WO2013098648A1

WO2013098648A1 - Unconventional chemical doping of organic semiconducting materials

Info

Publication number: WO2013098648A1
Application number: PCT/IB2012/003040
Authority: WO
Inventors: Thomas D. Anthopoulos
Original assignee: Imperial Innovations Ltd.
Priority date: 2011-12-30
Filing date: 2012-12-28
Publication date: 2013-07-04
Also published as: TW201348241A

Abstract

Compositions comprising doped organic semiconductors with high charge carrier mobilities are formed which comprise at least one polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces, at least one neutral molecular dopant, wherein the dopant is dopant is not evenly distributed throughout the composition. Methods of making the compositions are also described.

Description

UNCONVENTIONAL CHEMICAL DOPING OF ORGANIC SEMICONDUCTING

MATERIALS

RELATED APPLICATIONS

This application claims priority to US provisional application serial number

61/582,037 filed December 30, 2011, which is hereby incorporated by reference in its entirety for all purposes including figures, working examples, and claims.

BACKGROUND

The basic principle of doping in organic (small molecule and polymeric)

semiconductors is similar to that in inorganic semiconductors. In each case one has to introduce "impurities" i.e. foreign atoms or molecules that will either transfer an electron to the electron conducting energy band or state, for example, the lowest unoccupied molecular orbitals (LUMO) in the case of organics, causing n-type doping, or remove an electron from the hole conducting energy band/state, for example, the highest occupied molecular orbitals (HOMO) to generate a free hole and hence cause p-type doping.

Using this approach p-type as well as n-type doping in organic semiconductors and devices has been demonstrated. See, e.g., Pfeiffer et al. Org. Electr. 4, 89 (2003), Zhang et al Phys. Rev. B, 81, 085201 (2010). In most cases, the doping process is typically a bulk phenomenon with the dopant molecules/elements distributed evenly across the semiconductor although alternative methods such as remote doping have also been demonstrated. Zhao et al. Appl. Phys. Lett. 97, 123305 (2010). Materials used so far are mainly organics with relatively low charge carrier mobilities.

When it comes down to high charge carrier mobility organic semiconductors, however, the introduction of molecular dopants may cause disruption of the molecular packing, i.e. a key characteristic for obtaining high carrier mobility films and hence electronic devices, and lead to degradation in hole/electron mobility. As a result, conventional doping may be limited to organic materials with relatively low charge carrier mobilities. These are materials that do not self-assemble/pack very well (e.g. amorphous like structure in the solid state).

Accordingly, there is a need for compositions of, and methods for making, doped organic semiconductors with high charge carrier mobilities. Furthermore, there is a need to dope crystalline thin film transistors (TFTs) without substantially affecting the crystalline packing of the film. SUMMARY

Embodiments described herein include compositions and compounds, as well as methods of making, methods of using, inks, and devices comprising these compositions and compounds.

One embodiment provides for a method comprising: providing at least one liquid precursor composition formed by mixing at least (i) at least one hole or electron conducting organic material adapted to form an organic polycrystalline phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent; forming at least one solid film from the liquid precursor composition, wherein the solid film comprises the at least one organic

polycrystalline phase which comprises grain boundaries, and wherein the dopant is enriched at the grain boundaries.

Another embodiment provides for a composition comprising: at least one

polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces of the crystalline domains, and at least one neutral molecular dopant, wherein the dopant is enriched at the grain boundaries at the interfaces of the crystalline domains.

Another embodiment provides for a method comprising: providing an ink formed by mixing at least (i) at least one organic semiconductor adapted to form a polycrystalline phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent; forming at least one solid film from the ink, wherein the solid film comprises the at least one organic

semiconductor polycrystalline phase which comprises grain boundaries, and wherein the dopant is not evenly distributed throughout the solid film.

At least one advantage for at least one embodiment is excellent electron or hole mobility.

Another advantage for at least one embodiment includes doping a crystalline semiconductor with high charge carrier mobility in a single solution phase deposition.

Yet another advantage for at least one embodiment includes employing a dopant of varying structure and neutral charge to a crystalline material thereby allowing for flexibility in doping parameters and compositions.

A further advantage for at least one embodiment is that for small doping

concentrations the polycrystalline microstructure of a resulting blend film appears to remain the same without any noticeable changes. BRIEF DESCRIPTION OF THE FIGURES

Figure 1. Shows ultraviolet photoemission spectroscopy data measured for doped as well as undoped blend films (MoTDT diF-TES ADT:PTAA). No change in the energetics of the films is observed upon doping with MoTDT.

Figure 2. Shows the effect of doping the diF-TES ADT:PTAA blend films with MoTDT.

Figure 3. Shows an Arrhenius plot of the hole mobility measured in saturation for a doped and an undoped blend based organic TFTs (OTFTs). This suggests the hole transport mechanism in doped and undoped devices appear to be different.

Figure 4. Shows oscillation frequency as a function of applied voltage measured from a seven stage ring oscillator based on doped and undoped diF-TES ADT:PTAA blend semiconductor

Figure 5. Shows an exemplary diagram of transistors employed for the construction of the invert and ring oscillator circuits.

DETAILED DESCRIPTION

INTRODUCTION

All references cited herein are incorporated by reference in their entirety.

This application claims priority to US provisional application serial number

61/582,037 filed December 30, 2011, which is hereby incorporated by reference for all purposes in its entirety including figures, working examples, and claims.

