Organic light emitting diode with transparent electrode and method of making same

A transparent electrode is provided for an organic light emitting diode (OLED) device. The electrode may be made according to a method including: sputter-depositing a first layer of or including indium tin oxide (ITO) on a substrate; sputter-depositing a thin second metallic or substantially metallic layer on the glass substrate over the first layer to form an electrode structure, and heat treating the electrode structure at temperature(s) of at least about 400 degrees C. in order to thermally activate at least the first layer of or including ITO. The electrode structure may then be provided in an OLED device on the light-emitting side of the organic light emitting semiconductor layer.

Certain example embodiments relate to improved organic light emitting diode (OLED) devices, and/or methods of making the same. In particular, certain embodiments of this invention relate to a transparent electrode for an OLED device, and methods of making the same. In certain example embodiments, the electrode is made by sputter-depositing on a substrate a first transparent conductive oxide (TCO) layer (e.g., of or including ITO) and then a second conductive layer that is metallic or substantially metallic. The first TCO layer is located between the substrate and the second conductive layer. The first TCO layer is substantially more oxided than is the second layer, and the first and second layers are of different materials. The first and second conductive layers on the substrate may then be heat treated (HT) at high temperature(s) in order to thermally activate the first TCO layer and/or increase visible transmission of the electrode to be used in an OLED.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS

An organic light emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer(s) is a film of or based mainly on organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes in some cases. Generally, for example, at least one of these electrodes is transparent. OLEDs sometimes are used in television screens; computer monitors; small or portable system screens such as those found on mobile phones and PDAs; and/or the like. OLEDs may also sometimes be used in light sources for space illumination and in large-area light-emitting elements. OLED devices are described, for example, U.S. Pat. Nos. 7,663,311; 7,663,312; 7,662,663; 7,659,661; 7,629,741; 7,601,436, 2011/0193477, and 2009/0295283, the entire contents of all of which are hereby incorporated herein by reference.

A typical OLED comprises at least two organic layers—e.g., electron and hole transport layers—that are embedded between two electrodes. One electrode typically is made of a reflective metal. The other electrode typically is a transparent conductive layer supported by a glass substrate. The one electrode generally is the cathode, and the other electrode generally is the anode. Indium tin oxide (ITO), which is typically transparent, often is used at the front portion of the OLED as the anode.

FIG. 1is an example cross-sectional view of a typical OLED. The OLED includes glass substrate102, transparent conductive anode layer104, organic layer100, cathode layer110and cover glass112. The organic light emission layer100emits light, and light is generated by processes known from conventional OLEDs when electrons and holes injected into the organic layer100from different sides recombine. The organic layer100may include multiple layers. For example, in certain example instances the organic layer100may include a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer. An example shown inFIG. 1illustrates the organic semiconductor layer100including a hole transport layer (HTL), and electron transport layer (ETL), and an emitting layer (EL), where the ETL and emitting layer may or may not be present in one layer.

When a voltage is applied to the electrodes104and110, the charges start moving in the device under the influence of the electric field. Electrons leave the cathode, and holes move from the anode in opposite direction. For example, the recombination of these charges leads to the creation of photons with frequencies given by an energy gap between LUMO and HOMO levels of the emitting molecules, so that the electrical power applied to the electrodes is transformed into light. Different materials and/or dopants may be used to generate different colors, with the colors being combinable to achieve yet additional colors.

This disclosure relates to a design and method of making a transparent conductive electrode (e.g., anode) on the light-emitting side of the organic layer of an OLED. For example, referring to the OLED inFIG. 1, this disclosure relates to an improved electrode104on the light emitting side of the organic layer100and a method of making the same. The electrode may be based on ITO. A second thin metallic or substantially metallic layer may be deposited on top of the first layer of or including ITO. The first and second layers are deposited (directly or indirectly) on the substrate, and may be deposited for example via sputtering at approximately room temperature. The thin metallic or substantially metallic layer may be of a single metal (e.g., Ni, Pt, or Au), a mixture of Ni, Pt, and/or Au, or may be a metallic or substantially metallic alloy (e.g., NiCrMo, NiCrAlFe, NiTi, NiMo, or mixtures thereof). After the thin layer is deposited over the TCO, the substrate (e.g., glass or quartz substrate) with the TCO layer and the thin layer thereon is subject to heat treatment (HT) in order to (a) thermally activate at least the TCO layer for desired electrical and/or optical properties, (b) increase the work function (WF) of the electrode, and/or (c) increase visible transmission of the electrode. The thin film over the TCO is advantageous in that it (i) serves as an oxygen blocking layer during subsequent thermal activation of the ITO to reduce undesired excessive oxidation of the ITO during its thermal activation, and/or (ii) controls the Fermi level of the transparent electrode to minimize or reduce the electrical barrier with the Highest-Occupied-Molecular Orbital (HOMO) of the Hole Transport Layer (HTL) of the OLED.

