JP5995661B2 - 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 (2008)

  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. In addition, 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, several hundreds at the maximum. Only a photocurrent value of about nA can be obtained. Further, when ethanedithiol is used as a ligand, the semiconductor film is likely to be peeled off.

An object of the present invention is to provide a semiconductor film in which a high photocurrent value is obtained and film peeling is suppressed, and a method for manufacturing the semiconductor film, and an object thereof is to solve the problem.
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 photocurrent values are obtained and film peeling is suppressed.

In order to achieve the above object, the following invention is provided.
<1> an assembly of semiconductor quantum dots containing metal atoms;
At least one ligand coordinated to a semiconductor quantum dot and represented by the following general formula (I):
A semiconductor film.

(In the formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.)
<2> The semiconductor film according to <1>, wherein A in the general formula (I) is a substituent having 7 or less atoms.
<3> The semiconductor film according to <1> or <2>, wherein A in the general formula (I) is a hydrogen atom or a substituent containing OH.
<4> The semiconductor film according to any one of <1> to <3>, wherein the ligand is at least one selected from glycolic acid, glyceric acid, lactic acid, or derivatives of these compounds.
<5> The semiconductor film according to any one of <1> to <4>, wherein the semiconductor quantum dot has a diameter of 2 nm to 15 nm.
<6> The semiconductor film according to any one of <1> to <5>, wherein the semiconductor quantum dots include at least one selected from PbS, PbSe, InN, InAs, InSb, and InP.
<7> The semiconductor film according to any one of <1> to <6>, wherein the semiconductor quantum dots contain PbS.
<8> 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 to the substrate to form an assembly of semiconductor quantum dots. A semiconductor quantum dot assembly forming process;
A solution containing a second ligand represented by the following general formula (I) and having a molecular chain length shorter than that of the first ligand and a second solvent is applied to the assembly of semiconductor quantum dots. A ligand exchange step of exchanging the first ligand coordinated to the semiconductor quantum dot with the second ligand;
The manufacturing method of the semiconductor film which has this.

(In the formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.)
<9> The method for producing a semiconductor film according to <8>, wherein the first ligand is a ligand having 6 or more linear carbon atoms.
<10> The method for producing a semiconductor film according to <8> or <9>, wherein the semiconductor quantum dot assembly forming step and the ligand exchange step are performed twice or more.
<11> The method for producing a semiconductor film according to any one of <8> to <10>, wherein A in the general formula (I) is a substituent having 7 or less atoms.
<12> The method for producing a semiconductor film according to any one of <8> to <11>, wherein A in the general formula (I) is a hydrogen atom or a substituent containing OH.
<13> The method for producing a semiconductor film according to any one of <8> to <12>, wherein the ligand is at least one selected from glycolic acid, glyceric acid, lactic acid, or derivatives of these compounds.
<14> The method for producing a semiconductor film according to any one of <8> to <13>, wherein the semiconductor quantum dot has a diameter of 2 nm to 15 nm.
<15> The method for producing a semiconductor film according to any one of <8> to <14>, wherein the semiconductor quantum dots include at least one selected from PbS, PbSe, InN, InAs, InSb, and InP.
<16> The method for producing a semiconductor film according to any one of <8> to <15>, wherein the semiconductor quantum dots contain PbS.
<17> A solar cell comprising the semiconductor film according to any one of <1> to <7>.
<18> A light emitting diode comprising the semiconductor film according to any one of <1> to <7>.
<19> A thin film transistor comprising the semiconductor film according to any one of <1> to <7>.
<20> An electronic device comprising the semiconductor film according to any one of <1> to <7>.

ADVANTAGE OF THE INVENTION According to this invention, a high photocurrent value is obtained and the semiconductor film with 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 that can obtain a high photocurrent value and suppress film peeling.

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 (device for evaluation) 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 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 present invention will be described in detail.

<Semiconductor film>
The semiconductor film of the present invention has an assembly of semiconductor quantum dots containing metal atoms and at least one ligand (hereinafter referred to as “specific arrangement”) coordinated with the semiconductor quantum dots and represented by the following general formula (I). It may be referred to as a “position”.).

In formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.

In the semiconductor film of the present invention, since the semiconductor quantum dots are connected by coordination bonds with a specific ligand having a small number of atoms represented by the general formula (I), the interval between the semiconductor quantum dots is shortened. It is thought that there is. 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, it is considered that the electrical conductivity is increased and the photocurrent value can be increased.
In addition, it is considered that a 5-membered ring chelate is formed by hydroxyl group and carboxyl group OH in the general formula (I), thereby coordinating with high coordination power to the metal element on the surface of the semiconductor quantum dot. 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.

