JP6177515B2 - Semiconductor film, semiconductor film manufacturing method, solar cell, light emitting diode, thin film transistor, and electronic device - Google Patents

Description

  The present invention relates to a semiconductor film, a semiconductor film manufacturing method, a solar cell, a light emitting diode, a thin film transistor, and an electronic device.

  In recent years, research on high-efficiency solar cells called third-generation solar cells has been actively conducted. Among them, a solar cell using colloidal quantum dots has been reported to have improved quantum efficiency due to, for example, a multi-exciton generation effect, and has attracted attention (for example, see Non-Patent Document 1). However, in a solar cell using colloidal quantum dots (also referred to as a quantum dot solar cell), the conversion efficiency is about 7% at the maximum, and further improvement in conversion efficiency is required.

In such a quantum dot solar cell, since a semiconductor film made of an assembly of quantum dots serves as a photoelectric conversion layer, research on the semiconductor film itself made of an assembly of quantum dots has been actively conducted.
For example, semiconductor nanoparticles using a relatively long ligand having 6 or more hydrocarbon groups are disclosed (for example, see Patent Document 1).
As a technique for improving the characteristics of a semiconductor film composed of an assembly of quantum dots, a ligand molecule bonded to a colloidal quantum dot (for example, about 2 nm to 10 nm) is replaced with a shorter ligand molecule, It has been reported that electrical conductivity is improved (see, for example, Non-Patent Document 2). In Non-Patent Document 2, by replacing the oleic acid (molecular chain length of about 2 nm to 3 nm) around the PbSe quantum dots with ethanedithiol (molecular chain length of 1 nm or less), the quantum dots become close to each other and the electrical conductivity is increased. It has been reported to improve.

Japanese Patent No. 4425470

S. Geyer et al., “Charge transport in mixed CdSe and CdTe colloidal nanofilms”, Physical Review B (2010). J. et al. M.M. By Luther et al. “Structural, Optical, and Electrical Properties of Self-Assembled Films of PbSe Nanocyclics Treated with 1,2-Ethanidiol”, ACS Nano (200).

However, since the semiconductor film described in Patent Document 1 has a large ligand and insufficient proximity between the semiconductor quantum dots, the photoelectric conversion characteristics are not excellent. Even when butylamine used in Non-Patent Document 1 or ethanedithiol used in Non-Patent Document 2 is used as a ligand, for example, according to Non-Patent Document 1, it is about several hundred nA at the maximum. Only the photocurrent value can be obtained.
In discussing the photoelectric conversion characteristics of a semiconductor film, the ratio Ip / Id of the photocurrent value (Ip) to the dark current value (Id) under a certain bias is considered to be more essential. Considering the situation of non-patent literature, it is still difficult to realize high Ip / Id ₋ with the conventional semiconductor film.
Further, when ethanedithiol is used as a ligand, the semiconductor film is easily peeled off.

An object of the present invention is to provide a semiconductor film that can provide high Ip / Id ₋ and suppress film peeling, and a method for manufacturing the semiconductor film.
It is another object of the present invention to provide a solar cell, a light emitting diode, a thin film transistor, and an electronic device in which high Ip / Id ₋ is obtained and film peeling is suppressed, and to solve the problem.

In order to achieve the above object, the following invention is provided.
<1> an assembly of semiconductor quantum dots containing PbS or InP having a metal atom, and 3-mercapto-1-propanol, thioglycolic acid, a 3-mercapto-1-propanol derivative coordinated to the semiconductor quantum dots , and A semiconductor film comprising at least one ligand selected from thioglycolic acid derivatives .

<2> is a semiconductor film according to complex stability constant Logbeta ₁ between the ligand and the semiconductor quantum dots of the metal atoms is 8 or more <1>.

A < 3 > semiconductor quantum dot is a semiconductor film as described in <1> or < 2> whose average particle diameter is 2 nm-15 nm.

< 4 > A semiconductor quantum dot dispersion containing a semiconductor quantum dot containing PbS or InP, a first ligand coordinated to the semiconductor quantum dot, and a first solvent is provided on the substrate. A semiconductor quantum dot aggregate forming step for forming an aggregate, and an aggregate of semiconductor quantum dots having a molecular chain length shorter than that of the first ligand, and 3-mercapto-1-propanol, thioglycolic acid, A solution containing at least one second ligand selected from a 3-mercapto-1-propanol derivative and a thioglycolic acid derivative and a second solvent is applied to coordinate with the semiconductor quantum dots. A ligand exchange step of exchanging the first ligand for the second ligand, and a method for producing a semiconductor film comprising the assembly of semiconductor quantum dots and the second ligand It is.

< 5 > The method for producing a semiconductor film according to < 4 >, wherein the first ligand is a ligand having a main chain having at least 6 carbon atoms.

< 6 > The method for producing a semiconductor film according to < 4 > or < 5 >, wherein the semiconductor quantum dot assembly forming step and the ligand exchange step are performed twice or more.

< 7 > The semiconductor quantum dot is the method for producing a semiconductor film according to any one of < 4 > to < 6 >, wherein an average particle diameter is 2 nm to 15 nm.

< 8 > A solar cell comprising the semiconductor film according to any one of <1> to < 3 >.

< 9 > A light-emitting diode comprising the semiconductor film according to any one of <1> to < 3 >.

< 10 > A thin film transistor including the semiconductor film according to any one of <1> to < 3 >.

< 11 > An electronic device comprising the semiconductor film according to any one of <1> to < 3 >.

ADVANTAGE OF THE INVENTION According to this invention, high Ip / Id < _- > is obtained, and the semiconductor film by which film | membrane peeling is suppressed and its manufacturing method are provided.
In addition, according to the present invention, there are provided a solar cell, a light emitting diode, a thin film transistor, and an electronic device in which high Ip / Id ₋ is obtained and film peeling is suppressed.

It is the schematic which shows an example of a structure of the pn junction type solar cell to which the semiconductor film of this invention is applied. It is the schematic which shows the comb-type electrode substrate used in the Example. It is the schematic which shows the method of irradiating a monochromatic light to the semiconductor film produced in the Example. It is the schematic which shows the structure of the experimental system used for the light emission measurement in the Example. It is a figure which shows the measurement result of a photoluminescence for every ligand. It is a TEM image which shows the film | membrane formed using the semiconductor quantum dot dispersion liquid which the oleic acid coordinated to the semiconductor quantum dot (PbS). It is a TEM image which shows the film | membrane which carried out the ligand exchange of the oleic acid coordinated to the semiconductor quantum dot (PbS) to ethanedithiol.

  Hereinafter, the semiconductor film of the present invention and the manufacturing method thereof will be described in detail.

<Semiconductor film>
The semiconductor film of the present invention includes an assembly of semiconductor quantum dots having metal atoms, a ligand coordinated to the semiconductor quantum dots, and a ligand represented by the general formula (A) and a coordination represented by the general formula (B). A ligand, and at least one ligand selected from ligands represented by formula (C).
Hereinafter, "at least one selected from the ligand represented by the general formula (A), the ligand represented by the general formula (B), and the ligand represented by the general formula (C)" “Ligand” is also referred to as “specific ligand”.

In general formula (A), X ¹ represents —SH or —OH, and A ¹ and B ¹ each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents. However, ^{when A 1} and ^{B 1} are both hydrogen atom, ^{X 1} represents a -OH.
In general formula (B), X ² represents —SH or —OH, and A ² and B ² each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents. In the general formula (C), A ³ represents a hydrogen atom or atoms of 1 to 10 substituents. However, A ³ does not end with NH _{2 at the} end.
In addition, the ligand represented by the general formula (A), the ligand represented by the general formula (B), and the ligand represented by the general formula (C) are different from each other. .

