WO2008144759A2

WO2008144759A2 - Organic electrodes and electronic devices

Info

Publication number: WO2008144759A2
Application number: PCT/US2008/064426
Authority: WO
Inventors: Jan Bernkopf; Mathew K. Mathai; Darin W. Laird; Christopher T. Brown
Original assignee: Plextronics, Inc.
Priority date: 2007-05-21
Filing date: 2008-05-21
Publication date: 2008-11-27
Also published as: WO2008144759A3

Abstract

A device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance, the device further comprising a substrate to support the transistor. The transistor can be adapted for a bottom-gate configuration or a top-gate configuration. The transistor can be a field effect transistor, an organic field effect transistor, or a thin- film transistor. A polymer substrate can be used. Applications include printed electronics.

Description

ORGANIC ELECTRODES AND ELECTRONIC DEVICES

RELATED APPLICATIONS

This application claims the benefit of US provisional application serial no. 60/939,346 filed May 21, 2007, which is hereby incorporated by reference in its entirety.

BACKGROUND

Printed electronics is an important, relatively new technology and industry, and one important aspect of this technology is use of organic materials including organic semiconductors (OS), organic conductors (OC), and organic electronic devices. See, for example, Printed Organic and Molecular Electronics, Ed. D. Gamota et al., 2004 ("Gamota"). Printed electronics can allow replacement of conventional photolithographic and microfabrication processes which open up new avenues of manufacturing. Photolithography is described in for example Microchip Fabrication, 5^th Ed., P. Van Zant, 2004. Microfabrication is described in for example Fundamentals of Microfabrication, 2^nd Ed. M. J. Madou, 2002. For example, solution processing of organic materials can provide for low cost, large area mcinufacturLng on flexible substrates. See, for example, Sirringhaus, Adv. Mater. 2005, 17, 2411-2425. Printed electronics can provide continuous production processes, fast production speeds, low to moderate capital costs, and small to very large economic run lengths compared to conventional methods.

An important example of an organic material is conducting or conjugated oligomers and polymers including, for example, polyacetylene, polypyrrole, polyaniline, poly(phenylene vinylene), as well as polythiophene, including regioregular polythiophene, as well as copolymers, including block copolymers and copolymers with non-conjugated segments, including block copolymers with conjugated and non- conjugated segments. See, for example, US Patent No. 7,098,294 and 6,166,172 to McCullough et al. (Carnegie Mellon University) and US Patent Publication Nos. 2006/0076050; 2006/0078761; 2006/0118901; 2006/0175582; 2006/0237695; and 2007/0065590 (Plextronics). Important examples of applications include transistors, RFID tags, and sensors, as well as solar ceils and OLEDs.

One important parameter for use of organic materials in some organic electronic applications is mobility. In recent years, mobility values have risen to more practical levels. See, for example, Figure 1.1.22 in Gamota. However, practical problems remain including air stability, processing in ambient air, and scale-up of material properties from laboratory bench to commercial manufacture.

One important device in printed electronics is the transistor including thin film transistors and field effect transistors. These can include source electrode, drain electrode, channel (or semiconductor active layer), gate electrode, and gate insulator (or gate dielectric) structures. However, one important problem with transistors is reducing or eliminating various types of parasitic resistances and capacitances including, for example, contact resistance. For example, one problem is vertical misalignment and overlap in relatively low resolution printing processes, wherein undesired parasitic capacitance can be set up between the gate and the source or the gate and the drain. See, for example, US Patent No. 6,566,172 to Jackson et al. See, for example, Figure 1 below. A need exists to reduce or eliminate parasitic capacitance, particularly for high frequency appjications_z as parasitic problems can limit maximum operating frequency and capability to carry large currents. Moreover, contact resistance problems easily arise when organic materials and inorganic materials contact each other. Better inorganic-organic interfaces are needed.

In addition, a need exists to better engineer the organization of OS layers in the channel.

A need exists to engineer devices and materials to overcome these and other problems. Both individual materials are needed and combinations of materials which work together.

SUMMARY

Provided herein are devices, compositions, methods of making devices and compositions, and methods of using devices and compositions. A first aspect comprises reduction in parasitic capacitance. This can include use of source and drain as a shadow mask in a self-alignment process and self-aligned product.

For example, provided herein is a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

Also provided herein is a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding the conductive gate region; wherein the gate region does not substantially overlap with the source or with the drain.

Also provided herein is a method of making a device comprising: (A) providing a precursor device comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate precursor polymer film disposed on the gate insulator second side; (B) exposing the gate precursor polymer film to radiation passing through the channel to form a conductive gate in the film, wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

Also provided herein is a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding the conductive gate region; wherein the gate region does not substantially overlap with the source or with the drain, and wherein the device is prepared by: exposing the polymer film to radiation passing through the channel to form the gate. In another second aspect, a "deep gate" can be used to improve performance. For example, an embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one first gate material disposed on the gate insulator second side; wherein the first gate material does not substantially overlap with the source or the drain so as to minimize parasitic capacitance, the transistor further comprises a second gate material disposed away from the second side so that the first gate material is between the gate insulator and the second gate material.

Another third aspect includes materials useful in, for example, fabrication of transistors including photoacid generation and high conductivity. For example, one embodiment provides a composition comprising: a thiophene or pyrrole comprising at least one substituent which is photoactive and releases an acidic molecule upon exposure to radiation.

Another embodiment provides a composition comprising: a polymer comprising a conjugated polymer backbone and at least two different types of repeat units, wherein a first repeat unit comprises a nitrogen atom bonded to a protecting group which is thermally and/or photochemically labile and is adapted to form -NH upon removal of the protecting group, wherein a second repeat unit comprises an atom adapted to hydrogen bond with the -NH formed from the first repeat unit upon removal of the protective group.

