JP5152726B2 - Polysilane thin film absorbing near-infrared light and method for producing the same - Google Patents

Description

  The present invention relates to a polysilane thin film suitably used for solar cells and the like and a method for forming the same.

In recent years, solar cells using amorphous silicon films or polysilicon films are becoming widespread. As a method for forming such an amorphous silicon film or a polysilicon film that absorbs near infrared light, a chemical vapor deposition (CVD) method using a silicon hydride gas, a plasma CVD method, Photo CVD, vapor deposition, sputtering, etc. are used. In particular, in the plasma CVD method, not only a complicated and expensive apparatus such as a high-frequency generator is required, but also an expensive high vacuum apparatus is necessary.
On the other hand, apart from the CVD method as described above, formation of a silicon film by a coating method that does not require an expensive apparatus has been studied. As an example of a method for forming such a silicon film, a silicon film that is heated after being coated with liquid silicon hydride and then subjected to a decomposition reaction in the coating film through a thermal history including a temperature rising process. Has been reported (see Patent Document 1). Also reported is a method of applying a composition comprising a mixture of silicon fine particles obtained by pulverizing single crystal silicon and liquid silicon hydride on a substrate, and heating the resulting coating to form a polysilicon film. (See Patent Document 2). In addition, a liquid in which hydrogenated polysilane-modified silicon fine particles are dispersed is applied onto a substrate to form a coating film, and then a silicon film is formed by performing heat treatment or light irradiation on the substrate on which the coating film has been formed. A way to do this has also been reported. (See Patent Document 3)
Japanese Patent No. 3517934 JP-A-2005-332913 JP 2007-277038 A

  However, the method for forming a silicon film described in Patent Document 1 has a difficulty in requiring a complicated apparatus for handling liquid silicon hydride, and it is difficult to control the thickness of the silicon film. Further, in the method for forming a silicon film described in Patent Document 2, the work of removing the oxide film on the surface of the fine particles is complicated by using fine particles obtained by pulverizing single crystal silicon, and a uniform continuous film having no defects is obtained. Difficult to do. Further, since the silicon film is formed by mixing liquid silicon hydride and silicon fine particles, there is a problem that defects are likely to occur at the interface between the silicon fine particles and the silicon hydride during film formation. Moreover, in the method for forming a silicon film described in Patent Document 3, it is necessary to modify polysilane with silicon fine particles, and the band gap cannot be continuously changed.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a polysilane thin film that absorbs various near-infrared light without requiring a large facility and a method for manufacturing the same. To do.

（式中、Ｒ_１は、縮合多環芳香族基を表し、Ｒ_２は、アリール基又は縮合多環芳香族基のいずれかを表し、Ｒ_３は、アルキル基を表す。また、ｘ及びｙは、整数を表す。）
［２］前記加熱処理の温度及び／又は時間により、バンドギャップが制御されていることを特徴とする［１］の近赤外吸収性ポリシラン薄膜。
［３］基板上に下記の一般式で表される架橋ポリシラン薄膜を形成した後、加熱処理することにより該架橋ポリシラン薄膜の吸収スペクトルを変化させて、近赤外光を吸収するポリシラン薄膜とすることを特徴とする近赤外吸収性ポリシラン薄膜の製造方法。

（式中、Ｒ_１は、縮合多環芳香族基を表し、Ｒ_２は、アリール基又は縮合多環芳香族基のいずれかを表し、Ｒ_３は、アルキル基を表す。また、ｘ及びｙは、整数を表す。）
［４］前記加熱処理の温度及び／又は時間を調整することにより、前記架橋ポリシラン薄膜のバンドギャップを制御することを特徴とする［３］に記載の方法。 As a result of intensive studies to achieve the above object, the inventors can produce a polysilane thin film that absorbs near-infrared light by heating a coating film coated with a liquid containing a specific crosslinked polysilane. I got the knowledge that it would be possible.
The present invention has been completed based on these findings, and is as follows.
[1] A near-infrared light-absorbing polysilane thin film characterized in that a crosslinked polysilane thin film represented by the following general formula is heat-treated to absorb near-infrared light.