  A semiconductor quantum dot is a semiconductor particle including a metal atom, and is a nano-sized particle having a particle size of several nanometers to several tens of nanometers.

In the semiconductor film of the present invention, the semiconductor quantum dots are connected by a coordinate bond with a specific ligand having a small number of atoms represented by the general formula (A), (B), or (C). It is considered that the interval between dots is shortened. Therefore, it is considered that the semiconductor quantum dots are densely arranged and the wave function overlap between the semiconductor quantum dots can be strengthened. As a result, the electrical conductivity is increased, and the photocurrent value (Ip) can be increased. Therefore, it is considered that high Ip / Id ₋ can be obtained.
In the case of a ligand represented by the general formula (A) or (B), the specific ligand is represented by at least one thiol group (—SH) and X ¹ (or X ² ) in the molecule. -SH or -OH. The specific ligand represented by the general formula (C) has a thiol group and a —OH group of a carboxy group. The thiol group has a high complex stability constant and is considered to promote the complex formation between the metal atom of the semiconductor quantum dot and —SH or —OH. As a result, in order to strengthen the connection between the semiconductor quantum dots and the specific ligand, it is considered that the peeling of the semiconductor film including the semiconductor quantum dots and the specific ligand is suppressed.
Therefore, it is considered that the semiconductor film of the present invention can obtain a high photocurrent value and suppress film peeling.

The semiconductor film of the present invention is preferably a complex stability constant Logbeta ₁ between a particular ligand and the semiconductor quantum dots of the metal atoms is 8 or more.
Here, the complex stability constant is a constant determined by the relationship between the ligand and the metal atom to be coordinated, and is represented by the following formula (b).

  In formula (b), [ML] represents the molar concentration of the complex in which the metal atom and the ligand are bonded, [M] represents the molar concentration of the metal atom that can contribute to the coordination bond, and [L ] Represents the molar concentration of the ligand.

In practice, a plurality of ligands may coordinate to one metal atom. In the present invention, the ligand is represented by the formula (b) in the case where one ligand molecule coordinates to one metal atom. that the complex stability constant logβ _1, defined as an index of the strength of the coordination bond.
A complex stability constant logβ ₁ between the specific ligand and the metal atom of the semiconductor quantum dot is 8 or more, whereby a complex is easily formed.
Complex stability constant Logbeta _1, in combination with the semiconductor quantum dot and the ligand, the higher is desirable. If the ligand is multidentate like a chelate, the bond strength can be further increased. Generally, when the strength of the coordination bond is higher, the conventional long molecular chain ligand is efficiently substituted, and higher electrical conductivity is easily obtained. The value of the complex stability constant Logbeta ₁ specific ligand will vary by semiconductor quantum dot material constituting the semiconductor quantum dot is changed, the specific ligand, the molecular chain length is short and coordinated Since it is easy, it is applicable to various semiconductor quantum dot materials.
logβ ₁ is more preferably 8 or more, and further preferably 10 or more.

As a method of obtaining the complex stability constant logβ ₁ between the specific ligand and the metal atom of the semiconductor quantum dot in the semiconductor film of the present invention, spectroscopy, magnetic resonance spectroscopy, potentiometry, solubility measurement, chromatography, There are calorimetry, freezing point measurement, vapor pressure measurement, relaxation measurement, viscosity measurement, surface tension measurement and the like.
In the present invention, Sc-Database ver. The complex stability constant was determined by using 5.85 (Academic Software) (2010). logβ ₁ is Sc-Databese ver. If not in 5.85, A. E. Martell and R.W. M.M. Values described in Smith, Critical Stability Constants are used. If logβ ₁ is not described in Critical Stability Constants, the above-described measurement method is used, or the program PKAS method for calculating the complex stability constant (AE Martinell et al., The Determination and Use of Stability) Logβ ₁ is calculated using Constants, VCH (1988).
Hereinafter, the specific ligand and semiconductor quantum dot which comprise the semiconductor film of this invention are demonstrated.
First, the details of the specific ligand will be described.

[At least one coordination selected from a ligand represented by the general formula (A), a ligand represented by the general formula (B), and a ligand represented by the general formula (C) (Specific ligand)]
The semiconductor film of the present invention contains at least one specific ligand.
The semiconductor film of the present invention may contain two or more kinds of specific ligands. That is, all of the coordination bonds in the assembly of semiconductor quantum dots included in the semiconductor film of the present invention may be bonds by one specific ligand, and some of the coordination bonds may be represented by the general formula (A ), And the other coordination bond may be a bond by the specific ligand represented by the general formula (B).

In general formula (A), X ¹ represents —SH or —OH, and A ¹ and B ¹ each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents. However, ^{when A 1} and ^{B 1} are both hydrogen atom, ^{X 1} represents a -OH.
In general formula (B), X ² represents —SH or —OH, and A ² and B ² each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents.
In the general formula (C), A ³ represents a hydrogen atom or atoms of 1 to 10 substituents. However, A ³ does not end with NH _{2 at the} end.
In addition, the ligand represented by the general formula (A), the ligand represented by the general formula (B), and the ligand represented by the general formula (C) are different from each other. .

A ¹ and B ^{1 in} the general formula (A), A ² and B ² in the general formula (B), and A ³ in the general formula (C) have 1 to 10 atoms excluding the amino group (—NH ₂ ). When represented by the following substituents, the substituent having 1 to 10 atoms includes an alkyl group having 1 to 3 carbon atoms [methyl group, ethyl group, propyl group, and isopropyl group], and 2 to 3 carbon atoms. Alkenyl group [ethenyl group and propenyl group], alkynyl group having 2 to 4 carbon atoms [ethynyl group, propynyl group, etc.], cyclopropyl group, alkoxy group having 1 to 2 carbon atoms [methoxy group and ethoxy group], carbon number 2 to 3 acyl groups [acetyl group and propionyl group], C2 to C3 alkoxycarbonyl groups [methoxycarbonyl group and ethoxycarbonyl group], C2 acyloxy groups [ Cetyloxy group], C2-acylamino group [acetylamino group], C1-C3 hydroxyalkyl group [hydroxymethyl group, hydroxyethyl group, hydroxypropyl group], aldehyde group [-COH], hydroxy group [- OH], a carboxy group [-COOH], a sulfo group [-SO ₃ H], a phospho group [-OPO _{(OH) 2],} carbamoyl group [-CONH _2], a cyano group [-CN], the isocyanate group [-N = C = O], a thiol group [-SH], a nitro group [-NO _2], nitroxy group [-ONO _2], isothiocyanate group [-NCS], cyanate group [-OCN], thiocyanate group [-SCN] An acetoxy group [OCOCH ₃ ], an acetamide group [NHCOCH ₃ ], a formyl group [—CHO], a formyloxy group [—O CHO], formamide group [—NHCHO], sulfamino group [—NHSO ₃ H], sulfino group [—SO ₂ H], sulfamoyl group [—SO ₂ NH ₂ ], phosphono group [—PO ₃ H ₂ ], acetyl group Examples include [—COCH ₃ ], a halogen atom [fluorine atom, chlorine atom, bromine atom and the like], an alkali metal atom [lithium atom, sodium atom, potassium atom and the like] and the like.
However, A ³ does not end with NH _{2 at the} end. This is because A ³ does not become an amino group (—NH ₂ ), nor does it become a group having an amino group such as —CH ₂ —NH ₂ in which a part of the hydrogen atoms of the methyl group is substituted with an amino group. Means.

