Gate-bias-modulated organic semiconductor / organo-palladium composites for carbon monoxide sensing

Abstract

A semiconductor composite is provided comprising an organic semiconductor and an organo-palladium compound, which can be solution processed into semiconductor thin films for use in organic thin film transistors for carbon monoxide sensing. The semiconductor composite comprises a p-type organic semiconductor having a HOMO energy level ≥ −5.7 eV and an organo-palladium compound of formula PdLaXb, where L is an organophosphine ligand and X is an anion. Also provided are thin films made using the composite films, organic thin-film transistors (OTFTs) incorporating such films, and methods of making same.

Description

GATE-BIAS-MODULATED ORGANIC SEMICONDUCTOR / ORGANO-PALLADIUM COMPOSITES FOR CARBON MONOXIDE SENSING CROSS REFERENCE TO PRIOR APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 833,105, filed October 24, 2024, the entire contents of which are incorporated herein by reference.FIELD OF THE DESCRIPTION

[0002] The disclosure relates to chemical sensors and, more particularly, to organic semiconductor composites comprising an organo-palladium compound for use as the active layer in organic thin-film transistors (OTFTs) to detect carbon monoxide (CO) and other analytes at ambient temperature.BACKGROUND

[0003] CO is a colorless, odorless gas generated primarily by incomplete combustion and presents serious health risks at low parts-per-million (ppm) levels. Conventional CO sensors often employ transition-metal oxides (e.g., SnO2, WO3, ln2O3, CeO2, TiO2), which typically require elevated operating temperatures, increasing power draw thus posing limitations to their deployment. Organic thin-film transistors (OTFTs) offer low-cost, lightweight, and printable platforms with inherent signal amplification. However, most organic semiconductors exhibit negligible response to the relatively inert CO molecule.

[0004] Palladium compounds interact strongly with CO, but many Pd(ll) salts (e.g., PdCI2) undergo irreversible reduction induced by CO. This therefore undermines sensor reusability. The irreversible reduction of PdCI2and some other Pd(ll) compounds by CO is attributed to the strong oxidizing power of the Pd(ll) ion, which has a high standard reduction potential of up to 0.95 versus SHE (standard hydrogen electrode), corresponding to an absolute energy of -5.39 eV relative to a vacuum to make the Pd(ll)-CO interaction reversible.

[0005] There is a need for CO sensors that can operate at ambient temperatures and, in particular, a need for an OTFT sensing material that combines Pd-mediated CO interaction with reversible, low-power operation at ambient temperature.SUMMARY OF THE DESCRIPTION

[0006] In one aspect, a solution-processable organic semiconductor composite is provided, comprising an organic semiconductor, preferably a p-type ir-conjugated polymer having a HOMO energy level > -5.7 eV, and an organo-palladium compound of the general formula Pdl_aXb, where L is an organophosphine ligand and X is an anion. In preferred embodiments, L includes triphenylphosphine and X is halide, such as chloride, exemplified by bis(triphenylphosphine)palladium(ll) dichloride (abbreviated PdPC, also written Pd(PPh3)2CI2).

[0007] When incorporated into the active layer of a p-channel OTFT, the composite exhibits gate-bias-modulated, reversible sensitivity to CO at room temperature. Under negative gate bias, the organic semiconductor and the Pd(ll) complex are oxidized, enhancing Pd-CO coordination and modulating transistor characteristics (e.g., drain current, mobility, and threshold voltage). Removal of the bias allows the Pd(ll) complex to return to a neutral state, enabling recovery and reuse.

[0008] The disclosure further provides OTFT devices, printable inks, methods to make the composite and devices, and methods of detecting CO at ppb-ppm levels using bias programming to alternate between sensing and recovery states.BRIEF DESCRIPTION OF THE FIGURES

[0009] The features of certain embodiments will become more apparent in the following detailed description in which reference is made to the appended figures, brief descriptions of which are provided below.

[0010] Figure 1 : Schematic of a bottom-gate / bottom-contact OTFT structure.

[0011] Figure 2: Schematic of a bottom-gate / top-contact OTFT structure.

[0012] Figure 3: Frontier energy levels of PdPC, DPPT-TT, PdCI2, and PPh3.

[0013] Figure 4: Photographs of PdCI2and PdPC moistened with water, before and after exposure to CO (3 bar, 30 min).

[0014] Figure 5: Microscopic images of thin films of DPPT-TT and blended films including PdPC, spin coated on Si / SiO2 wafers: (a) DPPT-TT, (b) DPPT-TT + 2%PdPC, (c) DPPT-TT + 4%PdPC, (d) DPPT-TT + 8%PdPC, and (e) DPPT-TT + 16%PdPC.