(Assembly of semiconductor quantum dots)
A semiconductor quantum dot is a semiconductor particle comprising a metal atom, and is a nano-sized particle having a particle size of several nm to several tens of nm.
The aggregate of semiconductor quantum dots is a form in which a large number (for example, 100 or more per 1 μm 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.

In the present invention, the metal atom constituting the semiconductor quantum dot includes a semimetal atom typified by Si atom. The material constituting the semiconductor quantum dot (semiconductor quantum dot material) is, for example, a general semiconductor crystal (group IV semiconductor, compound semiconductor of group IV-IV, group III-V, group II-VI, group II, III And a nanoparticle (0.5 nm or more and less than 100 nm) of a compound semiconductor composed of a combination of three or more of group IV, group IV, group V, and group VI elements. Specifically, semiconductor materials having a relatively narrow band gap such as PbS, PbSe, InN, Ge, InAs, InGaAs, CuInS, CuInSe, CuInGaSe, InSb, Si, and InP can be given.
The semiconductor quantum dot includes at least one kind 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 according to the present invention 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 layer. Examples of the material constituting the coating layer include ZnS, ZnSe, ZnTe, ZnCdS, and the like.

Furthermore, when the semiconductor film of the present invention is applied to a solar cell application, the semiconductor quantum dot generates multi-exciton generation effect called multi-exciton generation effect in which two or more electron-hole pairs are generated by one high energy photon. In view of the enhancement of photoelectric conversion efficiency due to the effect, it is preferable that the band gap is narrower. 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.

  Moreover, it is desirable that the semiconductor quantum dot material is PbS or PbSe from the viewpoint of enhancing the multi-exciton generation effect and the ease of particle synthesis. InN is also desirable from the viewpoint of low environmental impact.

The diameter 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 diameter of the semiconductor quantum dot is reduced to a size equal to or less than the Bohr radius of the underlying electron, a phenomenon that the band gap of the semiconductor quantum dot changes due to the quantum size effect occurs. For example, it is said that II-VI semiconductors have a relatively large Bohr radius, and PbS has a diameter 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, when the diameter 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 size 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. Moreover, it is preferable that the thickness of the semiconductor film is 300 nm or less from the viewpoint of excessive carrier concentration and ease of manufacture.

(Ligand represented by general formula (I))
The ligand coordinated to the surface of the semiconductor quantum dot in the semiconductor film of the present invention has a structure represented by the general formula (I). In formula (I), A represents a substituent having 10 or less atoms other than NH ₂ or SH, and examples thereof include a hydrocarbon group such as a methyl group and an ethyl group, a hydroxyl group, and the like.
When the number of atoms of the substituent represented by A in the general formula (I) is 11 or more and the molecular chain length of the ligand is long, it acts as a steric hindrance between the semiconductor quantum dots and is high. It becomes difficult to achieve electrical conductivity.
Moreover, since the boiling point generally increases as the molecular weight increases, the solution containing the ligand represented by the general formula (I) used for the ligand exchange treatment itself remains in the film and acts as an impurity. There is a fear.

As a ligand (specific ligand) having a structure represented by the general formula (I), specifically, glycolic acid, L-lactic acid, D-lactic acid, L-malic acid, D-malic acid, glycerin Acid, 2-hydroxybutyric acid, L-tartaric acid, D-tartaric acid, tartronic acid, or derivatives thereof.
The semiconductor film of the present invention desirably contains at least one of glycolic acid, L-lactic acid, D-lactic acid, or derivatives thereof among the ligands represented by the general formula (I). In the case of any of the above ligands, for example, a higher photocurrent can be obtained as compared with the case where ethanedithiol is used as the ligand.
In addition, preferable ligands include L-malic acid, D-malic acid, glyceric acid, 2-hydroxybutyric acid, L-tartaric acid, D-tartaric acid, tartronic acid and the like.

In the case of the ligand represented by the general formula (I), a 5-membered ring chelate is formed by hydroxyl group and carboxyl group OH, thereby coordinating the metal element on the surface of the semiconductor quantum dot with high coordination power. I think that.
The substituent A in the general formula (I) may be a hydrocarbon group such as a methyl group or an ethyl group, or may be a hydroxyl group. When the substituent A is a hydroxyl group, it becomes a multidentate chelate and can form a better coordination bond.