Another embodiment provides a composition comprising: a polymer comprising a conjugated polymer backbone and at least two different types of repeat units, wherein a first repeat unit comprises a first heterocyclic ring comprising a nitrogen atom bonded to a protecting group which is thermally and/or photochemically labile and is adapted to form -NH upon removal of the protecting group, wherein a second repeat unit comprises a second heterocyclic ring different from the first. A fourth aspect relates to reduction in contact resistance. For example, one embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the source, the drain, or both comprise at least one polymer adsorbed to, or otherwise contacting or bonded to, the source, drain, or both to minimize contact resistance between the source and the channel, the drain and the channel, or both.

Another embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the source, the drain, or both comprise at least one polymer, oligomer, or small molecule adsorbed to the source, drain, or both to minimize contact resistance between the source and the channel, the drain and the channel, or both.

Other embodiments comprise methods of making and using the compositions and devices described herein.

In one or more of the embodiments provided herein, at least one advantage is that parasitic capacitance can be reduced or eliminated. This is particularly important for high frequency applications. Moreover, the benefits of eliminating photolithography and using solution processing can be achieved. Manufacturing can be simplified and more efficient. Vacuum and/or high temperatures can be avoided. Contact resistance can be reduced or eliminated.

One or more of the embodiments provided herein can be called a "smart gate."

BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates the problem of parasitic capacitance in a cross-sectional view. Figure 2 illustrates field effect transistor elements including a separation region and a perpendicular vertical zone. Figure 3 further illustrates misaligned metal gate.

Figure 4 illustrates a perspective view of a smart gate embodiment in bottom gate configuration.

Figure 5 illustrates a self-aligned smart gate in a bottom gate configuration in a cross- sectional view.

Figure 6 illustrates a self-aligned smart gate in a top gate configuration in a cross- sectional view.

Figure 7 illustrates a self-aligned source and drain extension in a cross-sectional view. Figure 8 illustrates steps in making a commercial target. Figure 9 illustrates a test bed embodiment including a deep gate. Figure 10 illustrates a deep gate configuration in a cross-sectional view. Figure 11 illustrates examples of polymers comprising conjugated repeat units. Figure 12 illustrates low molecular weight and high molecular weight photoactive dopant.

Figure 13 illustrates an example of polymer system which can be triggered to planarize and become conductive by heat and light.

Figure 14 illustrates representative synthetic schemes for high conductivity polymer. Figure 15 illustrates a chart with representative polymers and characteristics thereof. Figure 16 illustrates modification of source and drain to reduce contact resistance. Figure 17 shows exemplary materials for reduction in contact resistance. Figure 18 summarized materials which can be used for source/drain modification. Figure 19 illustrates extracting contact resistance.

DETAILED DESCRIPTION

INTRODUCTION AND CONTEXT All references cited herein are incorporated by reference.

Printed Electronics are generally known in the art. See for example, Printed Organic and Molecular Electronics, Ed. D. Gamota et al., 2004. For example, Chapters 1 and 2 describe organic semiconductors, Chapter 3 describes manufacturing platforms for printing circuits, Chapter 4 describes electrical behavior of transistors and circuits, Chapter 5 describes applications, and Chapter 6 describes molecular electronics. See also Pope et al., Electronic Processes in Organic Crystals and Polymers, 1999.

Field effect transistors, including organic field effect transistors, are generally known in the art and are semiconductor devices comprising an insulated gate electrode which controls current flow through the device. Gate electrode fabrication and FET fabrication are well known in the art. See for example US Patent No. 5,470,767; 6,429,450; 6,593,617; 7,029,945; 7,064,345.

Field effect transistors and testing thereof are known in the art. See for example Sirringhaus et al., Chem. Rev. 2007, 107, 1296-1323; Thin Film Transistors, (Ed. Kagan and Andry), 2003; US Provisional Application No. 60/850,267 to Stegamat et al. filed October 10, 2006 ("Field Effect Transistor Methods and Devices").

In addition, organic and polymer materials are generally known in the art. See, for example, Billmeyer, Textbook of Polymer Science, 3^rd Ed, John Wiley, 1984. Conducting polymers and patterning in field effect transistors is known. See for example US Patent No. 6,331,356. See also H.S. Nalwa, Handbook of Organic Conducting Molecules and Polymers, John Wiley, Chickester, 1997; Salaneck et al., Science and Applications of ^'Conducting Polymers, Adam Hilger, NY 1990. Polythiophenes, including soluble polythiophenes and regioregular polythiophenes, are described in for example US Patent No. 7,098,294 and 6,166,172.

US Patent No. 6,566,172 to Jackson et al describes an example of self-alignment for TFTs.

PARASITIC CAPACITANCE AND SELF-ALIGNMENT

In a present self alignment concept, material properties can be substantially altered by exposure to radiation in, for example, the UV-Vis range. For example, conductivity and/or solubility can be changed by, for example, photodoping wherein a doping reaction is induced by exposure to light. For example, conductivity can be changed over several orders of magnitude. Crosslinking can occur to render exposed material insoluble and unexposed parts can be removed, if desired, as it remains soluble.

The gate can be used as a mask, or the source and drain can be used as a mask, to define channel length between source and drain. Channel width can be also controlled in the mask. Channel length and width are shown in Figure 4 for example.

Figure 1 illustrates the parasitic capacitance (Cp) problem. Parasitic capacitance is generally known in the art. See for example US Patent Nos. 7,179,756 to Yamazaki; 7,068,418 to Kawase; 7,037,767 to Hirai; 6,847,048 to Yan; and 6,771,245 to Kanbe. The parameter ΔL illustrated in Figure 1 relates to the spatial overlap of gate with source and/or drain. It is desired to reduce the value of ΔL for both the source and drain with respect to the gate and preferably ΔL can be substantially eliminated or equal zero or effectively zero. The Cp problem can arise from low resolution processing, misalignment, and overlap.