The substituent may further have a substituent other than an amino group (—NH ₂ ) as long as the total number of atoms is 10 or less.
Since the number of atoms of the substituent is 10 or less, steric hindrance due to the ligand can be suppressed and the semiconductor quantum dots can be brought close to each other, so that the electrical conductivity of the semiconductor film can be increased.
From the viewpoint of shortening the distance between the semiconductor quantum dots, the substituent is preferably 7 atoms or less, and more preferably a hydrogen atom.

X ¹ in the general formula (A) and X ² in the general formula (B) are preferably —OH (hydroxy group) from the viewpoint of solubility when the specific ligand is an alcohol solution.

Specific examples of the compound represented by the general formula (A) include 1-thioglycerol, dimercaprol, 1-mercapto-2-butanol, 1-mercapto-2-pentanol and the like.
Specific examples of the compound represented by the general formula (B) include 3-mercapto-1-propanol and 2,3-dimercapto-1-propanol.
Specific examples of the compound represented by the general formula (C) include thioglycolic acid.

  The specific ligand is a derivative of a compound represented by the general formula (A) such as a 3-mercapto-1-propanol derivative or a thioglycolic acid derivative, a derivative of a compound represented by the general formula (B), Alternatively, a derivative of the compound represented by the general formula (C) may be used.

By using the above compound as the specific ligand, a higher photocurrent value can be obtained as compared with the case where ethanedithiol is used as the ligand. Among them, in particular, 3-mercapto-1-propanol or 2,3-dimercapto-1-propanol represented by the general formula (B) or thioglycolic acid represented by the general formula (C) is used as a ligand. In some cases, the effect of increasing Ip / Id ₋ is large.
Among the above three, Ip / Id can be further increased by using 3-mercapto-1-propanol or thioglycolic acid. Therefore, it can be seen that in the general formulas (B) and (C), A ² and A ³ are preferably hydrogen atoms.

Further, when the specific ligand is a ligand represented by the general formula (A) or the general formula (C), A ¹ and B ¹ in the general formula (A), and A in the general formula (C) ^{Even if 3} is a substituent having a relatively large number of atoms such as an ethyl group or a propyl group, a high Ip / Id can be obtained.
This is probably due to the following two reasons. That is, a dangling bond (dangling bond in an atom) of a metal atom in a semiconductor quantum dot, -SH represented by the general formula (A), and SH (or OH) represented by X ¹ are 5 By forming a member ring chelate, it becomes easy to obtain a high complex stability constant (log β). In the ligand represented by the general formula (C), the SH represented by the general formula (C), the OH of the carboxy group, and the dangling bond of the metal atom in the semiconductor quantum dot are a five-membered ring. By forming a chelate, a high complex stability constant (log β) can be easily obtained.
At the same time, steric hindrance between the semiconductor quantum dots is suppressed by chelate coordination between the metal atom and the specific ligand in the semiconductor quantum dots, and as a result, high electrical conductivity is easily obtained.

In the general formula (A), such a coordination mechanism includes the SH sulfur atom represented by the general formula (A), the carbon atom to which B ¹ is bonded, the carbon atom to which A ¹ is bonded, and X ^This is established in a five-atom relationship between the oxygen atom of OH represented by ¹ or the sulfur atom of SH and the metal atom of the semiconductor quantum dot. Therefore, even if A ¹ and B ¹ in the general formula (A) are substituents having a large number of atoms, it is considered that high coordination stability is obtained and electrical conductivity is likely to be high.
The same applies to the ligand represented by the general formula (C). The sulfur atom of SH represented by the general formula (C), the carbon atom to which A ¹ is bonded, and the carboxy represented by the general formula (C). It is established in the relationship of five atoms, that is, the carbon atom of carbonyl (> C═O) constituting the group, the oxygen atom of OH constituting the carboxy group represented by the general formula (C), and the metal atom of the semiconductor quantum dot. Is. Therefore, even if A ³ in the general formula (C) is a substituent having a large number of atoms, it is considered that high coordination stability is obtained and electrical conductivity is likely to be high.

[Assembly of semiconductor quantum dots having metal atoms]
The semiconductor film of the present invention has an aggregate of semiconductor quantum dots. Moreover, the semiconductor quantum dot has at least one kind of metal atom.
The aggregate of semiconductor quantum dots refers to a form in which a large number (for example, 100 or more per 1 μm ² square) of semiconductor quantum dots are arranged close to each other.
The “semiconductor” in the present invention means that the specific resistance value is 10 ⁻² Ωcm or more and 10 ⁸ Ωcm or less.

The semiconductor quantum dot is a semiconductor particle having a metal atom. In the present invention, the metal atom includes a semimetal atom typified by Si atom.
Examples of the semiconductor quantum dot material constituting the semiconductor quantum dot include a general semiconductor crystal [a) a group IV semiconductor, b) a compound semiconductor of group IV-IV, group III-V, or group II-VI, c) II. Compound semiconductor composed of a combination of three or more of Group, Group III, Group IV, Group V, and Group VI elements) (particles of 0.5 nm to less than 100 nm). Specific examples include semiconductor materials having a relatively narrow band gap such as PbS, PbSe, InN, InAs, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, Si, and InP.
The semiconductor quantum dot should just contain at least 1 type of semiconductor quantum dot material.

  The semiconductor quantum dot material preferably has a bulk band gap of 1.5 eV or less. By using such a semiconductor material having a relatively narrow band gap, high conversion efficiency can be realized when the semiconductor film of the present invention is used, for example, in a photoelectric conversion layer of a solar cell.

  The semiconductor quantum dot may have a core-shell structure in which a semiconductor quantum dot material is a nucleus (core) and the semiconductor quantum dot material is covered with a coating compound. Examples of the coating compound include ZnS, ZnSe, ZnTe, ZnCdS, and the like.

  Among the above, the semiconductor quantum dot material is preferably PbS or PbSe from the viewpoint of easy synthesis of the semiconductor quantum dots. It is also desirable to use InP and InN from the viewpoint of low environmental load and from the viewpoint of electrical conductivity.

Furthermore, when the semiconductor film of the present invention is applied to a solar cell application, the semiconductor quantum dot may have a narrower band gap in view of enhancement of photoelectric conversion efficiency due to a multi-exciton generation effect called a multi-exciton generation effect. preferable. Specifically, it is desirable that it is 1.0 eV or less.
From the viewpoint of narrowing the band gap and enhancing the multi-exciton generation effect, the semiconductor quantum dot material is preferably PbS, PbSe, or InSb.

The average particle size of the semiconductor quantum dots is desirably 2 nm to 15 nm. In addition, the average particle diameter of a semiconductor quantum dot means the average particle diameter of ten semiconductor quantum dots. A transmission electron microscope may be used to measure the particle size of the semiconductor quantum dots.
In general, semiconductor quantum dots include particles of various sizes from several nm to several tens of nm. In the semiconductor quantum dot, when the average particle diameter of the quantum dot is reduced to a size equal to or less than the Bohr radius of the underlying electron, a phenomenon occurs in which the band gap of the semiconductor quantum dot changes due to the quantum size effect. For example, it is said that II-VI semiconductors have a relatively large Bohr radius, and PbS has a thickness of about 18 nm. InP, which is a III-V group semiconductor, is said to have a Bohr radius of about 10 nm to 14 nm.
Therefore, for example, if the average particle size of the semiconductor quantum dots is 15 nm or less, the band gap can be controlled by the quantum size effect.

