Printed transparent electrodes using a blend of silver nanowires and metal oxide nanoparticles for fully printed electronic devices

Abstract

The present invention provides a novel method for the fabrication of transparent electrodes in fully printed electronic devices. With this method, highly conductive transparent blends of silver nanowires and metal oxide nanoparticles are effectively deposited as top and bottom electrodes using a wide range of printing techniques compatible with high volume manufacturing processes. The method is particularly useful for the fabrication of fully printed optoelectronic devices such as organic photovoltaics (OPVs), perovskite solar cells (PPVs), organic light emitting diodes (OLEDs), transparent heaters, sensors, etc. The main goal of the method is to replace evaporated silver metal contacts with transparent and highly conductive printed electrodes, improving the performance of optoelectronic devices and making them compatible with large scale manufacturing of fully printed electronics. The patent includes the material processing of silver nanowires:metal oxide nanoparticle blends and the precise sequence of printing steps. Application of the method results in the fabrication of functional, high performance fully printed electronic devices.

Description

[Brief description of the drawings]

[0001] [Figure 1A] FIG. 1 shows a cross section of a multi-layer solar device. [Figure 1B] FIG. 1B is a top view of the same layout level as in FIG. 1A. [Figure 2-1] FIG. 2A shows a cross section of a multilayer OLED device. [Figure 2-2] FIG. 2B is a top view of the same layout level as FIG. 2A. [Diagram 3] FIG. 1 depicts the sequential deposition of layers to form an OPV device that may incorporate the use of a blend of silver nanowires and metal oxide nanoparticles. [Figure 4] FIG. 1 depicts the sequential deposition of layers to form an OLED device that can incorporate the use of a blend of silver nanowires and metal oxide nanoparticles. [Diagram 5] Figure 5A shows an 18x18um image of the printed silver nanowire and metal oxide layer taken with an atomic force microscope. Figure 5B shows an illustration (top view) of this layer with (I) AgNWs and (II) metal oxide nanoparticles. Figure 5C shows an illustration (side view) of this layer with (I) AgNWs and (II) metal oxide nanoparticles. [Figure 6] FIG. 1 illustrates a typical manufacturing line for printed electronic devices (PV or LED) that can incorporate the layer-by-layer deposition and use of the blends described in this disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0002] Detailed Description of the Drawings In the drawings, the dimensions of the devices are not to scale and the relative sizes between the drawings and the layers they are made of do not correspond to their actual dimensions. The multi-layer structures appear as successive rectangles, each representing a thin film. In reality, the thin films are in physical contact with each other, ultimately creating the electronic device (PV or / and LED). In the specification, the designations first layer, second layer, etc. describe the order of layers starting from the base of the device, i.e. the flexible or non-flexible substrate. The terms "on" or "follows" refer to the order in which each device layer is printed, always starting from the substrate.

[0003] Electronic devices consist of the aforementioned thin films, which work collectively, each of which contributes individually to the final operation and performance of the device. Depending on the type of each device, its operation (PV or / and LED) is determined by its active layers, where certain physicochemical phenomena occur. For both printed OPV and OLED thin film technologies, the appropriate printing technique for each thin film layer is crucial for the manufacturing process of the entire electronic device. In the R2R manufacturing process, a thin flexible substrate is fed to the manufacturing line via rollers. Subsequent to the substrate processing, printing of each layer takes place. Each printed layer enters a high temperature chamber and a suitable drying environment. By printing the subsequent thin films one after the other, the final printed electronic device (OPV, PPV, or OLED) is formed. Finally, the printed device is guided to a take-up roll and separated into the desired size.

[0004] Figures 1A and 2A are cross-sectional views of OPV (Device 9) and OLED (Device 20) devices, respectively, embodied in the present disclosure, and Figures 1B and 2B are top views of corresponding embodiments of Devices 9 and 20, respectively, of Figures 1A and 2A.

[0005] In Figures 1A-1B and 3, an OPV device 9 may comprise a flexible substrate (10), a transparent electrode (11, 30), two buffer layers (12, 40, 14, and 60), an organic (e.g., for OPV) or semi-organic (e.g., for perovskite solar cells) photoactive layer (13, 50), and a top electrode layer (15, 70) made of blended silver nanowires and metal oxide nanoparticles printed using the slot-die technology claimed in this disclosure. In Figures 2A-2B and 4, an OLED device 20 may comprise a flexible substrate (10), a transparent electrode (11, 30), two buffer layers (16, 80, 18, 100), an organic light-emitting layer (17, 90), and the same top electrode layer as claimed in the solar cell device.

