JP2001358348A - Photoelectric conversion device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make low the internal resistance and recombination probability of a photoelectric conversion device and make high its conversion efficiency. SOLUTION: The photoelectric conversion device has at least an electron accepting type charge transfer layer, an electron donating type charge transfer layer, and a light absorbing layer present between these charge transfer layers, wherein one of these charge transfer layers is semiconductor crystal layers 17, 18 formed out of mixture crystals having two or more kinds of different aspects from each other, and at least one of the aspects is a needle-form crystal 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device and a method of manufacturing the same, and more particularly, to an electron-accepting type charge transport layer.
The present invention relates to a photoelectric conversion device having at least an electron donating type charge transport layer and a light absorbing layer existing between these charge transport layers, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a method of converting light energy into electric energy, a solar cell using a semiconductor junction such as silicon or gallium-arsenic is generally used. Above all, a single-crystal silicon solar cell and a polycrystalline silicon solar cell using a pn junction of a semiconductor, and an amorphous silicon solar cell using a pin junction are well known, and their practical use is progressing. However, silicon solar cells are expensive to manufacture and consume a lot of energy in the manufacturing itself, so long-term use is required to recover the introduction cost and energy consumption. It is mainly at this cost that the bottleneck of the current spread is.

On the other hand, in recent years, research on practical use of CdTe, CuIn (Ga) Se, and the like as second-generation thin-film solar cells has been progressing, but these materials have raised environmental and resource problems. .

As a method other than the above-mentioned semiconductor bonding, a wet solar cell utilizing a photoelectrochemical reaction occurring at an interface between a semiconductor and an electrolyte solution has been reported. Metal oxide semiconductors such as titanium oxide and tin oxide used in this wet solar cell can be manufactured at low cost as compared with silicon, gallium-arsenic, etc. also used in the dry solar cell, and especially, oxidized metal. Titanium is excellent in both photoelectric conversion characteristics and stability, and is expected as a future energy conversion material. However, since a stable optical semiconductor such as titanium oxide has a wide band gap of 3 eV or more, only ultraviolet light, which is about 4% of sunlight, can be used, and it cannot be said that the conversion efficiency is sufficiently high.

Accordingly, a photochemical cell (dye-sensitized solar cell) in which a dye is adsorbed on the surface of the optical semiconductor has been studied. In the early days, semiconductor single-crystal electrodes were used. The electrodes include titanium oxide, zinc oxide, cadmium sulfide,
And tin oxide. However, single-crystal electrodes have a low efficiency because of a small amount of dye adsorbed and are expensive, and attempts have been made to make the semiconductor electrodes porous. Tsubomura et al. Reported that dyes were adsorbed on a semiconductor electrode composed of porous zinc oxide with sintered fine particles to improve efficiency (NATURE, 261 (1976))
p402). Proposals for using a porous semiconductor electrode are disclosed in JP-A-10-112337 and JP-A-9-23.
No. 7641 discloses this.

Further, Graetzel et al. Reported that the performance of a silicon solar cell was obtained by further improving the dye and the semiconductor electrode (J. Am. Chem. Soc. 115 (1993) 6382; US Pat. No. 5,350,644). Here, a ruthenium-based dye is used as the dye, and anatase-type porous titanium oxide (TiO ₂ ) is used as the semiconductor electrode.

FIG. 6 is a schematic sectional view showing a schematic structure of a photochemical battery (hereinafter, referred to as a Graetzel type cell) using a Graetzel type dye-sensitized semiconductor electrode.

In FIG. 6, 64a and 64b are glass substrates, 65 and 66 are transparent electrode layers formed on the surface thereof, 61 is an anatase-type porous titanium oxide layer, and a porous state in which titanium oxide fine particles are bonded to each other. Made of conjugate. Reference numeral 62 denotes a dye bonded to the surface of the titanium oxide fine particles, which functions as a light absorbing layer.

Next, a method for manufacturing a Graetzel type cell will be described with reference to FIG.

First, a glass substrate 64 provided with a transparent electrode 65
A film of anatase type TiO ₂ fine particles 61 is formed on a.
Although there are various production methods, generally, a paste in which anatase-type TiO ₂ fine particles having a fine particle diameter of about 20 nm are dispersed is applied on an electrode, fired at 350 to 500 ° C., and baked at about 10 μm in thickness. Form a TiO ₂ fine particle film. At this time, the fine particles are appropriately bonded to each other, and the porosity is about 50% and the lathness factor (substantial surface area /
A film having a structure with an apparent surface area of about 1000 is obtained.