[0015] Figure 6: AFM height and (g-i) phase images (2 pm * 2 pm) of thin films of DPPT-TT and its blend films with 4% and 16% PdPC, respectively.

[0016] Figure 7: Out-of-plane XRD patterns of DPPT-TT, PdPC, and their blend films with different PdPC concentrations.

[0017] Figure 8: Transfer curves of OTFT devices with DPPT-TT, its blend films with varying concentrations of PdPC, and its blend film with 4% PdCI2as the active layers, measured at VDS = -15 V in dry air.

[0018] Figure 9: (a)-(e) IDS versus time (t) profiles of OTFT devices using different active layers, measured in dry air and upon exposure to 10 ppm CO in dry air for 4 minutes with GS and DS held at -15 V. (f) IDS— t profiles of an OTFT device with 4% PdPC-containing DPPT-TT exposed to 100 ppb and 1 ppm CO, both GS and VDS held at -15 V.

[0019] Figure 10: s-t profiles of an OTFT device with 4% PdCI2-containing DPPT-TT, measured in dry air (bottom curve) and up on exposure to 10 ppm CO (top curve), with VGs and VDS held at -15 V.

[0020] Figure 11 : | lDs|-t profiles of an OTFT device with a 4% PdPC-containing DPPT-TT film as the active layer, measured over 6 consecutive experiments under different gas atmospheres (dry air or 10 ppm CO) and different biases (VGs = DS = 0 V or VGs = DS = -15 V).

[0021] Figure 12: (a) Transfer curves an OTFT device with a 4% PdCI2-incorporated DPPT-TT film as the active layer, measured in dry air before and after a single sensing test with 10 ppm CO exposure, (b) |lDs|-t profiles of the same device in (a) during a second CO sensing test, following the initial 10 ppm CO exposure. The device underwent four consecutive experiments under varying gas atmospheres (dry air or 10 ppm CO) and different biases (VGs = DS = 0 V or VGs = DS = -15 V): (I) The device was turned on in dry air for 5 minutes, then turned off for 30 seconds; (II) The device was turned on in dry air for 30 seconds, exposed to 10 ppm CO for 30 seconds, exposed to dry air for 4 minutes, turned off, and kept in dry air for 20 minutes; (III) The device was turned on in dry air for 5 minutes, then turned off and kept in dry air for 20 minutes; (IV) The device was turned on in dry air for 30 seconds, exposed to 10 ppm CO for 30 seconds, and exposed to dry air for 4 minutes. The device was fabricated by spin-coating a DPPT-TT solution (5 mg polymer mL“1) with 4% PdCI2in chloroform :1,2-dichlorobenzene onto an OTS-treated Si / SiO2substrate with pre-patterned gold electrodes (L = 10 pm, W = 2000 pm) at 2000 rpm for 60 seconds, followed by annealing in a vacuum oven at 140 °C for 20 minutes.DETAILED DESCRIPTION

[0022] As used herein, the term “HOMO energy level” refers to the highest occupied molecular orbital energy, determined e.g., via cyclic voltammetry using ferrocene as reference.

[0023] “Organo-palladium compound” refers to a palladium complex ligated with one or more organic ligands, such as organophosphine ligands.

[0024] The term “OTFT” will be understood to include organic thin-film transistors having bottom-gate / bottom-contact and bottom-gate / top-contact architectures.

[0025] The terms “comprise”, “comprises”, “comprised” or “comprising” may be used in the present description. As used herein (including the specification and / or the claims), and unless stated otherwise, these terms are to be interpreted as open-ended terms and as specifying the presence of the stated features, integers, steps or components, but not as precluding the presence of one or more other feature, integer, step, component or a group thereof as would be apparent to persons having ordinary skill in the relevant art. Thus, the term "comprising" as used in this specification means "consisting at least in part of”. When interpreting statements in this specification that include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0026] The phrase “consisting essentially of’ or “consists essentially of’ will be understood as generally closed terms, with the exception of allowing inclusion of additional items, materials, components, steps, or elements, that do not materially affect the basic and novel characteristics or function of the item(s) used in connection therewith. For example, trace elements present in a composition, but not affecting the composition's nature or characteristics would be permissible if present under the “consisting essentially of’ language, even though not expressly recited in a list of items following such terminology. When using an open-ended term, such as “comprising” or “including”, it will be understood that direct support should be afforded also to “consisting essentially of’ language as well as “consisting of’ language as if stated explicitly and vice versa. In essence, use of one of these terms in the specification provides support for all of the others.