PCT/EP2011/056584, filed April 26, 2011 to The University of Princeton is hereby incorporated by reference in its entirety.

Compositions, compounds, derivatives, and materials that create organic

semiconductors with high charge carrier mobilities are known in the art. See, for example, PCT/EP2011/056584, filed April 26, 2011; Jones, et al, Adv. Fund. Mater., 2010, 20, 2330- 2337; Hamilton et al, Adv. Mater., 2009, 21, 1166-1171; Verlaak, et al, Appl. Phys. Lett. (2003), 82(5), 745-747; and Smith, et al, J. Mater. Chem. 2010, 20, 2562. Compositions, compounds, derivatives, and materials of this type may be doped by methods such as remote doping and other methods. See, for example, Zhao et al, Appl. Phys. Lett., 2010, 97, 123305. See also, Chen, et al, J. Phys. Chem. B, 2004, 108, 17329-17336. The compositions, compounds, derivatives, and/or materials of the prior art do not teach or suggest the embodiments disclosed herein.

COMPOSITIONS

At least one embodiment provides for a at least one polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces of the crystalline domains, and at least one neutral molecular dopant, wherein the dopant is enriched at the grain boundaries at the interfaces of the crystalline domains. Another embodiment provides for a at least one polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces of the crystalline domains, and at least one neutral molecular dopant, wherein the dopant is not evenly distributed throughout the solid film. The embodied compositions may further include at least one amorphous polymeric nonconducting or semi-conducting material.

POLYCRYSTALLINE ORGANIC SEMICONDUCTING MATERIALS

The polycrystalline organic semiconductor material may, in some embodiments, comprise a crystalline or semi-crystalline hole-transport material or a crystalline or semi- crystalline electron transport material.

In one embodiment, the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoacenes represented by formula (I).

wherein R₁-R₁0 independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, halogen, trialkylsilylethynyl, each optionally substituted with one or more halide, cyano, alkyl, or alkoxy groups, and n is 0 to 10.

In a preferred embodiment, the at least one polycrystalline organic semiconductor comprises a hole-transport material represented by the formula (II):

wherein R' is in each instance independently selected from Ci-Cio alkyl, aryl or heteroaryl, each optionally substituted with one or more halide, cyano, alkyl, or alkoxy groups.

In another embodiment, the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted

oligoheteroacenes represented by formula (III):

(III)

wherein the two X moieties independently are O, S, Se, NH; and Ri-R₈ independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, trialkylsilylethynyl, halogen, arylethynyl, heteroaryl ethynyl; and n is 0 to 10. In a preferred embodiment, the at least one

polycrystalline organic semiconductor comprises a hole-transport material represented by the formula (IV):

oligoheteroacenes represented by formula (V):

wherein X in each instant independently is O, S, Se, NH; Ri-Rg independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, trialkylsilylethynyl, halogen, arylethynyl,

heteroarylethynyl; and n and n' independently are 0 to 5.

In a preferred embodiment, the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoacene - fused thienothiophenes r

wherein Ri and R₂ are independently selected from H, alkyl, fluoroalkyl, aryl, heteroaryl, trialkylsilylethynyl, arylethynyl, and heteroarylethynyl; and n and n' are independently 0, 1 or 2.

In another embodiment, the at least one polycrystalline organic semiconductor comprises an electron-transport material that comprises optionally substituted arylenes or heteroaryl enes. Optionally substituted arylenes or heteroaryl enes are known in the art as electron-transport materials, and may be embodied, for example, in the references incorporated herein.

In yet another embodiment, the at least one polycrystalline organic semiconductor comprises an electron-transport material that is selected from perylene diimides represented by the formula (VII):

(VII) wherein Ri and R₂ are C1-C30 organic groups independently selected from a normal, branched, or cyclic alkyl, aryl, heteroaryl, alkyl-aryl, or alkyl-heteroaryl group optionally substituted with one or more halide, cyano, alkyl, or alkoxy groups. See, e.g., Nature Mater., 2009, 8, 952.

In yet another embodiment, the at least one polycrystalline organic semiconductor comprises an electron-transport material that is selected from naphthalene diimides represented by the formula (VIII):

wherein hAr is a heteroaryl; R¹ and R¹ are a C1-C30 organic group independently selected from a normal, branched, or cyclic alkyl, aryl, heteroaryl, alkyl-aryl, or alkyl-heteroaryl

2 3 group optionally substituted with one or more halide, cyano, alkyl, or alkoxy groups; R , R , and R⁴ are independently selected from hydrogen, halide, or a C1-C30 organic group independently selected from cyano, normal, branched, or cyclic alkyl, fluoroalkyl, aryl, heteroaryl, alkyl-aryl, acyl- and alkyl-heteroaryl groups, optionally substituted with one or more fluoro, cyano, alkyl, alkoxy groups.

Further examples of crystalline or semi-crystalline hole-transport materials embodied herein include pentacene or a substituted pentacene derivative such as TIPS pentacene (6,13- bis(triisopropyl-silylethynyl) pentacene), rubrene or a rubrene derivative, a metallo phthalocyanine, such as copper phthalocyanine or zinc phthalocyanine, or a regioregular alkyl polythiophene, whose structures are shown below.

