JPS5836469B2 - Chemically modified wet photovoltaic cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet photovoltaic cell, and more particularly to a chemically modified wet photovoltaic cell having an electrode having a sensitizing dye fixed to the surface of a light-transmitting semiconductor by covalent bonding.

Since photovoltaic cells have the function of converting light energy into electrical energy, their potential uses are extremely wide-ranging.For example, they are useful as light-sensitive elements in various optical monitoring devices, and are expected to continue to develop. In terms of objective, it can be a means of converting solar energy into electrical energy.

Looking at conventionally known photovoltaic cells, as dry type ones,
There is a p-
There are so-called solar cells that can be obtained by creating n-bonds, but since they require highly pure semiconductor crystals as their material, their manufacturing costs are inevitably high, and therefore their use is limited to special requirements. This makes it unsuitable as a general energy key conversion element.

In order to compensate for these drawbacks of solar cells, wet-type photovoltaic cells, which can operate satisfactorily even when using inexpensive semiconductors such as sintered bodies, have recently been studied.

However, the wet-type photovoltaic cells under consideration have the problem that any semiconductor material used dissolves at the cathode as a result of a photoelectrode reaction, which shortens the life of the electrode material. There is.

However, there are exceptional semiconductor electrodes that have almost no solubility problem, such as tin oxide, titanium oxide, and titanium strontium oxide, but all of these semiconductors are sensitive only to light in the ultraviolet region. Therefore, it is insufficient for use as a conversion element for solar energy that is widely distributed in the visible and near-infrared regions, and is therefore not worth employing.

For this reason, attempts have been made to expand the photosensitive wavelength range of stable semiconductors, which are only sensitive to ultraviolet light but do not cause the problem of dissolution due to photoelectrode reactions, to longer wavelengths. Those that utilize the sensitizing effect,
In other words, by adding a dye to the electrolyte solution that absorbs light at wavelengths longer than the characteristic absorption wavelength of the semiconductor electrode, it is possible to convert light energy at long wavelengths that are not absorbed by the semiconductor itself into electrical energy. .

Until now, spectroscopy has shown that in wet batteries in which a sensitizing dye is added to an electrolyte solution, some of the light energy with a wavelength longer than the characteristic absorption wavelength of the semiconductor itself is converted into electrical energy due to dye sensitization. Although it has been clarified by measuring photovoltaic force using light, the energy conversion efficiency is extremely low.
In the end, they came to the conclusion that such wet photovoltaic cells were of no practical use.

By the way, it has been clarified that the cause of the low efficiency is that the dye dissolved in the solution does not participate in dye sensitization, and only the dye adsorbed on the dissolution surface of the electrode contributes to dye sensitization. However, no means to solve the above-mentioned main problem has been proposed yet.

In view of the above-mentioned points, the present invention provides a chemically modified wet photovoltaic cell which is capable of converting long wavelength light energy into electrical energy by dye sensitization with high efficiency and has sufficient practicality. The purpose is to

Therefore, in the chemically modified wet photovoltaic cell of the present invention, in a wet photovoltaic cell using a semiconductor for one or both of the anode and the cathode, at least the cathode is a flat plate of a light-transparent n-type semiconductor or a flat plate covered with an n-type semiconductor thin film. It consists of electrode plates as chemically modified semiconductors with sensitizing dyes covalently fixed on the surface of the electrode plate, and these electrode plates are arranged parallel to each other in a layered manner together with an anode in an electrolyte solution. It is characterized by the fact that the electrode plate group is irradiated with light and the light is converted into electrical energy. Regarding the dye-sensitized wet cell consisting of polar electrodes, the present inventors published a paper (November 1976 issue of Nature, Vol. 264, 5).
No. 584, pp. 34.9-350], but
This wet type battery has a high conversion efficiency of light energy into electrical energy and has an o. Since it is extremely low at about 1% and is far from practical, in the present invention, this wet type photovoltaic cell has been improved to have the above-mentioned configuration, resulting in improved practicality.

In the chemically modified battery of the present invention, there is no chance for the dye to absorb light in the electrolyte solution, so there is no need to add dye during the use process, and light only comes from the dye covalently bonded to the electrode surface. , and thus efficiently converts light energy into electrical energy.

The chemically modified battery of the present invention can be roughly divided into the following three types with respect to its cathode, as shown in FIG.

(1) Each plate of Ia Kuiboo is chemically modified with only a single different type of pigment, and multiple plates are combined.

(2) A combination of Ib Quipuu plates each chemically modified with multiple types of dyes.

(3) Ic type - A combination of a plurality of plates chemically modified with a single type of dye and a plurality of plates chemically modified with multiple types of dyes.

As the semiconductor used in the present invention, the cathode has n
A p-type compound is used for the anode, and a p-type compound is used for the anode, but in any case, a compound is preferable because it is stable without problems such as dissolution due to the photoelectrode reaction during light irradiation, and an n-type compound is used. Examples of type semiconductors include oxides such as tin oxide, titanium oxide, and titanium strontium oxide.

