention involves an organic light-emitting device. The organic light-emitting device includes a plurality of active regions. Each of the plurality of active regions includes at least one organic layer. The organic light-emitting device further includes a first glass plate on which the plurality of active regions is applied, and a second glass plate. The plurality of active regions are disposed between the first and the second glass plates. The first and the second glass plates are at least partially transparent in the near infrared spectral range. The organic light-emitting device further includes a bonding material that includes a solder glass and is disposed between the first and the second glass plates. The bonding material defines areas that are separated by parallel horizontal and parallel vertical lines of the bonding material. Each of the areas includes at least one of the plurality of the active regions. The bonding material mechanically connects the first glass plate with the second glass plate and seals the active regions. The bonding material absorbs near infrared radiation. 
     In one embodiment, the areas are separated by double-lines of the bonding material. In another embodiment, each of the areas includes at least two of the plurality of active regions. In still another embodiment, the organic light-emitting device further includes pillars separating the at least two of the plurality of active regions within each of the areas. In yet another embodiment, the pillars are of a height that maintains a height between the first and the second glass plate. In another embodiment, the first and the second glass plates are transparent in the near infrared spectral range from 0.8 μm to 1.5 μm. In still another embodiment, the organic light-emitting device further includes first electrodes located on the first glass plate and second electrodes located atop the plurality of active regions such that the first electrodes are arranged in vertical lines and the second electrodes are arranged in horizontal lines. In yet another embodiment, the organic light-emitting device further includes spacer particles having a mean diameter that maintains a height between the first and the second glass plates. In another embodiment, the organic light-emitting device further includes at least one getter material, which binds harmful atmospheric gases and which is located between the first and the second glass plate and within at least one of the areas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 3  are illustrative schematic sectional views of an OLED-device according to the invention at different fabrication steps. 
         FIGS. 4 to 6  are illustrative schematic sectional views of an OLED-device during curing of bonding material with the help of near infrared radiation. 
         FIGS. 7A to 7E  are illustrative schematic top views of OLED-devices according to the invention at different fabrication steps of a batch process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with one embodiment of the invention,  FIGS. 1 ,  2  and  3  show cross-sectional views of an OLED-device at different process steps. Referring to  FIG. 1 , the OLED-device comprises one or more active organic layers  1  with organic active material sandwiched between two electrodes  2 ,  3  formed on a substrate  4  in an active region  5 . Electrical connections to the electrodes  2 ,  3  can be made by bond wires via bond pads  6 . When an electrical current is applied to the OLED-device, electrons and holes are injected into the organic material of the active organic layer  1  by the electrodes  2 ,  3 . The charge carriers recombine within the active organic layers  1  and the released energy is emitted as visible light. 
     To form a pixel matrix of a display, the upper and lower electrode  2 ,  3  can be patterned in strips perpendicular to each other. For the patterning of the upper electrode  3 , pillars, preferably with an overhanging structure, can be used. The patterning of electrodes is described in U.S. Pat. No. 6,699,728, U.S. Pat. No. 6,696,312, and U.S. Pat. No. 6,784,009, which are incorporated by reference herein for all purposes. 
     Usually the lower electrode  2  adjacent to the substrate  4  acts as an anode forming an electrical contact with ohmic characteristics to the adjacent active organic material of the active organic layer  1  and injects holes into it. Preferably, the anode  2  comprises a material with high work function for electrons and good transparency for the light emitted by the OLED-device. A suitable material for the anode  2  is, for example, Indium-Tin-Oxide (ITO). 
     As substrate  4 , a glass plate or a plate based on polymeric plastic material can be used. In order to reduce the overall thickness of the OLED-device as far as possible, a thin substrate  4  is often used. Polymeric plastic materials, for example foil, are particularly useful for the fabrication of flexible OLED-devices. Examples for these materials are poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(enthylene naphthalate) (PEN), polycarbonate (PC), polyimides (PI), polysulfones (PSO), poly(p-phenylene ether sulfone) (PES), polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS) and poly(methyl methyleacrylate) (PMMA). 
     The active organic layers  1  can comprise one or more hole injection layers, preferably adjacent to the anode  2  with reduced injection barrier for holes. Furthermore, the active organic layers  1  can comprise one or more hole transportation layers, one or more electron transportation layers and at least one emission layer. As active organic material of the active organic layers  1 , small molecules or polymeric material can be used. Materials based on small molecules are usually deposited by evaporation, while polymeric materials are usually deposited by solvent processes like doctor-blading, spin-coating, printing processes or other common solvent processes. 
