Photo-activated n-type dopant as well as preparation method and application thereof

Abstract

The invention discloses a photo-activated n-type dopant as well as a preparation method and application thereof. The n-type dopant provided by the invention is a viologen derivative, and the structural general formula of the n-type dopant is as shown in formula I, the dopant has good water-oxygen stability and doping capacity, can realize light-activated efficient n doping of an n-type organic polymer, is beneficial to long-time storage under a solution condition, and is also beneficial to large-area solution processing of a device.

Description

Technical Field

[0001] The invention belongs to the technical field of organic photoelectric materials, and in particular relates to a light-activated n-type dopant and a preparation method and application thereof. Background Art

[0002] As a method to efficiently improve the performance of materials and devices, doping is widely used in the fields of organic light-emitting diodes, organic field-effect transistors, organic solar cells and organic thermoelectric materials. For example, in solar cell devices, n-type doping of the interface between the electron transport layer and the semiconductor active layer can improve the energy transfer efficiency (Liang, ZQ et al, Achieving Efficient p-Type Organic Thermoelectrics by Modulation of Acceptor Unit in Photovoltaicπ-Conjugated Copolymers. Adv. Sci. 2022, 9, 2103646). In field effect transistors, doping of the semiconductor active layer can improve the mobility and switching ratio of the device (Li, W Het al, Pursuing High-Performance Organic Field-Effect Transistors through OrganicSalt Doping. Adv. Funct. Mater. 2022, 32, 2111285). In light-emitting diodes, doping can greatly improve the operating current and luminous brightness of the device (Yan, H. et al, Identifying the Electrostatic and Entropy-Related Mechanisms for Charge-Transfer Exciton Dissociation at Doped Organic Heterojunctions. Adv. Funct. Mater. 2021, 31, 2101892). In thermoelectric materials, doping can greatly improve conductivity and functional factors (Guo, X Het al, Transition metal-catalysed molecular n-doping of organic semiconductors. Nature. 2021, 599, 67-73). Therefore, in the field of organic optoelectronic materials, the research on high-efficiency dopants is of great significance.

[0003] Dopants are divided into p-type dopants and n-type dopants. Compared with p-type dopants, the development of n-type dopants is relatively slow. Ideal n-type dopants should meet the following conditions: 1. Strong reduction ability to achieve effective n-type doping; 2. The counter ions generated after doping are stable and will not affect the stability of the device due to dopants; 3. The dopant itself is stable, and the synthesis is simple and cheap; 4. The dopant has mild conditions for use, good solubility, and can be processed in solution; 5. The dopant has few side reactions and high efficiency during the doping process.

[0004] According to the chemical structure characteristics of n-type dopants, reported n-type dopants can be divided into alkali metals (active metals such as sodium and potassium), organic and inorganic salts, and negative hydrogen donor compounds. Most organic dopants are doped by thermal activation, resulting in poor stability, especially in solution. Therefore, it is of great significance to develop efficient and stable n-type dopants, especially dopants with photoactivation characteristics, which will be conducive to the large-scale preparation of optoelectronic devices. Summary of the invention

[0005] The present invention aims to provide a class of n-type dopants with a new chemical structure, stable solutions in air and light-activated. This class of dopants can be used to prepare n-type thermoelectric devices under air conditions, greatly simplifying the processing conditions. In addition, the dopant solution and the mixed solution of the dopant and the semiconductor can be stored for a long time under atmospheric conditions without affecting the performance.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In the first aspect, the present invention provides a viologen derivative, the general structural formula of which is as follows:

[0008]

[0009] In Formula I:

[0010] R1 and R2 each independently represent a C1-C50 straight-chain alkyl group, a branched alkyl group or an alkoxy group, a C7-C50 aromatic group, or a C5-C50 heteroalkyl group;

[0011] X1 and X2 each independently represent H, halogen, amino, hydroxy, alkyl, alkoxy, alkenyl, aryl or ester.

[0012] Furthermore, the straight-chain alkyl group is one or more of methyl, ethyl, n-propyl and n-butyl.

[0013] The branched alkyl group is isopropyl, tert-butyl, etc. The cycloalkyl group is cyclohexyl, adamantyl, etc.

[0014] Preferably, the aryl group is phenyl, benzyl, thienyl, and phenyl, thienyl, etc. containing one or more alkyl, alkoxy, amino, halogen, etc. substituents; the number of alkyl substituents in the aralkyl group is an integer of 1 to 4. More preferably, it is a phenyl group with one or more C1-C12 alkyl substituents; the halogen is preferably F, Cl.