  In general, a ligand coordinated on the surface of a semiconductor quantum dot is more efficient in replacing a long-chain ligand when the bond strength is higher, and higher electrical conductivity can be obtained. Is possible. Further, when the material constituting the semiconductor quantum dot is changed, the value of the complex stability constant logβ, which is the ease of modification of the ligand molecule to the semiconductor quantum dot, varies. Can be applied to various semiconductor quantum dots because of its short molecular chain length and easy coordination.

  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. In addition, the value of the specific ligand complex stability constant logβ ₁ varies depending on the semiconductor quantum dot material constituting the semiconductor quantum dot, but the specific ligand according to the present invention basically has a molecular chain length. Can be applied 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 is determined by using 5.85 (Academic Software) (2010). If there is no description in this database, A. E. Martell and R.W. M.M. Values described in Smith's Critical Stability Constants are used. For those not described yet, the above measurement method is used, or calculation is performed using the program PKAS method for calculating complex stability constants (AE Martinell et al., The Determination and Use of Stability Constants, VCH (1988)). To do.

In the general formula (I), as the substituent A having 10 or less atoms other than NH ₂ or SH, specifically, an alkyl group having 1 to 3 carbon atoms [methyl group, ethyl group, propyl group, and isopropyl Group], alkenyl group having 2 to 3 carbon atoms [ethenyl group and propenyl group], alkynyl group having 2 to 4 carbon atoms [ethynyl group, propynyl group and the like], cyclopropyl group, alkoxy group having 1 to 2 carbon atoms [methoxy Group and ethoxy group], an acyl group having 2 to 3 carbon atoms [acetyl group and propionyl group], an alkoxycarbonyl group having 2 to 3 carbon atoms [methoxycarbonyl group and ethoxycarbonyl group], an acyloxy group having 2 carbon atoms [acetyl group] An oxy group], an acylamino group having 2 carbon atoms [acetylamino group], a hydroxyalkyl group having 1 to 3 carbon atoms [hydroxymethyl group, Droxyethyl group, hydroxypropyl group], aldehyde group [—COH], hydroxy group [—OH], carboxy group [—COOH], sulfo group [—SO ₃ H], phospho group [—OPO (OH) ₂ ], cyano Group [—CN], isocyanate group [—N═C═O], nitro group [—NO ₂ ], nitroxy group [—ONO ₂ ], isothiocyanate group [—NCS], cyanate group [—OCN], thiocyanate group [—SCN], acetoxy group [OCOCH ₃ ], acetamide group [NHCOCH ₃ ], formyl group [—CHO], formyloxy group [—OCHO], formamide group [—NHCHO], sulfamino group [—NHSO ₃ H], Sulfino group [—SO ₂ H], phosphono group [—PO ₃ H ₂ ], acetyl group [—COCH ₃ ], halogen atom [Fluorine atom, chlorine atom, bromine atom and the like], alkali metal atom [lithium atom, sodium atom, potassium atom and the like] and the like.

As long as the substituent A is not NH ₂ or SH and the total number of atoms is 10 or less, the substituent A may further have a substituent.
When the number of atoms of the substituent A 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.
The substituent A preferably has 7 or less atoms, more preferably a hydrogen atom, from the viewpoint of bringing the semiconductor quantum dots closer to each other.

<Semiconductor film manufacturing method>
The method for producing the semiconductor film of the present invention is not particularly limited, but as a preferred production method, after forming an assembly of semiconductor quantum dots having a ligand on the surface on the substrate, the surface of the semiconductor quantum dots And a method of exchanging at least a part of the ligand coordinated with the ligand represented by the general formula (I).

  Specifically, the method for producing a semiconductor film of the present invention includes a semiconductor quantum dot dispersion containing a semiconductor quantum dot, a first ligand coordinated to the semiconductor quantum dot, and a first solvent on a substrate. The semiconductor quantum dot assembly forming step for forming an assembly of semiconductor quantum dots by attaching to the semiconductor quantum dot, and the assembly of semiconductor quantum dots are represented by the following general formula (I) and have a molecular chain rather than the first ligand: A ligand that exchanges a first ligand coordinated to a semiconductor quantum dot with a second ligand by applying a solution containing a second ligand having a short length and a second solvent An exchange process.

In formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.