[0027] For the purposes of the present description and / or claims, and unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present invention, inclusive of the stated value and has the meaning including the degree of error associated with measurement of the particular quantity. The term “about” generally refers to a range of numbers that one of ordinary skill in the art would consider as a reasonable amount of deviation to the recited numeric values (i.e., having the equivalent function or result). For example, this term “about” can be construed as including a deviation of ±10 percent of the given numeric value provided such a deviation does not alter the end function or result of the value. Therefore, a value of about 1% can be construed to be a range from 0.9% to 1.1%.

[0028] The term "and / or" can mean "and" or "or".

[0029] Unless stated otherwise herein, the articles “a” and “the”, when used to identify an element, are not intended to constitute a limitation of just one and will, instead, be understood to mean “at least one” or “one or more”.

[0030] This disclosure describes semiconductor composites comprising an organic semiconductor and an organo-palladium compound. Also described herein are methods for synthesizing the composites, the formation of an organic semiconductor layer using the composites in an electronic device, and applications of the device for chemical sensing, in particular CO sensing.

[0031] More particularly, the present description aims to address at least one of the deficiencies in the prior art discussed above by coordinating Pd(ll) with at least one electrondonating ligand to lower its oxidizing ability or raising the lowest unoccupied molecular orbital energy level (ELUMO). However, since this modification may compromise the complex’s sensitivity to CO, the description leverages the operational mechanism of OTFTs and the unique selection of a ligand. As p-channel OTFT devices require organic semiconductors with a highest occupied molecular orbital (EHOMO) in the range of approximately -5.0 eV to -5.6 eV for stable performance in ambient condition, under a negative gate bias (VGs), the organic semiconductor becomes positively charged, generating mobile electron holes that increase the drain current (IDS). If a Pd(ll) complex with an EHOMO similar to that of the host p-type semiconductor is incorporated into the active layer, it will also be oxidized under anegative VGs, rendering the Pd(ll) complex electron-deficient, enhancing its interaction (coordination) with CO, and thereby altering the OTFT characteristics. When the gate bias is removed, the Pd(ll) complex returns to its neutral state, becoming inert to CO and allowing for effective sensor recovery. By modulating the gate voltage ( GS) between 0 (off-state) and a negative bias (on-state), OTFT-based CO sensors with the organic semiconductor-Pd(ll) complex composite described herein exhibit both high sensitivity and reversibility for CO detection at ambient temperatures.

[0032] One or more embodiments described herein relate to composites consisting of a semiconducting polymer / organometallic compound, which in some embodiments serve as a sensing layer for CO sensors and potentially other types of chemical sensors. Embodiments also relate to methods of synthesizing a p-type polymer, such as poly[diketopyrrolopyrrole-thieno[3,2-b]thiophene] - which is commonly referred to in art by various acronyms, such as DPPT-TT, PDPPT-TT, PTT-DTDPP, DPP-TTT and others - and an organometallic compound, such as bis(triphenylphosphine)palladium(ll) dichloride (Pd(PPh3)2CI2) (1-10wt%), by dissolving same in a solvent, such as chloroform / 1,2-dichlorobenzene. The description thus relates to the field of gate voltage-regulated, efficient sensing of at least CO and potentially other chemical substances, in OTFT (also known as OFET) sensors. In some embodiments, the sensors may be provided in the form of printed, flexible, and / or lightweight, and potentially wearable CO sensors, which have the advantage of efficiently and economically safeguarding human life.

[0033] The semiconductor composite described herein may be produced by combining an organo-palladium compound with an organic semiconductor solution or dispersion. The solution may be used for solution-processing a semiconductor composite film for an electronic device. The method may involve isolating the composite by removing the solvent. The resulting composite can then be re-dissolved or re-dispersed to form a semiconductor composite solution or dispersion, which is used for solution-processing the film for electronic device applications.

[0034] Organic semiconductor

[0035] The organic semiconductor described herein may be any organic semiconductor, preferably a polymer, and more preferably a p-type ir-conjugated polymer, having a highest occupied molecular orbital (HOMO) energy level of -5.7 eV or higher, or preferably -5.6 eV or higher. The HOMO energy level may be determined by a common method such as a cyclic voltammetry (CV) technique using a reference such as ferrocene, using the equation: ELUMO(eV) = - (Eredonset -- 4.8 eV, where Eredonset and are the onset reduction potential of the organic semiconductor and the onset oxidation potential of ferrocene, respectively, relative to the Ag / AgCI reference electrode, and -4.8 eV is the highest occupied molecular orbital (HOMO) energy level of ferrocene.