(In the formula, R ₁ represents a condensed polycyclic aromatic group, R ₂ represents either an aryl group or a condensed polycyclic aromatic group, and R ₃ represents an alkyl group. X and y Represents an integer.)
[2] The near-infrared absorbing polysilane thin film according to [1], wherein the band gap is controlled by the temperature and / or time of the heat treatment.
[3] After forming a crosslinked polysilane thin film represented by the following general formula on the substrate, the absorption spectrum of the crosslinked polysilane thin film is changed by heat treatment to form a polysilane thin film that absorbs near-infrared light. A method for producing a near-infrared absorbing polysilane thin film.

(In the formula, R ₁ represents a condensed polycyclic aromatic group, R ₂ represents either an aryl group or a condensed polycyclic aromatic group, and R ₃ represents an alkyl group. X and y Represents an integer.)
[4] The method according to [3], wherein the band gap of the crosslinked polysilane thin film is controlled by adjusting the temperature and / or time of the heat treatment.

  According to the present invention, a polysilane thin film that absorbs near-infrared light can be produced simply by heat-treating the coating film, and further, the band gap of the polysilane film that absorbs near-infrared light by changing the time of the heating temperature. Can be continuously changed with good reproducibility.

The present invention will be described in more detail.
The crosslinked polysilane used in the present invention is represented by the following general formula.

In the above general formula, R ₁ represents a condensed polycyclic aromatic group such as a naphthyl group, anthracene group, phenanthrene group, or pyrene group, and R ₂ represents an aryl group such as a phenyl group, or a naphthyl group, an anthracene group, It represents any of condensed polycyclic aromatic groups such as a phenanthrene group and a pyrene group, R ₃ represents an alkyl group, and x and y represent integers. That is, in the crosslinked polysilane of the present invention, an aryl group or a condensed polycyclic aromatic group and an alkyl group are bonded to the side chain group of the one-dimensional silicon polymer, and the condensed polycyclic aromatic group is used as a side chain group at the crosslinking point. The group is bonded. Although it does not specifically limit as this alkyl group, A C1-C12 thing is preferable from availability.

The crosslinked polysilane represented by the above general formula of the present invention can be a near-infrared light-absorbing polysilane thin film only by heat-treating the coating film. Furthermore, the band gap of the polysilane thin film which absorbs near-infrared light can be changed continuously and with good reproducibility by changing the temperature and time of the heat treatment.
This effect in the present invention is unique to the crosslinked polysilane in which the side chain group at the crosslinking point is a condensed polycyclic aromatic group, and the side chain group at the crosslinking point is not a condensed polycyclic aromatic group. In the case of a phenyl group or an alkyl group, even if the heat treatment is performed, the absorption spectrum only decreases, and an increase in the absorption spectrum on the near infrared light side is not observed.
The reason can be considered that dissociation of the silicon-silicon bond at the cross-linking point and recombination due to recombination occur in the process of forming the near infrared light absorbing polysilane thin film by heat treatment. The bond is dissociated by heating, for example, silicon ions and silicon radicals are stabilized by the condensed polycyclic aromatic group of the side chain group, and recombination of the bond occurs, whereas it is stabilized by the alkyl group and phenyl group. It is thought that dissociation and decomposition occur before recombination of the bonds occurs.

で表される架橋ポリシランの場合、メチルフェニルジクロロシランと架橋剤であるナフチルトリクロロシランを任意の割合で混合して、ウルツカップリング反応により合成することにより製造することができ、架橋剤の量を制御することによって、二次元的な架橋点含量を変化させることができる。 The crosslinked polysilane of the present invention is easily produced by a known Wurtz coupling reaction.
That is, for example,

Can be produced by mixing methylphenyldichlorosilane and naphthyltrichlorosilane, which is a crosslinking agent, in an arbitrary ratio and synthesizing by a Wurtz coupling reaction. By controlling, the two-dimensional crosslinking point content can be changed.

