JPH01265574A - Photoelectric conversion element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a photoelectric conversion element.

[Prior Art] Amorphous silicon (hereinafter referred to as a-8i) can be formed into a large-area film at low cost by plasma CVD, so it has traditionally been applied to elements such as solar cells and optical sensors. It has been. For example, “Television Society Technical Report JVO1,
As shown in No. 10, No. 22ED983, a contact image sensor in which a photoelectric conversion element and a scanning circuit for driving the same are integrated on the same quartz substrate has been developed and put into practical use. a-8i used for this contact type image sensor
Photodiodes are required to have fast light response characteristics and low dark current characteristics. - Also, when applied to color sensors, high photosensitivity characteristics are required over the entire wavelength range of visible light. In order to satisfy the above-mentioned required characteristics, the lower electrode is made of transparent ITO (Indium-Tin-Oxid
There is a photodiode in which amorphous silicon is laminated on top of the amorphous silicon and an A1 alloy film is formed as the upper electrode.

[Problems to be Solved by the Invention] The film thickness of the transparent electrode has conventionally been determined based on the ease of patterning the transparent electrode, the required value of sheet resistance, etc.

Therefore, with the conventional transparent electrode film thickness, the reflectance of the incident surface of the photodiode at wavelengths around 400 to 450 nm increases, for example, due to the optical interference effect between the transparent electrode and amorphous silicon, or between the transparent protective film and the transparent electrode. That happened. A high reflectance means that the amount of light incident on the photodiode is low, and in this case, the amount of incident light with a wavelength of 400 to 450 nm is low.

On the other hand, the visible light of the a-3i photodiode (400
The spectral sensitivity characteristic in the wavelength range of 450 nm or less is lower than that in other wavelength ranges. For this reason, with the film thickness of conventional transparent electrodes, wavelengths of 400~
There were cases where the sensitivity of the photodiode decreased significantly near 450 nm.

Conventional amorphous silicon photodiodes have the above-mentioned problems. The present invention solves the above-mentioned problems, and its purpose is to provide an amorphous silicon photodiode that prevents a decrease in photosensitivity in a wavelength range with low spectral sensitivity.

[Means for Solving the Problems] The photoelectric conversion element of the present invention has a photoelectric conversion element having a photoelectric conversion layer, a transparent electrode, and a transparent protective film, and has a wavelength in a region where the spectral sensitivity of the photoelectric conversion layer is lowest. In contrast, the film thickness or refractive index of the transparent electrode or the transparent protective film is adjusted so that the reflectance of the wavelength light is the lowest.

[Example] FIG. 1 shows a structural diagram of the photoelectric conversion element of the present invention.

0 represents an insulating substrate, 1 represents an electrode, 2 represents a photoelectric conversion layer, 3 represents a transparent electrode, and 4 represents a transparent protective film. Incident light enters from the transparent protective film side in FIG.

The process will be explained below. First, approximately 7,000 Al-8i-Cu alloys, which will become electrodes 1, are formed on an insulating substrate O and patterned by photolithography. This insulating substrate may be of any material as long as it has heat resistance of 300° C. or more, but in this example a quartz substrate was used. Further, the electrode material is not limited to Al-9i-Cu alloy, but may be pure Al, metal Cr, etc., for example. A photoelectric conversion layer 3 is formed on this lower electrode 1 by plasma CVD method.
8i layer is deposited. A mixed gas containing silane gas as a main component is introduced into the chamber and decomposed by glow discharge to form an a-8i layer with a thickness of about 1 μm.

In the above steps, the substrate temperature is maintained at 240°C.

Next, ITO, which will become the transparent electrode 3, is formed on this a-8i layer. If the refractive index of ITO is 2.0 and the refractive index of transparent polyimide coated on the top layer is 1.7, the wavelength is 400~
The ITO film thickness at which the reflectance is minimum at 450 nm is 160 nm.
There are 0 people.