[0036] Non-limiting examples of organic semiconductor that may be used in the present description include the following:n, and

[0037] The terminal ends of the organic semiconductors may independently be any suitable group such as hydrogen, optionally substituted hydrocarbon with about 1 to about 60 carbon atoms, such as, for example, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, and substituted aryl, fluorocarbon, ester, amide, imide, cyano (CN), halogen (e.g., F, Cl, Br, or I), hydroxy (-OH), alkoxy, amino (-NH2), substituted amino, or any other suitable group, or other ir-conjugated polymer blocks;

[0038] In the above examples, n is the number of repeat units and may range from about 1 to about 1,000,000.

[0039] Orqano-palladium compound

[0040] The organo-palladium compound in the semiconductor composites described herein generally comprises palladium and an organophosphine ligand having the Formula (I) below:

[0041] PdLaXb (I),

[0042] where:

[0043] Pd is preferably Pd(ll) (or Pd2+);

[0044] L is an organophosphine ligand, such as but not limited to triphenylphosphine, tri(o-tolyl)phosphine, 1,3-bis(diphenylphosphino)propane (“dppp”), 1,2-bis(diphenylphosphino)ethane (“dppe”), 2, 2'-bis(diphenylphosphino)-1,1 '-binaphthyl (“BINAP”), or 1,1'-ferrocenediyl-bis(diphenylphosphine) (“dppf”));

[0045] X is an anion, such as but not limited to Cl“, Br“, l“, SO42-, CH3COO“, PO43-;

[0046] a is an integer from 1 to 4; and,

[0047] b is 0 or 2 / z (z is the valency of the anion X).

[0048] The concentration of the organo-palladium compound in the organic semiconductor composite with respect to the total weight of the organic semiconductor and the organo-palladium compound may be, for example, 0.1% to 50%, preferably, 0.5 % to 30%, or more preferably 1% to 10%.

[0049] Examples of organo-palladium compounds for the present description include but are not limited to one or more of the following compounds, their derivatives, and mixtures thereof: bis(triphenylphosphine)palladium(ll) dichloride (“PdPC”), [1,2-bis(diphenylphosphino)ethane]dichloropalladium(ll) “dppe-PdCI2”); (1 ,3-bis(diphenylphosphino)propane)palladium(ll) chloride (“dppp-PdCI2”); dichloro[2,2'-bis(diphenylphosphino)-1,1'-binaphthyl]palladium(ll); dichlorobis(tri-o-tolylphosphine)palladium(ll); and [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium(ll).

[0050] Composite Preparation and Film Formation

[0051] In general, and as further discussed below, semiconductor composites described herein may be prepared by dissolving or dispersing the organo-palladium compounds together with the organic semiconductor in a solvent or solvent blend (e.g., chlorobenzene, chloroform, 1,2-dichlorobenzene; alcohols; hydrocarbons; acetonitrile; water). One or more solvents may be used at any suitable ratio (e.g., 99:1 to 1:99 v / v). The solutions are optionally filtered (e.g., 0.2 pm PTFE) and deposited by liquid processing (e.g., spin at about 2000 rpm for about 60 s) to yield films (from about 40 to about 50 nm). The films may be thermally annealed and / or solvent-annealed. If thermally annealed, the process may preferably be conducted at a temperature of < 250 °C, preferably < 200 °C; for a period of time; and in air or an inert environment. These methods are described further below.

[0052] Various solvents can be used in the described method, and particularly those that are capable of dissolving and / or dispersing both the organo-palladium compound and theorganic semiconductor. Suitable solvents include liquid organic solvents and water. The liquid organic solvent may comprise, for example: an alcohol, such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and / or octanol; a hydrocarbon, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, xylene, and / or mesitylene; tetrahydrofuran; dichloromethane; tetrachloroethane; chloroform; chlorobenzene; dichlorobenzene; trichlorobenzene; nitrobenzene; cyanobenzene; acetonitrile; or any combinations thereof.

[0053] As noted above, one or more solvents may be used in the organic semiconductor composite solution. In embodiments where two or more solvents are used, each solvent may be present at any suitable volume ratio or weight ratio such as, for example, from about 99(solvent A): 1 (solvent B) to about 1 (solvent A):99(solvent B).

[0054] One or more organo-palladium compounds may be used in the method described herein. In embodiments where two or more organo-palladium compounds are used, each organo-palladium compound may be present at any suitable weight ratio or molar ratio such as, for example, from about 99(first organo-palladium compound): 1 (second organo-palladium compound) to about 1 (first organo-palladium compound):99(second organo-palladium compound).

[0055] The mixing of the organo-palladium compound(s) with the organic semiconductor(s) can be carried out at any suitable temperature that would known to persons skilled in the art for accelerating the mixing process. For example, the mixing may take place at a temperature in the range from room temperature (i.e., about 20 to about 25 °C) to about 250 °C.