In particular, when the semiconductor film of the present invention is applied to a solar cell, it is important to adjust the band gap to an optimum value by the quantum size effect regardless of the semiconductor quantum dot material. However, since the band gap increases as the average particle size of the semiconductor quantum dots decreases, a larger change in the band gap can be expected if the average particle size of the semiconductor quantum dots is 10 nm or less. Even if the semiconductor quantum dot is a narrow gap semiconductor as a result, it is easy to adjust the band gap optimal for the spectrum of sunlight. Therefore, the size of the quantum dot is more preferably 10 nm or less. Further, when the average particle size of the semiconductor quantum dots is small and the quantum confinement is remarkable, there is an advantage that the enhancement of the multi-exciton generation effect can be expected.
On the other hand, the average particle diameter of the semiconductor quantum dots is preferably 2 nm or more. By setting the average particle diameter of the semiconductor quantum dots to 2 nm or more, the effect of quantum confinement does not become too strong, and the band gap can be easily set to the optimum value. Further, by setting the average particle diameter of the semiconductor quantum dots to 2 nm or more, it is possible to easily control the crystal growth of the semiconductor quantum dots in the synthesis of the semiconductor quantum dots.

  The thickness of the semiconductor film is not particularly limited, but is preferably 10 nm or more, and more preferably 50 nm or more from the viewpoint of obtaining high electrical conductivity. In addition, the thickness of the semiconductor film is preferably 300 nm or less from the viewpoint of excessive carrier concentration and ease of manufacture.

  Although the manufacturing method of the semiconductor film of the present invention is not particularly limited, it is manufactured by the semiconductor film manufacturing method of the present invention from the viewpoint of shortening the interval between the semiconductor quantum dots and arranging the semiconductor quantum dots densely. It is preferable to do.

<Semiconductor film manufacturing method>
In the method for producing a semiconductor film of the present invention, a semiconductor quantum dot dispersion liquid containing a semiconductor quantum dot, a first ligand coordinated to the semiconductor quantum dot, and a first solvent is applied onto the substrate. In the semiconductor quantum dot assembly forming step for forming the dot assembly, and the semiconductor quantum dot assembly, the molecular chain length is shorter than that of the first ligand and the arrangement represented by the general formula (A) A second ligand and a second solvent which are at least one selected from a ligand, a ligand represented by formula (B), and a ligand represented by formula (C) A ligand exchanging step of exchanging a first ligand coordinated to a semiconductor quantum dot with a second ligand by applying a solution containing

In general formula (A), X ¹ represents —SH or —OH, and A ¹ and B ¹ each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents. However, ^{when A 1} and ^{B 1} are both hydrogen atom, ^{X 1} represents a -OH.
In general formula (B), X ² represents —SH or —OH, and A ² and B ² each independently represent a hydrogen atom or a substituent having 1 to 10 atoms (excluding an amino group). Represents.
In the general formula (C), A ³ represents a hydrogen atom or atoms of 1 to 10 substituents. However, A ³ does not end with NH _{2 at the} end.

  In the method for producing a semiconductor film of the present invention, the semiconductor quantum dot assembly forming step and the ligand exchange step may be repeated, and further, a dispersion drying step for drying the semiconductor quantum dot dispersion, a ligand solution A solution drying step for drying the substrate, a washing step for washing the semiconductor quantum dot aggregate on the substrate, and the like.

  In the method for producing a semiconductor film of the present invention, a semiconductor quantum dot aggregate is formed on a substrate by applying a semiconductor quantum dot dispersion on the substrate in the semiconductor quantum dot aggregate formation step. At this time, since the semiconductor quantum dots are dispersed in the first solvent by the first ligand having a molecular chain length longer than that of the second ligand, the semiconductor quantum dots are less likely to be in an aggregated bulk shape. . Therefore, by applying the semiconductor quantum dot dispersion liquid onto the substrate, the semiconductor quantum dot aggregate can be configured so that the semiconductor quantum dots are arranged one by one.

Next, by applying a solution of the specific ligand to the assembly of semiconductor quantum dots by the ligand exchange step, the molecular chain length is longer than that of the second ligand coordinated to the semiconductor quantum dots. Ligand exchange between the first ligand and the specific ligand is performed. The specific ligand has at least one thiol group (—SH) in the molecule as shown in the general formulas (A) to (C). As described above, the thiol group has a high complex stability constant. In the general formulas (A) and (B), the metal atom of the semiconductor quantum dot and —SH represented by X ¹ (or X ² ) are used. Or it is thought that complex formation with -OH is accelerated | stimulated. In the general formula (C), it is considered that the complex formation between the metal atom of the semiconductor quantum dot, -SH and -OH of the carboxy group is promoted.
Therefore, the specific ligand replaces the first ligand having a molecular chain length longer than that of the second ligand and coordinates with the semiconductor quantum dot. It is thought that it is easy to approach. When the semiconductor quantum dots are brought close to each other, it is considered that the electrical conductivity of the aggregate of semiconductor quantum dots is increased and a semiconductor film having a high photocurrent value can be obtained.
Furthermore, it is considered that the semiconductor quantum dots are connected to each other by a coordinate bond through a specific ligand, whereby the aggregate of semiconductor quantum dots becomes a strong semiconductor film and hardly peels off from the substrate.

[Semiconductor quantum dot assembly formation process]
In the semiconductor quantum dot assembly forming step, a semiconductor quantum dot dispersion liquid containing a semiconductor quantum dot, a first ligand coordinated to the semiconductor quantum dot, and a first solvent is applied on the substrate to form the semiconductor quantum dot To form an aggregate.
The semiconductor quantum dot dispersion liquid may be applied to the substrate surface, or may be applied to another layer provided on the substrate.
Examples of other layers provided on the substrate include an adhesive layer and a transparent conductive layer for improving the adhesion between the substrate and the assembly of semiconductor quantum dots.

-Semiconductor quantum dot dispersion-
The semiconductor quantum dot dispersion liquid contains a semiconductor quantum dot having a metal atom, a first ligand, and a first solvent.
The semiconductor quantum dot dispersion liquid may further contain other components as long as the effects of the present invention are not impaired.

(Semiconductor quantum dots)
The details of the semiconductor quantum dots containing metal atoms contained in the semiconductor quantum dot dispersion liquid are as described above, and the preferred embodiments are also the same.
In addition, the content of the semiconductor quantum dots in the semiconductor quantum dot dispersion liquid is preferably 1 mg / ml to 100 mg / ml, and more preferably 5 mg / ml to 40 mg / ml.
When the content of the semiconductor quantum dots in the semiconductor quantum dot dispersion liquid is 1 mg / ml or more, the semiconductor quantum dot density on the substrate is increased, and a good film is easily obtained. On the other hand, when the content of the semiconductor quantum dot quantum dots is 100 mg / ml or less, the film thickness of the film obtained when the semiconductor quantum dot dispersion liquid is applied once is hardly increased. Therefore, the ligand exchange of the 1st ligand coordinated to the semiconductor quantum dot in a film | membrane can fully be performed.

(First ligand)
The first ligand contained in the semiconductor quantum dot dispersion liquid functions as a ligand coordinated to the semiconductor quantum dot and has a molecular structure that is likely to cause steric hindrance, and the semiconductor quantum in the first solvent. It also serves as a dispersant for dispersing dots.
The first ligand has a longer molecular chain length than the second ligand described later. The length of the molecular chain is determined by the length of the main chain when there is a branched structure in the molecule. The ligand represented by the general formula (A), the ligand represented by the general formula (B), and the ligand represented by the general formula (C), which are the second ligands, Dispersion in an organic solvent system is difficult and does not correspond to the first ligand. Here, “dispersion” refers to a state where there is no sedimentation or turbidity of particles.