A film of ITO is formed by sputtering with 1,600 people, and patterned by photolithography. Excellent ITO patterning, CF 4
The a-8i layer is photolithographically patterned by plasma etching. Or the a-8i layer is ITO
Patterning may be performed using the pattern as a mask. On top of this, transparent polyimide as the transparent protective film 4 is applied using a spin cord to complete the process. PI-2566 for transparent polyimide,
Snee 300 (both are trade names) and the like are preferred, and both have a refractive index of about 1.7. The thickness of the transparent polyimide film is preferably about 5 μm in order to reduce the interference effect of light. Because transparent polyimide has high transmittance, 5μ
With a film thickness of about 1.0 m, light attenuation is not a problem.

FIG. 2 shows another embodiment of the photoelectric conversion element of the present invention. In this embodiment, by inserting the transparent thin film 5, the wavelength 40
The sensitivity in the range of 0 to 450 nm is further increased. Figure numbers 0 to 4 are the same as in Figure 1, and 5 is a transparent thin film. Also in this embodiment, incident light enters from the transparent protective film 4 side. The manufacturing process is the same as that shown in FIG. 1 up to the formation of the transparent electrode, and a transparent thin film is formed on the transparent electrode 3 shown in FIG. Transparent thin film is 250″C
Although any material with a certain degree of heat resistance may be used, a 5iOa film was used in this example. The refractive index of the transparent electrode 3 is 2.
0, the refractive index of SiO2 is 1.46, and the refractive index of the transparent protective film 4 is 1.7. In order to minimize the reflectance at a wavelength of 400 to 450 nm, the film thickness of SiO2 is 2000 nm, IT
The film thickness of O is assumed to be 1,700 people. Thereafter, a transparent protective film 4 is formed in the same manner as shown in FIG. 1 to complete the process.

FIG. 3 shows a third embodiment of the photoelectric conversion element of the present invention. In this embodiment, incident light enters from the transparent insulating substrate 6 side. Figure numbers 1 to 3 are the same as in FIG. 1, and 7 is a protective film.

The manufacturing process will be explained. First, a transparent electrode is formed on the transparent insulating substrate 6. Although any transparent insulating substrate may be used as long as it has a heat resistance of 300° C. or higher, a quartz substrate was used in this example. Moreover, ITO was used for the transparent electrode. The refractive index of the quartz substrate is 1.46, and the refractive index of ITO is 2.46. 0, in order to minimize the reflectance at a wavelength of 400 to 450 nm, the ITO film thickness is set to 1800 nm. After forming the ITO film, it is patterned by photolithography. I
The a-3i layer of the photoelectric conversion layer 2 is formed on the TO to a thickness of about 1 μm as in the case of FIG. 1, and the electrode 1 is laminated on top of the a-3i layer. For example, an Al-8i-Cu alloy is used for the electrode 1, but pure A
1 or Cr. In the case of Al-6i-Cu alloy,
Approximately 7,000 people deposited the film using sputtering and patterned it using photolithography. After patterning electrode 1, photolithography is performed on the a-3i layer, or C using electrode 1 as a mask.
Patterning is performed by Fa plasma etching. Next, a protective film 7 is formed on this to complete the process. In Figure 3,
Since the incident light enters from the transparent insulating substrate 6 side, the protective film 7 does not need to be transparent. For example, Photonice, PI-
A colored polyimide such as 400 (both trade names) may be used, or a transparent polyimide similar to that shown in FIG. 1 may of course be used.

