Synthesis method of benzimidazole derivative monomer and application of benzimidazole derivative monomer in N-type doping

Abstract

The invention belongs to the field of organic photoelectricity, and discloses a synthesis method of a monomer of a benzimidazole derivative and application of the monomer in N-type doping. The structure of a monomer of the benzimidazole derivative is shown in the specification. After the benzimidazole derivatives are connected in parallel to form the multi-site dopant, more electrons can be provided at the same time, and the doping efficiency and uniformity are remarkably improved. According to the multi-site design, the doping reaction is more sufficient, the electron injection energy barrier is reduced, the carrier mobility of a semiconductor is improved, the thermal stability of the device is enhanced, the electrical performance of the organic electronic device is integrally improved, and the service life of the organic electronic device is integrally prolonged. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the field of organic photoelectricity, and particularly relates to a method for synthesizing a monomer of a benzimidazole derivative and application thereof in N-type doping. Background Art

[0002] Doping technology can significantly improve the electrical properties of semiconductors by introducing specific impurities into the host semiconductor to generate free electrons or holes. Since the rise of the field of organic electronics, doping technology has been at the forefront of research and has played a key role in improving the conductivity of organic semiconductors. In recent years, by precisely doping organic semiconductors (OSCs), highly conductive polymers with conductivity comparable to that of metals have been successfully prepared. This achievement is considered a milestone breakthrough in this field. This technology has been widely used in a variety of organic electronic devices, including organic photovoltaics (OPVs), organic thermoelectrics (OTEs), quantum dot light-emitting diodes (QLEDs), perovskite photovoltaics, organic light-emitting diodes (OLEDs), and organic field-effect transistors (OFETs), to optimize their charge transport properties.

[0003] In organic semiconductors (OSCs), doping is done molecularly, rather than atomically, as is common in inorganic semiconductors. When a host molecule and a dopant molecule are adjacent, the difference in their energy levels drives charge transfer. Doping is generally categorized as P-type and N-type. N-type dopant materials are more susceptible to electron capture by oxidants and loss of stability in real-world environments. Therefore, preparing high-performance, air-stable N-type materials is more challenging than P-type. In 2010, N-DMBI (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole), a monomer for synthesizing benzimidazole derivatives, was used to perform N-type doping on organic field-effect transistors. However, the maximum conductivity of these doped PCBM films remains low. Therefore, developing N-type dopants is beneficial for improving the doping effect of organic semiconductors and promoting the development of organic optoelectronics. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of the prior art, the present invention primarily aims to provide a monomer of a benzimidazole derivative. This monomer has a relatively large molecular structure and, after doping, can form a relatively large conjugated plane. By adjusting the structure of the benzimidazole derivative, units with varying doping intensities can be obtained.

[0005] Another object of the present invention is to provide a method for preparing the monomer of the above-mentioned benzimidazole derivative.

[0006] Another object of the present invention is to provide applications of the aforementioned benzimidazole derivative monomers in the field of organic optoelectronics. Introducing these units into organic semiconductors can achieve improved conductivity and carrier mobility, and they possess significant potential as dopants. By adjusting the central heteroatom, the benzimidazole derivatives within a single molecule can be modified to achieve multiple doping, resulting in higher doping efficiency.

[0007] The purpose of the present invention is achieved through the following solutions:

[0008] A monomer of a benzimidazole derivative, whose chemical structure satisfies the following general formula:

[0009]

[0010] In the formula, R1 is one of hydrogen (-H), amino (-NH2), hydroxyl (-OH), alkyl having 1 to 6 carbon atoms, alkoxy (-OR), dialkylamino (-NR2), alkylamino (-NHR), amide (-NHCOR), acyloxy (-OCOR), etc.;

[0011] R2 is one of hydrogen (-H), hydroxyl (-OH), alkyl having 1 to 6 carbon atoms, alkoxy (-OR), etc.;

[0012] R3 is one of hydrogen (-H), amino (-NH2), hydroxyl (-OH), alkyl having 1 to 6 carbon atoms, alkoxy (-OR), dialkylamino (-NR2), alkylamino (-NHR), amide (-NHCOR), acyloxy (-OCOR), etc.;

[0013] In R1, R2 and R3, R of the alkoxy group (-OR), dialkylamino group (-NR2), alkylamino group (-NHR), amide group (-NHCOR) and acyloxy group (-OCOR) is methyl or ethyl.