The first TCO layer (e.g., of or including ITO) is substantially more oxided as deposited than is the second layer which is a thin metallic or substantially metallic layer. The thin metallic or substantially metallic layer may be either non-oxided or slightly oxided in different embodiments. In certain example embodiments, as deposited, the first TCO layer contains at least about 15% more oxygen, more preferably at least about 20% more oxygen, even more preferably at least about 30% more oxygen, and most preferable at least about 40% more oxygen, than does the subsequently deposited thin metallic or substantially metallic layer.

In certain example embodiments of this invention, there is provided method of making an organic light emitting diode (OLED) device, the method comprising: sputter-depositing a first layer comprising indium tin oxide (ITO) on a glass substrate; sputter-depositing a second metallic or substantially metallic layer on the glass substrate over and directly contacting the first layer comprising ITO to form an electrode structure, so that the first layer comprising ITO is located between at least the substrate and the second metallic or substantially metallic layer; heat treating the electrode structure including the substrate, the first layer comprising ITO, and the second metallic or substantially metallic layer, at temperature(s) of at least about 300 degrees C. in order to thermally activate the first layer comprising ITO; and providing the electrode structure in an OLED device so that an organic light emitting semiconductor layer is located between said electrode structure and another electrode. The sputter-depositing of the first and second layers may be performed at approximately room temperature.

In certain example embodiments of this invention, there is provided an OLED comprising: a transparent conductive electrode structure comprising a first layer comprising ITO and a second conductive layer on a substrate, the first layer comprising ITO being located between at least the substrate and the conductive layer; wherein the second conductive layer comprises one or more of Ni, Pt, Au, NiCrMo, NiCrAlFe, NiTi, NiCr, and NiMo; an organic light emitting layer located between said transparent conductive electrode structure and another electrode, and wherein said transparent conductive electrode structure is on a light emitting side of the organic light emitting layer.

In certain embodiments of this invention, there is provided an organic light emitting diode (OLED) comprising: a transparent conductive electrode structure comprising a first layer comprising indium tin oxide (ITO) and a second conductive layer on a substrate, the first layer comprising ITO being located between at least the substrate and the conductive layer; the first layer comprising ITO is thicker than the second metallic or substantially metallic layer, and the second metallic or substantially metallic layer has a work function of at least 4.5, more preferably of at least 4.6, and even more preferably of at least 4.7; and an organic light emitting layer located between said transparent conductive electrode structure and another electrode, and wherein said transparent conductive electrode structure is on a light emitting side of the organic light emitting layer.

These and other embodiments, features, aspect, and advantages may be combined in any suitable combination or sub-combination to produce yet further embodiments.

DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS

This disclosure relates to a design and method of making a transparent conductive electrode (e.g., anode) on the light-emitting side of the organic layer100of an OLED. The electrode may be based on ITO.

It is desirable for a light-emitting side electrode (e.g., anode) of an OLED to be highly conductive, have high optical transmission in the visible, and provide a low potential barrier for an effective hole injection into the HTL of the organic film/layer100. It is desirable for the electrode to have a small energy difference between its Fermi level and the HOMO of the HTL. It is also desirable for the electrode to be chemically stable so as to not significantly interact in an adverse manner with the HTL of the organic film/layer100.