[0056] The organic semiconductor composites described herein can be used in various electronic devices such as thin film transistors, photovoltaics, and resistors. The use of the organic semiconductor composites as semiconductors in electronic devices is illustrated herein using organic thin film transistors (OTFTs) for carbon monoxide sensors. It will be understood that the scope of the present description is not limited to such sensors.

[0057] Figure 1 illustrates a bottom-gate, bottom-contact OTFT configuration comprising a substrate, a gate electrode, a source electrode and a drain electrode, a gate dielectric layer, and an organic semiconductor layer comprising the semiconductor composite described herein.

[0058] Figure 2 illustrates a bottom-gate, top-contact OTFT configuration comprising a substrate, which is in contact with a gate electrode and a layer of a gate dielectric. Over the gate dielectric there is provided an organic semiconductor layer comprising the semiconductor composite described herein. Two conductive contacts, source electrode and drain electrode, are deposited on top of the organic semiconductor layer.

[0059] In one embodiment, the fabrication of an organic semiconductor thin film from the presently described semiconductor composite can be achieved by depositing the composite solution onto a substrate using a liquid deposition technique. This process can take place either before or after the formation of other optional layers on the substrate. Therefore, the liquid deposition of the organic semiconductor composite can be performed on a bare substrate or one that already contains layers, such as a conducting, semiconducting, or insulating layer.

[0060] As would be understood, the phrase "liquid deposition technique" refers to, for example, deposition of a semiconductor composite solution using a liquid process such as liquid coating or printing, where the liquid is a homogeneous or heterogeneous dispersion of the organic semiconductor and the organo-palladium compound in a liquid. The semiconductor composite described herein may be referred to as “ink” when printing is used. Examples of liquid coating processes may include, for example, spin coating, blade coating, rod coating, dip coating, drop casting, and the like. Examples of printing techniques may include, for example, lithography or offset printing, gravure, flexography, screen printing, stencil printing, inkjet printing, stamping (such as microcontact printing), and the like. Liquid deposition deposits a layer of the organic semiconductor of this invention having a thickness ranging from about 1 nanometer to about 1 millimeter, preferably from about 10 nanometers to about 500 nanometers.

[0061] In one embodiment, a thermal annealing process may be utilised for depositing the semiconductor composite. Such process may be conducted at a temperature of, for example, at or below about 250 °C. A lower heating temperature of below about 200 °C may be preferable where low-cost plastic substrates are utilized.

[0062] The heating can be performed for a time ranging from, for example, 1 second to about 24 hours, or from about 10 seconds to 1 hour. The heating can be performed in air or an inert atmosphere, for example, under nitrogen or argon.

[0063] In another embodiment, a solvent annealing process may be utilized, wherein the deposited organic semiconductor thin film is exposed to a solvent vapor.

[0064] The resulting organic semiconductor layer can be used in electronic devices such as thin film transistors, photovoltaic, and other electronic devices, which require a semiconductor.

[0065] As would be understood, the present description provides a thin film transistor comprising: (a) a dielectric layer; (b) a gate electrode; (c) a semiconductor layer; (d) a source electrode; (e) a drain electrode, and (f) a substrate; wherein the dielectric layer, the gate electrode, the semiconductor layer, the source electrode, the drain electrode and the substrate are in any sequence as long as the gate electrode and the semiconductor layer both contact the insulating dielectric layer, and the source electrode and the drain electrode both contact the semiconductor layer, and the semiconductor layer is comprised of the semiconductor composite comprising an organic semiconductor and an organo-palladium compound.

[0066] The substrate may be formed of various materials or combinations of materials. As would be understood, the choice of substrate material would be dependent on the intended application. For example, suitable substrate materials include silicon, metal films or sheets, glass plates or sheets, plastic films or sheets, paper, fabric, etc. For structurally flexible devices, substrates such as aluminum films or sheets, or plastic substrates like polyester, polycarbonate, and polyimide sheets, may be used. Alternatively, the substrate may be rigid for applications requiring such physical characteristic. The substrate thickness can similarly vary based on the desired use. For example, for a flexible or plastic substrate, the thickness may be from amount 10 micrometers to about 10 millimeters, or from about 50 micrometers to about 2 millimeters. For a rigid substrate, such as one made of glass and / or silicon, the thickness may be from about 0.4 millimeters to about 10 millimeters.