[0014] All alkyl groups having 1 to 6 carbon atoms are normal alkyl groups.

[0015] X is N, O, P, S or Se;

[0016] n is 2 or 3, that is, when X=O, S or Se, n=2, and when X=N or P, n=3.

[0017] Preferably, the monomer of the benzimidazole derivative has a chemical structure that satisfies one of the following structures:

[0018]

[0019] More preferably, the chemical structure of the monomer of the benzimidazole derivative satisfies one of the following structures:

[0020]

[0021]

[0022] A method for preparing the above-mentioned monomer of the benzimidazole derivative comprises the following steps:

[0023] The benzaldehyde derivative shown in formula 1, N,N'-di-R2-4,5-di-R3-1,2-phenylenediamine shown in formula 2 and a catalyst are reacted in a solvent to obtain the monomer of the benzimidazole derivative.

[0024]

[0025] The molar ratio of the compound represented by Formula 1 to the compound represented by Formula 2 is 1:n, wherein n is 2 or 3; the compound represented by Formula 2 is usually directly purchased; the compound represented by Formula 1 can be prepared by existing technology or directly purchased.

[0026] The catalyst is an acid, preferably at least one of acetic acid and formic acid; the catalyst meets the catalytic amount, preferably 0.1-0.3 mL of catalyst is used for every 1 mmol of the compound represented by formula 1.

[0027] The solvent is at least one of THF and MeOH; the amount of the solvent used is sufficient to completely dissolve the reactants.

[0028] The reaction refers to an ultrasonic reaction at room temperature until precipitation occurs; preferably, the reaction refers to placing the reaction in an ultrasonic cleaning machine with a power of 500-2000W and a frequency of 40kHz for an ultrasonic reaction for 1-5 hours until precipitation occurs, and adding a small amount of methanol or water as a poor solvent every 15 minutes during the process to precipitate the product, wherein when the solvent is THF, methanol is selected as the poor solvent, and when the volume is methanol, water is selected as the poor solvent;

[0029] After the reaction is completed, a purification step is also included. The purification step is to use a mixture of methanol and water to precipitate after a certain amount of precipitation appears in the reaction bottle, and filter and dry to obtain the product. The preferred ratio is methanol: water volume ratio = 1:1.

[0030] The compound represented by Formula 1 is preferably one of the following structures:

[0031]

[0032] The compound shown in Formula 2 is preferably one of the following structures:

[0033]

[0034] The monomers of the above-mentioned benzimidazole derivatives are used as N-type dopants in organic electronic devices, especially in organic semiconductors.

[0035] This invention, based on benzimidazole derivatives, increases the molecular volume and doping efficiency through coupling reactions. The standard dopant, N-DMBI, significantly enhances the n-type conductivity and overall device performance of organic semiconductors by providing electrons, lowering the injection barrier, and improving charge transport. However, the present invention combines benzimidazole derivatives in parallel to form a multi-site dopant, which can simultaneously provide more electrons, significantly improving doping efficiency and uniformity. This multi-site design enables a more complete doping reaction, lowers the electron injection barrier, improves semiconductor carrier mobility, and enhances the thermal stability of the device, ultimately improving the electrical performance and service life of organic electronic devices.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) The monomer of the benzimidazole derivative of the present invention has the ability of multiple doping and enhances the electron supply capacity: multiple sites in the same molecule can release more electrons simultaneously, thereby improving the overall doping efficiency.

[0038] (2) The monomers of the benzimidazole derivatives of the present invention can enhance the electron supply capacity, and multiple sites within the same molecule can release more electrons simultaneously, thereby improving the overall doping efficiency.

[0039] (3) The monomers of the benzimidazole derivatives of the present invention have the ability to achieve uniform doping distribution, and the multi-site design helps to achieve more uniform doping in the semiconductor, reduce local concentration differences, and thus optimize device performance.

[0040] (4) The monomer of the benzimidazole derivative of the present invention has the ability to reduce the electron injection barrier. More active sites are conducive to forming a more effective charge transfer channel, thereby reducing the electron injection barrier.

[0041] (5) The monomers of the benzimidazole derivatives of the present invention have the ability to improve device stability. The multi-site structure often has stronger molecular stability and heat resistance, which helps to improve the service life and operational stability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the NMR spectrum of the dopant O-bis (DMBI) prepared in Example 1.

