Method for producing doped organic semiconductor thin films

Abstract

The present invention relates to a doped organic semiconductor thin film and a method for manufacturing the same. The method for manufacturing the doped organic semiconductor thin film of the present invention involves dissolving a dopant material in a highly polar organic solvent so that doping does not occur in the solution when mixed with an organic semiconductor material, thereby eliminating the precipitation phenomenon of the composite dopant material in the doping process performed in the solution phase. Furthermore, the organic semiconductor thin film manufactured by this method has the effect of inducing a high level of doping and improving electrical conductivity.

Description

[Technical Field]

[0001] The present invention relates to organic semiconductors, and in particular to doped organic semiconductors. [Background technology]

[0002] Doping, which involves intentionally adding impurities to adjust electrical, optical, and structural properties, has become an essential technology in the semiconductor industry, known as the rice of cutting-edge industries. Molecular doping, which is similar to doping but involves dopants made of molecules rather than atoms that undergo a charge transfer reaction with semiconductors to form charge carriers, is being extensively studied as a technology for improving the electrical conductivity of various organic and inorganic semiconductors, adjusting energy levels, and changing light absorption properties.

[0003] Molecular doping transfers charge through the relative energy level difference between the semiconductor (host) and the dopant (guest), and adjusting this difference is a key technology element. For example, in p-doping, the semiconductor's highest occupied molecular orbital (HOMO) level must be higher than the dopant's lowest unoccupied molecular orbital (LUMO) level. While satisfying this condition can improve the performance of various electronic devices, the heat inevitably generated during device operation can cause dopant diffusion, hindering device stability. Among various dopant materials, organic dopants, which are made from organic compounds, are advantageous in terms of their molecular weight control, suppressing thermal diffusion, and improving device stability.

[0004] In particular, organic p-dopants are being used as a key material to reduce the driving voltage of photoelectric conversion elements and reduce power consumption due to their excellent driving stability, and demand for them is expected to increase further in the future.

[0005] It is generally known that when an organic semiconductor is doped in a solution, its solubility decreases rapidly, resulting in precipitation. The resulting precipitates of the doped organic semiconductor significantly reduce the uniformity of the thin film during the thin film coating process, acting as defects and hindering the operation and performance of electronic and photoelectric devices. In particular, since organic solvents with low polarity generally have low dopant solubility, the organic semiconductor solution is diluted during the mixing process of the dopant solution during the fabrication of the organic semiconductor thin film, which poses a problem in the fabrication process of photoelectric devices, where thickness control is crucial. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem of the present invention is to provide a doped organic semiconductor thin film and a method for producing the same.

[0007] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention provides a method for manufacturing a doped organic semiconductor thin film, the method comprising the steps of: preparing a composite doping solution containing an organic compound having a resonance structure with at least one cyan group (C≡N), a Lewis acid, and a first organic solvent; preparing an organic semiconductor solution containing an organic semiconductor material and a second organic solvent; mixing the composite doping solution and the organic semiconductor solution to prepare a mixed solution; and coating the mixed solution on a substrate to form a thin film, and evaporating the organic solvent in the thin film.

[0009] The first organic solvent may have a higher dielectric constant than the second organic solvent.

[0010] The first organic solvent may be an organic solvent having a stronger polarity than the second organic solvent and having a dielectric constant at room temperature of 16 to 50. For example, the first organic solvent may include at least one selected from acetone, acetonitrile (ACN), dimethylformamide (DMF), and combinations thereof, but is not limited thereto.

[0011] The second organic solvent may be an organic solvent having a weaker polarity than the first organic solvent and having a dielectric constant at room temperature of 1 to 15. For example, the second organic solvent may include at least one selected from dichlorobenzene (DCB), ethyl acetate (EtOAc), and combinations thereof, but is not limited thereto.

[0012] The mixed solution may be one in which the bonding between the organic compound and the Lewis acid is suppressed, and the organic semiconductor material is doped with a composite dopant compound formed by bonding the organic compound and the Lewis acid in a thin film after the organic solvent has evaporated.

[0013] The bond may be such that a cyan group (C≡N) of the organic compound and the Lewis acid form a Lewis pair.

[0014] The organic semiconductor material may include alkyl side chains in its molecular structure.

