JP2509635B2 - Method for producing metal chalcogenide particle dispersed film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The metal chalcogenide particle-dispersed film obtained by the production method of the present invention can be particularly used as a film-shaped semiconductor.
In particular, it is useful for optoelectronic elements such as electrophotographic photoreceptors, solar cells, and optical sensors that require a large area and a flexible shape.

[Prior Art] Metal chalcogenide compounds such as CdS, CdSe, and PbS are
A so-called II-V group compound semiconductor is a material necessary for, for example, an optoelectronic element. In general, it is more advantageous in terms of physical properties to use a semiconductor material as a single crystal, but there is a problem in that the production of the single crystal requires a capital investment and time, which results in a high cost. Therefore, the semiconductor particle-dispersed film is practical, especially for large-area devices. There are the following conventional methods for producing a semiconductor particle dispersed film. That is, a semiconductor is separately prepared, pulverized to an appropriate particle size, and then dispersed in a solution in which a polymer used as a dispersion medium is dissolved to form a film by a screen printing method.

At this time, in order to form a semiconductor film having excellent physical properties, the particle size of the semiconductor particles and the dispersion compatibility with the polymer are important.
Many patent applications have been filed by devising this point. Recently, Yamamoto et al. Prepared an organosol in the form of ultrafine particles when a metal chalcogenide was prepared in the presence of a polymer in an organic solvent, and a semiconductor particle-dispersed film with excellent conductivity was formed by casting this into a film. It has been reported to be obtained (Inorg.Chim.Acta., 104, L1,19
85).

On the other hand, by Bard et al., The Cd ²⁺ ion in the polymeric support film
By reducing with H ₂ S, the cadmium sulfide particles can be
It has been reported that it can be efficiently dispersed in the support membrane in situ (J. Am. Chem. Soc., 106, 6537, 1984). This method
Compared with the conventional casting method, there is no need to perform an operation to evaporate and distill off the solvent, so that there are significant improvements in terms of equipment and operating efficiency.

[Problems to be Solved by the Invention] In the method of Bard et al., Nafion (trademark), which is a cation exchange membrane, is used as a polymer supporting membrane.
It was dipped in an aqueous solution containing (NO ₃ ) ₂ and then successively dipped in a saturated H ₂ S aqueous solution to deposit cadmium sulfide particles in the Nafion membrane. We used this method to deposit a cadmium sulfide-dispersed Nafion membrane. When they were produced and examined for their film structure and physical properties, CdS particles were precipitated only in the vicinity of the surface within the support film, and a “cavity structure” in the center of the support film where cadmium sulfide particles did not exist was found. Given the. Moreover, in the dispersion film having such a structure, as shown in Table 1 (Reference Example 1), the ratio (i ph / id) of the current (i ph) flowing during light irradiation and the current (id) flowing during darkness is It was about 2, in other words, the current generated by photoexcitation of cadmium sulfide was in a state in which almost no observation was possible. Therefore, it has become necessary to develop a new method for efficiently producing a film having improved semiconductor physical properties by uniformly dispersing metal chalcogenide particles in the support film.

[Means for Solving Problems] In the method of Bard et al., The two-step process (sequential dipping method) as described above was adopted. However, in this case, a "cavitation structure" is produced. The reason for this is as follows. That is, the diffusion rate of Cd ²⁺ ions in the Nafion membrane penetrates into the Nafion membrane from the outside.
It has been experimentally confirmed that it is faster than the diffusion rate of H ₂ S. Therefore, before the H ₂ S in the saturation concentration of H ₂ S reaches the center of the Nafion membrane, Cd ²⁺ ions previously existing in the film diffuses toward the surface of the membrane. As a result, it is considered that H ₂ S and Cd ²⁺ meet at a relatively surface layer in the support film, and cadmium sulfide particles are deposited there. Based on such inference, the present inventors counter-diffuse an aqueous solution containing H ₂ S saturated water and Cd ²⁺ ions through the supporting film, so that the cadmium sulfide particles can form H ₂ S solution in the supporting film. It was confirmed that they were sequentially deposited from the side and were uniformly dispersed throughout the entire support film.

By extending this idea and adjusting the diffusion rate of transition metal ions and the diffusion rate of a reducing agent in the supporting film to a desired range by the concentration of charge, charged and uncharged polymeric materials other than Nafion It was confirmed that a film in which the metal chalcogenide particles were uniformly dispersed could be obtained in the same manner as above.

Examples of the polymer supporting membrane used in the present invention include a cation exchange membrane of perfluorosulfonic acid resin (Nafion) and a polymer membrane of porous polyethylene. However, it is preferable that the solvent in which the metal ion or the reducing agent is dissolved easily penetrates into the supporting film and does not dissolve the supporting film. As long as this is satisfied, there are no specific requirements for the material and shape of the support membrane. As the transition metal ion, an element selected from Group VIII, Group IB and Group IIB of the periodic table is preferable, and the cation is a nitrate group, an acetate group, an oxalate group or Cl ⁻ , Br ⁻ , I ^−, etc. It is used as a salt consisting of the anion of.

As the reducing agent having a chalcogen element (S, Se, or Te), H ₂ S, Na ₂ S, Na ₂ S ₂ O ₃ , Na ₂ Se, Na ₂ Se ₂ O ₃ , Na ₂
Te and the like can be exemplified.