Figure 2 further illustrates self alignment wherein a separation region is defined between the source and the drain and a perpendicular vertical zone extends away from the separation region.

Presently, devices can be made wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance. Overlap can be about 10 microns or less, or about five microns or less, or about one micron or less, or about 0.5 microns or less, or about 0.1 micron or less.

Figure 3 further illustrates the misalignment, overlap problem which, for example, can generate parasitic capacitance which can reduce performance in a ring oscillator. This can be particular important where, for example, a fast response is needed to a square wave signal is needed in for example display backplanes.

As described further below, the source, drain, channel, and gate insulator can be adapted to function as a mask for exposure of the gate to radiation. For example, thickness, transmission, and opacity can be controlled for mask behavior and selective passage of light or radiation.

SOURCE AND DRAIN ELEMENTS

Source and drain elements are generally known in the art. Examples are shown in Figures 1-2 and 4-6 and other figures. The elements can be adapted to be disposed on a gate insulator or a semiconductive layer. Known materials, thicknesses, shapes, and production methods can be used.

The source and drain can be separated as known in the art. A separation region can be designated as the region between the source and the drain. See for example Figure 2. This can have a length and a width as shown in Figure 4. The channel can be in or below (or above) this separation region.

A vertical perpendicular zone can be designated as extending away from the separation region in the direction of the second surface of the of the gate insulator as shown in Figure 2. The vertical perpendicular zone can be used in determining degree of alignment.

In one embodiment, the source and the drain each comprise only one component. However, in another embodiment, the source comprises two source components, and the drain also comprises two drain components, wherein one of the components comprises a polymer. The other component can comprise metal. See for example Figure 7. In this embodiment, the gate region does not substantially overlap with the source component comprising polymer, or with the drain component comprising polymer. Here, the polymer can act as an extension of the source and drain.

In particular, provided herein is a device comprising: a transistor comprising: at least one source, wherein the source comprises a polymer comprising conjugated repeat units; at least one drain, wherein the drain comprises a polymer comprising conjugated repeat units; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance. In this embodiment, the source and the drain can comprise two components each: one component is a metallic component and the other component is a polymer component. See Figure 7 for example.

GATE INSULATOR OR GATE DIELECTRIC

A gate insulator (or dielectric) element is generally known in the art. Known materials, thicknesses, processing methods, and shapes can be used. Gate insulator should be highly inert and stable to radiation pass through including UV-Vis radiation pass through. In particular, low K dielectric materials are important. It should have conductivity sufficiently low so it can function as a gate insulator. An example is polyvinylphenol. Photoresist materials can be used. Silsesquioxane materials can be used.

GATE

A gate element is generally known in the art, although certain materials for the gate are described below. A gate material should have conductivity sufficiently high to function as a gate. Presently, it can have a conductivity of at least 1 S/cm, or at least 10 S/cm, or at least 100 S/cm.

Gate materials are described further below. These can be formed from photoactive doping processes. Moreover, materials can be selected for high conductivity.

The gate can comprise at least one conductive polymer. The gate can comprise conductive polymer which is integral with surrounding insulating polymer. The integrated insulating polymer can be disposed on the gate dielectric.

The gate can be part of a single polymer film, wherein the film comprises conductive region which forms the gate and the film also comprises insulating material which surrounds the gate. The degree of photodoping can be, for example, at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 95%. The degree of photodoping can be adapted for a particular application to provide a sufficient conductivity.

The gate can be for example about 0.5 microns to about 2 microns, or about 1 micron thick.

GATE CONFIGURATIONS

Gate configurations are generally known in the art. Examples include top-gate (Figure 6), bottom-gate (Figure 5), and dual-gate.

OTHER COMPONENTS

Other components include for example the channel materials and substrates, which are known in the art.

A substrate can support the transistor and can comprise materials which are useful for printed electronics including for example flexible materials, polymers and plastics, materials capable of reel-to-reel processing, and the like. The substrate can comprise a polymer such as for example polyethylene napthalate (PEN) or polyethylene terephthalate (PET) or polyimide. Substrate can be glass or coated glass including hydrophobically modified glass.

Channel material can be organic as described in for example Gamota, Chapter 2. They can be small molecule, oligomeric, or polymeric. They can be for example ancenes, oligophenylenes, heterocycles, and oligomers.

Inks can be formulated based on colorants, binder, solvent, and additives.

METHODS OF MAKING

Figure 8 provides an overview for fabrication, as does Figures 5-7.

The key steps are providing the various elements as described herein in a precursor device which comprises at least one gate precursor polymer film disposed on the gate insulator second side, and then exposing the gate precursor polymer film to radiation passing through the channel to form a conductive gate in the film. Because of the mask effect, the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

Other method steps known in the art can be used. Vapor methods can be used to fabricate organic layers, particularly small-molecule materials. Solution methods can be used to fabricate organic layers, particularly polymeric materials. Chlorinated or aromatic solvents can be used. Solution processing includes for example spin-coating, spray-coating, and printing. Ink Jet printing can be used.

One preferred embodiment is that manufacture of transistor is carried out without conventional photolithography, although photoreactions can be used to raise the conductivity level of the gate material.

DEVICES AND DEVICE COMPONENTS

Circuits, integrated circuits, memory, sensor arrays, TFTs inverters, NOR gates, NAND gates, ring oscillators, OLEDs, PLEDs, solar cells, liquid crystal displays, flat panel displays, active matrix devices, display backplanes, RFID tags, and the like can be made. Individual gate electrode can be used for each transistor.

In particular, new materials described herein can be used in applications outside of transistors.

GBW (Gain Bandwidth Product) can be at least 100 kHz, or at least 1 MHz. See for example Tickle, Thin Film Transistors, 1969, p. 144.

