JPS61278171A - Thin film photoelectric conversion device - Google Patents

Abstract

PURPOSE:To form a thin film photoelectric conversion device which is excellent in various characteristics such as conversion efficiency, by providing regular projections and recesses on the substrate surface, and forming thereon electrode layers or semiconductor layers of a fixed film thickness, thereby constructing a photoelectric conversion device. CONSTITUTION:By passing through a roll for adjusting the surface condition when a glass substrate 1 is manufactured, projected and recessed portions having a pitch of 0.5mm, height of 0.22mm, opening angle of 90 deg., and radius of curvature of 35mum for the recessed and projected portions are formed on the surface of the glass substrate 1. Then, a transparent SnO2 electrode layer 2 is deposited with a thickness of 1mum on the recessed and projected surface of the glass substrate 1 by means of the CVD method. Further, a P-type a-Si layer, an I-type a-Si layer and an N-type a-Si layer are sequentially formed on the transparent electrode layer 2, and this is determined as an a-Si layer 3. Then, an Al electrode layer 4 is formed on the a-Si layer 3 with a thickness of 0.5mum by means of the vapor deposition method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thin film photoelectric conversion element. More specifically, the present invention relates to improving the conversion efficiency and other characteristics of thin film photoelectric conversion elements.

BACKGROUND OF THE INVENTION Photoelectric conversion elements can be broadly classified into energy conversion elements that convert optical energy into electrical energy and information conversion elements that convert optical information into electrical information based on their uses.

A typical example of the former type of energy conversion element is a solar cell that utilizes the photovoltaic effect. In light of the recent energy situation, solar cells are expected to be a new energy source in the future, and extensive research and development are being carried out, and some have already been put into practical use.

Development of energy conversion elements including solar cells,
The future challenges for research will likely be to lower costs and significantly improve energy conversion efficiency.

On the other hand, information conversion elements include photodiodes and phototransistors that utilize the photovoltaic effect, and photoconductive cells that utilize the photoconductive effect.

Various types of these information conversion elements have been developed and put into practical use with the recent development of optical communication technology, and one of the future research trends in information conversion elements is integration. That is, information conversion elements and electrical elements or other optical elements are formed on the same substrate to enable high-speed processing of information.

Under these circumstances, attention has recently been focused on thinning photoelectric conversion elements for the purpose of lowering the cost of energy conversion elements or integrating information conversion elements. Constructing photoelectric conversion elements with thin films not only makes it possible to integrate the elements, but also saves expensive semiconductor materials and allows the use of thin film formation methods suitable for mass production, reducing manufacturing costs. be done.

However, although thinning the film solves the problems of lowering the price and integration of photoelectric conversion elements, it is still insufficient in terms of characteristics such as photoelectric conversion efficiency, and there is still much room for further improvement. .

The conversion of light energy into electrical energy by the photovoltaic effect occurs when light incident on a photoelectric conversion element is absorbed by the semiconductor active region, where it forms electrons and holes. is separated by the internal electric field of the device.

This can be taken out as a photocurrent or photopotential and used as a power source, etc. This internal electric field can be realized by various means, for example, a pin type junction, a Schottky barrier, etc. are well known.

On the other hand, the photoconductive effect is based on the fact that light incident on a photoelectric conversion element is absorbed by a semiconductor, and electrons and holes formed by this light energy become carriers, increasing the electrical conductivity of the semiconductor.

Electrical output can be obtained by applying a bias voltage to this semiconductor from the outside.

Therefore, in a photoelectric conversion element that utilizes the photovoltaic effect or the photoconductive effect, the larger the scene absorbed by the semiconductor region, that is, if the intensity of the light is constant, the depth of light penetration into the semiconductor region becomes greater. It can be seen that the longer the length), the higher the concentration of formed electrons and holes, and the higher the conversion efficiency.