Pentacene TIPS-Pentacene

ar Poly(alkyl-thiophi

Metallo-phthalocyanine

AMORPHOUS POLYMERIC ORGANIC MATERIALS

In an embodiment, the composition further comprises at least one amorphous polymeric organic semiconductor or non-conducting material. The amorphous polymeric organic semiconductor material may be a known compound, such as those incorporated by reference herein. In another embodiment, the composition does not comprise an amorphous polymeric organic material. In another embodiment, the amorphous polymeric organic semiconductor or non-conducting material is a polymeric binder.

In one embodiment, the at least one amorphous polymeric organic material includes a polymer comprising optionally substituted arylamine units in the main chain or polymer backbone. The amorphous polymeric organic material can be selected from, for example, polymers comprising units with triarylamine or carbazole in the side chain.

In one embodiment, the at least one amorphous polymeric organic material comprises a material comprising sub-units represented by the formula IX:

wherein R_a is in each instance independently selected from Ci-Cio alkyl, optionally substituted aryl or heteroaryl, k is an integer from 0 to 5; and n can be, for example, from 10 to 1000 as a statistical average as known to those skilled in the art of polymer chemistry. The number average molecular weight can be, for example, 2,500 g/mol to 25,000 g/mol, and the value of n can be determined from the number average molecular weight and the molecular weight of the repeat unit.

In some embodiments, the at least one amorphous polymeric organic material can further comprise at least one amorphous polymer selected from optionally substituted poly(styrene), poly(a-methylstyrene) and poly(vinylbiphenyl), or polymethylmethacrylate).

In other embodiments, the amorphous polymeric organic material are in the form of a copolymer, block polymer or a mixture of two or more polymers. In additional

embodiments, the polymer is linear or branched, including star polymers, comb polymers, brush polymers, dendronized polymers, and dendrimers.

DOPANTS

The dopants embodied herein can be either p-dopants or n-dopants. In one embodiment, the dopant is a p-dopant that comprises a transition metal. In another embodiment, the dopant is an n-dopant that comprises a metal. The dopants embodied herein may comprise a known compound. In an embodiment, the dopant is characterized by selective segregation (e.g., the dopant molecules tend to segregate in specific places in the composition, such as grain boundaries within the film).

The embodiments herein are contemplated to include a wide range of dopant materials. In one embodiment, the dopant is a neutral molecular dopant, which is to say that it is not a zwitterionic or ionic molecule.

In many embodiments, the dopant is a p-dopant. In one embodiment, the p-dopant is a strong oxidant such as, for example, the known dopant Tetrafluoro TCNQ. In some embodiments, the p-dopant materials are transition metal complexes, such as those disclosed in WO 2008/061517, for example, which include structures 1 to 6 as shown below:

4 5 6 wherein M is transition metal, preferably Cr, Mo, or W, and Ri-Re are independently selected from H, substituted or unsubstituted Ci-Cio alkyl, Ci-Cio -thienyl, perfluorinated alkyl, phenyl, tolyl, N, N-dimethylaminophenyl, anisyl, benzoyl, CN or COOR₇ where R₇ is Ci-C5-alkyl; X is S, Se, NR₁₀, wherein Rio is alkyl, perfluoroalkyl, cycloalkyl, aryl, hetero aryl, acetyl or CN.

In an embodiment, the transition metal p-dopant comprises a complex represented by the formula (X):

(X)

wherein M is Cr, Mo or W, and R₁-R5 are independently selected from a C₁-C30 fluorinated alkyl, cyano, or an optionally substituted aryl, heteroaryl. This embodiment includes the preferred p-dopant Mo(tfd)₃ whose structure is shown below:

In an embodiment, the at least one dopant is a known n-dopant. In one embodiment, the known n-dopant causes the conductivity and/or electron mobility measurable in the composition comprising at least one polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces, and at least one dopant to be very substantially increased, preferably at least by a factor of two, or preferably at least by a factor of 10.

In another embodiment, the n-dopant has ionization energy, as measured by photoemission spectroscopy, of less than about 3.5 eV.

The dopant can be, for example, an n-dopant that comprises an alkali metal, transition metal, lanthanide metal, or actinide metal.

In another embodiment, the dopant comprises at least one transition metal sandwich complex represented by the formulas (XI-XIII):

wherein, M^vu is manganese or rhenium; M^vm is iron, ruthenium, or osmium; M^1X is rhodium or iridium; each R^cp and R^bz is individually selected from hydrogen or an optionally substituted C1-C12 alkyl group or C1-C12 phenyl group; x and x' are both independently selected from an integer from 1 to 5; and y and y" are both independently selected from an integer from 1-5 and y' is an integer from 1-6.

In another embodiment, the dopant comprises at least one transition metal sandwich complex represented by the formulas(XIV-XVI):

(XVI)

wherein M^vu is manganese or rhenium; M^vm is iron, ruthenium, or osmium; M^1X is rhodium or iridium; each R^cp, R^bz, and R^d is individually selected from hydrogen or an optionally substituted C1-C 12 alkyl or C1-C12 phenyl; x and x' are both independently selected from an integer from 1 to 5; and y and y" are both independently selected from an integer from 1-5; and y' is an integer from 1-6.

In another embodiment, the at least one dopant comprises dopant such as those disclosed in J. Am. Chem. Soc, 2010, 132, 8852, such as an N-DMBI derivative represented by the formula (XVII):

wherein R_ls R₂ are independently selected from alkyl, aryl or heteroaryl.