[0015] Preferably, the heteroatom in the heteroalkyl group is at least one of oxygen, sulfur and selenium; and the number of heteroatom substitutions is 1-10.

[0016] Preferably, R1 and R2 each independently represent a C1-C16 straight chain alkyl, branched alkyl or cycloalkyl group; further preferably a C1-C12 straight chain alkyl or branched alkyl group; further preferably a C1-C6 straight chain alkyl or branched alkyl group; further preferably a C1-C10 straight chain alkyl or branched alkyl group; more preferably, R1 is CH3 or n-octyl, R2 is CH3, and X1 and X2 are H.

[0017] Exemplarily, the viologen derivative is the following compound:

[0018]

[0019] In a second aspect, the present invention further provides a method for preparing the viologen derivatives, comprising the following steps:

[0020] Under light-proof conditions, the viologen ionic compound and the tetraphenylboric acid ionic compound are stirred in a solvent to react to generate a precipitate, which is filtered and washed to obtain the viologen derivative.

[0021] The general structural formula of the viologen ionic compound is VX, wherein V is a viologen cation, and X is an anion. Preferably, X is a chloride ion, a bromide ion or an iodide ion.

[0022] The molar ratio of the viologen ion compound to the tetraphenylborate ion compound is 1:(2-5), preferably 1:(2-3).

[0023] The solvent is a mixed solution of methanol and water, and the mixed volume ratio of the methanol to the water is (1-5):1, preferably 1:1.

[0024] The reaction conditions are: temperature of 25-60°C, preferably 25-35°C, and time of 2-72h, preferably 2-24h.

[0025] The cleaning solution used for the cleaning is a mixed solution of methanol and water, and the mixed volume ratio of the methanol to the water is 1:1.

[0026] Taking viologen chloride ion compounds and tetraphenylborate sodium ion compounds as examples, the synthesis route of the viologen derivatives is as follows:

[0027]

[0028] In a third aspect, the present invention further provides the use of the viologen derivatives as n-type dopants for light-activated doped semiconductor materials.

[0029] The semiconductor material is an organic small molecule semiconductor material, a polymer semiconductor material, a two-dimensional semiconductor material, a carbon nanotube or an inorganic semiconductor material.

[0030] The principle of the viologen derivatives as n-type dopants for semiconductor materials is as follows:

[0031]

[0032] As shown above, the molecule of formula I cannot be doped with n-type semiconductor materials before irradiation, but it can undergo intramolecular electron transfer under ultraviolet light, that is, the tetraphenylboron group transfers an electron to the viologen cation to generate a cation radical, which can dope the n-type semiconductor material.

[0033] The semiconductor material may be the following materials: N2200, TEG-N2200, PDNI2TEG-2Tz, PDNI2TEG-2T, PDNI2OD-Tz2, p(gNDI-gT2), PNDTI-BBT-DT, PNDTI-BBT-DP, pNB, pNB-Tz, pNB-TzDP. Its structural formula is as follows:

[0034]

[0035]

[0036] The doping amount of the viologen derivatives is in the range of 1-200 mol %, preferably 1-80 mol %, and more preferably 40-60 mol %.

[0037] The beneficial effects achieved by the present invention are as follows:

[0038] 1. The present invention provides a class of novel n-type dopants - viologen derivatives, which have simple synthesis and diverse structures. By changing the N atom and the substituents on the ring, the stability and electronic properties of the viologen derivatives can be regulated and the corresponding activation conditions, such as the wavelength of light, can be adjusted.

[0039] 2. The viologen derivatives provided by the present invention have excellent water-oxygen stability and solubility. Compared with the currently widely used n-type dopant N-DMBI, the mixed solution of the viologen derivatives and the organic semiconductor material can be stored in air for as long as 1 month. At the same time, its good stability and photothermal activation make the doping reaction of this type of dopant controllable, reducing the requirements for solution-processed semiconductor device processing.

[0040] 3. The viologen derivatives provided by the present invention can be used as n-type dopants to achieve efficient n-doping of organic small molecules and polymer materials, carbon nanotubes, inorganic semiconductors, etc. Due to their good stability and solubility, they meet the needs of solution processing of organic semiconductor materials. This achievement can be widely used in the field of electronics, such as light-emitting diodes, solar cells, field effect transistors and thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The H NMR spectrum of the representative compound in Example 1 in deuterated DMSO.