[0043] Figure 2 This is the NMR spectrum of the dopant N-tris (DMBI) prepared in Example 2.

[0044] Figure 3This is the mass spectrum of the dopant O-bis (DMBI) prepared in Example 1.

[0045] Figure 4 The mass spectrum of the dopant N-tris (DMBI) prepared in Example 2

[0046] Figure 5 The electrochemical data of the dopant P-tris (DMBI) prepared in Example 3 and the standard dopant N-DMBI are shown.

[0047] Figure 6 The electrochemical data of the dopant O-bis(DEBI) prepared in Example 4 and the standard dopant N-DMBI are shown.

[0048] Figure 7 The absorption spectra of the dopant O-bis (H-DMBI) prepared in Example 5 and the standard dopant N-DMBI doped into PCBM, respectively.

[0049] Figure 8 The absorption spectra of the dopant O-bis(H-DMMBI) and the standard dopant N-DMBI prepared in Example 6 doped into PCBM, respectively.

[0050] Figure 9 is the theoretically calculated SOMO energy level of the dopant O-bis (DMBI) prepared in Example 1.

[0051] Figure 10 This is the ESR spectrum of PCBM doped with the dopant O-bis (DMBI) prepared in Example 1.

[0052] Figure 11 This is the ESR spectrum of PCBM doped with the dopant N-tris (DMBI) prepared in Example 2.

[0053] Figure 12 EQE data of O-bis(H-DMBI) and O-bis(H-DMMBI) prepared in Examples 5 and 6 when doped in PCBM. DETAILED DESCRIPTION

[0054] The present invention will be described in further detail below with reference to the Examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the Examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0055] Example 1: Preparation of dopant O-bis (DMBI)

[0056] N1,N2-dimethylbenzene-1,2-diamine (0.12 g, 0.88 mmol) and 4,4'-oxybenzaldehyde (0.10 g, 0.44 mmol) were dissolved in methanol (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was sonicated in an ultrasonic bath for 5 hours. Small amounts of water were added every 15 minutes as a poor solvent to promote the precipitation of the product. Once a precipitate formed in the reaction system, the reaction was stopped and the product was purified by precipitation using a mixture of methanol and water (1:1 volume ratio). The product was filtered and dried to obtain 0.15 g of the product in a 73% yield. 1 H NMR and MS results showed that the obtained compound was the target product.

[0057] The chemical reaction equation for synthesizing the dopant O-bis (DMBI) is shown below:

[0058]

[0059] Figure 1 is the NMR image of the dopant O-bis (DMBI) prepared in Example 1, Figure 3 The mass spectrum of the dopant O-bis (DMBI) prepared in Example 1 shows that the target product is obtained.

[0060] Figure 9 Theoretical calculations for the dopant O-bis(DMBI) prepared in Example 1 show single-electron occupied molecular orbital (SOMO) energy levels of 2.626 eV and 2.638 eV, respectively. The shallow SOMO energy levels indicate low electron binding energy and ionization potential in the molecule, which facilitate efficient electron injection and transport, thereby lowering the energy barrier and improving N-type doping efficiency. This characteristic is primarily attributed to the effective regulation of the conjugated system in the molecular structure, resulting in a more uniform electron cloud distribution, a key principle for achieving high-performance N-type doping.

[0061] Figure 10 The ESR spectrum of the dopant O-bis (DMBI) doped PCBM (phenyl-C60-butyric acid methyl ester) prepared in Example 1. The solvent is chlorobenzene, the dopant O-bis (DMBI) concentration is 0.5 mg / L, and the PCBM concentration is 10 mg / L. The obvious signal peak indicates the presence of unpaired electron radicals in the system. The formation of the free radical is mainly attributed to the electron transfer reaction between the dopant and PCBM, which reduces the charge transfer barrier, thereby significantly improving the electrical properties of the N-type doped system.

[0062] Example 2: Preparation of dopant N-tris (DMBI)

[0063] N1,N2-dimethylbenzene-1,2-diamine (0.12 g, 0.88 mmol) and tris(4-formylphenyl)amine (0.10 g, 0.29 mmol) were dissolved in tetrahydrofuran (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was sonicated in an ultrasonic bath for 5 hours. During the reaction, a small amount of methanol was added as a poor solvent every 15 minutes to promote the gradual precipitation of the product. Once a precipitate appeared in the reaction system, the reaction was stopped, and the product was purified by precipitation using methanol. The product was filtered and dried to obtain 0.10 g of the product with a yield of 48%. 1 H NMR and MS results showed that the obtained compound was the target product.