Next, a dye is adsorbed on the electrode with fine particles. Various substances have been studied for the dye, but generally a Ru complex or the like is used. When the electrode is immersed and dried in a solution in which the dye is dissolved, the light absorbing layer 62 is bonded to the surface of the TiO ₂ fine particles. In this solvent, ethanol or acetonitrile, which dissolves the dye well, does not inhibit the adsorption of the dye to the electrode, and is electrochemically inactive even if it remains on the electrode surface, is used.

Next, a glass substrate 64b also having a transparent electrode 66 as a counter electrode is prepared, and an ultra-thin film such as platinum or graphite is formed on the surface. This thin film acts as a catalyst when transferring charges in redox.

Then, the electrolytic solution 63 is applied to the two electrodes 6.
Graetzel-type cells are completed when they are held between layers 5 and 66. As a solvent for the electrolytic solution, acetonitrile, propylene carbonate, or the like, which is electrochemically inert and can dissolve a sufficient amount of the electrolyte, is used. As for the electrolyte, stable ion redox couples such as I ⁻ / I ₃ ⁻ and Br ⁻ /
Br ₃ ^- or the like is used. For example, I ^- / I ₃ ^- mixing the ammonium salt and iodine iodine when making pairs.

Thereafter, it is preferable to seal the cells with an adhesive or the like in order to impart durability.

Next, the operating principle of the Graetzel type cell will be described. Light is incident on the Graetzel type cell from the left side of FIG. Then, the electrons in the dye constituting the light absorbing layer 62 are excited by the incident light, and move to the conduction band of titanium oxide. The dye which has lost electrons and is in an oxidized state quickly receives electrons from iodine ions in the electrolyte 63 and is reduced to return to the original state. The electrons injected into the titanium oxide layer 61 move between the titanium oxide fine particles by a mechanism such as hopping conduction and reach the transparent electrode layer (anode) 65. Also,
The iodine ion which has been oxidized by supplying electrons to the dye (I ₃ ⁻ ) receives electrons from the transparent electrode layer (cathode) 66 and is reduced to return to the original state (I ⁻ ).

As can be inferred from the above operating principle, in order for electrons and holes generated by the dye to efficiently separate and move, the energy level of the electrons in the excited state of the dye is TiO.
_It must be higher than the conduction band of ₂ , and the energy level of the holes in the dye must be lower than the redox level.

In order for such a Graetzel type cell to replace a silicon solar cell, higher energy conversion efficiency, higher short-circuit current, open-circuit voltage, shape factor, and durability are required.

[0018]

However, the above-described dye-sensitized semiconductor electrode of the prior art is obtained by applying a solution in which fine particles of titania are dispersed on a substrate having a transparent conductive film, followed by drying and sintering at a high temperature. Since the titanium oxide film was used, electron conduction tended to be scattered at the interface between the transparent electrode and the titania fine particles and at the interface between the titanium oxide fine particles. For this reason, the internal resistance generated at the interface between the transparent conductive film and the titanium oxide film and at the interface between the titanium oxide fine particles is increased, and as a result, the photoelectric conversion efficiency is reduced.

Further, since the dye-sensitized semiconductor electrode is formed of a sintered body of fine particles, it takes time to adsorb the dye to the fine particles near the transparent electrode, and the diffusion of ions in the electrolyte is slow. There were challenges.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a photoelectric conversion device capable of smoothly transferring and receiving electrons and having high conversion efficiency.

Another object of the present invention is to provide a photoelectric conversion device having a semiconductor electrode in which a light absorbing layer of a dye or the like or a charge transporting layer of an electrolyte or the like is quickly permeated or moved.

Another object of the present invention is to provide a photoelectric conversion device having a high open-circuit voltage.

Another object of the present invention is to provide a method for manufacturing a photoelectric conversion device having the above characteristics.

[0024]

The above objects can be attained by the photoelectric conversion device of the present invention and its manufacturing method.

That is, the photoelectric conversion device of the present invention is a photoelectric conversion device having at least an electron-accepting type charge transporting layer, an electron donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. Wherein any one of the charge transport layers is a semiconductor layer composed of a mixture of two or more different modes or compositions, and at least one of the semiconductor layers
It is characterized in that the type is a needle crystal.