[0015] In order to solve the above-mentioned problems, another aspect of the present invention can provide a doped organic semiconductor thin film, comprising: a composite dopant compound in which an organic compound having a resonance structure with at least one cyano group (C≡N) is bonded to a Lewis acid; and an organic semiconductor material doped with the composite dopant compound.

[0016] The bond may be such that a cyan group (C≡N) of the organic compound and the Lewis acid form a Lewis pair.

[0017] The bond may be formed during the formation of a thin film using a composite doping solution containing the organic compound, the Lewis acid, and an organic solvent, after the organic solvent has evaporated.

[0018] The organic solvent may have a dielectric constant of 16 to 50 at room temperature.

[0019] The organic solvent may be at least one selected from the group consisting of acetone, acetonitrile (ACN), dimethylformamide (DMF), and combinations thereof, but is not limited thereto.

[0020] The organic semiconductor material may include alkyl side chains in its molecular structure. [Effects of the Invention]

[0021] The method for manufacturing a doped organic semiconductor thin film of the present invention involves dissolving a dopant material in an organic solvent with strong polarity so that doping does not occur in the solution when mixed with an organic semiconductor material, thereby eliminating the precipitation phenomenon of the composite dopant material in the doping process performed in the solution phase. Furthermore, the organic semiconductor thin film manufactured by this method has the effect of inducing a high level of doping and improving electrical conductivity. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a flow chart of a method for manufacturing a doped organic semiconductor thin film according to an example of the present invention. [Figure 2] FIG. 2 shows (a) a schematic diagram illustrating a bond formed between an organic semiconductor material having a resonance structure and a Lewis acid depending on the polarity of a solvent, according to one embodiment of the present invention, and (b) a graph showing the LUMO levels of the organic material before and after Lewis acid bonding. [Figure 3] FIG. 3 is a photograph showing whether or not doping occurs depending on the type of organic solvent used in an organic semiconductor material according to an example of the present invention. [Figure 4]FIG. 4 is a graph (left) showing the UV-vis-NIR absorbance of an organic semiconductor compound solution doped with a dopant compound in one embodiment of the present invention, and a graph (right) showing the UV-vis-NIR absorbance after 7 days. [Figure 5] FIG. 5 shows a digital camera photograph (left) of an organic semiconductor compound thin film doped with a dopant ratio of 20 mol% in one embodiment of the present invention, and a graph (right) of the measured UV-vis-NIR absorbance of the thin film. [Figure 6] FIG. 6 shows a digital camera photograph (left) of an organic semiconductor compound thin film doped with a dopant ratio of 50 mol% in one embodiment of the present invention, and a graph (right) of the measured UV-vis-NIR absorbance of the thin film. [Figure 7] FIG. 7 shows digital photographs of the surface of a thin film taken immediately after deposition (left side) and 30 seconds after deposition (right side) when acetonitrile (ACN) was used as the dopant solvent in one embodiment of the present invention. [Figure 8] FIG. 8 shows a digital camera photograph of a thin film (left), a UV-vis-NIR absorbance graph (middle), and a UV-vis-NIR absorbance graph (right) of a PDPP3T organic semiconductor film doped in the same manner as the PCDTFBT organic semiconductor material doped at a molar ratio of 50% according to one embodiment of the present invention. [Figure 9] FIG. 9 shows a graph (left) of the UV-vis-NIR absorbance of an organic semiconductor thin film using a doping solution prepared by dissolving a doping material according to an embodiment of the present invention in ACN, and a graph (right) of the electrical conductivity of a doped organic semiconductor thin film prepared by dissolving the doping material in ACN and DMF solvents. [Figure 10] FIG. 10 shows digital photographs of organic semiconductor solutions using various organic solvents and thin films produced therefrom according to an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] While the present invention can be modified in various ways and can take various forms, specific embodiments are shown by way of example in the drawings and will be described in detail herein. However, it is not intended to limit the present invention to the particular disclosed form, but it should be understood that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. In describing the drawings, like reference numerals are used to refer to like elements.

[0024] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries should be interpreted to have a meaning consistent with the meaning they have in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless expressly defined in this invention.

[0025] Throughout the present specification, when any part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless otherwise specified.