From the viewpoint of improving the dispersion of the semiconductor quantum dots, the first ligand is preferably a ligand having at least 6 carbon atoms in the main chain, and a ligand having 10 or more carbon atoms in the main chain. Is more desirable.
Specifically, the first ligand may be either a saturated compound or an unsaturated compound. Decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, erucic acid, oleylamine , Dodecylamine, dodecanethiol, 1,2-hexadecanethiol, trioctylphosphine oxide, cetrimonium bromide and the like.
The first ligand is preferably one that hardly remains in the film when the semiconductor film is formed. Specifically, the molecular weight is preferably small.
Among the above, the first ligand is preferably at least one of oleic acid and oleylamine, from the viewpoint of making the semiconductor quantum dots have dispersion stability and hardly remaining in the semiconductor film.

  The content of the first ligand in the semiconductor quantum dot dispersion is desirably 10 mmol / l to 200 mmol / l with respect to the total volume of the semiconductor quantum dot dispersion.

(First solvent)
The first solvent contained in the semiconductor quantum dot dispersion liquid is not particularly limited, but is preferably a solvent that hardly dissolves the semiconductor quantum dots and easily dissolves the first ligand. The first solvent is preferably an organic solvent, and specific examples include alkanes [n-hexane, n-octane, etc.], benzene, toluene and the like.
Only 1 type may be sufficient as a 1st solvent and the mixed solvent which mixed 2 or more types may be sufficient as it.

Among the above, the first solvent is preferably a solvent that hardly remains in the formed semiconductor film. If the solvent has a relatively low boiling point, the content of residual organic substances can be suppressed when the semiconductor film is finally obtained.
Furthermore, those with good wettability to the substrate are naturally preferable. For example, when coating on a glass substrate, alkanes such as hexane and octane are more preferable.

  The content of the first solvent in the semiconductor quantum dot dispersion is preferably 90% by mass to 98% by mass with respect to the total mass of the semiconductor quantum dot dispersion.

-Board-
The semiconductor quantum dot dispersion is applied on the substrate.
There is no restriction | limiting in particular about the shape of a board | substrate, a structure, a magnitude | size, It can select suitably according to the objective. The structure of the substrate may be a single layer structure or a laminated structure. As the substrate, for example, a substrate made of glass, an inorganic material such as YSZ (Yttria-Stabilized Zirconia), a resin, a resin composite material, or the like can be used. Among these, a substrate made of a resin or a resin composite material is preferable from the viewpoint of light weight and flexibility.

  The resins include polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polystyrene, polycarbonate, polysulfone, polyethersulfone, polyarylate, allyl diglycol carbonate, polyamide, polyimide, polyamideimide, polyetherimide, poly Fluorine resins such as benzazole, polyphenylene sulfide, polycycloolefin, norbornene resin, polychlorotrifluoroethylene, liquid crystal polymer, acrylic resin, epoxy resin, silicone resin, ionomer resin, cyanate resin, crosslinked fumaric acid diester, cyclic polyolefin, aromatic Synthetic resins such as aromatic ethers, maleimide-olefins, cellulose, episulfide compounds, etc.

  As a composite material of an inorganic material and a resin, a composite plastic material of a resin and the following inorganic material can be given. That is, composite plastic material of resin and silicon oxide particles, composite plastic material of resin and metal nanoparticles, composite plastic material of resin and inorganic oxide nanoparticles, composite plastic material of resin and inorganic nitride nanoparticles, Composite plastic material of resin and carbon fiber, Composite plastic material of resin and carbon nanotube, Composite plastic material of resin and glass ferrule, Composite plastic material of resin and glass fiber, Composite plastic material of resin and glass bead , Composite plastic material of resin and clay mineral, composite plastic material of resin and particles having mica derivative crystal structure, laminated plastic material having at least one bonding interface between resin and thin glass, inorganic layer and organic By laminating layers alternately, at least once Like composite materials having a barrier property having a bonding interface is.

  Using a stainless steel substrate or a metal multilayer substrate in which stainless steel and a dissimilar metal are laminated, an aluminum substrate, or an aluminum substrate with an oxide film whose surface insulation is improved by subjecting the surface to oxidation treatment (for example, anodization treatment). Also good.

A substrate made of resin or resin composite material (resin substrate or resin composite material substrate) is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, workability, low air permeability, low moisture absorption, etc. It is preferable. The resin substrate and the resin composite material substrate may include a gas barrier layer for preventing permeation of moisture, oxygen, etc., an undercoat layer for improving the flatness of the resin substrate and the adhesion to the lower electrode, and the like. Good.
In addition, a lower electrode, an insulating film, or the like may be provided on the substrate. In that case, a semiconductor quantum dot dispersion liquid is applied to the lower electrode or the insulating film on the substrate.

  Although there is no restriction | limiting in particular in the thickness of a board | substrate, 50 micrometers-1000 micrometers are preferable, and it is more preferable that they are 50 micrometers-500 micrometers. When the thickness of the substrate is 50 μm or more, the flatness of the substrate itself is improved, and when the thickness of the substrate is 1000 μm or less, the flexibility of the substrate itself is improved and the semiconductor film can be used as a flexible semiconductor device. It becomes easier.

The method for applying the semiconductor quantum dot dispersion on the substrate is not particularly limited, and examples thereof include a method of applying the semiconductor quantum dot dispersion on the substrate, a method of immersing the substrate in the semiconductor quantum dot dispersion, and the like.
More specifically, as a method of applying the semiconductor quantum dot dispersion liquid on the substrate, spin coating method, dipping method, ink jet method, dispenser method, screen printing method, letterpress printing method, intaglio printing method, spray coating method, etc. The liquid phase method can be used.
In particular, the inkjet method, the dispenser method, the screen printing method, the relief printing method, and the intaglio printing method can form a coating film at an arbitrary position on the substrate and do not require a patterning step after the film formation. Therefore, the process cost can be reduced.

[Ligand exchange step]
In the ligand exchange step, the semiconductor quantum dot aggregate formed on the substrate by the semiconductor quantum dot aggregate formation step has a molecular chain length shorter than that of the first ligand, and a general formula (A ), A ligand represented by the general formula (B), and a second ligand that is at least one selected from a ligand represented by the general formula (C) And a solution containing the second solvent, the first ligand coordinated to the semiconductor quantum dots as the second ligand (specific ligand) contained in the ligand solution Exchange.

-Ligand solution-
The ligand solution contains at least a second ligand (specific ligand) and a second solvent.
The ligand solution may further contain other components as long as the effects of the present invention are not impaired.

(Second ligand)
The second ligand is the specific ligand described above, and the molecular chain length is shorter than that of the first ligand. The method for determining the length of the molecular chain length of the ligand is as described in the description of the first ligand.
The details of the specific ligand are also as described above.
In addition, when using alcohol as a 2nd solvent which a ligand solution contains, it is preferable that a specific ligand has a hydroxyl group (OH) in a molecule | numerator. When the specific ligand has a hydroxy group in the molecular structure, miscibility with alcohol can be increased. Moreover, when performing ligand exchange of a semiconductor quantum dot by the ligand solution containing the specific ligand which has a hydroxyl group, when alcohol is used as a 2nd solvent, ligand exchange is efficiently performed. It can be carried out.

  The content of the specific ligand in the ligand solution is preferably 5 mmol / l to 200 mmol / l, and more preferably 10 mmol to 100 mmol / l with respect to the total volume of the ligand solution.

(Second solvent)
The second solvent contained in the ligand solution is not particularly limited, but is preferably a solvent that easily dissolves the specific ligand.
Such a solvent is preferably an organic solvent having a high dielectric constant, and examples thereof include ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, and propanol.
Only 1 type may be sufficient as a 2nd solvent, and the mixed solvent which mixed 2 or more types may be sufficient as it.