DEEP GATE EMBODIMENT

If the gate does not have sufficient conductivity, a metallic deep gate can be deposited underneath the polymeric gate as a second gate or deep gate material. See for example Figures 9-10. This deep gate strongly reinforces the conductivity of the gate. Whether the gate has sufficient conductivity can vary from application to application. The deep gate can comprise conductive metal and can have a higher conductivity than the gate. In the deep gate embodiment, a first gate material can be disposed on the gate insulator second side, and a second gate material can be also present, disposed away from the second side so that the first gate material is between the gate insulator ana the second gate material.

The second gate material can be substantially overlapping with the source or the drain and can be applied by lower resolution methods.

Good ohmic contact can be established between the deep gate and the smart gate. See for example Tengstedt et al., Appl. Phys. Lett., 2006, 88, 053502.

PHOTOACTIVE HIGH CONDUCTIVITY MATERIALS

Light induced doping of a conjugated polymer to form a device gate can be carried out. Materials can be used which can be switched between insulating (e.g., 10^"9 S/cm) and conductive states (e.g., about 1 S/cm) by exposure to radiation. For example, the increase in conductivity can be at least 100, or at least 1,00OX or at least 1,000,00OX or at least l,000,000,000X (i.e., 10⁹). For example, one first material can be engineered to have high conductivity when doped. Another second material can be engineered to be photoactive and release doping agent to increase the conductivity of the first material. Hence, the first and second materials can be adapted to function together.

Figure 11 illustrates some polythiophenes which are reported to have relatively high conductivity.

Polymers, including polythiophenes and polypyrroles, can be used which have high levels of planarity, internal hydrogen bonding, and fused ring systems. Polymers, including polythiophenes, can be used as the photoactive dopant.

Figure 13 illustrates one exemplary approach wherein a polymer is initially provided in a protected state and heated to an unprotected state which provides for internal hydrogen bonding. Then, photoactive dopant is used to generate doping reaction and conductivity.

For materials and polymers described herein, solubilizing groups can be used to minimize rigid chain properties including use at the 3- and 4- positions of the pyrrole. Removable protecting groups can be used such as N-Boc. Hydrogen bonding can be used to induce planarity. This can help avoid need for a final chemical planarization step. Solubility of the polymer can be enhanced by temporarily breaking the hydrogen bond via for example temperature or pH adjustment.

The polymers can have enhanced solubility and processability, high conductivity, and environmental stability. The properties can be controllable based on for example structural purity, molecular interaction, and organization.

Organic synthetic reactions can be found in Smith and March, March's Advanced Organic Chemistry, 6^th Ed., 2007 and treatises cited therein at pages 1893-1894.. Other treatises include Comprehensive Organic Chemistry, Pergamon, 1979 and Comprehensive Heterocyclic Chemistry, 1984.

PHOTOACTIVE DOPANT

One embodiment provides a thiophene or pyrrole comprising at least one substituent which is photoactive and releases an acidic molecule upon exposure to radiation. The thiophene can be for example a low molecular weight thiophene or a polythiophene (or polythiophene derivative). The thiophene can comprise one thiophene ring. The pyrrole can be for example a low molecular weight pyrrole or a polypyrrole (or polypyrrole derivative). The pyrrole can comprise one pyrrole ring.

Known labile photoacid chemistry can be used. Figure 12 illustrates embodiments for low molecular weight and higher molecular weight dopant based on thiophene. See also for example for a photoactive polyaniline system, Lee et al., Macromolecules, 2004, 37, 4070-4074. See also Rosilio et al., Synthetic Metals, 1996, 83, 27-37; see also Rose et al., Report # AD-A264751, AFOSR-93-0288TP.

Use of polymeric materials can help prevent diffusion of the photoacid.

In one embodiment, the photoactive dopant can be incorporated into a polymeric backbone.

The substituent can comprise tosylate. The acidic molecule can be a sulfonic acid. The composition can comprise a dioxopyrrolothiophene. See for example Figure 12.

PROTECTED POLYMERS

A donor-acceptor conjugated repeating unit approach can be used. For example, Figure 14 illustrates exemplary synthetic methods for making protected polymers. The homopolymer of alkylenedioxypyrrole (ADOP) can possess the lowest oxidation potential, low band gap, high electrical conductivity, and aqueous compatability. The final polymerization step to make 15 can be carried out with universal GRIM methods as described in US provisional application 60/841,548 filed September 1, 2006 to McCullough et al (see also serial no. 11/849,229 filed August 31, 2007), or other methods used in the art to make regioregular polythiophenes. Other polymerization methods include, for example, thermal, nonoxidative (e.g., see Polec, I. et al., J. Pol. ScI. A Pol. Chem. 2003, 41, 1034.), and oxidative chemical (e.g., FeCI₃ reference Meng, H.; Wudl, F. Macromolecules 2001, 34, 1810.), and various metal promoted cross-couplings like StMIe, Suzuki, Negishi, or Kumada, methods known in the art.

Polymery can be soluble in organic solvents such as THF₇ chlorofornvtoluene, and xylene.

Figure 15 provides a chart which further illustrates protected polymers.

Polymer side groups, such as any of the R groups in any of Figures 12-15 or elsewhere in this application, including Rl and R2 in structure 3 of Figure 15, can be adapted to provide solubility and other properties. Examples of side groups include for example alkyl groups, including branched alkyl groups such as ethylhexyl; alkoxy groups including groups with a single oxygen and polyethers, wherein oxygen need not be directly attached to the ring; thioalkyl groups such as for example R=SR' where R' is alkyl such as C6-C12). Other R groups can be used as known in the art.