The injection levels of holes into the HTL and then into the emissive layer of the organic film/layer100are desired to be comparable with injection levels of electrodes from the cathode110. High-temperature deposited ITO has traditionally been used for anodes in OLEDs, and ITO has a sufficiently high Fermi level (or work function in its degenerated state). The balance in the carrier injection levels, however, may shift toward a more efficient electron injection due to (a) measures which are sometimes used to minimize the potential barrier between the cathode110and the ETL (and possibly the emitting layer, EL), such as for example incorporation of a thin LiF layer between an alloyed Al cathode110and tris(8-hydroxyquinoline)aluminum (Alq3) HTL/EL, etc., and (b) use of a non-optimized ITO for the anode such as ITO deposited at room temperature and not subsequently thermally activated. In such a case, the energy distance between the Fermi level of the ITO and its vacuum level may be insufficient which can lead to formation of a significant energy barrier between the ITO anode and the HOMO level of the HTL. Note that materials identified in the organic layer100are simply for purposes of example (e.g., Alq3 for the ETL/EL; and NPB for the HTL).

But room-temperature sputter-deposition of ITO is desirable in large-area sputter deposition scenarios because: less equipment is needed since there is no need to heat the substrate prior to and/or during deposition so as to reduce costs, sputtering rates are typically higher if the substrate (e.g., glass substrate) is not heated, and the process is often cleaner during room temperature deposition because out-gassing and other contamination effects can be suppressed. Accordingly, sputter deposition without intentional heating of the substrate offers certain cost advantages due, primarily, to the lower capital, lower maintenance and higher deposition rates.

However, when the ITO is deposited (e.g., sputter-deposited) at room temperature, post-deposition thermal activation of the ITO is often desired to optimize its opto-electrical properties. Higher temperatures of post-deposition heating allow better ITO properties. At about 350-500 C., however, typical ITO abruptly loses its conductivity when heated in air. A problem with post-deposition activation of the ITO is that its optimal crystallization temperature (about 550 degrees C.) is much higher than the temperature causing a drop in conductivity due to over-oxidation (about 370 degrees C.). Attempts to address this solely by providing a protective dielectric layer over the ITO have been found to be insufficient because of the desire for conductive properties of the electrode in the direction normal to the surface.

Certain example embodiments of this invention relate to a superstrate transparent ITO based electrode (e.g., anode) for OLEDs, which uses at least one layer10of approximately room temperature deposited ITO optimized in such a way as to provide optimal electrical and optical properties after post-deposition thermal activation. The ITO layer10is capped by a thin metal or metal alloy layer20, which protects the ITO layer10from over-oxidation during HT and optimizes the ITO Fermi level (or work function in the degenerated state) to minimize/reduce the potential barrier for the free holes for a better matching, or substantial matching, to the HTL of the OLED. The ITO layer10(10′) can be a single layer of or including ITO, a combination of layers of or including ITO with different oxidation states, or a combination of an ITO layer with another layer(s) of TCO material such as zinc oxide and/or indium zinc oxide.

Material(s) for the thin metallic or substantially metallic layer20may be chosen based on one or more of the following: (a) chemically and mechanically stable, (b) minimum interaction with the HTL, (c) having high work function (WF) for minimizing/reducing the potential barrier between the ITO and the HOMO of the HTL, and (d) having a small optical absorption in the visible upon the post-deposition HT/baking. Examples include the following single metals and their alloys: Ni (WF=5.01 eV), Pt (WF=6.4 eV), Au (WF=5.3 eV), NiCrMo (e.g., WF of about 4.7 eV with an approximate weight ratio Ni/Cr/Mo of 56/22/13 or 65/16/16), and NiCr (WF=4.6 eV). Other possible allows for layer20include NiCrAlFe, NiTi, and NiMo. Example NiCrMo inclusive alloys that may be used for metallic or substantially metallic layer20are described in U.S. Ser. No. 13/064,062, filed Mar. 3, 2011, the disclosure of which is hereby incorporated herein by reference. Such example NiCrMo alloys for layer20(20′) include NiCrMo alloys known as C22, BC1, B3, C4, C276 and C2000. The combination of the ITO10(10′) with a thin metal or metal alloy layer20(20′) determines the Fermi level (or WF) of the entire electrode. In certain embodiments of this invention, the metallic or substantially metallic layer20(and/or20′) has a work function of at least 4.5, more preferably of at least 4.6 or 4.7.

Metallic NiCrMo-based alloys (e.g. C22, etc.) for use as layer20(20′) are desired in certain example embodiments. Table 1 below show the composition of an example metallic NiCrMo alloy known as C22 that may be used for layer20(20′) for example. It will be appreciated that the NiCrMo based alloy for layer20(20′) includes more Ni than Cr, more Ni than Mo, and may include more Cr than Mo. Small amounts of other elements may also be present as set forth in Table 1 below.