[Semiconductor quantum dot assembly formation process]
Semiconductor quantum dot containing a metal atom, a first ligand coordinated to the surface of the semiconductor quantum dot (hereinafter sometimes referred to as “dispersion ligand”), and a semiconductor quantum dot containing a first solvent A dispersion is applied onto the substrate to form an assembly of semiconductor quantum dots.
The semiconductor quantum dot dispersion may be applied directly 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-
As the semiconductor quantum dot dispersion liquid, a dispersion liquid that does not have a low molecular weight ligand and contains semiconductor quantum dots having a relatively long molecular chain length is used. In a dispersion in which semiconductor quantum dots are dispersed, colloidal semiconductor quantum dots generally have a very long molecular chain ligand. Using a dispersion liquid containing semiconductor quantum dots having a ligand of such a long molecular chain (the number of atoms is 11 or more), a semiconductor quantum dot film (aggregation) on the substrate while the semiconductor quantum dot has a long molecular chain There is a method of applying a solution containing a ligand to be coordinated by ligand exchange or forming a substrate and immersing a substrate in the solution to advance the ligand exchange treatment in a film state. When such a method is used, a semiconductor film can be formed in a state where the semiconductor quantum dots do not aggregate because the liquid state has a very long molecular chain.

(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 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.

The semiconductor quantum dot dispersion liquid contains a semiconductor quantum dot containing 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.

(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.
As the first ligand, one having a molecular chain length longer than that of the second ligand represented by the general formula (I) used in the ligand exchange step is used. The ligand represented by the general formula (I) is difficult to disperse in an organic solvent system when used in a semiconductor quantum dot dispersion, and cannot be used as the first ligand. . Here, “dispersion” refers to a state where there is no sedimentation or turbidity of particles.
From the viewpoint of dispersibility, the first ligand contained in the semiconductor quantum dot dispersion liquid preferably has 6 or more linear carbon atoms, and more preferably has 10 or more linear carbon atoms. Specifically, it may be either a saturated compound or an unsaturated compound, such as 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.
Of the above, oleic acid is preferable from the viewpoint that the first ligand having 6 or more linear carbon atoms hardly disperses in the semiconductor film while imparting dispersion stability to the semiconductor quantum dots.

  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.

  Further, an electrode, an insulating film, or the like may be provided on the substrate. In that case, the semiconductor film of the present invention is formed on the electrode or the insulating film on the substrate.

[Ligand exchange step]
After forming the semiconductor quantum dot aggregate on the substrate, the semiconductor quantum dot aggregate is represented by the general formula (I), and the second ligand having a molecular chain length shorter than that of the first ligand A solution (ligand solution) containing a second solvent (hereinafter sometimes referred to as “exchange ligand”) is added. Thus, the first ligand (dispersing ligand) coordinated on the surface of the semiconductor quantum dots constituting the aggregate is replaced with the second ligand (for exchange) represented by the general formula (I) To the ligand).

-Ligand solution-
As the exchange ligand (second ligand) represented by the general formula (I), one having a molecular chain length shorter than that of the first ligand before exchange is used. Specifically, the specific ligand is as described above. When the ligand (first ligand, second ligand) used in the present invention is a branched molecule, the “molecular chain length” is defined by the main chain of the molecule.
The exchange ligand represented by the general formula (I) basically has high miscibility with alcohol since it contains a hydroxyl group, and is efficient when an alcohol system is used as the second solvent. Ligand exchange treatment can be performed. Further, for example, if the molecular structure has a hydroxyl group in the substituent A, the miscibility and solubility in an alcohol effective as a ligand solvent can be increased.

  The content of the exchange ligand in the ligand solution is preferably 5 mmol / l to 200 mmol / l, more preferably 10 mmol / l to 100 mmol / l, based on the total volume of the ligand solution. preferable.

-Second solvent-
The solvent (second solvent) contained in the ligand solution is not particularly limited as long as it dissolves the ligand represented by the general formula (I), but may be a solvent having a high dielectric constant. preferable. For example, ethanol, acetone, methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, butanol, and propanol can be mentioned.
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

  As a method for performing a ligand exchange treatment by applying a ligand solution containing the second ligand represented by the general formula (I) to an assembly of semiconductor quantum dots on the substrate, A method of applying a ligand solution containing a second ligand represented by the general formula (I) to an aggregate of semiconductor quantum dots, and a substrate on which the aggregate of semiconductor quantum dots is formed is represented by the general formula (I) The method of immersing in the ligand solution containing the 2nd ligand represented by these, etc. are mentioned.