[0064] The chemical reaction equation for synthesizing the dopant N-tris (DMBI) is shown below:

[0065]

[0066] Figure 2 is the NMR image of the dopant O-bis (DMBI) prepared in Example 2, Figure 4 The mass spectrum of the dopant N-tris (DMBI) prepared in Example 2 shows that the target product is obtained.

[0067] Figure 11 The ESR spectrum of the dopant N-tris (DMBI) doped with PCBM (phenyl-C60-butyric acid methyl ester) prepared in Example 2. The solvent is chlorobenzene, the concentration of the dopant N-tris (DMBI) is 0.5 mg / L, and the concentration of PCBM is 10 mg / L. Under the same conditions, the ESR spectrum peak of N-tris (DMBI) is significantly enhanced, indicating that a higher concentration of free radicals is generated during the doping process. This phenomenon suggests that the molecule has higher free radical formation and stabilization capabilities, and the extended conjugated system and optimized energy level matching in its molecular structure help promote efficient electron transfer, thereby achieving a better N-type doping effect.

[0068] Example 3: Preparation of dopant P-tris (DMBI)

[0069] N1,N2-dimethylbenzene-1,2-diamine (0.12 g, 0.88 mmol) and tris(tetrabenzaldehyde)phosphine (0.10 g, 0.29 mmol) were dissolved in tetrahydrofuran (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was sonicated in an ultrasonic bath for 5 hours. A small amount of methanol was added every 15 minutes as a poor solvent to promote the precipitation of the product. Once a precipitate appeared in the reaction system, the reaction was stopped, and the product was purified by precipitation using methanol. The product was filtered and dried to obtain 0.12 g of the product in a 59% yield.

[0070] The chemical reaction equation for synthesizing the dopant P-tris (DMBI) is shown below:

[0071]

[0072] Figure 5 The electrochemical data for the dopant P-tris (DMBI) prepared in Example 3 and the standard dopant N-DMBI (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole) are shown. The dopant P-tris (DMBI) prepared in Example 3 has a deeper HOMO energy level, indicating that P-tris (DMBI) has stronger electron bonding and higher ionization energy, making it less susceptible to oxidation in air and exhibiting better antioxidant stability.

[0073] Example 4: Preparation of dopant O-bis (DEBI)

[0074] N1,N2-diethylbenzene-1,2-diamine (0.14 g, 0.88 mmol) and 4,4'-oxybenzaldehyde (0.10 g, 0.44 mmol) were dissolved in methanol (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was sonicated in an ultrasonic bath for 5 hours. Small amounts of water were added every 15 minutes as a poor solvent to promote the precipitation of the product. Once a precipitate formed in the reaction system, the reaction was stopped and the product was purified by precipitation using a mixture of methanol and water (1:1 volume ratio). Filtering and drying yielded 0.08 g of the product in a 35% yield.

[0075] The chemical reaction equation for synthesizing the dopant O-bis (DEBI) is shown below:

[0076]

[0077] Figure 6 The electrochemical data of the dopant O-bis(DEBI) prepared in Example 4 and the standard dopant N-DMBI are shown. This shows that the dopant O-bis(DEBI) prepared in Example 3 has a deeper HOMO energy level. Similarly, O-bis(DEBI) has stronger electron bonding and higher ionization energy, making it less susceptible to oxidation in air and exhibiting better antioxidant stability.

[0078] Example 5: Preparation of dopant O-bis (H-DMBI)

[0079] Benzene-1,2-diamine (0.09 g, 0.88 mmol) and 4,4'-oxybenzaldehyde (0.10 g, 0.44 mmol) were dissolved in methanol (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was sonicated in an ultrasonic bath for 5 hours. Small amounts of water were added every 15 minutes as a poor solvent to promote the gradual precipitation of the product. Once a precipitate formed in the reaction system, the reaction was stopped, and the product was purified by precipitation using water. The product was filtered and dried to obtain 0.15 g of the product with a yield of 83%.