In all of the above embodiments, the transparent electrode 3, the transparent protective film 4,
When a material with a refractive index different from that of the above embodiment is used for the transparent thin film 5 and the transparent insulating substrate 6, the wavelength is 400 to 450 nm.
Figure 4.5 shows the spectral sensitivity characteristics of the photoelectric conversion element. Fourth
In the figure, a broken line 401 and a dashed-dotted line 402 are comparative examples,
A broken line 401 indicates the ITO film thickness of 200 mm in the structure shown in FIG.
Photoelectric conversion element with 0 people and no transparent protective film 4 (Comparative Example 1
) is the spectral sensitivity characteristic of - The dotted chain line 402 is the spectral sensitivity of a photoelectric conversion element (Comparative Example 2) in which the ITO film thickness was 2000 μm in the structure shown in FIG. Actual in Figure 4, *403
is the spectral sensitivity of the photoelectric conversion element in Fig. 1, and the dotted line 404 is the second
The spectral sensitivity characteristics of the photoelectric conversion elements shown in the figure are shown respectively. Fifth
In the figure, a broken line 501 is a comparative example, and is the spectral sensitivity characteristic of a photoelectric conversion element (comparative example 3) when the ITO film thickness is 2000 in the structure shown in FIG. Actual 1s502 is the spectral sensitivity characteristic of the photoelectric conversion element shown in FIG.

As is clear from FIG. 4.5, the photoelectric conversion element of the present invention has a spectral sensitivity that is 7 to 60% higher than the photoelectric conversion element of the comparative example at a wavelength of 400 to 450 nm. In practical applications, the intensity distribution of a light source is often weak in the wavelength range of 400 to 450 nm, so increasing the sensitivity in this wavelength range has a very large practical effect. On the contrary, at wavelengths of 500 to 550 nm, the photoelectric conversion element of the comparative example exceeds the spectral sensitivity of the photoelectric conversion element of the present invention, but at wavelengths of 500 to 550 nm, the absolute sensitivity of the photoelectric conversion element itself is large, and in terms of application, the intensity of the light source is Since the distribution is often strong in the wavelength range of 500 to 550 nm, there is no problem at all in practice.

[Effects of the Invention] As described above, according to the photoelectric conversion element of the present invention, it is possible to suppress a decrease in photosensitivity in a wavelength range where spectral sensitivity is low, and to achieve extremely good spectral sensitivity characteristics over the entire visible light range. . Therefore, it can be applied to color sensors, etc.
Its effects are enormous.

[Brief explanation of the drawing]

Figures 1.2.3 are structural diagrams of the photoelectric conversion element of the present invention. Figure 4.5 shows the spectral sensitivity characteristics of a photoelectric conversion element. 401 is the spectral sensitivity characteristic of Comparative Example 1 402 is the spectral sensitivity characteristic of Comparative Example 2 403 is the spectral sensitivity characteristic of the photoelectric conversion element in FIG. 1 404 is the spectral sensitivity characteristic of the photoelectric conversion element in FIG.
The spectral sensitivity characteristic 502 of is greater than or equal to the spectral sensitivity characteristic of the photoelectric conversion element shown in Fig. 3 ↓ Fig. 1 Incident light ↓ Fig. 2 Fig. 3 Wavelength (nrn) Fig. 4

Claims (4)

[Claims] (1) In a photoelectric conversion element having a photoelectric conversion layer, a transparent electrode, and a transparent protective film, the reflectance of light at the wavelength is the lowest for a wavelength in a region where the spectral sensitivity of the photoelectric conversion layer is lowest. . A photoelectric conversion element, wherein the thickness or refractive index of the transparent electrode or the transparent protective film is adjusted. (2) A transparent thin film is formed on the transparent electrode according to item 1,
2. The photoelectric conversion element according to item 1, wherein the thickness or refractive index of the transparent thin film is adjusted so that the reflectance of light at the wavelength described in item 1 is the lowest. (3) In a photoelectric conversion element having a transparent insulating substrate, a transparent electrode, and a photoelectric conversion layer, the film thickness or refractive index of the transparent electrode is adjusted so that the reflectance of the wavelength light described in item 1 is the lowest. A photoelectric conversion element characterized by: (4) The photoelectric conversion element according to item 1, wherein the photoelectric conversion layer is made of amorphous silicon.