Among the above, the second solvent is preferably a solvent that hardly remains in the formed semiconductor film. From the viewpoint of easy drying and easy removal by washing, alcohol or alkane having a low boiling point is preferable, and methanol, ethanol, n-hexane, or n-octane is more preferable.
In addition, the second solvent is preferably not mixed with the first solvent. For example, when an alkane such as hexane or octane is used as the first solvent, the second solvent is methanol or acetone. It is preferable to use a polar solvent such as
In addition, content of the 2nd solvent in a ligand solution is the remainder which deducted content of the specific ligand from the ligand solution total mass.

  The method for applying the ligand solution to the aggregate of semiconductor quantum dots is the same as the method for applying the semiconductor quantum dot dispersion on the substrate, and the preferred embodiment is also the same.

The semiconductor quantum dot assembly forming step and the ligand exchange step may be repeated. By repeating the semiconductor quantum dot assembly formation step and the ligand exchange step, the electrical conductivity of the semiconductor film having an assembly of semiconductor quantum dots coordinated with a specific ligand is increased, and the thickness of the semiconductor film is increased. Can be thickened.
The semiconductor quantum dot assembly formation step and the ligand exchange step may be repeated separately, but the ligand exchange step is performed after the semiconductor quantum dot assembly formation step is performed. It is preferable to repeat the cycle. By repeating the set of the semiconductor quantum dot assembly forming step and the ligand exchange step, unevenness of ligand exchange can be easily suppressed.
In addition, when performing a semiconductor quantum dot aggregate formation process and a ligand exchange process repeatedly, it is preferable to fully dry a film | membrane for every cycle.

It is expected that the photocurrent value of the semiconductor film increases as the exchange rate of the semiconductor quantum dot aggregate to the specific ligand in the ligand exchange increases.
In addition, it is sufficient that the ligand exchange between the first ligand and the second ligand (specific ligand) of the semiconductor quantum dot is performed in at least a part of the semiconductor quantum dot assembly. , 100% (number) may not replace the specific ligand.

(Washing process)
Furthermore, the manufacturing method of the semiconductor film of this invention may have the washing | cleaning process of wash | cleaning the semiconductor quantum dot aggregate | assembly on a board | substrate.
By having the washing step, excess ligands and ligands desorbed from the semiconductor quantum dots can be removed. Further, the remaining solvent and other impurities can be removed. The cleaning of the semiconductor quantum dot aggregate is performed by pouring at least one of the first solvent and the second solvent on the semiconductor quantum dot aggregate, or by removing the substrate on which the semiconductor quantum dot aggregate or the semiconductor film is formed. What is necessary is just to immerse in at least one of 1 solvent and 2nd solvent.
The cleaning by the cleaning process may be performed after the semiconductor quantum dot assembly forming process or may be performed after the ligand exchange process. Moreover, you may carry out after the repetition of the set of a semiconductor quantum dot aggregate formation process and a ligand exchange process.

(Drying process)
The manufacturing method of the semiconductor film of this invention may have a drying process.
The drying step may be a dispersion drying step for drying the solvent remaining in the semiconductor quantum dot assembly after the semiconductor quantum dot assembly forming step, or the ligand solution may be replaced with a ligand solution after the ligand exchange step. It may be a solution drying step for drying. Moreover, the comprehensive process performed after the repetition of the set of a semiconductor quantum dot aggregate formation process and a ligand exchange process may be sufficient.

A semiconductor film is manufactured on the substrate through the steps described above.
The obtained semiconductor film has high electrical conductivity and a high photocurrent value because the semiconductor quantum dots are coordinated with a specific ligand that is shorter than the conventional one. In addition, since the specific ligand has a high complex stability constant, the semiconductor film of the present invention composed of the semiconductor quantum dots and the specific ligand has stable coordination bonds, excellent film strength, Peeling is also suppressed.

<Electronic device>
Although the use of the semiconductor film of the present invention is not limited, the semiconductor film of the present invention has photoelectric conversion characteristics and hardly peels off, and thus can be suitably applied to various electronic devices having a semiconductor film or a photoelectric conversion film. .
Specifically, the semiconductor film of the present invention includes a photoelectric conversion film of a solar cell, a light emitting diode (LED), a semiconductor layer (active layer) of a thin film transistor, a photoelectric conversion film of an indirect radiation imaging apparatus, and a visible to infrared region. It can be suitably applied to a photodetector or the like.

<Solar cell>
A solar cell will be described as an example of an electronic device including the semiconductor film of the present invention or the semiconductor film manufactured by the method of manufacturing a semiconductor film of the present invention.
For example, a pn junction solar cell can be obtained by using a semiconductor film device having a pn junction including a p-type semiconductor layer including the semiconductor film of the present invention and an n-type semiconductor layer.
As a more specific embodiment of the pn junction solar cell, for example, a p-type semiconductor layer and an n-type semiconductor layer are provided adjacent to each other on a transparent conductive film formed on a transparent substrate. A form in which a metal electrode is formed on the n-type semiconductor layer can be mentioned.

An example of a pn junction solar cell will be described with reference to FIG.
FIG. 1 shows a schematic cross-sectional view of a pn junction solar cell 100 according to an embodiment of the present invention. A pn junction solar cell 100 includes a transparent substrate 10, a transparent conductive film 12 provided on the transparent substrate 10, a p-type semiconductor layer 14 formed of the semiconductor film of the present invention on the transparent conductive film 12, and p An n-type semiconductor layer 16 and a metal electrode 18 provided on the n-type semiconductor layer 16 are stacked on the type semiconductor layer 14.
When the p-type semiconductor layer 14 and the n-type semiconductor layer 16 are laminated adjacent to each other, a pn junction solar cell can be obtained.

As the transparent substrate 10, the same material as the substrate used in the method for producing a semiconductor film of the present invention can be used as long as it is transparent. Specifically, a glass substrate, a resin substrate, etc. are mentioned. In the present invention,
Examples of the transparent conductive film 12 include films made of In ₂ O ₃ : Sn (ITO), SnO ₂ : Sb, SnO ₂ : F, ZnO: Al, ZnO: F, CdSnO _{4, and the} like.

As described above, the semiconductor film of the present invention is used for the p-type semiconductor layer 14.
The n-type semiconductor layer 16 is preferably a metal oxide. Specific examples include metal oxides containing at least one of Ti, Zn, Sn, and In, and more specific examples include TiO ₂ , ZnO, SnO ₂ , and IGZO. The n-type semiconductor layer is preferably formed by a wet method (also referred to as a liquid phase method) in the same manner as the p-type semiconductor layer from the viewpoint of manufacturing cost.
As the metal electrode 18, Pt, Al, Cu, Ti, Ni, or the like can be used.

  Examples will be described below, but the present invention is not limited to these examples.

<Fabrication of semiconductor film device>
[Preparation of Semiconductor Quantum Dot Dispersion 1]
First, a PbS particle dispersion in which PbS particles were dispersed in toluene was prepared. As the PbS particle dispersion, PbS core Evidot (nominal particle size: 3.3 nm, 20 mg / ml, solvent toluene) manufactured by Evdent technology was used.
Next, 2 ml of the PbS particle dispersion was taken into the centrifuge tube, 38 μl of oleic acid was added, and then 20 ml of toluene was added to dilute the concentration of the dispersion. Thereafter, ultrasonic dispersion was performed on the PbS particle dispersion, and the PbS particle dispersion was thoroughly stirred. Next, 40 ml of ethanol was added to the PbS particle dispersion, followed by ultrasonic dispersion, and centrifugation was performed at 10,000 rpm, 10 minutes, and 3 ° C. After discarding the supernatant in the centrifuge tube, 20 ml of octane was added to the centrifuge tube and subjected to ultrasonic dispersion, and the precipitated quantum dots were well dispersed in the octane solvent. The obtained dispersion was concentrated using a rotary evaporator (35 hpa, 40 ° C.), and as a result, about 4 ml of semiconductor quantum dot dispersion 1 (octane solvent) having a concentration of about 10 mg / ml was obtained.
The average particle diameter of the PbS particles contained in the semiconductor quantum dot dispersion liquid 1 was 3 nm.
The average particle size of the semiconductor quantum dots is TEM (Transmission Electron Microscope).
The average of 10 semiconductor quantum dots by photographic observation in the transmission electron microscope) measurement. A TEI 80-300 manufactured by FEI Co. was used as a measuring device.