Further, as the p-type semiconductor, for example, gallium arsenide, gallium phosphide, silicon carbide, copper oxide, etc. can be used.

It is of course possible for the electrode to be made of only the above-mentioned semiconductor, but while such an electrode has the advantage of low electrical resistance, it also suffers from optical loss due to scattering, etc.
It is not necessarily suitable because it has low mechanical strength and is economically expensive.

As an advantageous product that does not have these disadvantages, there is a so-called coated electrode, such as Nesa Glass (trade name), which is made by coating the surface of a plate made of a material such as glass or quartz that is transparent in the wavelength range of the light used, with a thin film of the semiconductor. be able to.

Such a covered electrode preferably has a total thickness of about 1 mrn, and the thickness of the semiconductor thin film can range from 500 to several 1000X, but is preferably about IOOOA.

As the sensitizing dye, any dye can be used as long as it exhibits a sensitizing effect.

Examples include xanthene pigments such as rotamine B, rose bengal, eosin, and erythrosin, cyanine pigments such as quinocyanine and cributocyanin, basic dyes such as phenosafranin, cabri blue, thiocine, and methylene blue, chlorophyll, and zinc. Examples include polyphyrin compounds such as volphyrin and magnesium porphyrin, azo dyes, and anthraquinone dyes.

In the present invention, such a sensitizing dye must be covalently fixed (chemically modified) on the surface of the electrode plate.

Some of the sensitizing dyes cannot be chemically modified as they are, such as xynocyanine, cryptocyanine, and metal porphyrin. For example, by deriving the compound to a compound having an amine group, a carboxyl group, or a hydroxyl group, it can be made to suit the purpose.

The electrolyte solution of the chemically modified wet photovoltaic cell of the present invention includes an electrolyte material for imparting ionic conductivity, such as Na2So4.
, NACt, etc., and a reversible oxidation-reduction system that contributes to electron transport, such as a quinone-hydroquinone pair.

Examples of the solvent for the electrolyte solution include water, DMF, and acetonitrile, with water being preferred.

Further, the concentration of the electrolyte substance is 1 to 0. 1 m ot/
The concentration of the oxidation-reduction system is preferably in the range of 1 0 -' to 1 0 -' m
o4/dm'' range.

However, in the oxidation-reduction system, the solvent of the electrolyte solution is water, which acts as a reducing agent and generates oxygen at the cathode, and protons receive electrons at the anode to generate hydrogen. Although not necessarily required, in this case, a chemical energy conversion occurs in which hydrogen and oxygen are generated together with the conversion of light energy into electrical energy.

Several means can be employed to covalently immobilize (chemically modify) the sensitizing dye on the surface of the electrode plate, and examples of these means are given below.

Since the semiconductor used as the electrode material in the present invention is usually a metal oxide, the surface of the electrode plate has hydroxyl groups, and the chemical modification of the sensitizing dye as a sensitizer to the hydroxyl groups is , a sensitizing dye (expressed as 11 D 11).

), such as a siliconizing agent such as γ-aminopyrtriethoxysilane, cyanuric chloride, or the like.

An example of this can be expressed using a reaction formula as shown below.

In the method (a) above, γ-aminobutyltriethoxysilane as a compound having a functional group (intermediate compound) is reacted in advance with the hydroxyl group of the semiconductor on the surface of the electrode plate to form the intermediate compound. Chemical modification is carried out by making a compound and then condensing it with a carboxylic acid or an acid chloride derivative using a sensitizing compound D to form an amide bond.

In addition, the above-mentioned method 6) employs cyanuric chloride as an intermediate compound, uses its alcohol derivative or amine derivative as the sensitizing dye D, and performs chemical modification.

In both of the above methods (1') and υ), the sensitizing dye is chemically modified on the surface of the electrode plate via an intermediate compound, but the sensitizing dye is attached to the electrode plate without using such an intermediate compound. It is also possible to directly chemically modify the surface semiconductor.

An example of this can be expressed using a chemical formula as follows.

These means e) and (d) apply the carboxylic acid or alcohol derivative of the sensitizing dye D to the semiconductor on the surface of the electrode plate.
Chemical modification is carried out by forming an ester bond or an ether bond through dehydration condensation with the hydroxyl group.

The sensitizing dye-modified electrode produced by the above methods (3) and (d) not only has the sensitizing dye D located very close to the semiconductor surface, but also has a high sensitizing dye concentration per unit area. Therefore, the quantum effect of dye sensitization is large, and therefore energy conversion can be performed extremely effectively, and the means (→ and (d) above) simply involve a surface chemical bonding reaction without using an intermediate compound. Therefore, it is possible to economically modify electrodes with sensitizing dyes.