[0042] Figure 2 The carbon NMR spectrum of the representative compound in Example 1 in deuterated DMSO.

[0043] Figure 3 1 is the ESR spectrum of the representative compound in Example 1 before and after photo-activated doping with N2200; the dotted line is after photo-activated doping, and the solid line is before photo-activated doping.

[0044] Figure 4 The conductivity of the representative compound doped polymer N2200 in Example 1.

[0045] Figure 5 1 is the Seebeck coefficient and functional factor curve of the representative compound doped polymer N2200 in Example 1; the solid line is the Seebeck coefficient curve, and the dotted line is the functional factor curve. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0048] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0049] In the following examples, the polymer PNDI2TEG-2Tz is a compound synthesized according to the literature (L. Jan Anton Koster et al, N-Type Organic Thermoelectrics of Donor-Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States. Adv. Mater. 2018, 30, 1804290).

[0050] In the following examples, polymer N2200 was purchased from One Material Company.

[0051] Example 1. Synthesis of representative compounds of formula I

[0052] The structures of representative compounds shown in Formula I are as follows:

[0053]

[0054] Wherein: X1=X2=H, R1=R2=CH3.

[0055] The specific synthesis steps are as follows:

[0056] (1) At 25°C, 1 mM of a viologen chloride ion compound and 3 mM of a tetraphenylborate sodium ion compound were stirred in a mixed solution of methanol / water in a volume ratio of 1:1 for 2 hours, and a colored precipitate was generated;

[0057] (2) The obtained reaction system is filtered, and the precipitate is washed with a mixed solution of methanol / water in a volume ratio of 1:1 to obtain the target product.

[0058] like Figure 1 , Figure 2 The structural confirmation data are as follows: 1 H NMR (400MHz, d6-DMSO): δ9.23(d,J=4.0Hz,4H),8.69(d,J=6.4Hz,4H),7.23(br,16H),6.97(t,J=7.2Hz,16H),6.83(t,J=7.2Hz,8H),4.42(s,6H). 13 C NMR (100MHz, d6-DMSO): δ164.6,164.1,163.6,163.1,148.6,147.0,136.0,126.5,125.8,125.8,125.8,125.7,122.0,48.5.

[0059] Effect verification:

[0060] 1. Doping ability

[0061] The doping ability of the representative compound of formula I obtained in Example 1 was tested by the ESR method, with polymer N2200 as an example. The specific operation is as follows: the representative compound of formula I obtained in Example 1 was mixed and doped with polymer N2200 at a molar ratio of 0.6:1 to obtain a blended film, and then the ESR signals of the obtained blended film before and after illumination were compared by paramagnetic spectroscopy.

[0062] like Figure 3 As shown, the film formed by polymer N2200 itself has no ESR signal ( Figure 3 The solid line in the middle shows that the film has an ESR signal after light doping ( Figure 3 This indicates that the representative compound of Formula I obtained in Example 1 has doping ability and can be doped with polymer N2200.

[0063] 2. Doping with polymer N2200

[0064] The specific operation is as follows: the polymer N2200 is dissolved by heating with chloroform at 60°C for 2h, the compound obtained in Example 1 is dissolved with DMSO, the two solutions are mixed according to the doping amount of 10mol%-80mol% of the compound obtained in Example 1, and then stirred at 60°C for 15min to obtain a mixed solution; then 20μL of the mixed solution is taken and spun on a borosilicate glass sheet with a spinner speed of 2000rpm for 1min; then, the film is irradiated at a wavelength of 365nm at 140°C for 1min, and the conductivity of the film is tested in a vacuum environment using a four-probe method.

[0065] The test results are as follows:

[0066] like Figure 4 As shown, the conductivity of the film increases with the increase of doping concentration, and the maximum is 0.0045 / cm, which shows that the compound obtained in Example 1 can effectively dope polymer N2200.

[0067] like Figure 5 As shown in the figure, the Seebeck coefficient and functional factor of the film change with the doping concentration. The solid line is the Seebeck coefficient curve, and the dotted line is the functional factor curve. The Seebeck coefficient ranges from -750 to 193 μV K -1 .

[0068] 3. Doping with polymer PNDI2TEG-2Tz

[0069] The specific doping steps are the same as those of polymer N2200, and the doping ratio is 40 mol%.