[0067] The insulating dielectric layer, which separates the gate electrode from the source and drain electrodes and contacts the semiconductor layer, can be a composite films formed from an inorganic polymer, an organic polymer, or an inorganic-organic polymer. Examples of inorganic dielectric materials include silicon oxide, silicon nitride, aluminum oxide, barium titanate, and barium zirconate titanate. Examples of organic polymer dielectrics may include fluorinated polymers (e.g., Cytop), polyesters, polycarbonates, poly(vinyl phenol), polyimides, polystyrene, polymethacrylate(s), polyacrylate(s), and epoxy resin. Examples of inorganic-organic composite materials can include spin-on glass, such as polymethylsilsesquioxane (pMSSQ), or metal oxide nanoparticles dispersed in polymers like polyester, polyimide, or epoxy resin.

[0068] The dielectric layer thickness may range from about 1 nanometer to about 5 micrometers, such as from about 10 to about 1000 nanometers.

[0069] The active semiconductor layer is provided between and in contact with the dielectric layer and the source / drain electrodes. The semiconductor layer is composed of the organic semiconductor composite described herein. This layer typically has a thickness from about 10 nanometers to about 1 micrometer, such as from 20 nanometers to about 500 nanometers. In one embodiment, solution-based processes such as spin coating, casting, screen printing, stamping, or jet printing may be used to fabricate the semiconductor layer from the organic semiconductor composite solution described herein.

[0070] In one embodiment, the gate electrode may be made from a thin metal film, a conducting polymer film, a conducting composite, or the substrate itself (which may, for example, be a heavily doped silicon). Suitable materials for the gate electrode are one or more of gold, chromium, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or conducting polymers such as polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) (PSS / PEDOT). Conducting composites may contain carbon black, carbon nanotubes, graphene, graphite, or silver nanoparticles in a polymer binder, as well as silver-filled conductive thermoplastic inks.

[0071] The gate electrodes described herein can be fabricated by vacuum evaporation, sputtering, or coating from conducting polymer composite solutions or inks via spin coating, casting, or printing. The thickness of the gate electrode layer may range from about 10 nanometers to about 10 micrometers. In the case of metal films, the thickness may be from about 10 to about 1000 nanometers, whereas for polymer conductors the thickness may be from about 30 nanometers and about 10 micrometers. Various other thicknesses will be apparent to persons skilled in the art in view of the present description.

[0072] The source and drain electrodes described herein may generally be made from materials providing low resistance ohmic contact with the semiconductor layer. Such materials include those used for gate electrodes, such as silver, gold, nickel, aluminum, platinum, conducting polymers, and conductive inks (as described above). The thickness of the source and drain electrodes may range from about 10 nanometers to about 1 micrometer, such as from about 20 nanometers to about 500 nanometers.

[0073] The OTFT devices described herein generally comprise a semiconductor channel with a width W and length L. The semiconductor channel width may be, for example, from about 1 micrometer to about 10 millimeters, such as from about 10 micrometers to about 5millimeters. The semiconductor channel length may be, for example, from about 0.1 micrometer to about 1 millimeter, such as rom about 5 micrometers to about 100 micrometers.

[0074] In one embodiment, the present channel semiconductor layer is a thin film transistor formed using a method described herein to form a semiconducting layer, the method comprising: mixing an organo-palladium compound and an organic semiconductor in a solvent to form a semiconductor composite solution, depositing the semiconductor composite solution onto a substrate, and optionally annealing (heating or solvent annealing) the deposited semiconductor composite to form a semiconductor layer.

[0075] Examples

[0076] Embodiments of the present description will now be described by means of the following examples. It will be understood that the examples provided herein are included solely for the purpose of illustration and are not intended to be limiting in any way.

[0077] Example 1 : Preparation of organic semiconductor composite solutions and films using DPPT-TT and bis(triphenylphosphine)palladium(l I) dichloride (PdPC)

[0078] The chemical structures of the organic semiconductor, DPPT-TT (number average molecular weight, Mn, 30.6 kDa; polydispersity index, PDI = 3.23), and the organo-palladium compound, PdPC, used in this example are shown below:CI0H2I

[0079] The HOMO and LUMO energy levels of DPPT-TT and PdPC were determined from cyclic voltammetry and UV-Vis spectroscopy (Figure 3).

[0080] A mixture of DPPT-TT (10 mg), PdPC (2 mg, 4 mg, 8 mg, and 16 mg), and chlorobenzene (CB) (2.5 mL) was stirred in a vial at room temperature until all solids were dissolved. The solution was then filtered using a 0.2 pm Teflon® syringe filter to obtain anorganic semiconductor composite solution. The obtained solution was used for spin coating at 2000 rpm for 60 seconds onto glass and Si / SiO2wafer substrates, forming thin films with a thickness of approximately 40-50 nm inside the glove box.

[0081] Some of the thin films were further thermally annealed on a hot plate before being characterized using optical microscopy, XRD, and AFM. The results of these analyses are presented in Figures 5, 6, and 7.