[0006] Printed Electronic Devices Electronic devices may consist of multi-stacks containing conductive and semiconductive materials (e.g., organic solar cells, organic light-emitting diodes, perovskite solar cells). Such structures are fabricated as single or successive layers. Each device has its own unique multi-stack architecture and addresses different applications.

[0007] Organic solar cells and perovskite solar cells have a common structure. These devices harvest light and generate electrical energy. A solar cell may comprise a bottom electrode (anode or cathode), a buffer layer (electron or hole transport layer), a photoactive layer, a second buffer layer, and a top electrode. Both the top electrode and / or the bottom electrode may contain Ag nanowires and metal oxide nanoparticles (ZnO, AZO, SnO2, etc.) as a blend. The photoactive layer may consist of organic or inorganic blends, n- or p-doped semiconductors, metal compounds and / or halogens. As for the buffer layer, it may be n-doped and / or p-doped semiconductors, polymeric materials, metal oxide nanoparticles, etc.

[0008] An organic light-emitting diode (OLED) is a multilayer device consisting of an organic layer between two electrodes (i.e., anode and cathode) and two or more layers that inject and transport charge carriers (electrons and holes). The light-emitting layer comprises one or more layers capable of emitting light in different regions of the visible spectrum. The electrodes in an OLED architecture require a certain degree of transparency to allow the generated light to leave the device. Both the cathode and anode may contain Ag nanowires and blends of metal oxide nanoparticles (ZnO, Al-doped ZnO, SnO2, etc.).

[0009] AgNW: Synthesis and Use of Metal Oxide Nanoparticle Blends Blend AgNW: Metal oxide nanoparticles may consist of a mixture of silver nanowires combined with metal oxides. These metal oxides can be formed as nanoparticle microemulsions in a solvent compatible with the solvent of the silver nanowire solution. Such solvents may be water and / or certain alcohols. The blend of metal oxide nanoparticles and Ag nanowires can be produced under vigorous stirring with a magnetic or mechanical stirrer. The microscopic structure of the blend can be revealed using atomic force microscope images (Figure 5A). Based on these images, it can be observed that metal oxide microparticles and nanoparticles (Figure 5C_II) are deposited on the surface of the silver nanowires (Figure 5C_I) or between the silver nanowires (Figure 5B, Figure 5C). This phenomenon contributes to both the enhancement of the conductivity of the film and the uniformity of the layer, since in such an arrangement of particles the gaps between the nanowires are covered. The important parameter for forming a suitable film from this blend is that the printed film withstands high temperatures for a given period of time to achieve a quality sintering that contributes to the enhancement of the film's conductivity. Furthermore, a very important parameter during the formation of the membrane is the printing flow, which, together with the printing speed, determines the thickness of the layer produced.

[0010] The above blends can be used as electrodes in printed or semi-printed organic or semi-organic electronic devices as described in the previous paragraph. Furthermore, the same blends can also be used in surface printing techniques on transparent flexible polymer substrates to form transparent electrodes. Its use in multilayer printed electronic devices can be for the formation of cathodes or anodes, depending on whether there is a chemical agreement between the solvent of the blend and the previous layer.

[0011] As a method of using this solution, any printing technique is proposed that can match the material based on viscosity and chemical composition. In this disclosure, compatible techniques that can print or coat and fix this material are slot die, blade coating, spin coating, inkjet printing, gravure printing, flexography, and screen printing. In particular, the combination of printing the blend by these techniques and the correct drying conditions of the formed film leads to improved conductivity and homogeneity. The transparent electrodes patented herein can be full coated or printed in a specific pattern. Figure 6 shows the formation process of the printed electronic device as mentioned in the above provisions. The printing line (330) can be divided into six separate parts, including the handling and management of the printed substrate, and the printing stage (station) of the multi-layer structure. At the start (270), the flexible polymer substrate (120) is unwound from the supply roll (110) and moves on the roll (200) at a predetermined speed during printing. After being unwound, the substrate enters the first printing station (280) where the first nanolayer is printed. The printing technique (130) chosen depends on the structure to be formed. The printed substrate then enters a drying station where the substrate travels under a high temperature environment (230). Vapors during drying are collected by a suitable exhaust system (170). The printing technique varies depending on the layer to be printed. If there is no transparent electrode on the surface of the substrate, such a layer can be formed using the blend AgNW:metal oxide embodied in this disclosure in the first printing station. The printing of this layer can be done using slot-die coating and / or inkjet, or the techniques mentioned above. The process of printing all the other layers that make up the structure is similar to the previous one. Depending on the layer printed in each stage, the printing parameters for the printing flow, drying, and / or annealing of the layer are different. Once the printing process of all layers is finished, the printed flexible substrate is wound on a winder (210). [Explanation of symbols]