The solvent is selected from those which dissolve the above metal salt and reducing agent but not the supporting film, but the solvent dissolving the metal salt and the solvent dissolving the reducing agent do not necessarily have to be the same. Typically, polar solvents such as water, alcohol, dimethylformamide, acetonitrile and acetone are preferable.

As described above, the concentrations of the metal salt and the reducing agent are determined from the balance of the diffusion rates of both of them in the support film, and therefore the optimum concentrations are determined by the type of each constituent component. Generally speaking, the higher the concentration, the better in order to shorten the reaction time. Therefore, it is desirable to select a metal salt and a reducing agent that are easily soluble in the solvent used.

EFFECTS OF THE INVENTION By using the method disclosed in the present invention, it becomes possible to efficiently manufacture a flexible semiconductor particle dispersion film having a large area. Furthermore, the semiconductor particles were uniformly filled in the support film in the form of ultrafine particles, and photo-induced electron transfer occurred efficiently in the film, so that excellent semiconductor physical properties were exhibited.

Example 1 A Nafion 117 membrane (manufactured by DuPont, film thickness: about 200 μm) purified by boiling in concentrated nitric acid for 3 hours and then in ion-exchange distilled water for 5 hours was sandwiched between two-chamber separate cells, and was placed on one side of the cell. Is a 100 mM Cd (CH ₃ COO) ₂ aqueous solution,
The other side was filled with deionized water. H ₂ S was bubbled on the ion-exchanged water side for a predetermined time. After the reaction, the membrane was immersed in a large amount of distilled water, stirred, and thoroughly washed to remove unreacted cadmium ion and H ₂ S. The membrane colored from yellow to orange with the reaction time. The change with time of the content of cadmium sulfide deposited in the film is shown in FIG. In addition, based on the result of observing the cross section of the obtained film under a stereoscopic microscope (80 times), a schematic diagram of the dispersed state of cadmium sulfide in the film
It is also shown in the figure. As shown in FIG. 2, the visible absorption spectrum of the film thus obtained (absorption edge 515 nm)
Was in agreement with the cadmium sulfide described in the literature.

Example 2 As in Example 1, Nafion was used as a supporting film.
As the reducing agent, a 500 mM Na ₂ S aqueous solution was used instead of H ₂ S, and the reaction was performed with a 100 mM Cd (CH ₃ COO) ₂ aqueous solution for 13 hours to obtain an orange cadmium sulfide-dispersed Nafion film.

Example 3 Porous polyethylene (trademark Hypore 30
0, Asahi Kasei Co., Ltd., pore size 0.5 μm, film thickness 50 μm) was used, and this was sandwiched between two-chamber separate cells for one side cell.
100 mM Cd (CH ₃ COO) ₂ aqueous solution, 500 in the other cell
By adding mM Na ₂ S aqueous solution and reacting for 10 hours,
An orange cadmium sulfide dispersed polyethylene film was obtained.

Example 4 By using the same purified Nafion as that used in Example 1 as the supporting membrane, by reacting a 100 mM CuSO ₄ aqueous solution and a H ₂ S saturated aqueous solution for 10 hours in the same manner as in Example 1,
A black copper sulfide-dispersed Nafion film was obtained.

Reference Example 1 After purifying a commercially available Nafion 117 membrane as shown in Example 1, this was first immersed in a 500 mM Cd (NO ₃ ) ₂ aqueous solution for 1 hour, and then further immersed in a H ₂ S saturated aqueous solution for 10 minutes. After the reaction, the obtained yellow film was washed with a large amount of distilled water, sandwiched between two indium-tin oxide (ITO) coated glass electrodes, 0.5 V was applied between both electrodes, and irradiation was performed with a 650 W tungsten halogen lamp. (Light source-sample distance 40 cm, heat ray removal water filter 5 cm, sample surface light intensity 200 mW · cm ^-2 )
The photo-induced current (i ph) under was measured. Table 1 shows
Shows the value of i ph that reached a steady state after voltage application, and the ratio (i ph / id) to the current value (id) in the dark was also shown.

Reference Examples 2 to 4 Cadmium sulfide dispersion films A, B and C obtained in Example 1
(As shown in FIG. 1) was sandwiched between two ITO-coated glass electrodes, and the pH and i were measured according to the method described in Reference Example 1.
ph / id asked. As shown in Table 1, the iph / id was almost 1 in the film having the "cavity structure" having a portion where the cadmium sulfide particles were not present in the supporting film, and the effect of light irradiation was not observed. On the other hand, in the film in which cadmium sulfide was uniformly dispersed as in Reference Example 4, the i ph / id value was 430.
Also reached.

[Brief description of drawings]

FIG. 1 shows the relationship between the reaction time of Cd ²⁺ and H ₂ S in the Nafion film, the cadmium sulfide content, and the dispersion state. In the schematic diagram of the rectangular film structure in the figure, the black portion represents the region where the cadmium sulfide particles are present, and the white portion represents the hollow region. FIG. 2 shows a visible absorption spectrum of a cadmium sulfide-dispersed Nafion film.

Claims (1)

(57) [Claims] 1. A method of supporting a solution containing a transition metal ion and a solution containing a reducing agent containing a chalcogen element in dispersing the metal chalcogenide particles in a supporting film selected from a perfluorosulfonic acid resin film or a porous polyethylene film. A method for producing a metal chalcogenide particle-dispersed film, which comprises diffusing and permeating into the film from opposite surfaces through the film.