Another effect of the unique doping of the present embodiments may be to narrow the threshold voltage variation between different thin-film transistors. Thus, by narrowing the threshold voltage variation, thin- film transistors manufactured in a similar manner can provide more consistent electronic properties. In some embodiments, it is believed that this narrowed threshold voltage may be seen in, for example, the improved performance of a 7- stage ring oscillator. In one embodiment, the variation between two transistors manufactured in the same manner is within the range of about ±5%, ±4%, ±3%, ±2%, ±1%, ±0.1%, ±0.01%, ±0.001% or ±0.0001%. The dopant may be present in the composition at a concentration effective to cause a desired change in the electronic properties of the material or the device in which the material is incorporated. In one embodiment, the dopant is present at a concentration from about 0.001 to about 2.0 percent by weight of the composition. In another embodiment, the dopant is present from about 0.0001 to about 2.0 percent by weight of the composition. In another embodiment, the dopant is present in an amount less than 2.0 percent by weight of the composition.

In one embodiment, the dopant is at least one p-dopant and the hole-mobility of the semiconductor or composition is at least 0.2 cm 2 / V-s, at least 0.5 cm 2 / V-s, or at least 1.0 cm / V-s. In another embodiment, the dopant is a n-dopant and the electron mobility of the semiconductor or composition is at least 0.2 cm 2 / V-s, or at least 0.5 cm 2 / V-s, or at least 1.0 cm / V-s.

In another embodiment, the dopant concentration is in an amount such as to narrow the device parameter spread by at least 20%, or at least 30%>, or at least 40%>, or at least 50%>, or at least 50% or more. In another embodiment, the dopant concentration is in an amount such the threshold voltage of the composition or device is reduced by at least 50%>, or at least 60% or at least 70% as compared to the same composition or device that lacks the dopant.

In some embodiments the at least one dopant comprises two or more dopants. In some embodiments, the number of dopants present in the composition is 1, 2, 3, 4, or 5 dopants. These dopants may be a combination of any dopant disclosed herein, or in addition to a dopant disclosed herein, additionally another dopant known in the art.

GRAIN BOUNDARIES

In an embodiment, the composition comprises at least one polycrystalline organic semiconductor comprising crystalline domains and grain boundaries at the interfaces. In another embodiment, the composition can further include an amorphous polymeric organic compound. The grain boundary can be the interface between two crystalline grains or two crystalline domains or it may be between a crystalline domain and the amorphous polymeric organic compound.

CRYSTALLINE DOMAINS

The crystalline domains of the present embodiments comprise an organic

semiconducting material. In some embodiments, the crystalline domain is substantially free of components other than the organic semiconducting material. In other embodiments, the crystalline domain is 95, 98, 99, 99.5, 99.9 or 99.99 percent free of components other than the organic semiconducting material. In some embodiments, components other than the organic semiconducting material, such as, for example, a dopant or amorphous polymeric organic compound may be present within the crystalline domain. In an embodiment, when the dopant is present within the crystalline domain, it is present in a lower concentration than the concentration of dopant at the grain boundary.

In another embodiment, a crystalline domain may comprise an aligned polycrystalline domain.

METHODS OF MAKING FILMS

Methods of making films for OTFTs are recited and contemplated below. In at least one embodiment, there is provided a method for forming at least one solid film comprising: providing at least one liquid precursor composition formed by mixing at least (i) at least one hole or electron conducting organic material adapted to form an organic polycrystalline phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent; forming at least one solid film from the liquid precursor composition, wherein the solid film comprises the at least one organic polycrystalline phase which comprises grain boundaries, and wherein the dopant is enriched at the grain boundaries. In some embodiments, the liquid precursor additionally comprises at least one hole or electron conducting organic material adapted to form an organic amorphous phase.

In another embodiment, the method comprises: providing an ink formed by mixing at least (i) at least one organic semiconductor adapted to form a polycrystalline phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent; forming at least one solid film from the ink, wherein the solid film comprises the at least one organic semiconductor polycrystalline phase which comprises grain boundaries, and wherein the dopant is not evenly distributed throughout the solid film. The ink of this embodiment may be formed by additionally mixing at least one organic material which is a polymer binder for the organic semiconductor polycrystalline phase.

In an embodiment, the liquid precursor is formed by dissolving, suspending or otherwise incorporating the at least one polycrystalline organic semiconductor material and the at least one dopant in one or more organic solvents. Optionally, the amorphous polymeric organic compound, or polymer binder, which can be a semiconducting material or a nonconducting material is also incorporated into the liquid precursor. It is contemplated that the different materials i.e. (i) small-molecule semiconductor, (ii) amorphous polymeric organic compound or polymer binder and/or (iii) dopant molecule can be prepared as separate solutions that are mixed at a later stage to form the final blend solution. The solvents involved are generally more than one: one for the optional polymer binder and the small molecule semiconductor and a different one for the dopant. Three different solvents for each optional blend component can be used. Additional compounds may be incorporated into the liquid precursor.

In an embodiment, the deposition is achieved by known techniques, such as for example, solution processes in which film forming materials such as polymers are dissolved in common organic solvents to form the liquid precursor, then applied as solutions to a substrate by spinning coating or ink jet printing.

In an embodiment, the solid film is formed by evaporation of the at least one organic solvent from the deposited liquid precursor. Optional additional liquid compounds, if present in the liquid precursor, may be evaporated or cured, thereby resulting in a solid film. The liquid precursor is generally deposited on a solid surface, such as a substrate. The substrate may already contain other coatings, because the solid substrate can eventually take a variety of physical forms. Forms include, for example, for devices and field effect transistors, including bottom gate, top contact, and bottom contact, top gate field effect transistors.