[Preparation of Semiconductor Quantum Dot Dispersion 2]
First, InP particles were synthesized, and an octane dispersion of InP particles coordinated with oleylamine was prepared.

-Preparation of octane dispersion of oleylamine modified InP particles-
In a glove box under a N ₂ gas atmosphere, put 30 ml of 1-octadecene, 1.81 ml of oleylamine, 0.60 g of anhydrous indium chloride, 0.49 ml of trisdimethylaminophosphine, and a magnetic stirring bar in a three-necked round bottom flask. It was. Next, the three-necked round bottom flask was taken out from the glove box in a state of being sealed with a stopper with a three-way valve, and set in an aluminum block thermostat with a magnetic stirrer. Thereafter, the three-way valve was operated, N ₂ gas was passed through the flask, and heating of the aluminum block thermostatic bath was started while the mixture was vigorously stirred with a magnetic stirring bar. The temperature of the aluminum block thermostat was raised to 150 ° C. in about 30 minutes and held there for 5 hours. Thereafter, the heating was stopped, and the three-necked round bottom flask was cooled to room temperature using a blower fan.

The product was taken out from the three-necked round bottom flask, and unreacted products and by-products were removed by centrifugation using a centrifuge. The product (InP particles) was purified using ultra-dehydrated toluene as a good solvent and dehydrated ethanol as a poor solvent. Specifically, the process of dissolving the product in a good solvent, redispersing the dissolved InP particles in a poor solvent, and centrifuging the resulting InP particle dispersion was repeated. An ultrasonic cleaner was used for redispersion. After repeated centrifugation of the InP particle dispersion, dehydrated ethanol remaining in the InP particle dispersion was removed by distillation under reduced pressure using a rotary evaporator. Finally, an octane dispersion having an oleylamine-modified InP particle concentration of 1 mg / ml in which the extracted InP particles were dispersed in octane was obtained.
Observation of the obtained InP particles by TEM revealed that the average particle size was about 4 nm.

-Preparation of semiconductor quantum dot dispersion 2-
In the preparation of the semiconductor quantum dot dispersion 1, the semiconductor quantum dot dispersion 2 having an InP particle concentration of 1 mg / 1 ml was similarly used except that an octane dispersion of oleylamine-modified InP particles was used instead of the PbS particle dispersion. Prepared.

(Preparation of ligand solution)
1 mmol of the ligands shown in the “Compound Name” column of the “Ligand” column of Table 1 was separated and dissolved in 10 ml of methanol to prepare a ligand solution having a concentration of 0.1 mol / l. In order to promote the dissolution of the ligand in the ligand solution, ultrasonic irradiation was performed so that the ligand remained as little as possible.

〔substrate〕
As the substrate, a substrate having 65 pairs of comb-shaped platinum electrodes shown in FIG. 2 on a quartz glass was prepared. As the comb-type platinum electrode, a comb-type electrode (model number 012126, electrode interval 5 μm) manufactured by BAS was used.

[Manufacture of semiconductor films]
(1) Semiconductor quantum dot aggregate formation process The prepared semiconductor quantum dot dispersion liquid 1 or semiconductor quantum dot dispersion liquid 2 was dropped on a substrate, and then spin coated at 2500 rpm to obtain a semiconductor quantum dot aggregate film.

(2) Ligand exchange step Further, a methanol solution (ligand solution) of the ligands shown in Table 1 is dropped on the semiconductor quantum dot assembly film, and then spin-coated at 2500 rpm to form the semiconductor film. Obtained.

(3) Cleaning process 1
Next, only methanol, which is a solvent for the ligand solution, was dropped on the semiconductor film and spin-coated.

(4) Cleaning process 2
Furthermore, only the octane solvent was dropped on the semiconductor film after the cleaning in the cleaning step 1 and spin-coated.

By repeating the series of steps (1) to (4) for 15 cycles, a semiconductor film having a thickness of 100 nm made of an assembly of PbS quantum dots and subjected to ligand exchange was obtained.
As described above, a semiconductor film device having a semiconductor film on a substrate was produced.

Table 1 shows the combinations of the semiconductor quantum dot dispersion liquid and the ligand solution in Examples and Comparative Examples. In Table 1, “PbS” in the “seed” column of the “semiconductor quantum dot” column uses the semiconductor quantum dot dispersion 1, and “InP” indicates the semiconductor quantum dot Dot dispersion 2 was used.
The types of ligands contained in the ligand solution are the ligands shown in the “Compound Name” column of the “Ligand” column of Table 1.

Note that “A” in the “ligand”, “general formula”, and “seed” columns means that the ligand is represented by the general formula (A), and “B” means that the ligand is represented by the general formula. It means that it is represented by (B), and “C” means that the ligand is represented by the general formula (C). Ligands that cannot be represented by the general formulas (A) to (C) were indicated as “−”. “Number of A” represents the number of atoms of A ¹ , A ² or A ³ , and “Number of B” represents the number of atoms of B ¹ or B ² .

<Evaluation of semiconductor film>
Various evaluation was performed about the semiconductor film of the obtained semiconductor film device.

1. Electrical conductivity The electrical conductivity of the semiconductor film was evaluated by using a semiconductor parameter analyzer for the produced semiconductor film device.
First, the voltage applied to the electrode was swept between −5 to 5 V without irradiating the semiconductor film device with light, and the IV characteristics in the dark state were obtained. The current value with a +5 V bias applied was adopted as the dark current value Id.
Next, to evaluate the photocurrent values while irradiating monochromatic light (irradiation intensity 10 ¹³ photons) to the semiconductor film device. Note that the apparatus shown in FIG. 3 was used to irradiate the semiconductor film device with monochromatic light. The wavelength of the monochromatic light was systematically changed between 280 nm and 700 nm. The increase in current from the dark current when irradiating light with a wavelength of 280 nm was taken as the photocurrent value Ip.
The evaluation results are shown in Table 1.

2. Film peeling from substrate For the semiconductor film devices of Examples and Comparative Examples, the film peeling of the semiconductor film was evaluated by visual observation. Table 1 shows the presence or absence of film peeling.

3. Complex stability (log β ₁ )
The complex stability constant (log β ₁ ) of the ligand included in the semiconductor film of Example 3 was determined using Sc-Database ver. When 5.85 (Academic Software) (2010) was searched, log β ₁ = 8.5.

As shown in Table 1, the oleic acid ligand coordinated to the semiconductor quantum dot is subjected to ligand exchange, and the semiconductor quantum dot is formed with the specific ligand represented by the general formulas (A) to (C). It was found that high Ip / Id ₋ can be obtained by tying the semiconductor film (Comparative Example 1) to which the conventional ethanedithiol is coordinated.
In addition, as for the semiconductor film coordinated with ethanedithiol, remarkable film peeling occurred with the naked eye, whereas in the semiconductor film device of the example, no film peeling was observed, and high roughness was realized.

  Thus, it was shown that by producing a semiconductor film in which a specific ligand is coordinated to a semiconductor quantum dot, high Ip / Id can be realized and film peeling is suppressed.