[0026] The terms "about," "substantially," and the like used throughout the specification of the present invention are used to mean a numerical value or a value close to the numerical value when the manufacturing and material tolerances inherent in the stated meaning are given, and are used to prevent unscrupulous infringers from unfairly using the disclosure in which precise or absolute numerical values ​​are stated to aid in the understanding of the present invention.

[0027] Method for producing doped organic semiconductor thin films FIG. 1 is a flow chart of a method for manufacturing a doped organic semiconductor thin film according to an example of the present invention.

[0028] Referring to FIG. 1, the present invention provides a method for producing a doped organic semiconductor thin film.

[0029] First, an organic compound containing a resonance structure with at least one cyan group (C≡N) is mixed with a first organic solvent to obtain a first mixed solution. Separately, a Lewis acid that bonds with the cyan group (C≡N) is mixed with the first organic solvent to obtain a second mixed solution. The first mixed solution and the second mixed solution are mixed in a certain ratio to prepare a composite doping solution.

[0030] The organic compound may include an organic resonance structure having at least one, for example, two or more, cyano groups (C≡N) in the molecule. The cyano group (C≡N) is an electron withdrawing group (EWG) and may represent a Lewis base, which attracts electrons from the resonance structure and donates them to a Lewis acid. The organic compound may combine with a Lewis acid material (described later) to form a Lewis pair, forming a composite dopant compound with strong doping properties in an organic semiconductor thin film, or it may itself be used as an organic dopant material.

[0031] The organic compound can be represented by the following Chemical Formula 1. [Chemical formula 1] RC≡N

[0032] The R may include, as an organic resonance structure, at least one selected from, for example, an aromatic ring, a quinone-based ring, a double bond, a triple bond, an allene, a butadiene, a polyene, an oxocarbon, an analogous oxocarbon, a radialene, an analog thereof, and a derivative thereof. Specifically, R may include at least one selected from the compounds represented by the following chemical formulas 2 to 24, but is not limited thereto.

[0033] [ka]

[0034] [ka]

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] The organic compound may be a p-type or n-type organic dopant, for example, a p-type organic dopant, and may include at least one selected from the group consisting of tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrafluoro-tetracyanoquinodimethane (FTCNQ), 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F2TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,3,5,6-tetrafluoro-tetracyanoquinodimethane (F4TCNQ), analogs thereof, and derivatives thereof. In one specific example, the organic compound may be, but is not limited to, 2,3,5,6-tetrafluoro-tetracyanoquinodimethane (F4TCNQ).

[0041] The organic compound can be dissolved in a first organic solvent described below to prepare a first doping solution. The concentration of the first doping solution can be, but is not limited to, 0.5 to 30 mg / mL, specifically 1 to 20 mg / mL, for example, 2 to 10 mg / mL.

[0042] The Lewis acid (LA) can bond with a cyanide group present in the molecule of the organic compound in the organic semiconductor thin film described below to form a composite dopant compound that dopes the organic semiconductor material. The bond can include a Lewis pair formed between the cyanide group (C≡N) acting as a Lewis base in the organic compound and the Lewis acid, such as a covalent bond, a coordinate bond, or a secondary bond including these, such as a van der Waals bond or a dipole-dipole bond. In one specific example, the Lewis acid can include at least one selected from the group consisting of tris(pentafluorophenyl)borane (BCF), bis(pentafluorophenyl)zinc (Zn(CF)), boron tribromide (BBr), molybdenum chloride (MoCl), and combinations thereof, but is not limited thereto.

[0043] The Lewis acid material can be dissolved in a first organic solvent described below to prepare a second doping solution, which may have a concentration of 20 to 200 mg / mL, specifically 50 to 150 mg / mL, for example 80 to 120 mg / mL, but is not limited thereto.

[0044] The first organic solvent may be a solvent having Lewis basicity or a polar organic solvent having a high dielectric constant. Specifically, the first organic solvent may have a higher dielectric constant than the second organic solvent described below. Specifically, the first organic solvent may have a dielectric constant of 16 to 50, more specifically 18 to 45, and in one specific example, 20 to 40 at room temperature. In the mixed doping solution, the first organic solvent, having strong polarity, has the effect of suppressing the formation of a composite dopant material formed by Lewis bonding with the Lewis acid material. For example, the first organic solvent may be at least one selected from acetone, acetonitrile (ACN), dimethylformamide (DMF), and combinations thereof.