[0080] The chemical reaction equation for synthesizing the dopant O-bis (H-DMBI) is shown below:

[0081]

[0082] Figure 7 The absorption spectra of the dopant O-bis(H-DMBI) prepared in Example 5 and the standard dopant N-DMBI, doped in PCBM (10 mg / L) at the same concentration (0.5 mg / L), were obtained using chlorobenzene as the solvent. This indicates that O-bis(H-DMBI) enables more efficient electron transfer when interacting with PCBM, forming more dopant complexes and generating a higher free carrier concentration. This phenomenon demonstrates its superior doping efficiency and increased stability in practical applications, helping to improve the conductivity and performance of N-type semiconductor devices.

[0083] Example 6: Preparation of dopant O-bis (H-DMMBI)

[0084] 4,5-Dimethyl-1,2-phenylenediamine (0.12 g, 0.88 mmol) and 4,4'-oxybenzaldehyde (0.10 g, 0.44 mmol) were dissolved in methanol (5 mL) under nitrogen. Two drops of acetic acid were added, and the mixture was ultrasonically reacted in an ultrasonic bath for 5 hours. Small amounts of water were added every 15 minutes as a poor solvent to promote the precipitation of the product. Once a precipitate formed in the reaction system, the reaction was stopped, and the product was purified by precipitation using water. The product was filtered and dried to obtain 0.18 g of the product with an 88% yield.

[0085] The chemical reaction equation for synthesizing the dopant O-bis(H-DMMBI) is shown below:

[0086]

[0087] Figure 8The absorption spectra of the dopant O-bis(H-DMMBI) prepared in Example 6 and the standard dopant N-DMBI, doped in PCBM (10 mg / L) at the same concentration (0.5 mg / L), were obtained using chlorobenzene as the solvent. Similarly, O-bis(H-DMMBI) can achieve more efficient electron transfer when interacting with PCBM, forming more doped complexes and thus generating a higher free carrier concentration. This phenomenon verifies its superior doping efficiency and higher stability in practical applications, helping to improve the conductivity and performance of N-type semiconductor devices.

[0088] Example 7: Preparation of perovskite devices

[0089] (1) A pre-made fluorine-doped tin oxide (FTO) glass with a sheet resistance of 15 Ω was ultrasonically cleaned with acetone, detergent, deionized water, and isopropyl alcohol in sequence, and then plasma treated for 10 minutes.

[0090] (2) Spin-coat a 2 mg / mL PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) chlorobenzene solution onto the FTO at a speed of 4000 rpm. After spin-coating, anneal at 100°C for 10 minutes to obtain a hole transport layer with a thickness of 5 nm.

[0091] (3) Spin-coat a 2 mg / mL aluminum oxide suspension in isopropanol on the surface of the hole transport layer at a dispersion speed of 4000 rpm and anneal at 100 °C for 5 min to obtain an Al2O3 layer with a thickness of 10 nm;

[0092] (4) Spin-coat the active layer (pvk) on the surface of the Al2O3 layer. The specific steps are as follows: dissolve FAI (675.2 mg), MABr (23.1 mg), MACl (44.1 mg), CsI (56.6 mg), PbBr2 (81.8 mg), PbI2 (1997.9 mg) (5% PbI2 excess) in DMF (2400 μL) and DMSO (600 μL) (where FA is formamidine and MA refers to methylammonium), prepare the perovskite precursor solution, stir the precursor solution for 2-3 hours and then filter. Use a pipette to measure 100 microliters of the perovskite precursor solution and spin-coat it on the device at a speed of 4000 rpm. Anneal at 100 degrees Celsius for 20 minutes to obtain the active layer Cs 0.05 (FA 0.95 MA 0.05 ) 0.95 Pb;

[0093] (5) Different electron transport layers (ET) were spin-coated on the active layer. The configuration method of the electron transport layer was to mix equal volumes of a 0.5 mg / mL chlorobenzene solution of a dopant and a 40 mg / mL chlorobenzene solution of PCBM (phenyl-C60-butyric acid methyl ester) to obtain a doped PCBM. The mixture was stirred at 500 rpm for 20 minutes at room temperature. The mixed solution was filtered and coated. The concentration of the undoped PCBM chlorobenzene solution was 20 mg / mL. The rotation speed during the spin coating process was 4000 rpm. After the spin coating, the coating was annealed at 100 degrees Celsius for 10 minutes to obtain an electron transport layer with a thickness of 25 nm.