4). Emission spectrum of semiconductor quantum dots As can be seen from the evaluation results of the examples and comparative examples shown in Table 1, the electrical conductivity of the semiconductor film is improved by bringing the semiconductor quantum dots close to each other using a specific ligand. can do. However, if the semiconductor quantum dots are too close to each other, the semiconductor quantum dots are likely to be aggregated. Semiconductor quantum dots are expected to become bulky when aggregated.
The semiconductor film desirably retains physical properties as a semiconductor quantum dot while exhibiting good electrical characteristics. In particular, when considering application of a semiconductor film to an LED or a solar cell, it is difficult to obtain absorption and emission of a target wavelength unless the semiconductor film has physical properties as a semiconductor quantum dot.

This can be judged from the peak wavelength of a PL (Photo Luminescence) spectrum in a semiconductor quantum dot having a ligand.
Therefore, PL spectra of the semiconductor films in Examples 1 to 3 and Comparative Examples 1 to 5 among the Examples were measured. For reference, the PL spectra of the PbS semiconductor quantum dot film (Comparative Example 9) and the PbS bulk (Comparative Example 10) with oleic acid coordinated without ligand exchange were also measured.

Here, the film of Comparative Example 9 was obtained in Example 1 without performing the processes (2) and (3) among the processes (1) to (4) in “Manufacturing the semiconductor film”. It is a membrane. Note that the film of Comparative Example 9 was an insulating film that did not exhibit electrical conductivity because the semiconductor quantum dots were not close to each other.
The PbS bulk is a general II-VI group semiconductor, which is a single crystal of PbS, has a size larger than 100 nm, and has no quantum size effect.

The configuration of the experimental setup used for the photoluminescence measurement is schematically shown in FIG. This experimental apparatus mainly includes a laser irradiator 20, a total reflection mirror 22, a dichroic mirror 24, lenses 26 and 28, and a spectroscope 32. The laser light emitted from the laser irradiator 20 is converted into a total reflection mirror 22, The structure reaches the measurement sample (semiconductor film of the evaluation device) 30 and the spectroscope 32 through the dichroic mirror 24 and the lenses 26 and 28, respectively.
FIG. 5 shows the PL spectrum. In addition, in FIG. 5, each PL spectrum in Example 1 (curve A), Example 3 (curve B), Comparative example 1 (curve C), and Comparative example 9 (curve D) was shown.
In addition, the peak wavelengths in each ligand are summarized in Table 2.

As can be seen from FIG. 5 and Table 2, the peak wavelength of the PbS semiconductor quantum dots (Comparative Example 9) in which oleic acid was coordinated without ligand exchange was about 1100 nm. On the other hand, in the semiconductor films of Examples 1 to 3 and Comparative Examples 1 to 5, it can be seen that the peak wavelength is shifted to the long wave side by about 60 nm to 120 nm.
The shift of the peak wavelength to the long wavelength side is because the confinement potential of the semiconductor quantum dots is reduced due to the proximity of the semiconductor quantum dots by ligand exchange, and the band gap is effectively reduced. is there. The decrease in the band gap is the largest and is about 100 meV.

  On the other hand, in the case of PbS bulk (Comparative Example 10), since the band gap is about 0.37 eV, the emission peak exists at about 3350 nm. Therefore, if the semiconductor quantum dots of the semiconductor film are aggregates, it is considered that the emission peak of the semiconductor film composed of the aggregates of semiconductor quantum dots appears around 3350 nm.

  On the other hand, as shown in Examples 1 to 3, the semiconductor film of the semiconductor quantum dots coordinated with a specific ligand has a short semiconductor quantum dot interval, and has high electrical conduction characteristics via the semiconductor quantum dots. On the other hand, it was confirmed that the physical properties (such as a band gap) of the semiconductor quantum dots were retained.

5. Average particle diameter of semiconductor quantum dots The average particle diameter of the semiconductor quantum dots was measured with a TEM apparatus. As a measuring apparatus, TITAN 80-300 manufactured by FEI was used. Two types of samples were prepared. One is a sample obtained by drop-casting the semiconductor quantum dot dispersion 1 on a Si substrate, collected by a sampling knife, and placed on a measurement stage. The other is that a spin coat film having undergone ligand exchange with ethanedithiol is formed on a quartz glass substrate, and is similarly collected with a sampling knife. In other words, the latter sample is a semiconductor film obtained in the same manner except that a quartz glass substrate was used as the substrate in the production of the semiconductor film of Comparative Example 1.

  FIG. 6 shows a TEM image when the semiconductor quantum dot dispersion liquid 1 is drop-cast. From FIG. 6, it was confirmed that the average particle diameter (average of 10 dots) of the quantum dots was 3 nm. Moreover, since oleic acid which is a long chain fatty acid remains coordinated without ligand exchange, it can be seen that the interval between the semiconductor quantum dots is very wide (2 nm to 4 nm).

  On the other hand, a TEM image of the spin coat film subjected to ligand exchange is shown in FIG. Although it is a semiconductor film coordinated by ethanedithiol whose Ip / Id is not so high, it can be seen that the structure is such that the intervals between the semiconductor quantum dots are narrowed and the semiconductor quantum dots are densely packed. Therefore, it was confirmed that the main factor of the electrical conductivity improvement in the semiconductor film of the present invention in which the specific ligand is coordinated to the semiconductor quantum dots is the proximity of the semiconductor quantum dots.

14 p-type semiconductor layer 16 n-type semiconductor layer 20 laser irradiator 22 total reflection mirror 24 dichroic mirror 26 lens 28 lens 30 spectroscope 32 measurement sample (semiconductor film)
100 pn junction solar cell

Claims (11)

An assembly of semiconductor quantum dots comprising PbS or InP with metal atoms;
At least one ligand selected from 3-mercapto-1-propanol, thioglycolic acid, a 3-mercapto-1-propanol derivative, and a thioglycolic acid derivative , which is coordinated to the semiconductor quantum dot;
A semiconductor film comprising: The semiconductor film according to claim 1, wherein a complex stability constant logβ ₁ between the ligand and the metal atom of the semiconductor quantum dot is 8 or more. The semiconductor quantum dots have an average particle size of 2nm~15nm claim 1 or a semiconductor film according to claim 2. A semiconductor quantum dot dispersion containing a semiconductor quantum dot containing PbS or InP, a first ligand coordinated to the semiconductor quantum dot, and a first solvent is provided on the substrate, and an assembly of semiconductor quantum dots Forming a semiconductor quantum dot assembly to form
The aggregate of the semiconductor quantum dots has a shorter molecular chain length than the first ligand, and 3-mercapto-1-propanol, thioglycolic acid, a 3-mercapto-1-propanol derivative, and thioglycol The first ligand coordinated to the semiconductor quantum dot by applying a solution containing a second ligand which is at least one selected from an acid derivative and a second solvent is used as the first ligand. A ligand exchange step for exchanging the two ligands;
And a method for producing a semiconductor film comprising an assembly of the semiconductor quantum dots and the second ligand. The method of manufacturing a semiconductor film according to claim 4 , wherein the first ligand is a ligand having at least 6 carbon atoms in the main chain. The method for producing a semiconductor film according to claim 4 or 5 , wherein the semiconductor quantum dot assembly forming step and the ligand exchange step are performed twice or more. The semiconductor quantum dots have an average particle size of 2nm~15nm claims 4 to method of manufacturing a semiconductor film according to any one of claims 6. A solar cell provided with the semiconductor film of any one of Claims 1-3 . A light emitting diode provided with the semiconductor film of any one of Claims 1-3 . A thin-film transistor provided with the semiconductor film of any one of Claims 1-3 . An electronic device provided with the semiconductor film of any one of Claims 1-3 .