JPS6295868A - Photoelectric conversion element - Google Patents

Abstract

PURPOSE:To extend spectroscopic sensitivity up to the short wavelength side without lowering photo response rate of photoelectric conversion element by forming a thin film of CdS on the surface of photoconductive film mainly consisting of CdSe at the side of incident light. CONSTITUTION:A CdSe film 2 is formed on a substrate 1 at the side of photoelectric conversion element and a mixing film of CdS and halogenide of Cd which is flux of CdS is formed on the substrate 3 at the side of mixing material for surface processing. These CdSe film 3 and CdS film 4 are approximately provided opposed to each other and these are subjected to the heat processing under such condition. In the course of this heat processing, CdCl2 works as the flux and thereby the CdSe particles are melted at the surface and grow as the particles. Thereby, a heat processing film can be completed. In addition, an extremely thin (for example, several thousand Angstrom ) CdS layer 6 is formed simultaneously with the activating processing at the surface of CdSe film used as the photoconductive film during such heat processing. The planar type electrode 7 is formed by the lift-off method and a photoelectric conversion element can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a photoelectric conversion element suitable for use in facsimiles and character image reading/input devices.

<Conventional technology> Conventionally, for the photoconductive film of a contact type image sensor for image reading! /1 C in which CdS and CdSe are dissolved in any ratio
A d5Se film is used, and the spectral sensitivity characteristics and optical response speed mainly change depending on this ratio. As the percentage of solid solution approaches CdSe, the optical response becomes faster, but the peak of spectral sensitivity shifts from the center of the visible region from 520 nm to 720 nm.

FIG. 5 is a diagram showing spectral sensitivity characteristics for each ratio of solid solution.

As is clear from FIG. 5, pure CdSe has a spectral sensitivity peak around 725 nm, and has main sensitivity around red light. Therefore, it cannot be said to be a suitable photoelectric conversion element when it is necessary to read a red character image. On the other hand, pure CdS is suitable for reading red character images, but has the disadvantage that the optical response speed is slower than that of CdSe.

<Problems to be solved by the invention> As described above, the photoresponse speed and the spectral sensitivity characteristics tend to contradict each other, and even if the proportion of solid solution is appropriately adjusted, the photoelectric conversion has intermediate characteristics between the two. There was a problem that only elements could be obtained.

The present invention was devised in view of the above circumstances, and aims to provide a photoelectric conversion element that has a photoresponse speed equivalent to that of pure CdSe and has excellent spectral sensitivity characteristics.

<Means for solving the problems> In order to achieve the above object, the photoelectric conversion element of the present invention has the following features:
On the light incident side surface of the photoconductive film mainly composed of CdSe,
It is configured to form a thin layer of CdS.

<Function> By forming an extremely thin CdS layer on the light incident side surface of the photoconductive film mainly composed of CdSe as described above, the spectral sensitivity can be increased while maintaining the optical response speed equivalent to that of the CdSe film. It can be extended to the short wavelength side.

<Example> Hereinafter, an example of the present invention will be described in detail together with a manufacturing method thereof with reference to the drawings.

FIG. 1 is a preliminary substrate layout diagram illustrating a surface treatment method for manufacturing an embodiment of the photoelectric conversion element of the present invention.

In FIG. 1, 1 is the substrate on the photoelectric conversion element side, 2 is the CdSe film formed on this substrate 1, 3 is the substrate on the surface treatment mixture side, and 4 is the film formed on the substrate 3 on the surface treatment mixture side. The above CdSe film 2 is a mixed film of CdS and Cd halide, which is a fluxing agent. of)\logenides (e.g. cac+2
) E4.5 molar ratio, 10% by weight of a low-melting glass frit with a glass transition temperature of 400°C, and an appropriate amount of α-terpineol containing a small amount of ethyl cellulose were mixed and sufficiently dispersed, and a coating paste was applied onto the glass substrate 1. After coating by screen printing method, it was coated at 100℃ in N2 gas atmosphere
It is prepared by drying for a few minutes. In addition, in the same manner, the above mixed film (4 is CdS powder and its flux, Cd -
・After coating a film paste sufficiently dispersed by mixing an appropriate amount of chloride and an appropriate amount of α-terpineol containing a small amount of ethyl cellulose on the glass substrate 3 by screen printing, It is prepared by drying at ℃ for 30 minutes. Cd prepared as above
Se film 3 and CdS film 4 are placed close to each other as shown in FIG.
For example, 0.4 mist to 0.8 rtrm) and heat-treated in this state at 300°C for 30 minutes and 500°C for 1 hour. During this heat treatment process, CDC+2 acts as a flux and C
dSe particles achieve grain growth while melting together in the epidermis,
Finally, a heat-treated film formed by aggregation of grains with an average grain size of 2 to 3 μm is completed.0 Also, during this heat treatment process, an extremely thin layer (for example, several A Cd5 layer 6 (see FIG. 2) of 1,000 λ) is formed at the same time as the activation process.