The produced cross-linked polysilane is dissolved in a solvent to form a solution, and is applied onto the substrate by a method such as a spin coating method in which the solution is applied while rotating at high speed. A general-purpose solvent is used as a solvent at the time of application, and among these, toluene and tetrahydrofuran are preferably used.
The substrate used in the present invention is not particularly limited as long as it has heat resistance at the temperature of the heat treatment, and those generally used in the field can be used. For example, in addition to a transparent substrate such as quartz glass, an insulating substrate such as silicon oxide, a conductive substrate such as indium oxide-tin oxide (ITO), or the like can be used.

  In the present invention, the heating means for the crosslinked polysilane film formed on the substrate is not particularly limited, but it is preferably performed under vacuum. In addition, by changing the temperature and time of the heat treatment, the band gap of the polysilane thin film that absorbs near infrared light can be changed continuously and with good reproducibility. In order to obtain a thin film, it is preferably carried out at 400 ° C. or higher, preferably 500 ° C. or higher, for 1 to 36 hours, preferably 6 to 12 hours.

Next, the present invention will be described more specifically based on examples, but the present invention is not limited to the following examples.
Example 1
Using methylnaphthyldichlorosilane and naphthyltrichlorosilane which is a crosslinking agent, polymethylnaphthylsilane having a naphthyl group introduced at a crosslinking point was obtained. The resulting polysilane had a crosslinking point content of 50%. In addition, the content of 50% of cross-linking points indicates that 50 of the 100 Si atoms in the polysilane main chain are cross-linked with another polysilane main chain. The approximate degree of polymerization was x = y = 40.
The obtained crosslinked polysilane was dissolved in toluene, and a thin film was formed on a quartz substrate by spin coating.
The obtained thin film was heated under vacuum at various heating temperatures for 30 minutes, then cooled to room temperature, and an ultraviolet-near infrared absorption spectrum was measured under the atmosphere.
FIG. 1 shows the obtained absorption spectrum.
From the figure, it can be seen that as the heating temperature increases, the absorption width of 4.2 eV becomes wider as the absorption decreases, and the tail begins to be pulled toward the low energy side. This result suggests that the band gap is reduced by heating the crosslinked polymethylnaphthylsilane thin film in which the naphthyl group is introduced at the crosslinking point.

(Example 2)
Next, the change in absorption spectrum after heating with the heating temperature of the polymethylnaphthylsilane thin film with 50% crosslinking used in Example 1 fixed at 500 ° C. was examined.
The result is shown in FIG. As is apparent from the figure, as the heating time increases, the absorption width widens with the decrease in the absorption peak of 5.5 eV, and begins to skirt toward the low energy side. This change in absorption spectrum can also be confirmed by the color of the polysilane thin film changing from colorless and transparent to brown and transparent as the heating time increases. This suggests that the band gap decreases with increasing heating time.

(Example 3)
Instead of the 50% crosslinked polymethylnaphthylsilane thin film of Example 1, a 20% crosslinked polymethylnaphthylsilane thin film was used, and the change in absorption spectrum due to the difference in heating time at 500 ° C. was examined.
The result is shown in FIG. It showed the same spectral change as the 50% crosslinked polysilane thin film, but the rate of decrease of the absorption peak at 5.5 eV was large.

Example 4
In order to examine the effect of the heating temperature, the heating temperature in Example 3 was lowered to 450 ° C., and the change in absorption spectrum due to the difference in heating time was examined.
The result is shown in FIG. As with the heating temperature of 500 ° C., as the heating time increases, the absorption width widens with the decrease in the absorption peak of 5.5 eV, and begins to skirt toward the low energy side. However, there is little way to spread the hem. These results indicate that a constant heating temperature is required to control the band gap.