As a conventional example 1 of a thin film photoelectric conversion element, the structure of an amorphous silicon (hereinafter referred to as a-3i) thin film solar cell is shown in the fifth example.
As shown in the figure. That is, a flat glass substrate 11, a Sn○2 transparent electrode layer 12 provided on the upper surface thereof, an a-3i layer 13 provided on the transparent electrode layer 12, and an a-3i layer 13 provided on the a-3i layer 13. The electrode layer 14 is composed of an AI electrode layer 14. Here, the a-3i layer 13 has a pln type junction structure, and the p-type a-3i layer, i
A type a-3i layer and an n-type a-3i layer are stacked.

With this configuration, light incident from the glass substrate 11 side is guided to the a-3i layer 13, where it is photoelectrically converted, and the 5
This is to generate an electromotive force between the n02 transparent electrode layer 12 and the AI electrode layer 14.

However, the surface of the glass substrate 11,
and the interface between the transparent electrode 12 and the transparent electrode 12 and a-3i
Due to the reflection of the incident light at the interface with the layer 13,
The amount of light incident on the a-3i layer 13 becomes small. Furthermore, since the interfaces of each layer are flat and parallel, for example, when light enters the glass substrate 11 perpendicularly, a-
Similarly, the light is perpendicularly incident on the 5i layer 13, and the light tries to pass through the a-3i layer 13 through the shortest distance.

As a result, the conversion efficiency of the element decreased, making it impossible to obtain desired characteristics.

FIG. 6 shows a configuration of a second conventional example devised for the purpose of improving photoelectric conversion efficiency. This conventional example 2 differs from the conventional example 1 shown in FIG. 5 in that fine irregularities are formed on the surface of the SnO□ transparent electrode layer 12, and an a-3i layer 13 is provided thereon. The SnO□ transparent electrode layer 12 can be formed, for example, by the CVD method, but fine irregularities on the surface are
It is formed by changing the set conditions such as temperature or pressure during the VD reaction. By providing these fine irregularities, light incident on the transparent electrode layer 12 from the glass substrate 11 is refracted or diffracted in irregular directions at the interface between the transparent electrode layer 12 and the a-3i layer 13. - Penetrates into the 3i layer 13. Therefore, most of the light incident perpendicularly on the glass substrate 11 travels obliquely within the a-3i layer 13;
The optical path length within the −3i layer 13 becomes longer, resulting in improved photoelectric conversion efficiency.

However, in general, the thickness of the transparent electrode layer 12 is set to several micrometers or less in order to improve transparency, so it is very thin.
It is difficult with current technology to form desired regular irregularities on the transparent electrode layer 12. Therefore, the formed unevenness becomes non-uniform, the optical path length within the a-5i layer 13 is not sufficiently increased, and the a-3i formed on the uneven transparent electrode layer 12
Since the thickness of layer 13 is non-uniform, transparent electrode layer 12 and AI
This may cause deterioration of the characteristics of the element, such as a decrease in shunt resistance with the electrode layer 14.

Table 1 below shows various characteristics of the solar cell according to Conventional Example 1.2 having the configuration shown in FIGS. 5 and 6, which was manufactured in this manner. However, in Conventional Example 2, irregularities of approximately 0.1 μm are provided on the surface of the transparent electrode layer 12 having a thickness of 1 μm.

Table 1 As shown in Table 1, although the conversion efficiency of Conventional Example 2 in which fine irregularities were formed on the surface of the transparent electrode layer 120 is slightly higher than that of Conventional Example 1, it is still insufficient. there were.

In addition to these conventional methods, there is also a method of installing an anti-reflection film to reduce reflection loss, but since anti-reflection films are only effective for light in a specific wavelength range, sufficient characteristics cannot be obtained. There wasn't.

Problems to be Solved by the Invention As described above, the problems of cost reduction and integration of solar cells and other photoelectric conversion elements are being solved by thinning the films. However, various properties such as conversion efficiency are still insufficient, and further improvement is desired.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thin film photoelectric conversion element having excellent properties such as conversion efficiency.