A method for manufacturing a photoelectric conversion device according to the present invention is directed to a photoelectric conversion device having at least an electron-accepting type charge transporting layer, an electron donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. Forming a semiconductor mixed crystal layer on the substrate by applying and baking a semiconductor mixture solution comprising a semiconductor mixture of two or more different modes or compositions on the substrate, and forming the semiconductor mixed crystal on the substrate. The layer is any one of the charge transport layers.

Further, the method for manufacturing a photoelectric conversion device according to the present invention comprises:
A method for manufacturing a photoelectric conversion device having at least an electron-accepting type charge transporting layer, an electron-donating type charge transporting layer, and a light-absorbing layer existing between these charge transporting layers, comprising a solution containing a semiconductor needle crystal. Forming a needle-shaped crystal semiconductor layer by applying the mixture on a substrate and baking it. Further, a single substance or a mixture having a different form or composition from the needle-shaped crystal is attached to the semiconductor layer, and a semiconductor mixture is formed on the substrate. Forming a crystal layer, wherein the semiconductor mixed crystal layer is any one of the charge transport layers.

The method for manufacturing a photoelectric conversion device according to the present invention
A method for manufacturing a photoelectric conversion device having at least an electron-accepting type charge transport layer, an electron-donating type charge transporting layer, and a light absorbing layer present between these charge transporting layers, wherein needle-like crystals are formed on a substrate. Growing, forming a semiconductor mixed crystal layer on the substrate by attaching a single substance or a mixture having a different form or composition to the needle crystal to the needle crystal, and forming the semiconductor mixed crystal layer on the charge transport layer. It is characterized by any one.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The main feature of the photoelectric conversion device according to the present invention is that needle-like crystals are used for an electron-accepting (n-type) or electron-donating (p-type) charge transport layer. The acicular crystal is a so-called whisker, and is made of an acicular single crystal having no defect or an acicular crystal containing a helical transition or the like. Further, as shown in FIGS. 8 (a), 8 (b) and 8 (c), the needle-like crystal is obtained by growing a larger number of needle-like crystals than one point including a tetrapod (registered trademark) shape (FIG. 8 (a)). ))
Includes those formed in dendrites (FIG. 8 (b)) and those grown in polygonal lines (FIG. 8 (c)).

The needle-shaped crystal includes a cylinder, a cone, a cone having a flat tip, a column having a sharp tip, and a flat tip. In addition, triangular pyramids, square pyramids,
Hexagonal pyramids, other polygonal pyramids and those whose flat ends are flat, triangular prisms, quadrangular prisms, hexagonal prisms, other polygonal prisms, or triangular prisms, quadrangular prisms, hexagonal prisms with sharp ends, and other polygons It includes a columnar shape and a flat one with its tip, and further includes these broken line structures.

The mixed crystal is a semiconductor layer in which one of the charge transport layers is a mixture of two or more kinds of different modes or compositions, and one or more of the semiconductor layers includes a needle-like crystal. Shall mean. FIGS. 10A and 10B show examples of the state of the mixed crystal.
(C). 10 (a) shows the case where particles are attached around the needle crystal, FIG. 10 (b) shows the case where needles are attached around the needle crystal, and FIG.
(C) consists of a needle-like crystal with a film-like substance attached around it.

In order to explain the effects of the acicular crystal and the mixed crystal thereof, the present invention will be described in comparison with a conventional Graetzel type cell. <Configuration of Photoelectric Conversion Device of the Present Invention> First, the configuration of the present invention will be described.

In a dye-sensitized cell such as the above-described Graetzel type cell, since the light absorption of one dye layer is not sufficient, the surface area is increased to increase the substantial light absorption. The present invention is not limited to dye sensitization but can be widely used in general for photoelectric conversion devices having a structure in which the surface area is increased due to insufficient light absorption. As a method for enlarging the surface, it is simple to disperse and join the fine particles as in the Graetzel type cell, but there is a problem that the transfer of electrons is not sufficiently efficient. For example, in the above Graetzel type cell, the case where light is incident from the transparent electrode layer 65 side serving as the anode having the titanium oxide semiconductor layer 61 is compared with the case where light is incident from the transparent electrode layer 66 side serving as the cathode. Is often better in photoelectric conversion efficiency. This is not only a difference in the amount of light absorbed by the dye, but also the probability that electrons excited by the light absorption move through the titanium oxide semiconductor layer 61 and reach the transparent electrode layer 65 serving as an anode. It suggests that it decreases as you move away. That is, this suggests that a Graetzel type cell having many crystal grain boundaries has not achieved sufficiently efficient electron transfer.