[0094] (6) Finally, a 7 nm thick hole blocking layer BCP and a 120 nm thick metal Ag layer were evaporated on PCBM. The device structure was ITO / HT / Al2O3 / pvk / PCBM / BCP / Ag.

[0095] Table 1 Polymer device performance

[0096]

[0097] As shown in Table 1, the parallel connection of benzimidazole derivatives to form a multi-site dopant can simultaneously provide more electrons, significantly improving doping efficiency and uniformity. The overall performance is superior to that of the traditional N-type dopant N-DMBI.

[0098] The EQE data of the perovskite devices prepared by doping O-bis(H-DMBI) and O-bis(H-DMMBI) in PCBM prepared in Examples 5 and 6 are shown in Figure 2. Figure 12 As shown in Figure 2, a higher EQE indicates that the dopant excels in enhancing the generation and collection efficiency of photogenerated carriers, meaning it more effectively promotes electron injection and transport, thereby improving photoelectric conversion performance. This reflects the dopant's optimized effect on the electronic structure of PCBM, enhancing the separation efficiency of electron-hole pairs and providing a solid theoretical basis for the realization of high-efficiency N-type semiconductor devices. Its doping in PCBM has shown significant device enhancement and can be applied to OLEDs.

[0099] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A monomer of a benzimidazole derivative, characterized in that Its chemical structure satisfies the following general formula: In the formula, R1 is one of -H, -NH2, -OH, an alkyl group having 1 to 6 carbon atoms, -OR, -NR2, -NHR, -NHCOR, and -OCOR; R2 is one of -H, -OH, an alkyl group with 1 to 6 carbon atoms, and -OR; R3 is one of -H, -NH2, -OH, an alkyl group with 1 to 6 carbon atoms, -OR, -NR2, -NHR, -NHCOR, and -OCOR; R in R1, R2, and R3 is limited to methyl or ethyl; X is N, O, P, S or Se; n is 2 or 3, that is, when X=O, S or Se, n=2, and when X=N or P, n=3.

2. The monomer of the benzimidazole derivative according to claim 1, characterized in that Its chemical structure satisfies one of the following structures:

3. The monomer of the benzimidazole derivative according to claim 1, characterized in that Its chemical structure satisfies one of the following structures:

4. A method for preparing a monomer of a benzimidazole derivative according to any one of claims 1 to 3, characterized in that The following steps are involved: The benzaldehyde derivative represented by Formula 1, the N,N'-di-R2-4,5-di-R3-1,2-phenylenediamine represented by Formula 2, and a catalyst are reacted in a solvent to obtain the monomer of the benzimidazole derivative; R1 is one of -H, -NH2, -OH, an alkyl group with 1 to 6 carbon atoms, -OR, -NR2, -NHR, -NHCOR, and -OCOR; R2 is one of -H, -OH, an alkyl group with 1 to 6 carbon atoms, and -OR; R3 is one of -H, -NH2, -OH, an alkyl group with 1 to 6 carbon atoms, -OR, -NR2, -NHR, -NHCOR, and -OCOR; R in R1, R2, and R3 is limited to methyl or ethyl; X is N, O, P, S or Se; n is 2 or 3, that is, when X=O, S or Se, n=2, and when X=N or P, n=3.

5. The method for preparing a monomer of a benzimidazole derivative according to claim 4, wherein: The molar ratio of the compound represented by Formula 1 to the compound represented by Formula 2 is 1:n, wherein n is 2 or 3.

6. The method for preparing a monomer of a benzimidazole derivative according to claim 4, wherein: The catalyst is an acid, preferably at least one of acetic acid and formic acid.

7. The method for preparing a monomer of a benzimidazole derivative according to claim 4, wherein: The solvent is at least one of tetrahydrofuran and methanol; the amount of the solvent is sufficient to completely dissolve the reactants.

8. The method for preparing a monomer of a benzimidazole derivative according to claim 4, wherein: The reaction is carried out by ultrasonication at room temperature until precipitation occurs.

9. Use of a monomer of the benzimidazole derivative according to any one of claims 1 to 3 as an N-type dopant in an organic electronic device.

10. Use of a monomer of the benzimidazole derivative according to any one of claims 1 to 3 as an N-type dopant in an organic semiconductor.

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