  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 formation step and the ligand exchange step may be alternately repeated. By repeating the semiconductor quantum dot assembly formation step and the ligand exchange step, the electrical conductivity of the semiconductor film having the assembly of semiconductor quantum dots coordinated with the second 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 second ligand in the ligand exchange increases.
In addition, the effect of this invention will be acquired if the ligand exchange with the 1st ligand of a semiconductor quantum dot and the 2nd ligand is performed in at least one part of the semiconductor quantum dot aggregate | assembly. Therefore, 100% (number) may not be exchanged with the second ligand, and it is sufficient that the second ligand represented by the general formula (I) is partially modified.

[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, it is possible to remove the dispersing ligand and the excess exchange ligand that are desorbed from the semiconductor quantum dots. 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. The organic solvent used in the ligand exchange treatment is preferably used, although it may be immersed in at least one of the first solvent and the second 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 remaining after the ligand exchange step. It may be a solution drying step for drying the solution. In addition, when the semiconductor quantum dot assembly forming step and the ligand exchange step are repeated, it is a comprehensive step performed after repeating the set of the semiconductor quantum dot assembly forming step and the ligand exchange step. Also good.

By passing through each process demonstrated above, the semiconductor film of this invention is manufactured on a board | substrate.
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 section 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.

<Production of evaluation 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 Evident 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 another 20 ml of toluene was added to obtain a PbS particle 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.
In addition, the average particle diameter of the semiconductor quantum dots was calculated as an average of 10 semiconductor quantum dots by photographic observation in TEM (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 preparation of 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 / ml was prepared in the same manner 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 ligand shown in the “Compound” column of the “Ligand” column in 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 solution application step Further, a methanol solution (ligand solution) of the ligands shown in Table 1 was dropped on the semiconductor quantum dot assembly film, and then spin-coated at 2500 rpm to obtain a semiconductor film. Got.

(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 step 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, an evaluation device having a semiconductor film on a substrate was produced.

[Evaluation]
1. Electrical conductivity The electrical conductivity of the semiconductor film was evaluated by using a semiconductor parameter analyzer for the manufactured evaluation device.
First, the voltage applied to the electrode was swept between −5 to 5 V without irradiating the evaluation 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 evaluation device. Note that the apparatus shown in FIG. 3 was used to irradiate the evaluation device with monochrome 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. In Table 1, CTAB is cetrimonium bromide.

2. Film peeling from substrate For the evaluation 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.

  As shown in Table 1, by modifying the surface of the semiconductor quantum dot (PbS) with a ligand represented by the general formula (I), the photocurrent is higher than that of the ethanedithiol-modified semiconductor film of Comparative Example 1. Value / dark current value was found.

  In Example 6 using InP as the semiconductor quantum dot, although the current value is not so high, ethanedithiol is arranged by using glycolic acid as a ligand, as in the case of using PbS as the semiconductor quantum dot. A higher photocurrent value was observed as compared with Comparative Example 10 as a ligand. Thus, it can be seen that the present invention can provide a high photocurrent regardless of the material of the semiconductor quantum dots.

  Further, it was found that when the ligand is ethylenediamine (Comparative Example 2), both the photocurrent value and the dark current are remarkably lowered. This result suggests that good electrical conduction characteristics cannot be obtained with simple primary amines and diamines. This is probably because log β is not so high and the coordination of the ligand is not so advanced. Therefore, it is estimated that oleic acid remains as a ligand molecule and inhibits carrier transport between semiconductor quantum dots.

  In addition, the ethanedithiol-modified semiconductor films of Comparative Examples 1 and 10 showed significant film peeling with the naked eye, whereas no film peeling was observed in each example.

  As described above, it was shown that high photocurrent and electrical conductivity can be realized by preparing a semiconductor film in which a specific ligand represented by the general formula (I) is modified on a semiconductor quantum dot.

3. 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.
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 device for evaluation) 30 and the spectroscope 32 through the dichroic mirror 24 and the lenses 26 and 28, respectively.

  FIG. 5 and FIG. 6 show the measurement results of photoluminescence for each ligand. The peak wavelengths for each ligand are summarized in Table 2.

