Printable Functional Materials For Plastic Electronics Applications

Abstract

A printable active material formulation comprises a matrix comprising a gelation material and a solvent; and at least one conductive material. A printable cathode formulation comprises a matrix comprising a thermoplastic resin and a solvent; and at least one conductive material. An organic light emitting or photovoltaic device may be manufactured using these formulations, for example by roll-to-roll printing.

Claims

1. A printable active material formulation, comprising: a matrix comprising a gelation material and a solvent; and at least one conductive material.

2. The printable active material formulation according to claim 1, wherein the gelation material comprises a cellulose derivative.

3. The printable active material formulation according to claim 2, wherein the cellulose derivative comprises at least one of an O-alkyl cellulose derivative, a hydroxyalkyl cellulose, ethyl cellulose, methyl cellulose, propyl cellulose or hydroxypropylmethylcellulose.

4. (canceled)

5. The printable active material formulation according to claim 1, wherein the solvent is a low vapor pressure solvent.

6. The printable active material formulation according to claim 5, wherein the solvent is mesitylene (1,3,5-trimethylbenzene), ethylene glycol, diethylene glycol, ethylene glycol butyl ether, diethylbenzene, tetrahydronapthalene or dichlorobenzene.

7. The printable active material formulation according to claim 1, wherein the conductive material is a polymer.

8. The printable active material formulation according to claim 7, wherein the conductive material is a light emitting polymer.

9. The printable active material formulation according to claim 7, wherein the polymer is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PVV) or poly(3-hexylthiophene-2,5-diyl) (P3HT).

10. (canceled)

11. A printable cathode formulation, comprising: a matrix comprising a thermoplastic resin and a solvent; and at least one conductive material.

12. The printable cathode formulation according to claim 11, wherein the formulation comprises two or more conductive materials.

13. The printable cathode formulation according to claim 11, wherein the at least one conductive material comprises a low work-function material and a high work-function material.

14. The printable cathode formulation according to claim 11, wherein at least one conductive material comprises a low work-function metallic material and a high work-function metallic material.

15. The printable cathode formulation according to claim 11, wherein the at least one conductive material comprises a metal oxide.

16. The printable cathode formulation according to claim 11, wherein the thermoplastic resin comprises polyurethane or an epoxy resin.

17. The printable cathode formulation according to claim 11, wherein the thermoplastic resin is cross-linked by amines, anhydrides, phenols or thiols.

18. The printable cathode formulation according to claim 11, wherein the solvent comprises 2-butoxy ethanol (ethylene glycol butyl ether) or butyl carbitol (diethylene glycol butyl ether).

19. A method of manufacturing a printable active material formulation according to claim 1, the method comprising the steps of: forming a matrix comprising a gelation material and a solvent; and adding at least one conductive material to the matrix.

20. The method according to claim 19, wherein the gelation material comprises a cellulose derivative.

21. The method according to claim 19, wherein the method further comprises the step of sonicating the gelation material and the solvent to produce a homogeneous solution.

22. The method according to claim 21, wherein the conductive material is added following sonication of the homogeneous solution of the gelation material and the solvent.

23. A method of manufacturing a printable cathode formulation in accordance with claim 11, the method comprising the steps of: forming a matrix comprising a thermoplastic resin and a solvent; and adding at least one conductive material to the matrix.

24. The method according to claim 23, wherein the method includes the step of adding a low work-function material and a high work-function material to the matrix.

25. The method according to claim 24, wherein the low work-function material and high work-function material are added as particles.

26-36. (canceled)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0035] Specific embodiments will now be described by way of example only and with reference to the following figures wherein:

[0036] FIG. 1 illustrates a device in an embodiment of the invention, wherein the device is a simple OLED device; and

[0037] FIG. 2 illustrates a device in an embodiment of the invention, wherein the device is a simple OSC device.