As shown inFIG. 2, after deposition of a first layer10of or including ITO, a high work function (WF) thin metallic or substantially metallic layer20is deposited on the substrate102over (e.g., optionally directly contacting) the first layer. The first and second layers (10and20) are deposited (directly or indirectly) on the substrate, and may be deposited for example via sputtering at approximately room temperature (or possibly at an elevated temperature in certain embodiments). The thin metallic or substantially metallic layer20may be of a single high work function metal (e.g., Ni, Pt, or Au), a mixture of Ni, Pt, and/or Au, or may be a high work function metallic or substantially metallic alloy (e.g., NiCrMo, NiCrAlFe, NiTi, NiMo, or mixtures thereof). After the thin layer20is deposited over the TCO10, the substrate (e.g., glass or quartz substrate)102with the TCO layer10and the thin layer20thereon is subject to heat treatment (HT)30in order to (a) thermally activate at least the TCO layer10for desired electrical and/or optical properties, (b) increase the work function (WF) of the electrode (10and/or20), and/or (c) increase visible transmission of the electrode (10and/or20). After the heat treatment30, the electrode structure is provided in an OLED device so that an organic light emitting semiconductor layer (included in film/layer100) is located between said electrode structure10′,20′,102and another electrode110as shown inFIG. 3. The thin film20over the TCO10is advantageous in that the thin metallic or substantially metallic film20(i) serves as an oxygen blocking layer during subsequent thermal activation of the ITO10to reduce undesired excessive oxidation of the ITO layer10during its thermal activation, and/or (ii) controls the Fermi level of the transparent electrode to minimize or reduce the electrical barrier with the Highest-Occupied-Molecular Orbital (HOMO) of the Hole Transport Layer (HTL) of the OLED.

The first TCO layer (e.g., of or including ITO)10is substantially more oxided as deposited than is the second layer20which is a thin metallic or substantially metallic layer. The thin metallic or substantially metallic layer20may be either non-oxided or slightly oxided in different embodiments. In certain example embodiments, as deposited, the first TCO layer10contains at least about 15% more oxygen, more preferably at least about 20% more oxygen, even more preferably at least about 30% more oxygen, and most preferable at least about 40% more oxygen, than does the subsequently deposited thin metallic or substantially metallic layer20. Again, the thin metallic or substantially metallic layer20as deposited may contain little or no oxygen, and little or no nitrogen.

Thus, a transparent superstrate electrode10,20(or10′,20′), such as an anode, for OLED devices includes at least two layers, namely an ITO based layer10(10′ after HT) and a thin metal inclusive layer20(20′ after HT) originally deposited on substrate102. The stoichiometry of the ITO layer10as deposited is optimized to ensure optimal/desired ITO electrical and optical characteristics upon HT (e.g., baking). The capping metal or metal alloy layer20serves as an oxygen blocking layer during subsequent thermal activation of the ITO10to reduce undesired excessive oxidation of the ITO layer10during its thermal activation, so as to prevent or reduce degradation of the opto-electrical properties of the ITO. The high WF metal or metal alloy layer20also has been found to significantly reduce the potential barrier between the ITO10,10′ and the HOMO of the HTL in the OLED, compared to if the layer20was not present between the ITO and the HTL.

While heat treatment (HT) of the layers10and20is desirable in preferred embodiments of this invention at least in order to activate the ITO to desired level(s), this invention is not so limited and it is possible to omit heat treatment of the layers10,20in certain alternative embodiments of this invention. In non-HT embodiments, the high WF metallic or substantially metallic layer20(20′) in an OLED will still minimize or reduce the potential barrier between the ITO10(10′) and the HOMO of the HTL in the OLED, and be advantageous in this respect.

Optionally, bus bars (not shown) may also be provided on the substrate102so as to electrically contact the transparent electrode in certain example embodiments. For example, either before or after the heat treating30, a conductive film of one or more layers may be deposited on the substrate102over electrode layers10(or10′) and20(or20′). The conductive film may be etched after the thermal activation30, into a pattern defining the bus bars over layer20′. For purposes of example, the conductive bus bar film (not shown) may be of a multilayer film of Cr/Al/Cr in certain example embodiments. The bus bars are not shown in the drawings for purposes of simplicity.