In one embodiment, the polymer is engineered to provide for internal hydrogen bonding. See for example an Mullekon et al, Mater. ScL & Eng. 2001, 32, 1; see also Zotti et al., Macromolecules, 1994, 27, 1938. Internal hydrogen bonding and rigid monomer units can be used to induce planarity.

In another embodiment, the polymer is engineered to not provide for internal hydrogen bonding.

In these polymers, a first repeat unit can be present which comprises a nitrogen atom bonded to a protecting group. The protecting group can be thermally or photochemically labile and can be adapted to form -NH upon removal of the protecting group. The first repeat unit can comprise a heterocyclic ring including a five membered ring. Fused rings can be used. The first repeat unit can comprise a pyrrole. The pyrrole can be substituted at the 3- and 4- positions, for example. For example, the first repeat unit can comprise a 3,4-alkylenedioxypyrrole. The length of the alkylene can be varied as know in the art (e.g., C2, C3, and the like). The protecting group can be for example Boc.

In these polymers, a second repeat unit can be present which comprises an atom adapted to hydrogen bond with the -NH formed from the first repeat unit upon removal of the protective group. The atom can be for example oxygen or nitrogen. The oxygen can be part of a carbonyl. The second repeat unit can comprise a heterocyclic ring including a five membered ring. Fused_, rings can be used. The second repeat unit can comprise a thiophene. The thiophene can be substituted at the 3- and 4- positions. The second repeat unit can comprise a thienopyrazine.

In an alternative embodiment, the second repeat unit merely comprises a heterocyclic ring different from the first but does not necessarily provide an atom for hydrogen bonding with the first repeat unit.

The polymer can comprise alternating units comprising the first and second repeat units (e.g., form an alternating copolymer).

REDUCTION IN CONTACT RESISTANCE

Problems related to contact resistance can be reduced or eliminated by selective attachment of injection modifying organic functionality to source and drain. Contact resistance can generate undesired heat which can lead to instability and non-uniformity in performance. An ohmic contact can be formed between the source-channel and the drain-channel interfaces. Electrode-selective surface dopants can be used to reduce this contact resistance. Improved charge injection efficiency can be achieved. The injection efficiency can be for example at least 80%, or at least 95%. The following equation can be used:

R (OFET) = Rc(D) + Rc(S) + R(CL)

Where Rc(D) is the contact resistance associated with the drain electrode, Rc(S) is the contact resistance associated with the source electrode R(CL) is the resistance associated with the channel. Also, injection efficiency can be:

η = R(CL)/[Rc(D) + Rc(S) + R(CL)]

Contacts that exhibit η > 0.95 are considered ohmic and near ideal situation where Rc = 0.

A Schottsky-Mott injection approach can be used. See for example Jespersen et al., J. Am. Chem. Soc, 2007, 129, 2803; Asadi et al., J. Mater. Chem., 2007, 17, 1947. In this approach, to a first approximation, an Ohmic contact is established when the work function (Wf) of the metal is not more than about 0.3 eV from the valence band of the semiconductor (HOMO). Materials can be designed to exhibit both adequate field- effect semiconducting behavior while achieving a matched HOMO to the metal contact.

Alternatively, a Fermi-level pinning approach can be used. See for example Wu, J. Am. Chem. Soc, 2006, 128, 4202.

A variety of polymers, oligomers, and small molecules, and mixtures thereof, can be used to modify and improve injection. Some of these, for example, are provided in Figure 18. Small molecules can have, for example, molecular weight of about 1,000 g/mol or less, or even 500 g/mole or less. In particular, a variety of polymers, including conjugated polymers, including a polythiophene, including regioregular polythiophene can be used to modify injection. Polymer can comprise conjugated repeat units and be homopolymers or copolymers. The polymer can comprise a functionality which adsorbs to gold such as for example - SH. The -SH can be bonded to a spacer or linker (e.g., alkylene thiol). The polymer can comprise functionality in the side groups, or in the end group including one or both end groups. Figure 16 illustrates one approach to reduce contact resistance.

The polymer can be adapted with use of spacers which modify electron density by withdrawing and releasing electron density. Figure 17 illustrates another approach for materials engineered to reduce contact resistance, wherein a perfluorinated material is used.

In one approach, materials can be used which are stronger acids and are polyacids.

DEEVICE ANALYSIS

Figures 20 and 21 illustrate measurement of contact resistance. See Shade et al., J. Appl. Phys. 59(5), 1986, 1982-1987 (Shade-Smith test).

Contact resistance can be evaluated with use of FET substrates with different channel lengths. Contact resistance can be measured on functional OFET devices with different channel length (L) with the same channel width. The resistance will be extracted from the dependence of OFET resistance on L as shown for example in Figure 19.

Device overlap between gate and drain and between gate and source can be measured by methods known in the art including cross-sectional analysis and microscopies and spectroscopies.

ADDITIONAL SUPPORTING REFERENCES

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- Somnez, Chem. Mater., 15 (2003) 4923. PREFERRED EMBODIMENTS

A first embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

In this device, the transistor can be adapted for a bottom-gate configuration cr a top-gate configuration.

In this device, the transistor can be a field effect transistor, an organic field effect transistor, or a thin-film transistor.

In this device, the device can further comprise a substrate to support the transistor.

In this device, the device can further comprise a substrate to support the transistor and the substrate can comprise a polymer.

In this device, the channel can comprise organic material.

In this device, the channel can comprise at least one polymer comprising conjugated backbone units.

In this device, the source and drain each can comprise at least one metal.

In this device, the gate insulator can comprise at least one low K dielectric material.

In this device, the source and the drain can be disposed on the gate insulator first surface and the gate can be disposed on the gate insulator second surface.

In this device, the source, drain, channel, and gate insulator can be adapted to function as a mask for exposure of the gate to radiation.

In this device, the gate can comprise conductive polymer.