     The upper electrode  3  opposite the lower electrode  2  usually serves as a cathode. To minimize the injection barrier for electrons, the cathode  3  is preferably comprises a metal or a compound material with a low work function for electrons. Such materials are generally sensitive to corrosion or other degenerating mechanisms. For OLED-devices with polymeric active organic material, metals like Ca or Ba are often used for the cathode  3 . In order to protect these sensitive materials against external influences such as atmospheric gases and to guarantee a good electrical contact, a layer of Al or Ag (not shown) is placed on top of cathode  3 . 
     Besides the cathode  3 , the active organic layer  1  can also be impaired by external influences. Therefore, the active regions  5  comprising the electrode layers  2 ,  3  and the active organic layer  1  are encapsulated with a cap  7  as hermetically as possible. As cap  7 , a glass plate or a metal part can be used. Furthermore, the cap  7  should be mounted without direct contact to the active organic layer  1  or electrodes  2 ,  3  to avoid causing any damage to these functional parts of the OLED-device. To avoid direct contact between the active organic layer  1  and the cap  7 , the cap has a cavity corresponding to the active region  5  of the OLED-device. Alternatively, it is also possible to use a plane plate as cap  7 . The use of a plane plate as cap  7 , which is in direct contact with the active organic layer  1  can improve the encapsulation of the device, since the active organic layer  1  is not in contact with air. 
     For the encapsulation of the OLED-device, a thermally curable bonding material  8  such as epoxy adhesive or solder glass is deposited on a sealing region  9  of the substrate  4  ( FIG. 2 ) surrounding the active region  5  with the functional parts of the OLED-device. Further, the active region  5  can comprise support posts or spacer particles to avoid contact between the cap  7  and the functional parts in the active region  5 . The use of spacer particles for the encapsulation of OLED-devices is described in documents WO 01/45140 and WO 01/44865, which are incorporated herein by reference for all purposes. If spacer particles or support posts are used, it can be helpful to deposit the bonding material  8  on the support posts or spacer particles as well. Alternatively or additionally, the bonding material  8  can be deposited on the regions of the cap  7  which will contact the substrate  4  after assembly. The bonding material  8  can be deposited by means of dispensing or printing methods, for example screen printing. 
     After depositing the bonding material  8 , the cap  7  is mounted onto the substrate  4  as shown in  FIG. 3 . If epoxy adhesive is used as bonding material  8 , an initial UV-irradiation step may be necessary to initiate the curing process. 
     Subsequently, the bonding material  8  is cured by applying a broadband near infrared radiation  10  with wavelengths centered in the range of 0.8 to 1.5 μm. This sort of near infrared radiation  10  is particularly suited to achieve a homogenous drying or curing of polymeric adhesives and avoids an overheating of the polymeric surface of the adhesive sometimes caused by other kinds of infrared radiation  10 . A further characteristic of this process is that very high energy densities up to 1.5 MW/m 3  can be used, which considerably reduces the time required for curing the bonding material. 
     Since the bonding material  8  is sandwiched between the cap  7  and the substrate  4 , it is necessary for the application of the near infrared radiation  10  that at least the cap  7  or the substrate  4  is made of a material transparent to near infrared radiation  10 , such as glass, and a near infrared source  11  emitting the near infrared radiation  10  is positioned on the side of the transparent material in such a way that the infrared radiation  10  can reach the bonding material  8   
     In one embodiment of the invention, the near infrared radiation  10  is focused to yield a radiation spot with a diameter of 5 mm or a line focus with a confinement of 1 to 2 mm. Preferably, the near infrared radiation  10  emitted by the near infrared radiation source  11  is focused, for example by means of a reflector  12 , in such a way that the maximum energy density is located inside the bonding material  8  as schematically shown in  FIG. 4 . 
     In another embodiment of the invention, non-focused near infrared radiation  10  is used to cure the bonding material  8  as schematically shown in  FIG. 5 . 
     To protect the active organic layer of the OLED-device against residual near infrared radiation  10 , it can be helpful to use a shadow mask  13 . It can be used in connection with unfocussed near infrared radiation  10 , as schematically shown in  FIG. 6 , or focused near infrared radiation  10  (not shown). 
     To avoid damage of the active organic layer or other functional parts of the OLED-device by permeating harmful atmospheric gases, the active region can comprise a getter material, for example Ba, which can bind them chemically or physically. The getter material can be arranged for example as a layer (not shown) on the surface of the cap arranged opposite the active region. The getter material can also be included in the bonding material  8 . Getter materials for OLED-devices are described in more detail in US published application Nos. 2004-0051449 and US 2004-0048033, which are incorporated herein by reference for all purposes. 
       FIGS. 7A to 7E  show different steps of a batch process using at least one line-focused near infrared source  11  for the encapsulation of several OLED-devices according to one embodiment of the invention. 
     As described above in more detail, the functional parts of several OLED-devices are processed on a substrate  4 . 