Means for Solving the Problems As a result of various studies and studies aimed at developing a thin film photoelectric conversion element with excellent conversion efficiency and various other properties, the inventor of the present invention created regular irregularities on the surface of the substrate, We have found that it is effective to form a photoelectric conversion element by forming a thick electrode layer or semiconductor layer.

That is, the thin film photoelectric conversion element of the present invention includes a substrate having an uneven surface, and a multilayer thin film formed on the surface of the substrate and consisting of a semiconductor layer, a transparent electrode layer sandwiching the semiconductor layer, and an electrode layer. It is characterized by having.

Further, in a preferred embodiment of the present invention, the substrate is made of glass, and FIG. 1 shows a cross-sectional view of the thin film photoelectric conversion element of the present invention in this embodiment.

Hereinafter, explanation will be given along this cross-sectional view.

First, irregularities of a desired size are formed on the surface of the glass substrate 1. The forming method is as follows: (1) Prepare a roll with unevenness on the cylindrical surface as a roll for adjusting the surface condition, and press this roll against the surface of the glass substrate in the glass softening temperature range during glass substrate production. Apply surface treatment.

(2) After manufacturing a glass substrate with a flat surface, the surface is roughened by etching.

The etching method is HF5HF+N
In addition to the wet etching method using H4F, HF+HN03, etc. as an etching liquid, the plasma etching method using HF, CHF3, etc. as an etching gas, a sputter etching method or an ion beam etching method can be used.

(3) After manufacturing a glass substrate with a flat surface, the surface is subjected to mechanical processing such as cutting and polishing.

After forming the unevenness as described above, heat treatment may be performed for the purpose of stabilizing the surface shape of the glass substrate 1 and recovering the crystallinity of the glass surface.

Suitable materials for the transparent electrode layer 2 formed on the glass substrate 1 are 5nOz and ITO, which have excellent transparency and conductivity, and are formed to a film thickness of 0.5nm by CVD or vapor deposition.
It is formed with a thickness of about 0.01 to 5 μm.

In addition, as the semiconductor layer 3 in which photoelectric conversion is performed, materials such as a-3i and GaAs, which have a large light absorption coefficient, can be used.
- ■ Group compound semiconductors and II-VI group compound semiconductors can be used, for example, in the case of a -3i, the film thickness is 0.
．． Approximately 5 to 1 μm, in the case of GaAs, the film thickness is 1 to 2 μm
It is formed by a plasma CVD method, a sputtering method, a vapor deposition method, or the like. Note that when configuring a photovoltaic element such as a solar cell, a pn junction, a pin
It is necessary to form a junction or a heterojunction.

For the electrode layer 4, which is the uppermost layer, a metal material with high reflectance and good conductivity is suitable, and examples include AI and Ag in particular. Formed by law etc.

In addition to the configuration shown in FIG. 1, the scope of the present invention also naturally includes a photovoltaic element in which a Schottky barrier type or MIS type solar cell is configured on a substrate having an uneven shape.

Effect By using the above-described configuration, simply by forming a thin film of a constant thickness on a substrate, the surface of the thin film has an uneven shape similar to that of the substrate surface. Furthermore, since the substrate is much thicker than the transparent electrode layer with a thickness of several μm or less, in which unevenness was attempted to be provided on the surface in Conventional Example 2, the unevenness of an appropriate size is formed on the surface of the substrate. It is easy to form with high precision. Therefore, the surface of the thin film formed on the substrate can have an uneven shape with excellent uniformity.

For example, in the case of the structure shown in FIG. 1, if the transparent electrode layer 2, the semiconductor layer 3'J6, and the electrode layer 4 are sequentially laminated on the glass substrate 1 with a constant thickness, each interface will have similar unevenness. It becomes a shape.

As a result, it passes through the glass substrate 1 and further transmits the transparent electrode layer 2.
As shown in FIG. 2, the light that enters the semiconductor layer 3 from above is first split into refracted light and reflected light at point A, and then this reflected light enters the semiconductor layer 3 again at point B and is refracted. Produce light. In this way, multiple reflection and refraction of the incident light is performed at the interface between the transparent electrode layer 2 and the semiconductor layer 3, so the amount of reflected light at this interface is reduced.