(Comparative Example 1)
A polysilane thin film formed on a substrate in the same manner as in Example 1 except that a polymethylnaphthylsilane thin film having no crosslinking point was used instead of the polysilane thin film having a naphthyl group introduced at the crosslinking point in Example 1. Was subjected to heat treatment, and an ultraviolet-near infrared absorption spectrum was measured.
As a result, even when the heating temperature of the polymethylnaphthylsilane thin film having no crosslinking point was changed and heated, the absorption spectrum only decreased. From this result, it was found that the crosslinking point had an effect on the heating effect.

(Comparative Example 2)
Instead of the polysilane thin film in which a naphthyl group is introduced at the crosslinking point of Example 1, a polymethylphenylsilane thin film in which a phenyl group is introduced at the crosslinking point or a polydihexylsilane thin film in which an alkyl group is introduced at the crosslinking point is used. The crosslinked polysilane thin film formed on the substrate was heat-treated in the same manner as in Example 1 except that the ultraviolet-near infrared absorption spectrum was measured.
As a result, the absorption spectrum only decreased even when the heating temperature of the crosslinked polysilane thin film having a phenyl group or an alkyl group introduced at the crosslinking point was changed regardless of the crosslinking point content. Further, even when a polyphenylsilylene thin film having a crosslinking point content of 100% (two-dimensional polysilane) or a polyalkylsilylene thin film was heated, the same result was obtained.
From these results, it was found that the side chain group at the crosslinking point affects the heating effect.

  The crosslinked polysilane of the present invention can be a near-infrared light-absorbing polysilane thin film only by heat-treating the coating film, and further, by changing the temperature and time of the heat treatment, Because the band gap of polysilane thin film that absorbs light can be changed continuously and with good reproducibility, various functional materials such as solar cells, electroluminescence (EL), sensors, etc. It can be expected to be used as

The figure which shows the change of the absorption spectrum when changing the heating temperature and heating the polymethylnaphthylsilane thin film of 50% bridge | crosslinking by which the naphthyl group was introduce | transduced into the crosslinking point for 30 minutes. The figure which shows the change of the absorption spectrum by the difference in the heating time at 500 degreeC of the polymethylnaphthylsilane thin film of 50% bridge | crosslinking by which the naphthyl group was introduce | transduced into the crosslinking point. The figure which shows the change of the absorption spectrum by the difference in the heating time at 500 degreeC of the polymethylnaphthylsilane thin film of 20% bridge | crosslinking by which the naphthyl group was introduce | transduced into the crosslinking point. The figure which shows the change of the absorption spectrum by the difference in the heating time at 450 degreeC of the polymethylnaphthylsilane thin film of 20% bridge | crosslinking by which the naphthyl group was introduce | transduced into the crosslinking point.

Claims (4)

A near-infrared absorptive polysilane thin film characterized in that a crosslinked polysilane thin film represented by the following general formula is heat-treated to absorb near-infrared light.

(In the formula, R ₁ represents a condensed polycyclic aromatic group, R ₂ represents either an aryl group or a condensed polycyclic aromatic group, and R ₃ represents an alkyl group. X and y Represents an integer.)   The near-infrared absorptive polysilane thin film according to claim 1, wherein the band gap is controlled by the temperature and / or time of the heat treatment. A cross-linked polysilane thin film represented by the following general formula is formed on a substrate, and then the absorption spectrum of the cross-linked polysilane thin film is changed by heat treatment to form a polysilane thin film that absorbs near-infrared light. A method for producing a near-infrared absorbing polysilane film.

(In the formula, R ₁ represents a condensed polycyclic aromatic group, R ₂ represents either an aryl group or a condensed polycyclic aromatic group, and R ₃ represents an alkyl group. X and y Represents an integer.)   The method according to claim 3, wherein a band gap of the crosslinked polysilane thin film is controlled by adjusting a temperature and / or time of the heat treatment.

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