[0070] After doping, the conductivity of the obtained film is up to 0.51S / cm, and the Seebeck coefficient ranges from -367 to 115μVK -1 .

[0071] From the improvement of conductivity and the sign of Seebeck coefficient (negative value), it can be concluded that the compound obtained in Example 1 can be used as an n-dopant to achieve doping of n-type polymer PNDI2TEG-2Tz, and its performance is better than that of commercial N-DMBI. In addition, the device prepared by spin coating in air has a conductivity value equivalent to that of the device prepared under nitrogen conditions, which proves that this type of dopant can be used for solution spin coating of doped semiconductor films in air, greatly simplifying the device preparation requirements.

[0072] 4. Stability

[0073] The stability of the solution after the compound obtained in Example 1 was mixed with the polymer PNDI2TEG-2Tz and the polymer N2200 was characterized by the B1500 conductivity measurement method. The specific steps are as follows:

[0074] The compound obtained in Example 1 was mixed with the polymer PNDI2TEG-2Tz at a doping amount of 40 mol% to obtain a mixed solution A; the compound obtained in Example 1 was mixed with the polymer N2200 at a doping amount of 60 mol% to obtain a mixed solution B; the two mixed solutions were respectively prepared by spin coating at zero day and 30 day storage, and the electrical properties of the films were tested. The storage conditions are: in an air environment at room temperature and away from light.

[0075] The electrical properties of the films prepared at 0 days and 30 days were compared.

[0076] Table 1 Film properties

[0077] polymer Doping amount <![CDATA[Conductivity (S cm -1 )]]> <![CDATA[Conductivity (S cm -1 )(at 30 days)]]> PNDI2TEG-2Tz 40mol% 0.51 0.52 N2200 60mol% 0.0026 0.0028

[0078] As shown in Table 1, the conductivity of the two films did not change substantially before and after 30 days, and the conductivity of the films was not affected by the storage time, which shows that the compound obtained in Example 1 has good stability.

[0079] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A viologen derivative, the general structural formula of which is as follows: In Formula I: R1 and R2 each independently represent a C1-C50 straight-chain alkyl group, a branched alkyl group or an alkoxy group, a C7-C50 aromatic group, or a C5-C50 heteroalkyl group; X1 and X2 each independently represent H, halogen, amino, hydroxy, alkyl, alkoxy, alkenyl, aryl or ester.

2. The viologen derivative according to claim 1, characterized in that: The straight-chain alkyl group is one or more of methyl, ethyl, n-propyl and n-butyl; The branched alkyl group is isopropyl or tert-butyl; The cycloalkyl group is cyclohexyl or adamantyl; The aryl group is phenyl, benzyl, thienyl, and phenyl and thienyl containing one or more alkyl, alkoxy, amino, and halogen substituents; The number of alkyl substituents in the aralkyl group is an integer of 1 to 4; The heteroatom in the heteroalkyl group is at least one of oxygen, sulfur and selenium; The number of heteroatom substitutions is 1-10.

3. The viologen derivative according to claim 1 or 2, characterized in that: R1 and R2 each independently represent a C1-C16 straight-chain alkyl group, a branched-chain alkyl group or a cycloalkyl group.

4. The viologen derivative according to any one of claims 1 to 3, characterized in that: R1 is CH3 or n-octyl, R2 is CH3, and X1 and X2 are H.

5. The method for preparing the viologen derivative according to any one of claims 1 to 4, comprising the following steps: Under light-proof conditions, the viologen ionic compound and the tetraphenylboric acid ionic compound are stirred in a solvent to react to generate a precipitate, which is filtered and washed to obtain the viologen derivative.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the viologen ion compound to the tetraphenylborate ion compound is 1:(2-5); The solvent is a mixed solution of methanol and water, and the mixed volume ratio of the methanol to the water is (1-5):1; The reaction conditions are: temperature of 25-60°C and time of 2-72h; The cleaning solution used for the cleaning is a mixed solution of methanol and water, and the mixed volume ratio of the methanol to the water is 1:

1.

7. Use of the viologen derivative according to any one of claims 1 to 4 as an n-type dopant for photoactivated doped semiconductor materials.

8. The use according to claim 7, characterized in that: The semiconductor material is an organic small molecule semiconductor material, a polymer semiconductor material, a two-dimensional semiconductor material, a carbon nanotube or an inorganic semiconductor material.

9. The use according to claim 7 or 8, characterized in that: The doping amount of the viologen derivative is 1-200 mol%.

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