Therefore, the above-mentioned means (3) and (d) can be said to be optimal for chemically modifying the surface of the semiconductor electrode with the sensitizing dye in the present invention.

As a method other than 0), (TO), so → and (d) above, the hydroxyl group of the semiconductor on the surface of the electrode plate is treated with thionyl chloride to form a chloride, and then a Grignard reagent or a lithium compound of sensitizing dye D is reacted. There is a method (e) for chemically modifying the surface of the electrode plate with the sensitizing dye by substituting the sensitizing dye D.

This means can be expressed by the following chemical formula.

Electrodes chemically modified with sensitizing dyes produced by the above-mentioned methods (a), (b), (c), (d) or (O) are shown in Figure 1 depending on the type of sensitizing dye employed. It is of the type Ia, Ib or Ic mentioned above.

FIG. 2 shows an example of the arrangement of electrode plates formed by chemically modifying the sensitizing dye in the chemically modified wet photovoltaic cell of the present invention.

In FIG. 2, Ila is a tamp in which the negative and anode plates 2, 2, . . . are arranged in parallel, and nb is the electrode plate 2'
．． 2'... is a cathode, and 3,3... is a type in which a mesh plate made of metal or carbon material that allows smooth transmission of light is used as an anode.
is a type in which the electrode plates 2", 2", . be.

In FIG. 2, symbols i, 1', i'' indicate the progress of light.

The mutual spacing between each electrode is not particularly limited, but
Determined by considering internal resistance.

In addition, the number of electrode plates arranged varies depending on the scale of the battery, but it can be 10 to 50 for normal ones, and 30 to 50 for normal ones.
Approximately one sheet is suitable.

FIG. 3 shows an example of the structure of the color-sensitized wet photovoltaic cell of the present invention.

In FIG. 3, reference numeral 5 indicates a container body (usually made of plastic), 6 indicates an electrode plate as a sensitizing dye chemically modified semiconductor, and 7 indicates an anode.

Further, numeral 8 indicates a reflecting mirror (for example, made of metal thin film), and 9
indicates an electrolyte solution, and 10 indicates a condensing lens.

In this battery, light 11 enters the interior of the battery via a condensing lens 10 and passes through electrode plates 6, 6, 6, . . . is absorbed and converted into electrical energy.

The light reaches the other end wall, that is, the reflecting mirror 8, is reflected, goes back to its original direction, passes through the electrode plates 6, 6, and so on again, is absorbed by the sensitizing dye, and is converted into electrical energy. However,
Usually, along the way, the light loses its energy.

Electrical energy is taken out from the battery through cathodes 6, 6 and 6.
. . . and the anode 7, γ via any means.

An example of manufacturing a dye-sensitized wet cell according to the present invention will be described below.

A Pyrex (trade name) substrate whose surface was coated with tin oxide was immersed in 1 t of methylene chloride solution containing 5 g of Rhodamine B and 5 g of dicyclohexylupodiimide, and left at room temperature for 24 hours to coat the surface of the tin oxide electrode with Rhodamine B. It is immobilized (chemically modified) by an ester bond.

Thereafter, the Pyrex plate is taken out and unreacted substances are washed and removed with methylene chloride.

Ten chemically modified tin oxide electrode plates (20 electrode surfaces) thus obtained were layered in parallel with 0.2M Na2 containing IXIO-''M hydroquinone + quinone (1:1).
The electrode plate is placed in an aqueous solution (electrolyte solution) as shown in FIG. 3, and light is irradiated from a direction perpendicular to the electrode plate through a condenser lens.

It has been confirmed that the light is reflected by the reflecting mirror 8 and passes through a total of 40 electrode-solution interfaces.

For the anode 7, a platinum plate is used. The apparent quantum efficiency of spectral sensitization by the separated light is about a factor of 15 at the absorption peak of rhodamine B at 570 mm.

[Brief explanation of the drawing]

Figure 1 shows the distribution type of sensitizing dye (Ia
, Ib, Ic), and FIG. 2 shows an example of the arrangement of the electrode plates (
FIG. 3 shows an example of the structure of the battery. 1.1', 1"... light, 2.2', 2"...
...7-Σ electrode plate, 3...Mesh anode plate, 4.
... Anode, 5 ... Container body, 6 ...
Cathode plate, 7... Positive, 8... Anti-91 mirror, 9... Electrolyte solution, 10... Collection-7
and lens, 11... light.

Claims (1)

[Claims] 1. In a wet photovoltaic cell in which one or both of the anode and cathode are made of a semiconductor, at least the cathode has a sensitizing dye covalently bonded to the surface of a light-transparent n-type semiconductor flat plate or a flat plate coated with an n-type semiconductor thin film. 1. A chemically modified wet photovoltaic cell comprising a number of fixed electrode plates, which are arranged parallel to each other in a layered manner together with an anode in an electrolyte solution.