These can be made via the standard techniques for synthesizing organic electronic devices well known to those of ordinary skill in the art of organic electronics, as illustrated in part by the various prior art referenced herein and incorporated by reference.

The present embodiments also contemplate inks. In some embodiments, an ink can comprise the liquid precursor. In another embodiment the ink is used in a method comprising providing an ink formed by mixing at least (i) at least one organic semiconductor adapted to form a polycrystalline phase, (ii) optionally, at least one organic material which is a polymer binder for the organic semiconductor polycrystalline phase, (iii) at least one molecular dopant, and (iv) at least one solvent; and forming at least one solid film from the ink, wherein the solid film comprises the at least one organic semiconductor polycrystalline phase which comprises grain boundaries, and wherein the dopant is not evenly distributed throughout the solid film.

In an embodiment, the organic semiconductor is a polycrystalline organic

semiconductor material as disclosed herein. In one embodiment, the at least one organic material which is a polymer binder for the organic semiconductor polycrystalline phase is a hole or electron conducting organic material adapted to form an organic amorphous phase, or it is an amorphous polymeric non-conducting material or it is a an amorphous polymeric organic semiconductor. In an embodiment, the dopant comprises a dopant embodied herein. In another embodiment, method includes the at least one organic material which is a polymer binder for the organic semiconductor polycrystalline phase

WORKING EXAMPLES

Example 1. Formation of Liquid Precursor and Solid Film

To an organic blend containing 2,8-difluoro-5,l l-bis(triethylsilylethynyl)

anthradithiophene (diF-TESADT) and amorphous p-type polymer poly(triarylamine) (PTAA) polymer in tetraline was added an amount of the known p-dopant organometallic complex Mo tris-[l,2-bis(trifluoromethyl)ethane-l,2-dithiolene] (MoTDT) dissolved in chlorobenzene. The doping concentration was tuned by controlling the amount of the solid concentration in the dopant solution added to the pristine semiconducting solution. The solution was deposited onto a substrate and a composite film was formed by evaporation of the solvent.

Example 2. Fabrication of Ring Oscillators based on Bottom-gate, Bottom-contact

Transistors

Integrated circuits and a number of discrete transistors were fabricated using polyvinylphenol (PVPh) as gate dielectric employing the bottom-gate, bottom-contact device architecture shown in Figure 5 where a generic structure of polyvinylpyrrolidone (PVP i.e. the dielectric) based transistors employed for the construction of the invert and ring oscillator circuits. Here the SAM is the self-assembled monolayer pentafluorobenzene thiol (PFBT) used as contact work function modifier in order to improve the hole injection from the gold (Au) electrode into the HOMO level of the hole transporting small molecule.

The detailed fabrication process is described elsewhere (see, e.g., G. H. Gelinck et al, Nature Mater. 3, 106 (2004)). In brief, the circuit structure consisted of gold electrodes and interconnects and a 300 nm layer of polyvinylpyrrolidone (PVP) patterned to form vertical interconnects (vias). Source and drain electrodes were treated with pentafluorobenzene thiol solution (PFBT) prior to semiconductor deposition to improve charge injection and material crystallisation within the channel (see, e.g., D. J. Gundlach, et al., Nature Mater. 7, 216 (2008)). Semiconductor blend processing was carried out by spin coating followed by annealing at 100 °C for 150 sec in N₂. For the best performance, integrated circuits were further annealed in vacuo (10^~5 mbar) for 30 min at 100 °C. Electrical measurements were carried out in vacuo and in the dark at room temperature. The stage delay (i_d) for each of the ring oscillators was calculated from the measured oscillation frequency (f_osc) using i_d = (l/2nf_osc), where n is the number of inverting stages. Charge carrier mobility was calculated from the transfer characteristics using a geometric capacitance (Q) for the PVP layer of 10 nF/cm , as determined by impedance measurements.

Example 3. Fabrication of Top-gate, bottom-contact Transistors

Top-gate, bottom-contact transistors were fabricated on glass substrates with evaporated gold source-drain electrodes (S-D) that were treated with a pentafluorobenzene thiol (PFBT) self-assembled monolayer acting as the work function modifier. The transistor channel length and width was varied between 20-100 μιη and 0.5-2.0 mm, respectively. The semiconductor consisted of a blend of diF-TESADT and PTAA, with and without the dopant molecule. The gate dielectric comprised of a 900 nm thick layer of the fluoropolymer CYTOP that was also spin cast directly onto the blend semiconductor and annealed at 100 °C for 5 minutes in nitrogen ambient. The gate electrode was then formed by thermal evaporation of aluminium using a shadow mask directly onto the CYTOP layer.

Example 4 Device Morphology

The morphology of the formed composite film was investigated using polarized light microscopy (PLM). No indication of any disruption in the crystalline domains of the composite films could be observed. Electronic measurements of the doped films using transistor structures revealed significant changes of the electronic characteristics of the devices upon doping. For instance upon doping of the films with different amounts of MoTDT the threshold voltage of the transistors was found to shift towards more positive gate voltages (i.e. closer to zero volt gate bias), a rather desirable characteristic. The latter observation most likely indicates a reduction in the density of traps at the

semiconductor/dielectric interface with increasing doping concentration.