[0045] The mixed solution may be a mixture of the organic compound material and the Lewis acid material contained in the first mixed solution and the second mixed solution in a molar ratio of 1:1 to 1:10, specifically 1:1 to 1:7, more specifically 1:1 to 1:5, and in one specific example, 1:1 to 1:4, but is not limited thereto.

[0046] Separately, a step of preparing an organic semiconductor solution in which the organic semiconductor material is dissolved in a second organic solvent can be carried out.

[0047] The second organic solvent may be a polar organic solvent that is soluble in the organic semiconductor material and has a low dielectric constant, specifically, a dielectric constant of 1 to 15 at room temperature, more specifically, a dielectric constant of 3 to 12, and in one specific example, a dielectric constant of 5 to 10.

[0048] The organic semiconductor material is an organic material that can be doped with the above-mentioned composite dopant compound, and specifically, may be an organic semiconductor material having an alkyl side chain in its molecular structure. The organic semiconductor material having an alkyl side chain in its molecular structure may be a material that is likely to aggregate in solution during the doping process and generate a precipitate. Examples of the organic semiconductor material include PDPP3T (Poly{2,2'-[(2,5-bis(2-hexyldecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)dithiophene]-5,5'-diyl-alt-thiophen-2,5-diyl}), PCDTFBT (Poly[(5-fluoro-2,1,3-benzothiadiazole-4,7-diyl)(4,4-dihexadecyl The hydroxybenzoates may include, but are not limited to, 4H-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl)(6-fluoro-2,1,3-benzothiadiazole-4,7-diyl)(4,4-dihexadecyl-4H-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl)), P3HT (Poly(3-hexylthiophene-2,5-diyl)), and combinations thereof.

[0049] The concentration of the organic semiconductor solution may be, but is not limited to, 1 to 50 mg / mL, specifically 3 to 40 mg / mL, more specifically 5 to 30 mg / mL, for example 7 to 20 mg / mL.

[0050] Next, a step of mixing the composite doping solution and the organic semiconductor solution to prepare a mixed solution may be performed.

[0051] The mixed solution is a mixture of the composite doping solution and the organic semiconductor solution, and the dopant ratio of the composite doping solution may be 5 to 70 mol%, specifically 10 to 60 mol%, for example 20 to 50 mol%, based on the total mole number of the organic semiconductor material and the composite dopant material.

[0052] The mixed solution contains the organic compound material, the Lewis acid material, and the organic semiconductor material in an organic solvent. The first organic solvent, which has a strong polarity, preferentially reacts and bonds with the Lewis acid, thereby restricting the reaction between the cyanide group of the organic compound and the Lewis acid, i.e., the formation of a Lewis pair, and suppressing the formation of a composite dopant compound. In this mixed solution, in which the formation of a composite dopant compound is suppressed, the Lewis acid and the cyanide group can bond after the solvent is evaporated during the thin film fabrication process described below, forming a p-type composite dopant compound with strong oxidizing properties, enabling very high levels of doping. Therefore, the mixed solution can be referred to as a doping solution with latent doping ability, which does not undergo a reaction in solution but induces doping after the thin film is formed. When the first organic solvent is an organic solvent with a low polarity similar to the second organic solvent, the cyanide group of the organic compound and the Lewis acid react first to form a composite dopant compound, such as F4TCNQ:BCF or P3HT, which precipitates during the fabrication of the mixed solution, resulting in the formation of a precipitate in the solution. This is undesirable because, when carrying out the thin film manufacturing process described below, an organic semiconductor thin film may be formed that is not uniform and has irregularities.

[0053] Thereafter, the mixed solution may be coated on a substrate to form a thin film, and the organic solvent in the thin film may be evaporated.

[0054] The thin film may be formed by a solution-based thin film formation method commonly known in the art, including, but not limited to, dip coating, bar coating, spray coating, brush coating, spin coating, slot die coating, solution coating, gravure coating, roll coating, dropping, printing, etc.