Similarly, the amount of reflected light also decreases at the interface between the glass substrate 1 and the transparent electrode layer 2.

Furthermore, as can be seen from FIG. 2, the traveling direction of the refracted light penetrating into the semiconductor layer 3 is different from the direction of the incident light, so that the optical path length within the semiconductor layer 3 becomes longer.

In addition, since a material with high reflectance is used for the electrode layer 4,
The light that is not absorbed within the semiconductor layer 3 is reflected at the interface with the electrode layer 4 and passes through the semiconductor layer 3 again.
The optical path length becomes even longer.

Moreover, since each layer is sequentially formed on the glass substrate 1 having an uneven shape with good uniformity, the thickness of the semiconductor layer 3 becomes uniform. Here, even if the unevenness formed on the glass substrate 1 has a sharp local part, since the transparent electrode layer 2 is deposited on top of this, the upper surface of the transparent electrode layer 2 becomes a continuous surface. The semiconductor layer 3 formed in this manner has an appropriate unevenness. Therefore, unlike the conventional example 2, the shunt resistance between the transparent electrode layer 2 and the electrode layer 3 does not become small.

Thus, the thin film photoelectric conversion element of the present invention has extremely high conversion efficiency. That is, in a photoconductive element, there is a large difference between the resistance value in the bright state and the resistance value in the dark state, and in the photovoltaic element, the generated electric power becomes large. Furthermore, unlike the reduction in the amount of reflected light caused by an antireflection film, the present invention achieves a reduction in reflection loss for light in a wide wavelength range.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the same extent by the following examples.

Described. A comparison of these results shows that the solar cell according to the present invention has very excellent characteristics.

In addition, in the above Example 1.2, a solar cell was constructed, but
It goes without saying that other photovoltaic elements or photoconductive elements can exhibit similarly excellent characteristics.

Effects of the Invention As described in detail above, according to the present invention, the unevenness provided on the substrate surface reduces reflection loss in photoelectric conversion and increases the optical path length in a thin film such as a semiconductor layer.

Therefore, various characteristics of photoelectric conversion, such as significantly improved conversion efficiency in a wide wavelength range, are achieved.

Thus, the thin film photoelectric conversion element according to the present invention can be used as a solar cell,
This makes it extremely suitable for use as optical sensors, photoconductive cells, and the like.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing an example of the structure of the thin film photoelectric conversion element of the present invention, Fig. 2 is an explanation showing multiple reflection/refraction due to an uneven surface (main reference numbers) 1.11...Glass substrate, 2.12...・Transparent electrode layer,
3...Semiconductor layer, 4...Electrode layer, 13...a
-81 layer, 14...Δl electrode layer Patent applicant Director of the Agency of Industrial Science and Technology Tatsu Todoroki Figure 1 Figure 2 1...Tsu grave n 3-+1 shock 12・aBM
taA 4-t&4 Figure 3 Figure 4 Envoy No. 5 6 11...T Ras Ivy 1 Tomb 13...a
” -Si layer

Claims (6)

[Claims] (1) A thin film photovoltaic device characterized by having a substrate having an uneven surface, and a multilayer thin film formed on the surface of the substrate and consisting of a semiconductor layer, a transparent electrode layer sandwiching the semiconductor layer, and an electrode layer. conversion element. (2) The thin film photoelectric conversion element according to claim 1, wherein the semiconductor layer has any one of a pn junction, a pin junction, and a heterojunction. (3) The thin film photoelectric conversion element according to claim 1 or 2, wherein the substrate is made of glass. (4) The thin film photoelectric conversion element according to claim 3, wherein the uneven shape of the substrate is formed by roll forming. (5) The thin film photoelectric conversion element according to claim 3, wherein the uneven shape of the substrate is formed by etching. (6) The thin film photoelectric conversion element according to claim 3, wherein the uneven shape of the substrate is formed by machining.