On the photoconductive film produced as described above, planar electrodes 7 having an electrode spacing of 50 μm, an electrode width of 60 μm, and an electrode pitch of 125 μm, as shown in FIG. 2, are formed by a lift-off method to produce a photoelectric conversion element.

In addition, in FIG. 2, 5 is activated CdSe.
The film 6 is a thin CdS layer formed on this CdSe film.

The spectral sensitivity characteristics of the photoelectric conversion element thus produced are shown in FIG.

In FIG. 3, the dotted line is the spectral sensitivity characteristic of a conventional CdSe film, and the solid line is the spectral sensitivity characteristic of a CdSe film with a CdS thin layer formed on the surface by performing the above-described surface treatment.

As is clear from FIG. 3, the CdSe film with a thin CdS layer formed on its surface has very excellent spectral sensitivity characteristics.

FIG. 4 shows the relationship between the photoresponse time and the irradiation light intensity of a CdSe film with a KCdS thin layer formed on its surface. Here, the photoresponse time is 50% of the steady photocurrent when the photoelectric conversion element is irradiated with light.
Rise time τ to reach the value.

and the falling time τd from when the light irradiated to the photoelectric conversion element is cut off until it attenuates to 50% of the steady photocurrent. CdSe film with CdS thin layer formed on the surface and C
There is no difference in the response time of a CdSe film without a dS thin layer, and forming a CdS thin layer on the surface does not have an adverse effect on the photoresponse time, and as shown in Figure 4, it is fully satisfactory as a photoelectric conversion element. It can be seen that the photoresponse time slows down.

In the above embodiment, a case was described in which a CdS thin layer was formed on a photoconductive film using vapor during firing of a mixture of CdS and Cd halide, but the present invention is not limited to this, and sputtering method, etc. It goes without saying that the CdS thin layer may be formed on the photoconductive film by other thin film forming methods. Don't slow down the response speed

[Brief explanation of drawings]

FIG. 1 is a substrate layout diagram for explaining a surface treatment method for producing an embodiment of the photoelectric conversion element of the present invention, and FIG. 2 is a diagram showing the structure of an embodiment of the photoelectric conversion element of the present invention. , FIG. 3 is a diagram showing the spectral sensitivity characteristics of the photoelectric conversion element of the present invention, and FIG.
The figure shows the relationship between the photoresponse time and the irradiation light intensity of the photoelectric conversion element of the present invention, and Figure 5 shows the spectral sensitivity characteristics for each solid solution ratio of CdS and CdSe. I... Substrate on the photoelectric conversion element side, 2... CdSe film, 3
...Substrate on the surface treatment mixture side, 4...CdSi,
5... CdSe film subjected to activation treatment, 6... CdS thin layer, 7... Electrode, 8... Arrow indicating light incidence. Agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 Figure 2 Collection of assets Figure 4

Claims (1)

[Claims] 1. In a photoelectric conversion element having a photoconductive film containing CdSe as a main component, a thin layer of CdS is formed on the surface of the photoconductive film, and the surface of the thin CdS layer is the optical signal incident side. A photoelectric conversion element characterized by: 2. The photoconductive film according to claim 1, wherein the CdS thin layer is formed by surface-treating the photoconductive film with vapor during firing of a mixture of CdS and Cd halides. conversion element. 3. The CdS thin layer is composed of the photoconductive film, CdS and Cd
2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is formed on the photoconductive film by arranging and firing a mixed film made of a mixture of halides.