  The semiconductor film not subjected to ligand exchange treatment (Experimental Example 1) had an emission peak of about 1100 nm, whereas the semiconductor film subjected to ligand exchange treatment had an emission wavelength of about 60 nm to 120 nm on the long wave side. You can see that it has shifted to. Such a shift of the emission wavelength to the long wave side (red shift) reduces the confinement potential of the semiconductor quantum dots by effectively reducing the confinement potential of the semiconductor quantum dots by the ligand exchange process, thereby effectively reducing the band gap. It seems to suggest that it has declined. The largest is a decrease of about 100 meV.

On the other hand, in the case of bulk PbS, since the band gap is about 0.37 eV and the emission peak exists at about 3350 nm, if the semiconductor quantum dots are aggregated into a bulk shape, the emission peak is around this. Should appear.
Therefore, it is considered that the distance between the semiconductor quantum dots is reduced by the ligand exchange treatment, and the physical properties (band gap, etc.) as the semiconductor quantum dots are maintained while showing good conduction characteristics through the semiconductor quantum dots. .
Note that 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.

4). Average particle diameter (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. 7 shows a TEM image when the semiconductor quantum dot dispersion liquid 1 is drop-cast. From FIG. 7, it was confirmed that the average particle diameter (average of 10 dots) of the quantum dots was 3 nm. Moreover, since the oleic acid which is a long chain fatty acid remains coordinated without ligand exchange, it turns out that the space | interval of a semiconductor quantum dot is very wide (2 nm-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.

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 (20)

An assembly of semiconductor quantum dots containing metal atoms;
Coordinated to the semiconductor quantum dots, and at least one ligand represented by the following general formula (I):
A semiconductor film.

(In the formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.)   The semiconductor film according to claim 1, wherein A in the general formula (I) is a substituent having 7 or less atoms.   The semiconductor film according to claim 1, wherein A in the general formula (I) is a hydrogen atom or a substituent containing OH.   4. The semiconductor film according to claim 1, wherein the ligand is at least one selected from glycolic acid, glyceric acid, lactic acid, or derivatives of these compounds. 5.   The semiconductor film according to claim 1, wherein the semiconductor quantum dot has a diameter of 2 nm to 15 nm.   The semiconductor film according to any one of claims 1 to 5, wherein the semiconductor quantum dot includes at least one selected from PbS, PbSe, InN, InAs, InSb, and InP.   The semiconductor film according to claim 1, wherein the semiconductor quantum dots contain PbS. A semiconductor quantum dot is formed by providing a semiconductor quantum dot dispersion liquid containing a semiconductor quantum dot, a first ligand coordinated to the semiconductor quantum dot, and a first solvent on a substrate. A dot assembly forming process;
A solution containing a second ligand represented by the following general formula (I) and having a molecular chain length shorter than that of the first ligand and a second solvent is applied to the aggregate of the semiconductor quantum dots. A ligand exchange step of exchanging the first ligand coordinated to the semiconductor quantum dot with the second ligand;
The manufacturing method of the semiconductor film which has this.

(In the formula (I), A represents a hydrogen atom or a substituent having 10 or less atoms other than NH ₂ or SH at the end.)   The method of manufacturing a semiconductor film according to claim 8, wherein the first ligand is a ligand having 6 or more linear carbon atoms.   The method for producing a semiconductor film according to claim 8 or 9, wherein the semiconductor quantum dot assembly forming step and the ligand exchange step are performed twice or more.   The method for producing a semiconductor film according to any one of claims 8 to 10, wherein A in the general formula (I) is a substituent having 7 or less atoms.   The method for producing a semiconductor film according to claim 8, wherein A in the general formula (I) is a hydrogen atom or a substituent containing OH.   The method for producing a semiconductor film according to any one of claims 8 to 12, wherein the ligand is at least one selected from glycolic acid, glyceric acid, lactic acid, or derivatives of these compounds.   The method of manufacturing a semiconductor film according to claim 8, wherein the semiconductor quantum dot has a diameter of 2 nm to 15 nm.   The method of manufacturing a semiconductor film according to claim 8, wherein the semiconductor quantum dots include at least one selected from PbS, PbSe, InN, InAs, InSb, and InP.   The method of manufacturing a semiconductor film according to claim 8, wherein the semiconductor quantum dots contain PbS.   A solar cell provided with the semiconductor film of any one of Claims 1-7.   A light emitting diode provided with the semiconductor film of any one of Claims 1-7.   A thin-film transistor provided with the semiconductor film of any one of Claims 1-7. An electronic device provided with the semiconductor film of any one of Claims 1-7.