In this device, the gate can comprise conductive polymer which is integral with surrounding insulating polymer. In this device, the gate can comprise conductive polymer which is integral with surrounding insulating polymer, and the insulating polymer can be disposed on the gate dielectric.

In this device, the gate can be part of a single polymer film, wherein the film can comprise conductive region which forms the gate and the film also can comprise insulating material which surrounds the gate.

In this device, the source can comprise two source components, wherein one source component can comprise polymer, and wherein the drain can comprise two drain components, wherein one drain component can comprise polymer, and the gate in this embodiment does not substantially overlap with the source component comprising polymer or with the drain component comprising polymer.

In this device, the source and drain each can comprise only one component.

In this device, the overlap can be characterized by a value of about one micron or less.

In this device, the overlap can be characterized by a value of about 0.5 micron or less.

In this device, the transistor can be an organic field effect transistor, wherein the channel can comprise organic materia^ and wherein the gate can comprise conductive polymer.

Another device is a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding the conductive gate region; wherein the gate region does not substantially overlap with the source or with the drain.

In this device, the transistor can be adapted for a bottom-gate configuration or a top-gate configuration.

In this device, the device can further comprise a substrate to support the transistor. In this device, the channel can comprise organic material.

In this device, the gate region can comprise conductive polymer.

In this device, the source, drain, channel, and gate insulator can be adapted to function as a mask for exposure of the polymer film to radiation.

In this device, the source can comprise two source components, wherein one source component can comprise polymer, and wherein the drain can comprise two drain components, wherein one drain component can comprise polymer, and the gate region does not substantially overlap with the source component comprising polymer or with the drain component comprising polymer.

In this device, the source and drain can each comprise only one component.

In this device, the overlap can be characterized by a value of about one micron or less, and wherein the transistor is an organic field effect transistor, wherein the channel comprises organic material, and wherein the gate region comprises conductive polymer.

Another embodiment is a method of making a device comprising: (A) providing a precursor device comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining^ second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate precursor polymer film disposed on the gate insulator second side; (B) exposing the gate precursor polymer film to radiation passing through the channel to form a conductive gate in the film, wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

In this method, the radiation can be UV- Vis radiation.

In this method, the precursor device can further comprise a substrate and the radiation passes through the substrate.

In this method, the precursor device can further comprise a substrate but the radiation does not pass through the substrate. In this method, the device can be adapted for top-gate or bottom-gate configuration.

In this method, the exposing step can result in crosslinking of the gate precursor polymer film.

In this method, the exposing step can result in an increase in conductivity of at least IOOX in forming the conductive gate.

In this method, the exposing step can result in an increase in conductivity of at least 1,000,00OX in forming the conductive gate.

In this method, the gate precursor polymer film can comprise at least one polymer comprising conjugated units.

In this method, the radiation can be UV-Vis radiation, and the exposing step can result in crosslinking of the gate precursor polymer film and also result in an increase in conductivity of at least 1,000,00OX in forming the conductive gate and the gate precursor polymer film can comprise at least one polymer comprising conjugated units.

Another embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding J:he conductive gate region; wherein the gate region does not substantially, overlap with the source or with the drain, and wherein the device is prepared by: exposing the polymer film to radiation passing through the channel to form the gate.

In this device, the radiation can be UV-Vis radiation.

In this device, the precursor device can further comprise a substrate and the radiation can pass through the substrate.

In this device, the precursor device can further comprise a substrate but the radiation in one embodiment does not pass through the substrate.

In this device, the device can be adapted for top-gate or bottom-gate configuration.

In this device, the exposing step can result in crosslinking of the polymer film.

In this device, the exposing step can result in an increase in conductivity of at least IOOX in forming the conductive gate. In this device, the exposing step can result in an increase in conductivity of at least 1,000,00OX in forming the conductive gate.

In this device, the gate precursor polymer film can comprise at least one polymer comprising conjugated units.

In this device, the radiation can be UV-Vis radiation, and the exposing step can result in crosslinking of the polymer film and also result in an increase in conductivity of at least 1,000,00OX in forming the gate, and wherein the polymer film can comprise at least one polymer comprising conjugated units.

Another embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one first gate material disposed on the gate insulator second side; wherein the first gate material does not substantially overlap with the source or the drain so as to minimize parasitic capacitance, the transistor further comprises a second gate material disposed away from the second side so that the first gate material is between the gate insulator and the second gate material.

In this device, the second gate material can comprise metal.

In this device, the second gate material can have a higher conductivity than the first gate material.

In this device, the second gate material can substantially overlap with the source or the drain.

In this device, the device can further comprise a substrate to support the transistor. In this device, the device can further comprise a substrate to support the transistor and the substrate comprises a polymer.

In this device, the channel can comprise organic material.

In this device, the source and drain can each comprise at least one metal.

In this device, the first gate material can comprise conductive polymer.

In this device, the first gate can comprise conductive polymer which is integral with surrounding insulating polymer.

In this device, the gate is part of a single polymer film, wherein the film comprises conductive region which forms the gate and the film also comprises insulating material which surrounds the gate.

In this device, the source can comprise two source components, wherein one source component comprises polymer, and wherein the drajnj:ornprises two drain components, wherein one drain component comprises polymer, and the gate does not substantially overlap with the source component comprising polymer or with the drain component comprising polymer.

In this device, the transistor can be an organic field effect transistor, wherein the channel comprises organic material, and the first gate material comprises conductive polymer. Also provided is a composition comprising: a thiophene or pyrrole comprising at least one substituent which is photoactive and releases an acidic molecule upon exposure to radiation.

In this composition, the thiophene or pyrrole can be, respectively, a polythiophene or a polypyrrole.

In this composition, the thiophene or pyrrole can be, respectively, a thiophene compound comprising one thiophene ring or a polypyrrole compound comprising one pyrrole ring.