[0055] The organic solvent includes at least one selected from the first organic solvent and the second organic solvent described above, and evaporates during the process of forming the thin film. Specifically, most of the organic solvent, for example, the entire organic solvent, may evaporate, and no organic solvent may remain in the thin film.

[0056] After the organic solvent is completely evaporated, the cyanide group of the organic compound in the organic semiconductor thin film reacts with the Lewis acid to form a p-type composite dopant compound having strong oxidizing properties. The composite dopant compound can act as a doping material having strong oxidizing properties to dope the organic semiconductor material to a high level.

[0057] The composite dopant compound may be formed by bonding the organic compound and the Lewis acid, and may contain at least one Lewis pair, specifically, a bond between the cyano group and the Lewis acid, in its molecular structure.

[0058] The produced thin film may have a thickness on the nanometer level, for example, a thickness of several tens to several hundreds of nanometers.

[0059] In order to more specifically explain the present invention, preferred experimental examples according to the present invention will be described in more detail below with reference to the accompanying drawings. However, the present invention is not limited to the examples described herein and may be embodied in other forms.

[0060] Experimental example: Synthesis of mixed doping solution F4TCNQ:BCF The first doping solution was prepared by dissolving F4TCNQ, an organic compound with a cyan group, in the first organic solvent at 2-10 mg / mL. The materials used for the first organic solvent were acetone (Acetone), acetonitrile (ACN), and dimethylformamide (DMF). Separately, the Lewis acid material tris(pentafluorophenyl)borane (BCF) was dissolved in the first organic solvent at 100 mg / mL to prepare the second doping solution. Each doping solution was heated at 90 °C to prevent precipitation and ensure complete dissolution.

[0061] A composite doping solution was prepared by mixing the cyanide-containing organic compound material and Lewis acid material contained in the first and second mixed solutions in a molar ratio of 1:2 to 1:4. The color of the composite doping solution was different from before mixing, confirming that a reaction had occurred between the two materials. All of the above processes were carried out in a nitrogen atmosphere.

[0062] Example: Formation of organic semiconductor thin films doped with mixed doping solutions As organic semiconductor materials, PDPP3T (Poly{2,2'-[(2,5-bis(2-hexyldecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)dithiophene]-5,5'-diyl-alt-thiophen-2,5-diyl}) and PCDTFBT (Poly[(5-fluoro-2,1,3-benzothiadiazole-4,7-diyl)(4,4-dihexadecyl-4H-cyclopenta[ An organic semiconductor solution was prepared by dissolving P3HT (Poly(3-hexylthiophene-2,5-diyl)) or P3HT (6-fluoro-2,1,3-benzothiadiazole-4,7-diyl) (4,4-dihexadecyl-4H-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl) in dichlorobenzene (DCB), a second organic solvent, to a concentration of 10 mg / mL. This organic semiconductor solution and the mixed doping solution prepared in the previous experimental example were mixed so that F4TCNQ was 20-50 mol% relative to the total moles of the organic semiconductor material and composite dopant material. The solution was then applied to a cleaned glass substrate and spin-coated at 1000 rpm for 60 seconds to form a doped organic semiconductor thin film several tens of nanometers thick.

[0063] The presence or absence of doping was confirmed by the presence or absence of precipitation in the mixed doping solution.

[0064] FIG. 2 shows (a) a schematic diagram illustrating a bond formed between an organic semiconductor material having a resonance structure and a Lewis acid depending on the polarity of a solvent, according to one embodiment of the present invention, and (b) a graph showing the LUMO levels of the organic material before and after Lewis acid bonding.

[0065] Referring to FIG. 2, the organic compound (F4TCNQ) having a cyan group in its resonance structure of the present invention can form a bond between an organic semiconductor material and a Lewis acid (BCF) in a non-polar organic solvent to form a composite dopant compound (F4TCNQ-BCF4).

[0066] In addition, in a polar organic solvent, the organic compound (F4TCNQ) does not form a bond with the Lewis acid (BCF), but instead the material used in the polar organic solvent can react with the Lewis acid (BCF) to form a bond, thereby suppressing the formation of complex compounds.

[0067] The organic compound (F4TCNQ) alone has a high LUMO level, but when the composite dopant compound (F4TCNQ-BCF4) is formed, the LUMO level becomes low enough to allow hole transfer into the organic semiconductor material.