Referring toFIGS. 2-3, there is provided a method of making an electrode for use in an organic light emitting diode (OLED) device. A first layer10of or including ITO is sputter deposited on a substrate (e.g., of or including glass or quartz)102, and then there is performed sputter-depositing of a second metallic or substantially metallic layer20on the substrate102over and directly contacting the first layer10of ITO to form an electrode structure (seeFIG. 2). Sputter-depositing of the ITO layer10and sputter-depositing of the metallic or substantially metallic layer20may each comprise sputter-depositing at approximately room temperature. As sputter-deposited the first layer of or including ITO10is substantially more oxided than is the second metallic or substantially metallic layer20(layer20may or may not be slightly oxided). As sputter-deposited, the second metallic or substantially metallic layer20may contain little or no oxygen and little or no nitrogen. Then, the structure including substrate102and layers10,20is heat treated30at temperature(s) of at least about 300 degrees C. in order to thermally activate at least the ITO layer10. The heat treating (HT)30may comprise heat treating the structure102,10,20at temperature(s) of at least about 400 degrees C., more preferably of at least about 500 degrees C., more preferably of at least about 550 degrees C. in certain example embodiments. The heat treatment may be, for example, at about 550 degrees C. for a period of from about 0.5 to 30 minutes (e.g., about two minutes).

As sputter-deposited and prior to HT30, the first layer10of or including ITO may contain at least 15% more (more preferably at least 20% more, even more preferably at least 30% more, and still more preferably at least 40% more (mol %)) oxygen than the second metallic or substantially metallic layer20. In certain example embodiments, the ITO layer10(or10′) may be thicker than the metallic or substantially metallic layer20(or20′), and the metallic or substantially metallic layer20(or20′) has a work function (WF) of at least 4.5 (more preferably at least 4.6, and even more preferably at least 4.7) in certain example embodiments. In certain example embodiments, the ITO layer10(10′) may be at least 50 nm thicker (more preferably at least 100 nm thicker) than the metallic or substantially metallic layer20(20′).

In certain example embodiments, sputter-depositing of the ITO layer10may be performed by sputtering at least one ceramic target of indium, tin and oxygen (e.g., In/Sn ratio in the target and resulting layer of from 80/20 to 95/5, so that there is more In present than Sn), or alternatively the ITO layer10may be sputter deposited using at least one metal target of InSn in an atmosphere including both argon and oxygen gas (e.g., same In/Sn ratios in the target and layer as identified above for the ceramic target sputtering). Sputter-depositing of the metallic or substantially metallic layer20may be performed by sputtering a metal target (e.g., an Ni target, a Pt target, an Au target, or an NiCrMo target) in an atmosphere including argon gas and either entirely or mostly devoid of oxygen gas.

The ITO layer10may be from about 100-200 nm thick (e.g., about 150 nm thick), and the metallic or substantially metallic layer20may be from about 0.5 to 50 nm thick, more preferably from about 1 to 20 nm thick (e.g., about 10 nm thick).

After heat treating30, the electrode structure102,10′,20′ may have a visible transmission of at least about 75%, more preferably of at least about 80%, more preferably of at least about 82%, and most preferably of at least about 84%. Moreover, after the heat treating30, the heat treated electrode (e.g., layer10′ and/or layer20′) may have a specific resistivity of less than or equal to about 0.30 mOhms-cm, more preferably less than or equal to about 0.27 mOhms-cm, and/or a Fermi level in excess of 3.2 eV.

While the substrate102may be of or including glass in preferred embodiments, it is also possible that the substrate may be of a different transparent material such as quartz in alternative embodiments.

After the heat treating/thermal activation30, the electrode structure described above (e.g., including the heat treated layers10′ and20′, and optionally the substrate102) is provided in an OLED device as shown inFIG. 3so that an organic semiconductor film/layer100, including an organic light emitting semiconductor layer, is located between the electrode structure and another electrode such as cathode110. For example, after the heat treating, the organic layer/film100and cathode may be deposited on the substrate over the electrode structure. At least one layer in the organic film/layer100emits light, and light is generated when electrons and holes injected into the organic film/layer100from different sides recombine. The organic film/layer100may include multiple layers, but always includes at least one light emitting layer. For example, in certain example embodiments, organic film/layer100may include a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and an electron injection layer. An example shown inFIG. 3illustrates the organic semiconductor film/layer100including a hole transport layer (HTL), and electron transport layer (ETL), and an emitting layer, where the ETL and emitting layer may or may not be present in one layer. When a voltage is applied to the electrodes10′,20′ and110, the charges start moving in the device under the influence of the electric field. Electrons leave the cathode110, and holes move from the anode10′,20′ in the opposite direction, so that the electrical power applied to the electrodes is transformed into light.FIG. 3illustrate that the electrode110is a cathode, and the transparent electrode including the ITO10′ is the anode, however the “cathode” and “anode” may be reversed in certain example embodiments so that the cathode may be transparent and include layers10′ and20′.