In this composition, the acidic molecule can be a sulfonic acid.

In this composition, the substituent can comprise tosylate.

In this composition, the composition can comprise the thiophene but not the pyrrole.

In this composition, the composition can comprise the pyrrole but not the thiophene.

In this composition, the radiation can be UV-Vis radiation.

In this composition, the composition can comprise a dioxopyrrolothiophene.

Another composition can be formed by exposing this composition to radiation.

In this composition, the polymer can comprise alternating units comprising the first and second repeat units.

In this composition, the first and second repeat units can each comprise at least one heterocyclic ring.

In this composition, the first repeat unit can comprise a pyrrole. In this composition, the first repeat unit can comprise a pyrrole substituted at the 3- and 4-positions.

In this composition, the first repeat unit can comprise a 3,4-alkylenedioxypyrrole.

In this composition, the second repeat unit can comprise a thiophene.

In this composition, the second repeat unit can comprise a thiophene substituted at the 3- and 4-positions.

In this composition, the second repeat unit can comprise a thienopyrazine.

In this composition, the atom can be a nitrogen atom.

In this composition, the atom can be an oxygen atom.

In this composition, the protecting group can be Boc.

In this composition, the first repeat unit can comprise a pyrrole, and the second repeat unit can comprise a pyrrole different from the first repeat unit pyrrole.

In this composition, the first repeat unit can comprise a pyrrole, and the second repeat unit can comprise a pyrrole.

In this composition, the second repeat unit can comprise cyclopentadithiophene.

In this composition, the first repeat unit can comprise a pyrrole and the second repeat unit can comprise a thiophene.

In this composition, the polymer can comprise alternating units comprising the first and second repeat units, wherein the first repeat unit comprises a pyrrole and the second repeat unit comprises a thiophene.

In this composition, the first repeat unit can comprise a 3,4-alkylenedioxypyrrole and the second repeat unit can comprise a thienopyrazine.

In this composition, the first repeat unit can comprise a pyrrole, the second repeat unit can comprise a thiophene, the atom can be a nitrogen, and the protecting group can be Boc.

Another composition can be prepared by exposing this composition to heat or light to induce formation of -NH.

Still another composition is provided comprising: a polymer comprising a conjugated polymer backbone and at least two different types of repeat units, wherein a first repeat unit comprises a first heterocyclic ring comprising a nitrogen atom bonded to a protecting group which is thermally and/or photochemically labile and is adapted to form -NH upon removal of the protecting group, wherein a second repeat unit comprises a second heterocyclic ring different from the first.

In this composition, the first heterocyclic ring can be a pyrrole.

In this composition, the second heterocyclic ring can be a thiophene.

In this composition, the second heterocyclic ring can be a dihydropyrrolothiophene.

In this composition, the second heterocyclic ring can be part of a cyclopentadithiophene.

In this composition, the second heterocyclic ring can be part of a dithienyopyrrole.

In this composition, the protective group can be Boc.

In this composition, the first heterocyclic ring can comprise 3,4- alkylenedioxypyrrole.

Another composition can be prepared by exposing this composition to heat or light.

Another embodiment provides a device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the source, the drain, or both comprise at least one polymer adsorbed to the source, drain, or both to minimize contact resistance between the source and the channel, the drain and the channel, or both.

In this device, the polymer can comprise conjugated repeat units.

In this device, the polymer can comprise a polythiopene.

In this device, the polymer can comprise a regioregular polythiopene.

In this device, the polymer can comprise -SH functionality. In this device, the polymer can comprise side groups comprising an -SH functionality.

In this device, the polymer can comprise end groups comprising an -SH functionality.

In this device, the polymer can comprise an alkylene thiol.

In this device, the polymer can comprise a perfluorinated alkylthiol.

In this device, the polymer can comprise an aryl thiol.

In this device, the polymer can comprise a perflourinated thiol.

In this device, the polymer can comprise a 2-thiothiophene.

In this device, the thiol can be linked to the polymer via a spacer group.

In this device, the thiol can be linked to the polymer via a perfluorinated spacer group.

In this device, the thiol can be linked to the polymer via an aryl perfluorinated spacer group.

In this device, the thiol can be linked to the polymer via an electron-withdrawing spacer group.

In this device, the thiol can be linked to the polymer via an electron-releasing spacer group.

In this device, the polymer can comprise at least two thiols.

In this device, the polymer can comprise at least three thiols.

In this device, the polymer can comprise at least twenty-five thiols.

In this device, the device can provide for interfacial doping of the channel material.

In this device, the polymer can comprise acid functionality.

In this device, the polymer can comprise redox functionality.

In this device, the polymer can comprise redox functionality which dopes channel material.

In this device, the source, the drain, or both can comprise at least one adsorbed small molecule.

In this device, the source, the drain, or both can comprise at least one adsorbed oligomer.

In this device, the source, the drain, or both can comprise at least one adsorbed polymer.

END OF PREFERRED EMBODIMENTS

Claims

WHAT IS CLAIMED IS:

1. A device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate disposed on the gate insulator second side; wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance, the device further comprising a substrate to support the transistor.

2. The device according to claim 1, wherein the transistor is adapted for a bottom-gate configuration or a top-gate configuration.

3. The device according to claim 1, wherein the transistor is a field effect transistor, an organic field effect transistor, or a thin-film transistor.

4. The device according to claim 2, wherein the substrate is a polymer substrate.

5. The device according to claim 1, wherein the substrate comprises a polymer.

6. The device according to claim 1, wherein the channel comprises organic material.

7. The device according to claim 1, wherein the channel comprises at least one polymer comprising conjugated backbone units.

8. The device according to claim 1, wherein the source and drain each comprise at least one metal.

9. The device according to claim 1, wherein the gate insulator comprises at least one low K dielectric material.

10. The device according to claim 1, wherein the source and the drain are disposed on the gate insulator first surface and the gate is disposed on the gate insulator second surface.