[0068] [Table 1]

[0069] Table 1 shows the dielectric constant of organic solvents according to an example of the present invention. Figure 3 shows photographs confirming whether or not doping occurs depending on the type of organic solvent used in the organic semiconductor material according to an example of the present invention.

[0070] Referring to Table 1 and Figure 3, when the organic semiconductor material PDPP3T is dissolved in dichlorobenzene (DCB), and F4TCNQ, an organic compound having a cyan group, is dissolved in dichlorobenzene (DCB) or ethyl acetate (EtOAc), and the organic semiconductor (PDPP3T) solution and the organic compound solution are mixed at 50 mol%, the organic semiconductor (PDPP3T) is doped and precipitates in the solution. The dielectric constants of the organic solvents ethyl acetate (EtOAc) and dichlorobenzene (DCB) are 6.02 and 9.93, respectively, making them low-polarity solvents. This indicates that doping occurs in the solution when the organic semiconductor material and the organic compound are dissolved in low-polarity organic solvents ethyl acetate (EtOAc) or dichlorobenzene (DCB). On the other hand, when the organic compound material having a cyan group is dissolved and mixed in acetonitrile (ACN) or dimethylformamide (DMF), which have strong polarity (in this case, the solvent of the organic semiconductor solution is dichlorobenzene (DCB), which has weak polarity), it is confirmed that the organic semiconductor material PDPP3T is not doped and no precipitate is formed. In this case, the dielectric constants of the organic solvents, acetonitrile (ACN) and dimethylformamide (DMF), are 37.5 and 36.7, respectively, making them highly polar solvents. Therefore, when the organic compound having a cyan group is dissolved in a highly polar organic solvent and the organic semiconductor material is dissolved in a weakly polar organic solvent and mixed to form a mixed solution, the Lewis acid reacts with the strongly polar solvent instead of the cyan group (C≡N), suppressing the doping of the organic semiconductor material, and therefore it is confirmed that no organic semiconductor precipitate is formed.

[0071] FIG. 4 is a graph (left) showing the UV-vis-NIR absorbance of an organic semiconductor compound solution doped with a dopant compound in one embodiment of the present invention, and a graph (right) showing the UV-vis-NIR absorbance after 7 days.

[0072] Referring to FIG. 4, when doping an organic semiconductor with a dopant compound using various organic solvents, the absorbance characteristics of the solution do not change significantly even after one week, demonstrating excellent stability.

[0073] FIG. 5 shows a digital camera photograph (left) of an organic semiconductor compound thin film doped with a dopant ratio of 20 mol% in one embodiment of the present invention, and a graph (right) of the measured UV-vis-NIR absorbance.

[0074] 5, a dopant solvent (dichlorobenzene (DCB), ethyl acetate (EtOAc), acetonitrile (ACN), or dimethylformamide (DMF)) was mixed with F4TCNQ and BCF to form a doping solution, and PDPP3T dissolved in dichlorobenzene (DCB) was used as an organic semiconductor solution. These solutions were mixed at a dopant ratio of 20 mol% to form a mixed solution, and this mixed solution was spin-coated to form an organic semiconductor thin film. As a result, when DCB and EtOAc, organic solvents with low polarity, were used as the dopant solvent, the organic semiconductor thin film was not uniform and precipitates remained on the surface. However, when ACN and DMF, organic solvents with strong polarity, were used as the dopant solvent, no precipitates were found on the surface of the thin film, and a uniform thin film was formed.

[0075] FIG. 6 shows a digital camera photograph (left) of an organic semiconductor compound thin film doped with a dopant ratio of 50 mol% in one embodiment of the present invention, and a graph (right) of the measured UV-vis-NIR absorbance of the thin film.

[0076] Referring to Figure 6, a mixed solution was prepared by mixing acetone, acetonitrile (ACN), or dimethylformamide (DMF) as a dopant solvent with F4TCNQ and BCF to form an organic compound solution, and PDPP3T dissolved in dichlorobenzene (DCB) as an organic semiconductor solution at a dopant ratio of 50 mol%. This mixed solution was then spin-coated to form an organic semiconductor thin film. The results show that doping is successful when an organic solvent with relatively strong polarity is used as the dopant solvent, resulting in the formation of a smooth thin film without the formation of precipitates. Furthermore, UV-vis-NIR absorbance measurements show a rapid decrease in the neutral PDPP3T peak near 800 nm, while a rapid increase in the polaron peak indicates smooth doping.