[0082] Example 2: Device fabrication and evaluation using the organic semiconductor composite solutions in Example 1 as channel materials for OTFT.

[0083] n+-Si / SiO2wafers with prepatterned gold electrodes (channel length (L) of 10 pm and channel width (W) of 2000 pm) were obtained from Fraunhofer IPMS, where the doped Si and thermally grown SiO2layers (230 nm) were used as the gate electrode and gate dielectric, respectively.

[0084] The wafers were rinsed with acetone, then isopropanol, before being dried with nitrogen, and treated for 15 minutes under oxygen plasma. Wafers were then treated with 1% octyltrichlorosilane in toluene at 70 °C for 45 minutes, followed by rinsing with toluene, then isopropanol, and drying with nitrogen. Wafers were dried in a vacuum oven at 70 °C for 1h. Polymer composite solutions with various concentrations of PdPC prepared in Example 1 were spin-coated on the prepared wafers at 2000 rpm for 60 seconds, before being annealed in a vacuum oven at 140 °C for 20 minutes.

[0085] Devices were characterized with a pair of Keithley 2400s on a Nextron™ probe station with beryllium tipped probes in dry air. Charge carrier mobility was calculated from the saturation region. Carrier mobility (p) was calculated in the saturation regime using the equation: IDS = Op (W / 2L)(VGS-VT)2, where IDS is the drain current, Ci is the capacitance of the gate dielectric (1.50 x 10-4Fnr2), and VGSandTare the gate voltage and threshold voltage, respectively, and W and L are width and length of the active channel. TheTwas determined by extrapolating the linear fit of (|IDS|)1 / 2versus VGScurve.

[0086] CO sensing tests were conducted by flowing a mixture of CO gas and dry air at the desired concentration into a chamber housing the OTFT device on the Nextron™ micro probe station, at a flow rate of (1 SLPM (“standard liters per minute”)), either prior to or during the device measurements. The device performance data is presented in Figures 8, 9, and 11.

[0087] Example 3

[0088] A semiconductor solution using DPPT-TT only without PdPC was prepared. This solution was used to deposit pure DPPT-TT films and fabricate OTFT devices for CO sensing as described in Examples 1 and 2. The optical microscopy, XRD, and AFM results are presented in Figures 5, 6, and 7. The device performance data is presented in Figures 8 and 9.

[0089] Example 4

[0090] A semiconductor dispersion using DPPT-TT as the organic semiconductor and PdCh as an additive (4 wt%) was prepared. This dispersion was used (without filtering) to deposit pure DPPT-TT films and to fabricate OTFT devices for CO sensing as described in Examples 1 and 2. The device performance data is presented in Figures 8, 10, and 12.

[0091] Although the above description includes reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art. Any drawings provided herein are solely for the purpose of illustrating various aspects of the description and are not intended to be drawn to scale or to be limiting in any way. The scope of the claims appended hereto should not be limited by the preferred embodiments set forth in the above description but should be given the broadest interpretation consistent with the present specification as a whole. The disclosures of all references in the present description herein are incorporated herein by reference in their entirety.

Claims

WE CLAIM:

1. An organic semiconductor composite comprising: (i) an organic semiconductor having a highest occupied molecular orbital (HOMO) energy level of -5.7 eV or higher; and (ii) an organo-palladium compound of Formula IPdLaXb(I),wherein:- L is an organophosphine ligand;- X is an anion having a valence of z;- a is 1 to 4; and,- b is 0 or 2 / z where z is the valence of X.

2. The composite of claim 1 , wherein the Pd is Pd(ll).

3. The composite of claim 1 or 2, wherein the organic semiconductor is a p-type TT-conjugated polymer.

4. The composite of any one of claims 1 to 3, wherein the HOMO energy level is -5.6 eV or higher.

5. The composite of any one of claims 1 to 4, wherein the organophosphine ligand comprises triphenylphosphine, tri(o-tolyl) phosphine, 1 ,3-bis(diphenylphosphino)propane, 1,2-bis(diphenylphosphino)ethane, 2, 2'-bis(diphenylphosphino)-1,1 '-binaphthyl, or 1,1'-ferrocenediyl-bis(diphenylphosphine).

6. The composite of any one of claims 1 to 5, wherein the organic semiconductor has the formula:wherein the terminal ends of the formula each independently comprises: hydrogen; an optionally substituted Ci to C6o hydrocarbon; alkyl; substituted alkyl; alkenyl; substituted alkenyl; alkynyl; substituted alkynyl; aryl; substituted aryl; fluorocarbon; ester; amide; imide; -CN; halogen; -OH; alkoxy; -NH2; substituted amino; or other ^-conjugated polymer blocks; and,n is from 1 to 1,000,000.