In certain example embodiments, in one or more steps not shown, CRI matching layers, antireflective (AR) coatings, and/or the like may be provided in the OLED device in order to increase optical transmission in the visible. For example, an AR layer(s) may be provided either between the layer10(or10′) and substrate102, or on the major surface of substrate opposite the layers10′,20′. In certain example embodiments, a layer of or including silicon nitride and/or silicon oxide may be provided between the substrate102and the ITO layer10(or10′).

These techniques similarly may be used in inorganic light emitting diodes (ILEDs), polymer light emitting diode (PLEDs), and/or other diode applications.

As used herein, the terms “on,” “supported by,” and the like should not be interpreted to mean that two elements are directly adjacent to one another unless explicitly stated. In other words, a first layer may be said to be “on” or “supported by” a second layer, even if there are one or more layers therebetween.

In certain embodiments of this invention, there is provided a method of making an electrode for use in an organic light emitting diode (OLED) device, the method comprising: sputter-depositing a first layer comprising indium tin oxide (ITO) on a substrate; sputter-depositing a second metallic or substantially metallic layer on the substrate over and directly contacting the first layer comprising ITO to form an electrode structure, so that the first layer comprising ITO is located between at least the substrate and the second metallic or substantially metallic layer, wherein as sputter-deposited the first layer comprising ITO is substantially more oxided than is the second metallic or substantially metallic layer; and heat treating the electrode structure including the substrate, the first layer comprising ITO, and the second metallic or substantially metallic layer, at temperature(s) of at least about 300 degrees C. in order to thermally activate the first layer comprising ITO.

In the method of the immediately preceding paragraph, the first layer may consist essentially of ITO.

In the method of any of the preceding two paragraphs, as sputter-deposited, the second metallic or substantially metallic layer may contain little or no oxygen.

In the method of any of the preceding three paragraphs, the substrate may be of or comprises glass.

In the method of any of the preceding four paragraphs, as sputter-deposited, the first layer comprising ITO may contain at least 15% more (more preferably at least 20% more, even more preferably at least 30% more, and still more preferably at least 40% more (mol %)) oxygen than the second metallic or substantially metallic layer.

In the method of any of the preceding five paragraphs, the first layer comprising ITO may be thicker than the second metallic or substantially metallic layer, and the second metallic or substantially metallic layer has a work function of at least 4.5 (more preferably at least 4.6, and even more preferably at least 4.7).

In the method of any of the preceding six paragraphs, the first layer comprising ITO may be at least 50 nm thicker (more preferably at least 100 nm thicker) than the second metallic or substantially metallic layer.

In the method of any of the preceding seven paragraphs, said heat treating may comprise heat treating the electrode structure including the substrate, the first layer comprising ITO, and the second metallic or substantially metallic layer, at temperature(s) of at least about 400 degrees C., more preferably of at least about 500 degrees C., more preferably of at least about 550 degrees C. The heat treatment may be, for example, at about 550 degrees C. for a period of from about 0.5 to 30 minutes (e.g., about two minutes).

In the method of any of the preceding eight paragraphs, said sputter-depositing of the first layer comprising ITO and/or said sputter-depositing of the second metallic or substantially metallic layer may each comprise sputter-depositing at approximately room temperature.

In the method of any of the preceding nine paragraphs, said first layer comprising ITO may be sputter-deposited on the substrate so as to directly contact the substrate.

In the method of any of the preceding ten paragraphs, said sputter-depositing of the first layer comprising ITO may comprise sputtering a ceramic target comprising indium, tin and oxygen; and said sputter-depositing of the second metallic or substantially metallic layer may comprise sputtering a metal target.