[0077] FIG. 7 shows digital photographs of the surface of a thin film when acetonitrile (ACN) was used as the dopant solvent in one embodiment of the present invention, in which the mixed doping solution was dropped onto a substrate and then coated with an organic semiconductor thin film (left side) and when the mixed doping solution was dropped onto a substrate and then coated with an organic semiconductor thin film 30 seconds later (right side).

[0078] Referring to Figure 7, to confirm the role of the dopant solvent, a mixed doping solution using ACN as the dopant solvent was dropped onto a substrate and held for 30 seconds before spin-coating an organic semiconductor thin film. As a result, it was confirmed that a non-uniform thin film was formed. This indicates that the reaction between F4TCNQ and BCF is suppressed, while ACN, with its low boiling point, preferentially evaporates, causing doping, resulting in the formation of a non-uniform thin film. This result may indicate that the Lewis acid binds to the dopant solvent for latent doping instead of the CN group, suppressing the formation of a dopant with strong oxidizing properties. However, in the thin film, the solvent evaporates, forming a bond between the Lewis acid and the CN group, exhibiting strong oxidizing properties and reacting with the organic semiconductor.

[0079] FIG. 8 shows a digital camera photograph of a thin film (left), a UV-vis-NIR absorbance graph (middle), and a UV-vis-NIR absorbance graph (right) of a PDPP3T organic semiconductor film doped in the same manner as the PCDTFBT organic semiconductor material doped at a molar ratio of 50% according to one embodiment of the present invention.

[0080] 8, when the conjugated polymer PCDTFBT is doped using the dopant solution of the present invention (a solution of F4TCNQ:BCF dissolved in ACN), the strong polar solvent ACN prevents the formation of precipitates in the solution, forming a uniform thin film and achieving a very high level of doping. Therefore, when a solvent with strong polarity and Lewis basicity is used, the formation of the dopant is suppressed in the solution, but after the thin film is formed, a composite dopant with strong oxidizing properties is formed after the solvent evaporates, allowing the organic semiconductor to be doped.

[0081] FIG. 9 shows a graph (left) of the UV-vis-NIR absorbance of an organic semiconductor thin film using a doping solution prepared by dissolving a doping material according to an embodiment of the present invention in ACN, and a graph (right) of the electrical conductivity of a doped organic semiconductor thin film prepared by dissolving the doping material in ACN and DMF solvents.

[0082] 9, the doping materials F4TCNQ:BCF, F4TCNQ, and BCF were dissolved in ACN, a strong polar organic solvent, to prepare doping solutions. The electrical conductivity of the organic semiconductor thin films doped with these doping materials was measured at 16.51 S / cm and 0.036 S / cm, respectively. In particular, in the case of BCF, doping did not occur, making it impossible to measure the electrical conductivity. Furthermore, the doping materials F4TCNQ:BCF, F4TCNQ, and BCF were dissolved in DMF, a weak polar organic solvent, to prepare doping solutions. The electrical conductivity of the organic semiconductor thin films doped with these doping materials was measured at 2.77 S / cm, 0.010 S / cm, and 0.0018 S / cm, respectively. Therefore, when F4TCNQ:BCF is used as the doping material, improved doping ability can be confirmed by using ACN or DMF as the dopant solvent. In particular, when ACN, a polar organic solvent, is used, better doping is possible and the electrical conductivity of the organic semiconductor thin film can be improved.

[0083] FIG. 10 shows digital photographs of organic semiconductor solutions using various organic solvents and thin films produced from the solutions according to an example of the present invention.