11. The device according to claim 1, wherein the source, drain, channel, and gate insulator are adapted to function as a mask for exposure of the gate to radiation.

12. The device according to claim 1, wherein the gate comprises conductive polymer.

13. The device according to claim 1, wherein the gate comprises conductive polymer which is integral with surrounding insulating polymer.

14. The device according to claim 1, wherein the gate comprises conductive polymer which is integral with surrounding insulating polymer, and the insulating polymer is disposed on the gate dielectric.

15. The device according to claim 1, wherein the gate is part of a single polymer film, wherein the film comprises conductive region which forms the gate and the film also comprises insulating material which surrounds the gate.

16. The device according to claim 1, wherein the source comprises two source components, wherein one source component comprises polymer, and wherein the drain comprises two drain components, wherein one drain component comprises polymer, and the gate does not substantially overlap with the source component comprising polymer or with the drain component comprising polymer.

17. The device according to claim 1, wherein the source and drain each comprise only one component.

18. The device according to claim 1, wherein the overlap is characterized by a value of about one micron or less.

19. The device according to claim 1, wherein the overlap is characterized by a value of about 0.5 micron or less.

20. The device according to claim 1, wherein the transistor is an organic field effect transistor, wherein the channel comprises organic material, and wherein the gate comprises conductive polymer.

21. A device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding the conductive gate region; wherein the gate region does not substantially overlap with the source or with the drain.

22. The device according to claim 21, wherein the transistor is adapted for a bottom- gate configuration or a top-gate configuration.

23. The device according to claim 21, wherein the transistor is a field effect transistor, an organic field effect transistor, or a thin-film transistor.

24. The device according to claim 21, further comprising a substrate to support the transistor.

25. The device according to claim 21, wherein the channel comprises organic material.

26. The device according to claim 21, wherein the gate region comprises conductive polymer.

27. The device according to claim 21, wherein the source, drain, channel, and gate insulator are adapted to function as a mask for exposure of the polymer film to radiation.

28. The device according to claim 21, wherein the source comprises two source components, wherein one source component comprises polymer, and wherein the drain comprises two drain components, wherein one drain component comprises polymer, and the gate region does not substantially overlap with the source component comprising polymer or with the drain component comprising polymer.

29. The device according to claim 21, wherein the source and drain each comprise only one component.

30. The device according to claim 21, wherein the overlap is characterized by a value of about one micron or less, and wherein the transistor is an organic field effect transistor, wherein the channel comprises organic material, and wherein the gate region comprises conductive polymer.

31. A method of making a device comprising: (A) providing a precursor device comprising: at least one source; at least one drain; at least one channel; at least one gate insulator comprising (i) a first surface defining a first side, and (ii) a second surface defining a second side and opposing the first surface and first side, wherein the source and the drain are disposed on the gate insulator first side; at least one gate precursor polymer film disposed on the gate insulator second side; wherein the precursor device further comprises a substrate;

(B) exposing the gate precursor polymer film to radiation passing through the channel to form a conductive gate in the film, wherein the gate does not substantially overlap with the source or the drain so as to minimize parasitic capacitance.

32. The method according to claim 31, wherein the radiation is UV-Vis radiation.

33. The method according to claim 31, wherein the radiation passes through the substrate.

34. The method according to claim 31, wherein the precursor device further comprises a substrate and the radiation substantially passes through the substrate, and the radiation is UV-Vis radiation.

35. The method according to claim 31, wherein the device is adapted for top-gate or bottom-gate configuration.

36. The method according to claim 31, wherein the exposing step results in crosslinking of the gate precursor polymer film.

37. The method according to claim 31, wherein the exposing step results in an increase in conductivity of at least IOOX in forming the conductive gate.

38. The method according to claim 31, wherein the exposing step results in an increase in conductivity of at least 1,000,00OX in forming the conductive gate.

39. The method according to claim 31, wherein the gate precursor polymer film comprises at least one polymer comprising conjugated units.

40. The method according to claim 31, wherein the radiation is UV-Vis radiation, and wherein the exposing step results in crosslinking of the gate precursor polymer film and also results in an increase in conductivity of at least l,000,000X in forming the conductive gate and wherein the gate precursor polymer film comprises at least one polymer comprising conjugated units.

41. A device comprising: a transistor comprising: at least one source; at least one drain; at least one channel; at least one gate insulator; at least one polymer film comprising a conductive gate region and insulating region surrounding the conductive gate region; wherein the gate region does not substantially overlap with the source or with the drain, and wherein the device is prepared by: exposing the polymer film to radiation passing through the channel to form the gate.

42. The method according to claim 41, wherein the radiation is UV-Vis radiation.

43. The method according to claim 41, wherein the precursor device further comprises a substrate and the radiation passes through the substrate.

44. The method according to claim 41, wherein the precursor device further comprises a substrate but the radiation does not pass through the substrate.

45. The method according to claim 41, wherein the device is adapted for top-gate or bottom-gate configuration.

46. The method according to claim 41, wherein the exposing step results in crosslinking of the polymer film.

47. The method according to claim 41, wherein the exposing step results in an increase in conductivity of at least IOOX in forming the conductive gate.

48. The method according to claim 41, wherein the exposing step results in an increase in conductivity of at least 1,000,00OX in forming the conductive gate.

49. The method according to claim 41, wherein the gate precursor polymer film comprises at least one polymer comprising conjugated units.

50. The method according to claim 41, wherein the radiation is UV-Vis radiation, and wherein the exposing step results in crosslinking of the polymer film and also results in an increase in conductivity of at least l,000,000X in forming the gate, and wherein the polymer film comprises at least one polymer comprising conjugated units.