Example 5. Determining Shift in the Fermi Energy Level

Next, measurement of the shift in the Fermi energy level (EF) in the semiconducting blend films with increasing doping concentration was investigated. This was done using the ultraviolet photoemission spectroscopy (UPS) method. Obtained results are reproduced in Figure 1, and did not show any strong signature of conventional doping i.e. a shift in the Fermi level with increasing MoTDT concentration. These results are further quantified in Table 1. Table 1. Fermi level with increasing MoTDT concentration

Ι ΛΙ.) t litl

PTAA 5.16 2.70

AD T : PTAA

7.84 5.59

Example 6. Measuring electrical parameters obtained for the diF-TESADT:PTAA blend transistors doped with MoTDT at various concentrations

Next, the electrical parameters obtained for the diF-TESADT:PTAA blend transistors doped with MoTDT at various concentrations (1 wt%, 0.5 wt%, 0.1 wt% and 0 wt%).

Parameters obtained assuming a gate geometric capacitance of 1.2 nF/cm . Here W and L are the channel width and length respectively, while μ_ϋη and μ_8αΐ represent the linear and saturation mobilities extracted from the same devices. As summarized by Table 2, it was observed that the threshold voltage (VT) of these blend transistors reduces with increasing MoTDT concentration while the hole mobility remains relatively high even for doping concentrations up to 1 wt%. These results are further shown by the plots in Figure 2, which shows transfer and output characteristics of a diF-TESADT:PTAA blend organic transistors doped with MoTDT. The concentrations of the p-type doping in the semiconductor film are 0 wt% (a) and 0 wt% (b) in diF-TES ADT:PTAA.

Table 2. Summary of the electrical parameters obtained for the diF-TESADT:PTAA blend transistors

MoTDT W L Min IJsat V_T VON ION/OFF ss wt% (μ/ν) (μ/ν) (cm²/V.s) (V) (V) (A/A) (V/dec)

1.0 1500 100 0.96 1.16 0.1 ϊ .ϊό² 34.7

0.5 1500 100 1.07 1.38 -3.0 no⁴ 12.0

0.1 1500 100 0.97 1.62 -9.9 ΐ.ΐο⁶ 8.8

0 1000 50 1.45 2.67 -16.9 7.10⁴ 10.8

Example 7. Effect of Doping on Trap Deactivation Temperature

To investigate the effect of doping on trap deactivation, temperature dependent measurements were performed and the activation energies for hole transport were extracted. The results are summarized in Figure 3 and show that the hole transport mechanism in doped and undoped devices appear to be different. Figure 3 shows an Arrhenius plot of the hole mobility measured in saturation for a doped and an un-doped blend based OTFTs. Specifically, in the case of the undoped devices hole transport exhibited two distinct regimes; one observed at low (T < 120 K) and one at high temperature regime (T > 120 K). In the case of the doped sample, a single activation energy was present throughout the temperature range with the sample exhibiting consistently higher mobilities across the entire temperature range investigated.

Example 8. Effect of Device Comprising diF-TES ADT:PTAA Blends with MoTDT

In order to further investigate the effects of molecular doping of diF-TES ADT:PTAA blends with MoTDT a 7-stage ring oscillators based on bottom-gate, bottom-contact OTFTs was fabricated as described in the previous examples. In this case the blend semiconductor, with and without the dopant, was spin cast directly onto the circuit substrate followed by electrical characterization in inert atmosphere (nitrogen ambient). A representative set of results is shown in Figure 4 where the oscillation frequency of the 7-stage ring oscillator is plotted as a function of applied voltage for both doped as well as undoped film based circuits.

Claims

What is Claimed is:

1. A method comprising:

providing at least one liquid precursor composition formed by mixing at least (i) at least one hole or electron conducting organic material adapted to form an organic polycrystalline phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent; forming at least one solid film from the liquid precursor composition, wherein the solid film comprises the at least one organic polycrystalline phase which comprises grain boundaries, and wherein the dopant is enriched at the grain boundaries.

2. The method of claim 1, wherein the liquid precursor additionally comprises at least one hole or electron conducting organic material adapted to form an organic amorphous phase.

3. The method of claim 1, wherein the dopant is a p-dopant.

4. The method of claim 1, wherein the dopant is an organometallic complex.

5. The method of claim 1, wherein the dopant comprises a complex represented by the formula (X):

wherein M is Cr, Mo or W, and Ri-Re are independently selected from a C₁-C30 fluorinated alkyl, cyano, or an optionally substituted aryl, heteroaryl.

6. The method of claim 1, wherein the dopant is an n-dopant.

7. The method of claim 1, wherein the dopant is an n-dopant that comprises

metal, transition metal, lanthanide metal, or actinide metal.

8. The method of claim 1 , wherein the at least one hole or electron conducting organic material that is adapted to form an organic crystalline phase comprises a hole-transport material.

9. The method of claim 1 , wherein the at least one hole or electron conducting organic material adapted to form an organic crystalline phase comprises a hole-transport material comprising one or more organic compounds comprising two or more conjugated aryl or heteroaryl rings.

10. The method of claim 1 , wherein the at least one hole or electron conducting organic material adapted to form at least one organic polycrystallme phase comprises a hole-transport material comprising one or more organic compounds comprising two or more conjugated aryl or heteroaryl rings substituted and one or more silyl moieties.