[0084] Referring to Figure 10, an organic semiconductor thin film was fabricated using a solution in which an organic semiconductor solution in which the organic semiconductor P3HT was dissolved in DCB was mixed with a doping solution in which F4TCNQ was dissolved in DCB, ACN, or DMF at a molar ratio of 20%. The results confirmed that when F4TCNQ, an organic compound containing a cyan group, was dissolved in ACN or DMF, which have strong polarity, a precipitation phenomenon occurred when mixed with the organic semiconductor P3HT solution due to the strong reaction between F4TCNQ and P3HT. This result differs from the results obtained when the organic semiconductor material of the present invention is doped with a composite dopant compound. When the organic compound containing a cyan group fully functions as a p-type dopant, a reaction between the p-dopant and P3HT occurs when a polar organic solvent is used, resulting in doping.

[0085] As described above, the method for manufacturing a doped organic semiconductor thin film of the present invention enables a solution-phase doping process for organic semiconductor materials having alkyl side chains, which are difficult to dope because they are likely to aggregate and generate precipitates in solution during the doping process. Therefore, the method can be applied to a wide range of fields, including light-emitting devices such as organic light-emitting diodes and quantum dot light-emitting diodes, photoelectric devices such as perovskite solar cells and organic solar cells, transistors, thermoelectric devices, electrochemical devices, spin devices, sensors, catalysts, and electrodes.

[0086] It should be noted that the embodiments of the present invention disclosed in this specification and the drawings are merely specific examples presented to aid in understanding, and are not intended to limit the scope of the present invention. It will be obvious to those skilled in the art to which the present invention pertains that other modifications based on the technical concept of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims

1. preparing a composite doping solution comprising an organic compound containing a resonance structure having at least one cyano group (C≡N), a Lewis acid, and a first organic solvent; preparing an organic semiconductor solution comprising an organic semiconductor material and a second organic solvent; mixing the composite doping solution with the organic semiconductor solution to prepare a mixed solution; and a step of coating the mixed solution on a substrate to form a thin film, and evaporating the organic solvent in the thin film.

2. The method of claim 1 , wherein the first organic solvent has a higher dielectric constant than the second organic solvent.

3. 3. The method of claim 2, wherein the first organic solvent has a dielectric constant of 16 to 50 at room temperature.

4. 3. The method for producing a doped organic semiconductor thin film according to claim 2, wherein the second organic solvent has a dielectric constant of 1 to 15 at room temperature.

5. 4. The method of claim 3, wherein the first organic solvent comprises at least one selected from the group consisting of acetone, acetonitrile (ACN), dimethylformamide (DMF), and combinations thereof.

6. 5. The method of claim 4, wherein the second organic solvent comprises at least one selected from the group consisting of dichlorobenzene (DCB), ethyl acetate (EtOAc), and combinations thereof.

7. In the mixed solution, the bonding between the organic compound and the Lewis acid is suppressed, 2. The method for producing a doped organic semiconductor thin film according to claim 1, wherein the organic solvent is evaporated from the thin film, and the organic semiconductor material is doped with a composite dopant compound formed by combining the organic compound and the Lewis acid.

8. 8. The method for producing a doped organic semiconductor thin film according to claim 7, wherein the bond is formed by a cyano group (C≡N) of the organic compound and the Lewis acid forming a Lewis pair.

9. The method for producing a doped organic semiconductor thin film according to claim 1 , wherein the organic semiconductor material contains alkyl side chains in its molecular structure.

10. A doped organic semiconductor thin film comprising a complex dopant compound in which an organic compound containing a resonance structure having at least one or more cyan groups (C≡N) is bonded to a Lewis acid, and an organic semiconductor material doped with the complex dopant compound.

11. 11. The doped organic semiconductor thin film of claim 10, wherein the bond is a Lewis pair formed between a cyan group (C≡N) of the organic compound and the Lewis acid.

12. 12. The doped organic semiconductor thin film according to claim 11, wherein the bond is formed after the organic solvent is evaporated during the thin film formation using a composite doping solution containing the organic compound, the Lewis acid, and an organic solvent.

13. 13. The doped organic semiconductor thin film according to claim 12, wherein the organic solvent has a dielectric constant of 16 to 50 at room temperature.

14. 14. The doped organic semiconductor thin film according to claim 13, wherein the organic solvent is at least one selected from the group consisting of acetone, acetonitrile (ACN), dimethylformamide (DMF), and combinations thereof.

15. 11. The doped organic semiconductor thin film of claim 10, wherein the organic semiconductor material comprises alkyl side chains in its molecular structure.

Images