     The bonding material  8  is dispensed or otherwise deposited in rims surrounding the active regions  5  of the OLED-devices and a plurality of caps  7  are positioned above for encapsulation. Furthermore, the plurality of caps  7  can be integrated on a cap substrate, such as a metal or glass plate. The plate can be plane or provide cavities corresponding to the active regions  5  of the OLED-device on the substrate  4 . 
     The bonding material  8  forms rims, which are arranged along, parallel vertical lines and parallel horizontal lines. The rims of the bonding material  8  are deposited in such a way that they define rectangular active regions  5  with width a* and height b* arranged in a regular grid such that adjacent active regions  5  are spaced from each other at a horizontal distance d H  and at vertical distance d V . In the following, the vertical lines are numbered from the left side to the right side by V 1  to V 8  and the horizontal lines from the bottom to the top by H 1  to H 6 . 
     To cure the bonding material  8 , a near infrared source  11  emitting line-focused radiation is positioned parallel to the outer vertical line V 1  of the grid on the left side above the rims formed by the bonding material  8 . By shifting the near infrared source  11  by the distance a* to the right, the next line V 2  of bonding material  8  is cured. In a subsequent step, the radiation source  11  is shifted by the distance d H  to the right to start curing the bonding material  8  surrounding the next array of OLED-devices with the vertical line V 3 . Instead of shifting the near infrared source  11  to the right, it is also possible to shift the substrate  4  to the left. In the same way as the rims of bonding material  8  limiting the vertical sides of the rectangular areas are cured, the rims of bonding material  8  limiting the horizontal sides of the rectangular areas can be cured in subsequent steps. 
     If the horizontal and vertical distances a=a*+d H  and b=b*+d V  are large enough to position two near infrared wire sources  11   a  and  11   b  parallel to each other within these distances, the number of irradiation steps can be reduced. For example, for near infrared wire sources of the Company Adphos, the minimum distance between two line-focused wire sources is 50 mm. As shown in  FIG. 7B , the vertical lines V 1  and V 3  limiting adjacent active regions can be cured in a single step by means of two vertical infrared wire sources  11   a  and  11   b  arranged parallel to each other. By shifting the near infrared wire sources  11   a ,  11   b  by the distance  2   a  to the left (or the substrate to the right), the vertical lines V 5  and V 7  the bonding material  8  can be cured in a subsequent step (see  FIG. 7B ). In the next step the near infrared wire sources  11   a ,  11   b  are positioned in such a way that the infrared wire source  11   a  is parallel above the vertical line V 2  and that the infrared wire source  11   b  is parallel to the vertical line V 4  to cure them. The other vertical lines V 6  and V 8  of bonding material  8  are cured by shifting the infrared wire sources  11   a ,  11   b  to the right (or the substrate to the left) by the distance  2   a  (see  FIG. 7C ). The distances a, a*, b and b* can have values of a few mm up to several cm. 
     The curing of the horizontally arranged rims of bonding material  8  forming the horizontal lines H 1  to H 6  by means of two horizontal wire sources  11   a  and  11   b  arranged parallel to each other at a distance b is shown in  FIGS. 7D and 7E . As described for the vertical lines V 1  to V 8  of the bonding material  8 , the horizontal lines H 1  to H 6  of bonding material  8  can be cured in subsequent steps by shifting the near infrared wire sources  11   a ,  11   b  or the substrate  4 . 
     In a first step, the infrared wire sources  11   a ,  11   b  are positioned in such a way above the bonding material  8  that the wire source  11   a  is positioned parallel above the horizontal line H 1  and the wire source  11   b  is positioned parallel above the horizontal line H 3 . After curing the horizontal lines H 1  and H 3 , the near infrared wire sources  11   a ,  11   b  are shifted to the top by the distance  2   b  and the horizontal line H 5  is cured. Equivalently to the curing of the vertical lines V 1  to V 8 , the near infrared wire sources  11   a ,  11   b  are then positioned in such a way that the wire source  11   a  is positioned parallel above the horizontal line H 2  and the wire source  11   b  is positioned parallel above the horizontal line H 4  (see  FIG. 7D ). By shifting the near infrared wire sources  11   a ,  11   b  to the top by the distance  2   b  (or the substrate to the bottom) the remaining horizontal line H 6  can be cured (see  FIG. 7E ). 
     After curing all rims of bonding material  8 , the OLED-devices can be separated, for example by sawing. 
     The method for encapsulation is not limited to OLED-devices. Furthermore, it is particularly suited for the encapsulation of organic solar cells or organic photodetectors. 
     The scope of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which particularly includes any combination of the features, which are described in the claims, even if this feature or this combination of features is not explicitly referred to in the claims or in the examples.