[0012] 9 Devices 10 Flexible substrate 11 Transparent electrode 12 Buffer layer 13 Photoactive layer 14 Buffer layer 15 Upper electrode layer 16 Buffer Layer 17 Upper electrode layer 18 Buffer Layer 20 Devices 30 Transparent electrode 40 Buffer Layer 50 Photoactive layer 60 Buffer Layer 70 Upper electrode layer 80 Buffer Layer 90 Upper electrode layer 100 Buffer Layer 110 Supply Roll 120 Flexible Polymer Substrate 130 Printing Technology 140 Printing Technology 150 Printing Technology 160 Printing Technology 170 Exhaust System 180 Exhaust System 190 Exhaust System 200 rolls, exhaust system 210 Winding machine 230 High temperature environment 240 High temperature environment 250 High temperature environment 260 High temperature environment 270 start 280 Printing Station 290 Printing Station 300 Printing Stations 310 Printing Station 320 End 330 Printing Line

Claims

1. 1. A method comprising forming a transparent printed electrode, the transparent printed electrode being printed using a metal oxide / organic / inorganic nanoparticle ink (e.g., SnO, ZnO, AZO, MoO, WO ３ (e.g., Ag, Cu) nanowire ink.

2. 2. The method of claim 1, wherein the transparent printed electrode can be used as a top or bottom electrode in printed electronic devices, such as PPV, OPV, OLED, etc.

3. 10. The method of claim 1, wherein the transparent printed electrode of claim 2 can be printed using slot-die coating, blade coating, spin coating, inkjet printing, gravure printing, flexographic printing, and screen printing techniques.

4. The method of claim 1 , wherein the nanowires are coupled to the nanoparticles without being heated above 40° C.

5. The transparent printed electrode according to claim 3, characterized in that the manufacturing method of the completely printed PPV can be printed or coated on the PPV above or below the buffer electrode (top electrode or bottom electrode, respectively).

6. 4. The transparent printed electrode according to claim 3, characterized in that it can be printed or coated as a top or bottom electrode on multi-layer thin film devices such as OPVs (single junction, multi-junction, tandem, etc.), OLEDs (single junction, polymer, host-emitter, etc.), dye-sensitized solar cells (DSSCs), transparent heaters, etc.

7. The transparent printed electrode according to claim 5 or 6, wherein the metal oxide is SnO and the metal nanowires are Ag.

8. The compatibility of the blend of silver nanowires and tin dioxide nanoparticles with the state-of-the-art printing technique slot-die coating and the non-destructive interlayer interaction of the semiconducting material of the buffer layer according to claims 1, 2 and 3 characterize this type of material blend that can be used for the fabrication of high performance conductive electrodes of other optoelectronic devices such as OPV, OLED, DSSC, etc.

9. 7. The transparent printed electrode of claims 3, 4, 5 and 6, which increases the output of printed electronic devices compared to methods in which each layer (metal oxide nanoparticles and metal nanowires) is printed separately or layer on top of each other and not printed as a blend.

10. 4. The transparent printed electrode of claim 3, characterized in that it can be printed or coated onto multi-layer thin film devices reducing the manufacturing steps of printed electronic devices (e.g. OPV, PPV, DSSC, OLED) without the need for costly vacuum processes.

11. Fabrication of fully printed high efficiency perovskite solar cells according to claim 4, characterized in that large scale perovskite PV devices (modules and panels) on flexible substrates can be fabricated in a single coating technique by using slot-die coating of the transparent printed electrodes of claim 3, a printing technique fully compatible with large scale manufacturing.

12. 5. Large scale fabrication of perovskite PV and other optoelectronic devices according to claims 3 and 4, characterized in that the fabrication process of printed optoelectronic devices can be scaled up to high volume roll-to-roll manufacturing lines.

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