7. The composite of any one of claims 1 to 6, wherein X is Cl“, Br, l“, SO42-, CH3COO-, or PO43-.

8. The composite of any one of claims 1 to 7, wherein the organo-palladium compound comprises bis(triphenylphosphine)palladium(ll) dichloride (Pd(PPh3)2CI2).

9. The composite of any one of claims 1 to 8, wherein the organo-palladium compound is present from about 0.1 to about 50 wt%, from about 0.5 to about 30 wt%, or from about 1 to about 10 wt%, relative to the combined weight of the organic semiconductor and the organo-palladium compound.

10. The composite of any one of claims 1 to 9, wherein the organic semiconductor comprises DPPT-TT or a functional derivative thereof.

11. The composite of any one of claims 1 to 10, which is solution-processable into a thin film having a thickness from about 10 to about 500 nm, or from about 20 to about 300 nm.

12. The composite of any one of claims 1 to 11 , in the form of a printable ink in one or more solvents, wherein the one or more solvents are: chlorobenzene, chloroform, dichlorobenzene, trichlorobenzene, nitrobenzene, cyanobenzene, alcohols, hydrocarbons, ethers, chlorinated solvents, acetonitrile, water, and any combinations thereof.

13. An organic thin-film transistor (OTFT) comprising a substrate, a gate electrode, a dielectric layer, a semiconductor layer, and source and drain electrodes, wherein the semiconductor layer comprises the composite of any one of claims 1 to 12.

14. The OTFT of claim 13, wherein the OTFT is configured as bottom-gate / bottom-contact or bottom-gate / top-contact.

15. The OTFT of claim 13 or 14, wherein the substrate comprises silicon, glass, or a flexible polymer.

16. The OTFT of any one of claims 13 to 15, wherein the semiconductor layer has a thickness of 20-500 nm.

17. The OTFT of any one of claims 13 to 16, wherein the channel length L is from about 5 to about 100 pm and the channel width W is from about 10 pm to about 5 mm.

18. The OTFT of any one of claims 13 to 17, wherein the dielectric is SiO2, AI2O3, SiNx, BaTiO3, Ba(Zr,Ti)O3, Cytop, polyimide, PMMA, pMSSQ, and / or poly(vinyl phenol).

19. The OTFT of any one of claims 13 to 18, wherein the thickness of the dielectric is from about 10 to about 1000 nm.

20. The OTFT of any one of claims 13 to 19, wherein the source and / or drain electrodes comprise Au, Ag, Ni, Pt, or PEDOT:PSS.

21. A method of making an organic semiconductor composite film, comprising:- mixing an organo-palladium compound of Formula I:PdLaXb(I)with an organic semiconductor in one or more solvents to form a composite solution;- depositing the composite solution onto a substrate by liquid deposition; and, - optionally annealing the deposited film, wherein the annealing comprises thermal annealing at a temperature of < 250 °C; and / or solvent annealing.

22. The method of claim 21 , wherein the liquid deposition comprises spin coating, blade / rod coating, casting, or printing.

23. The method of claim 21 or 22, wherein the organo-palladium compound is Pd(PPh3)2CI2and the composite includes from about 1 to about 10 wt% of the organo-palladium compound.

24. The method of any one of claims 21 to 23, wherein the mixing is conducted at a temperature from about 20 °C to about 200 °C.

25. The method of any one of claims 21 to 24, wherein, prior to the depositing, the composite is isolated and re-dissolved.

26. A method of detecting the presence or concentration of carbon monoxide, CO, comprising:- providing an OTFT according to any one of claims 13 to 20;- applying a negative gate bias to place the OTFT in an on-state;- exposing the semiconductor layer to a gas sample;- measuring at least one transistor parameter, wherein the transistor parameter is drain current, carrier mobility, and / or threshold voltage; and- detecting the presence or concentration of CO based on a change in the measured parameter.

27. The method of claim 26, further comprising removing the gate bias to allow recovery of the sensor between exposures.

28. The method of claim 26 or 27, wherein the detecting occurs at ambient temperature.

29. The method of any one of claims 26 to 28, wherein the gas sample includes CO in a concentration between parts-per-billion and tens of parts-per-million.

30. The method of any one of claims 26 to 29, wherein the organo-palladium compound is Pd(PPh3)2CI2and the semiconductor comprises DPPT-TT.

31. An OTFT carbon monoxide sensor comprising the composite of any one of claims 1 to 12 as an active semiconductor layer, the sensor being gate-bias-programmable for reversible CO sensing at ambient temperature.

32. The sensor of claim 31 , wherein the sensor is in the form of a printed, flexible, or wearable device.

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