1 1. The method of claim 1 , wherein the at least one hole or electron conducting organic material adapted to form an organic polycrystallme phase comprises a hole-transport material represented by the formula (II) or (IV):

wherein R' is in each instance independently selected from Ci-Cio alkyl, optionally substituted aryl or heteroaryl.

12. The method of claim 2, wherein the at least one hole or electron conducting organic material which is adapted to form an organic amorphous phase comprises an optionally substituted poly(arylamine) that contains aryl moieties in the polymer backbone.

13. The method of claim 2, wherein the at least one hole or electron conducting organic material adapted to form an organic amorphous phase comprises an optionally substituted poly(triarylamine) .

14. The method of claim 2, wherein the at least one hole or electron conducting organic material adapted to form an amorphous phase comprises a copolymer comprising at least one optionally substituted poly(triarylamine).

15. The method of claim 2, wherein the at least one hole or electron conducting organic material adapted to form an organic amorphous phase comprises a compound represented by the formula (IX):

wherein

R_a is in each instance independently selected from Ci-Cio alkyl, optionally substituted aryl or heteroaryl;

k is an integer from 0 to 5;

n is 10 to 1000.

16. The method of claim 2, wherein the at least one hole or electron conducting organic material adapted to form an organic crystalline phase has a molecular weight of about 1 ,000 g/mole or less, and the at least one hole or electron conducting organic material adapted to form an organic amorphous phase has a number average molecular weight of at least 1 ,000.

17. The method of claim 2, wherein the dopant is present in an amount of from 0.001 to 2.0 percent by weight of the composition consisting of the at least one hole or electron conducting organic material adapted to form an organic crystalline phase, the at least one hole or electron conducting organic material adapted to form an organic amorphous phase, and the at least one dopant when the solvent is removed.

18. The method of claim 1 , wherein the liquid precursor composition is formed on a substrate wherein the forming step comprises an inkjet coating or spin coating step.

19. The method of claim 1, wherein the at least one solvent is an organic solvent.

20. The method of claim 1, wherein the at least one solvent is selected from the group comprising tetraline, chlorobenzene, dichlorobenzene, chloroform, and THF.

21. A composition comprising:

at least one polycrystallme organic semiconductor comprising crystalline domains and grain boundaries at the interfaces of the crystalline domains, and at least one neutral molecular dopant, wherein the dopant is enriched at the grain boundaries at the interfaces of the crystalline domains.

22. The composition of claim 21, wherein the polycrystallme organic semiconductor is a small molecule having a molecular mass of less than 3000 Da.

23. The composition of claim 21, comprising additionally an amorphous polymeric organic semiconductor.

24. The composition of claim 21, comprising additionally an amorphous polymeric nonconducting material.

25. The composition of claim 21, wherein the dopant is present at a concentration of 0.001 to 2.0 percent by weight of the composition.

26. The composition of claim 21, wherein the organic semiconductor has a hole mobility of at least 0.5 cm /V-s and the at least one dopant is a p-dopant.

27. The composition of claim 21, wherein the at least one dopant is a p-dopant that comprises a transition metal.

28. The composition of claim 21, wherein the at least one dopant comprises a complex represented by the formula (X):

wherein M is Cr, Mo or W, and R -R4 are independently selected from a C₁-C30 fluorinated alkyl, cyano, or an optionally substituted aryl, heteroaryl.

29. The composition of claim 21, wherein the organic semiconductor has an electron mobility of at least 0.5 cm / V-s and the at least one dopant is a n-dopant.

30. The composition of claim 21, wherein the at least one dopant comprises an N-DMBI derivative represented by the formula (XVII):

wherein R_ls R₂ are independently selected from alkyl, aryl or heteroaryl.

31. The composition of claim 21 , wherein the at least one dopant comprises transition metal sandwich complexes represented by the formula (XI-XIII):

(R^bz)y (R^cp)x ( ^cp)x

_Mvii _Mvm

M^ix

(XI) or ^(K >^y (XII) or ^{(K )χ'} (XIII) wherein, M^vu is manganese or rhenium; M^vm is iron, ruthenium, or osmium; M^1X is rhodium or iridium; each R^cp and R^bz is individually selected from hydrogen or an optionally substituted Ci-Ci₂ alkyl group or Ci-Ci₂ phenyl group; x and x' are both independently selected from an integer from 1 to 5; and y and y" are both independently selected from an integer from 1-5 and y' is an integer from 1-6.

32. The composition of claim 21, wherein the at least one dopant comprises transition metal san ich complexes represented by the formula (XIV-XVI):

(XVI) wherein M^vu is manganese or rhenium; M^vm is iron, ruthenium, or osmium; M^1X is rhodium or iridium; each R^cp, R^bz, and R^d is individually selected from hydrogen or an optionally substituted C_\-Cn alkyl or C_\-Cn phenyl; x and x' are both independently selected from an integer from 1 to 5; and y and y" are both independently selected from an integer from 1-5; and y' is an integer from 1-6.

33. The composition of claim 21, wherein the at least one polycrystalline organic semiconductor comprises a hole-transport material comprising one or more organic compounds comprising two or more conjugated aryl or heteroaryl rings.

34. The composition of claim 21, wherein the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoacenes represented by the formula (I):

(I) wherein R₁-R₁₀ independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, halogen, trialkylsilylethynyl, and n is 0 to 10.

35. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises a hole-transport material represented by the formula (II):

36. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoheteroacenes represented by the formula (III):

wherein X independently are O, S, Se, NH; Ri-R₈ independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, trialkylsilylethynyl, halogen, arylethynyl, heteroarylethynyl; and n is O to 10.

37. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises a hole-transport material represented by the formula (IV):

38. The composition of claim 21, wherein the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoheteroacenes represented by the formula (V):

wherein X independently are O, S, Se, NH; Ri-R₈ independently are H, alkyl, fluoroalkyl, alkoxy, aryl, heteroaryl, trialkylsilylethynyl, halogen, arylethynyl, heteroarylethynyl; and n and n' independently are 0 to 5.

39. The composition of claim 21, wherein the at least one polycrystalline organic semiconductor comprises a hole-transport material that is selected from optionally substituted oligoacene-fused thienothiophenes represented by the formula VI):

(VI)

40. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises an electron-transport material that comprises optionally substituted arylenes.

41. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises an electron-transport material that is selected from perylene diimides represented by the formula (VII):

wherein Ri and R₂ are C1-C30 organic groups independently selected from a normal, branched, or cyclic alkyl, aryl, heteroaryl, alkyl-aryl, or alkyl-heteroaryl group optionally substituted with one or more halide, cyano, alkyl, or alkoxy groups.

42. The composition of claim 21, wherein the at least one polycrystallme organic semiconductor comprises an electron-transport material that is selected from naphthalene diimides represented by the formula (VIII):

wherein hAr is a heteroaryl; R¹ and R¹ are a C1-C30 organic groups independently selected from a normal, branched, or cyclic alkyl, aryl, heteroaryl, alkyl-aryl, or alkyl-heteroaryl

43. The composition of claim 21 , comprising additionally an amorphous polymeric organic semiconductor selected from polymers comprising optionally substituted arylamine units in the main chain.

44. The composition of claim 21 , comprising additionally an amorphous polymeric organic semiconductor selected from polymers comprising units with triarylamine or carbazole in the side chain.

45. The composition of claim 21 , comprising additionally an amorphous polymeric organic semiconductor with sub-units represented by the formula (IX):

(IX)

wherein

k is an integer from 0 to 5;

n is 10 to 1000.

46. The composition of claim 21 , comprising additionally at least one amorphous polymer selected from optionally substituted poly(styrene), poly(a-methylstyrene) and

poly(vinylbiphenyl), or polymethylmethacrylate.

47. An ink comprising a composition of claim 21.

48. An ink comprising a composition of claim 21 , wherein the ink is suitable for spin coating or ink jet printing.

49. A device comprising the composition of claim 21.

50. A device that is a field effect transistor comprising the composition of claim 21.

51. A field effect transistor comprising the composition of claim 21 in which the threshold voltage is reduced by at least 50% as compared to the same composition that lacks the dopant.

52. A method comprising:

providing an ink formed by mixing at least (i) at least one organic semiconductor adapted to form a polycrystallme phase, (ii) at least one neutral molecular dopant, and (iii) at least one solvent;

forming at least one solid film from the ink, wherein the solid film comprises the at least one organic semiconductor polycrystallme phase which comprises grain boundaries, and wherein the dopant is not evenly distributed throughout the solid film.

53. The method of claim 52, wherein the ink is formed by additionally mixing at least one organic material which is a polymer binder for the organic semiconductor polycrystallme phase.

54. The method of claim 52, wherein the dopant is an organometallic complex.

55. The method of claim 52, wherein the dopant is a p-dopant that comprises a transition metal.

56. The method of claim 52, wherein the dopant comprises a complex represented by the formula (X):

wherein M is Cr, Mo or W, and R -R4 are independently selected from a C1-C30 fluorinated alkyl, cyano, or an optionally substituted aryl, heteroaryl.

57. The method of claim 52, wherein the dopant is an n-dopant.

58. The method of claim 52, wherein the dopant is an n-dopant that comprises an alkali metal, transition metal, lanthanide metal, or actinide metal.

59. The method of claim 52, wherein the at least one hole or electron conducting organic material that is adapted to form an organic crystalline phase comprises a hole-transport material.

60. The method of claim 52, wherein the at least one hole or electron conducting organic material adapted to form an organic crystalline phase comprises a hole-transport material comprising one or more organic compounds comprising two or more conjugated aryl or heteroaryl rings.

61. The method of claim 52, wherein the at least one hole or electron conducting organic material adapted to form at least one organic polycrystallme phase comprises a hole-transport material comprising one or more organic compounds comprising two or more conjugated aryl or heteroaryl rings substituted and one or more silyl moieties.

62. The method of claim 52, wherein the at least one hole or electron conducting organic material adapted to form an organic polycrystallme phase comprises a hole-transport material represented by the formula (II) or (IV):

63. The method of claim 53, wherein the at least one organic material which is a polymer binder for the organic semiconductor polycrystalline phase comprises at least one hole or electron conducting organic material which is adapted to form an organic amorphous phase comprises an optionally substituted poly(arylamine) that contains aryl moieties in the polymer backbone.

64. The method of claim 52, wherein the ink is formed on a substrate, wherein the forming step comprises an inkjet coating or spin coating step.

65. The method of claim 52, wherein the at least one solvent is an organic solvent.

66. The method of claim 52, wherein the at least one solvent is selected from the group comprising tetraline, chlorobenzene, di-chlorobenzene, chloroform, and THF.