[0038] The device architecture illustrated in FIG. 1 shows a simple OLED device, comprising a flexible or rigid substrate 5, an ITO or any other high work function transparent conductor (bottom electrode) 4, a hole transport layer 3, typically PEDOT:PSS, an active emissive layer 2, and a low work function metal cathode (top electrode) 1. FIG. 2 shows the design of a simple OSC device comprising a flexible or rigid substrate 10, a transparent conductor (bottom electrode) 9 of ITO or any other high work function material, an electron transport layer 8, typically PEDOT:PSS, a solar cell active polymer 7, and a low work function metal cathode (top electrode) 6.

[0039] The device architectures in FIGS. 1 & 2 are for illustrative purposes only, and these structures can be either normal (as drawn) or inverted with transparent top electrodes and/or made more complex with the inclusion of further layers, not limited to: hole transport layers, electron blocking layers, hole blocking layers and/or electron injection layers.

[0040] The printable active material formulation may be a screen printable nanocomposite blend containing conductive polymers which may be used for OLED and OSC applications.

[0041] In one embodiment, the method of producing the printable active material formulation comprises the steps of dispersing ethyl cellulose at a specific weight percentage into a low vapour pressure solvent such as mesitylene followed by sonication for a prolonged time in order to produce a homogenous solution. Typically, the cellulose derivative dissolves in the solvent to form a three dimensional gel matrix. This solution of ethyl cellulose in mesitylene is used as a matrix for preparing different types of nanocomposite blends by incorporating conductive polymers such as PFO, MEH-PPV and P3HT. The nanocomposite blends produced in this manner display optimum characteristics suitable for screen printing application. These formulations are ideal for screen printing onto a range of substrates including ITO coated PET and FTO coated glass producing a film thickness between 200 to 300 nanometers. In this case, devices fabricated using screen printed active materials displayed comparable brightness and photovoltaic performance to the conventional OLEDs and OSCs with vapour deposited active materials.

[0042] The printable cathode composition may be developed using solution blending process where a thermoplastic resin matrix comprising a solvent was formed, and wherein finely ground particles of a low work-function metal were mixed with relatively high work-function metal particles and subsequently loaded onto the thermoplastic resin matrix. Such a composition containing metallic particles with dissimilar work-functions acts as a high performance cathode material for OLEDs and OSCs. In case of OLEDs this composition is able to provide low turn-on voltage with attractive device performance.

EXAMPLES

[0043] The following examples describe the fabrication of a fully screen printable organic light emitting diode using screen printable active material along with a cathode which was also deposited using a screen printing technique.

Example 1

[0044] FIG. 1 shows the device architecture of an OLED that was fabricated on a 2?2 sheet of ITO coated PET (150?/?) which was cleaned thoroughly using isopropyl alcohol. A hole transport layer (HTL) was then screen printed onto the clean ITO substrate followed by its drying at 120? C. for 15 minutes. A conductive polymer such as PEDOT: PSS was used as a HTL in this case. The emissive layer was made of PFO which was blended with a 2.5 wt % ethyl cellulose dispersion in mesitylene. The amount of PFO in this nanocomposite blend was approximately 1.6% by weight. This nanocomposite blend of PFO and ethyl cellulose was then screen printed onto the HTL coated ITO-PET substrate followed by its curing at 120? C. for 10 minutes. Finally, a cathode material containing 33 wt % Mg and 33 wt % Ag was deposited on the top the PFO based active layer using screen printing technique. The cathode material deposited in this case normally takes 10 minutes to sinter at 120? C.

Example 2

[0045] The same approach as described in Example 1 was used to manufacture a fully screen printable organic solar cell (FIG. 2) on a 1?1 flexible substrate based on ITO coated PET (60?/?). The substrate was first cleaned using isopropyl alcohol followed by deposition of a thin layer of PEDOT: PSS using screen printing technique. The PEDOT: PSS layer was then annealed at 120? C. for 15 minutes prior to screen printing the P3HT: PCBM/ethyl cellulose based active layer on top. The active layer was also annealed at 120? C. for 15 minutes followed by screen printing the Mg/Ag cathode as a back contact.