In the method of any of the preceding eleven paragraphs, the first layer comprising ITO may be from about 100-200 nm thick (e.g., about 150 nm thick).

In the method of any of the preceding twelve paragraphs, the second metallic or substantially metallic layer may be from about 0.5 to 50 nm thick, more preferably from about 1 to 20 nm thick (e.g., about 10 nm thick).

In the method of any of the preceding thirteen paragraphs, after said heat treating the electrode structure may have a visible transmission of at least about 80%, more preferably of at least about 82%, and most preferably at least about 84%.

In the method of any of the preceding fourteen paragraphs, after said heat treating, the method may include providing the electrode structure in an OLED device so that an organic light emitting semiconductor layer is located between said electrode structure and another electrode.

In the method of any of the preceding fifteen paragraphs, the second metallic or substantially metallic layer may comprise or consist essentially of one or more of Ni, Pt, and Au.

In the method of any of the preceding sixteen paragraphs, the second metallic or substantially metallic layer may comprise or consist essentially of one or more of NiCrMo, NiCrAlFe, NiTi, NiCr, and NiMo.

In the method of any of the preceding seventeen paragraphs, the second metallic or substantially metallic layer may comprise or consist essentially of NiCrMo as deposited and/or after HT.

In certain embodiments of this invention, there is provided an organic light emitting diode (OLED) comprising: a transparent conductive electrode structure comprising a first layer comprising indium tin oxide (ITO) and a second conductive layer on a substrate, the first layer comprising ITO being located between at least the substrate and the conductive layer; wherein the second conductive layer comprises one or more of Ni, Pt, Au, NiCrMo, NiCrAlFe, NiTi, NiCr, and NiMo; an organic light emitting layer located between said transparent conductive electrode structure and another electrode, and wherein said transparent conductive electrode structure is on a light emitting side of the organic light emitting layer.

In certain embodiments of this invention, there is provided an organic light emitting diode (OLED) comprising: a transparent conductive electrode structure comprising a first layer comprising indium tin oxide (ITO) and a second conductive layer on a substrate, the first layer comprising ITO being located between at least the substrate and the conductive layer; the first layer comprising ITO is thicker than the second metallic or substantially metallic layer, and the second metallic or substantially metallic layer has a work function of at least 4.5, more preferably of at least 4.6, and even more preferably of at least 4.7; and an organic light emitting layer located between said transparent conductive electrode structure and another electrode, and wherein said transparent conductive electrode structure is on a light emitting side of the organic light emitting layer.

In the OLED of any of the preceding two paragraphs, the substrate may be a glass substrate.

In the OLED of any of the preceding three paragraphs, the first layer comprising ITO may contain at least 15% more (more preferably at least 20% more) oxygen than does the second conductive layer.

In the OLED of any of the preceding four paragraphs, the first layer comprising ITO may be at least 50 nm thicker (more preferably at least 100 nm thicker) than the second conductive layer.

In the OLED of any of the preceding five paragraphs, the second conductive layer may be metallic or substantially metallic.

In the OLED of any of the preceding six paragraphs, the first layer comprising ITO may be from about 100-200 nm thick (e.g., about 150 nm thick).

In the OLED of any of the preceding seven paragraphs, the second conductive layer may be from about 0.5 to 50 nm thick, more preferably from about 1 to 20 nm thick (e.g., about 10 nm thick).

In the OLED of any of the preceding eight paragraphs, the electrode structure comprising the first layer comprising ITO, the second conductive layer, and the substrate, may have a visible transmission of at least about 80%, more preferably of at least about 82%, and most preferably at least about 84%.

In the OLED of any of the preceding nine paragraphs, the second conductive layer may comprise or consist essentially of one or more of NiCrMo, NiCrAlFe, NiTi, and NiMo.

In the OLED of any of the preceding ten paragraphs, the second conductive layer may comprise or consist essentially of NiCrMo which may or may not be oxidized.

In the OLED of any of the preceding eleven paragraphs, the second conductive layer may comprise or consist essentially of one or more of Ni, Pt, Au, NiCr, and NiCrMo.

In the OLED of any of the preceding twelve paragraphs, the metal of the second conductive layer has a work function (WF) of at least 4.5, more preferably of at least 4.6.

In the OLED of any of the preceding thirteen paragraphs, the first layer may consist essentially of ITO.