FIGS. 1A and 1B are views showing an example of the configuration of a photoelectric conversion device according to the present invention. In FIG. 1, reference numeral 10 denotes a substrate with electrodes, 11 denotes an absorption layer-modified semiconductor mixed crystal layer, 12 denotes a charge transport layer, and 13 denotes a substrate with electrodes. The substrate with electrodes 10 is, for example, a glass substrate 1 on which a transparent electrode layer 15 is provided.
4, the absorption layer-modified semiconductor mixed crystal layer 11 is composed of a semiconductor needle crystal 17 and a light absorption layer 16 formed on the surface thereof. The semiconductor needle-like crystal 17 becomes one charge transport layer, and the light absorption layer 16 is provided between the charge transport layer and the charge transport layer 12.

When comparing the mixed crystal layer of the present invention with the fine particle crystal layer, the probability that electrons or holes generated by photoexcitation are scattered by the grain boundaries before moving to the collecting electrode is smaller in the mixed crystal layer. In particular, as shown in FIG. 1 (b), all the needle-shaped crystals are formed with one end bonded to an electrode, and when a different kind of microcrystal is sintered on the needle-shaped crystal, the electron Or in moving the hall, Graetzel
Compared with the mold cell, the influence of the grain boundary is almost eliminated.

In the photoelectric conversion device according to the present invention, the mixed crystal is an n-type wide gap semiconductor or a p-type wide gap semiconductor. When the mixed crystal is an n-type wide gap semiconductor, a p-type wide gap semiconductor, an electrolyte containing a redox (oxidation-reduction) pair, and an electron such as a polymer conductor are sandwiched by a light absorbing layer 16 such as a dye. A donor type charge transport layer 12 is required. Conversely, when the mixed crystal is a p-type wide gap semiconductor, an electron-accepting type charge transport layer 12 is required with the light absorbing layer 16 interposed therebetween.

The light irradiation surface is determined by which surface the transparent electrode is used. The configuration shown in FIG. 2A is an example in which a transparent electrode is used on the semiconductor crystal layer side similarly to the Graetzel type cell. The configuration shown in FIG. 2B is the opposite configuration, and either configuration may be used as long as the absorption and reflection of irradiation light to the light absorption layer is small. Also, as shown in FIG.
There is also a configuration that can be used by light irradiation from either surface. These configurations depend on the method for manufacturing the semiconductor needle-shaped crystals and the method and composition of the charge transport layer to be combined. For example, when producing a needle-like crystal by oxidizing a metal substrate, light cannot be irradiated from the needle-like crystal surface. When a needle-like crystal surface is formed by a low-temperature process such as firing of a needle-like crystal powder, it can be formed without deteriorating the transparent electrode layer.

FIGS. 9A and 9B are diagrams showing a specific example of the structure of the mixed crystal. Grae shown in FIG.
Compared to the tzel type cell, the effect of the grain boundary is almost eliminated, so that the movement of electrons and holes can be easily performed.
Further, the semiconductor crystal 18 is adsorbed as shown in FIG. 9B, so that the influence of the grain boundaries is small and the roughness factor can be improved. Further, even if any surface is irradiated with light, the irradiated light can reach a wide range. Therefore, many electrons can be transferred, and a cell of a photoelectric conversion device with high conversion efficiency can be manufactured.

Next, the mixed crystal used in the present invention will be described. <Regarding Needle-Shaped Crystals and Mixed Crystals> In cells using a light-absorbing layer having a low absorption efficiency per layer, such as the above Graetzel type cell, roughness is increased by using a fine particle film having a high porosity to increase the surface area. Although the factor is increased, the roughness factor can be increased as long as the aspect ratio is large, and the roughness factor can be further increased by sintering the microcrystals around the needle-shaped crystal even if the aspect ratio is large.

The cross section of the needle-shaped crystal depends on the crystal.
Triangles, squares, hexagons, and other polygons, some of which are almost circular. The sides do not necessarily have to be equal, and the lengths of the sides may be different. As described above, the needle-shaped crystals include those having a sharp tip as well as those having a sharp tip. Although it depends on the light absorptivity, the aspect ratio of at least the acicular crystal is 5 or more, preferably 1
It is preferably 0 or more, more preferably 100 or more. The diameter of the needle-shaped crystal is also preferably 1 μm or less, and preferably 0.1 μm or less.

Here, the aspect ratio means the ratio of the length to the diameter when the cross-section of the needle-shaped crystal is circular or nearly circular, and the cross-section of the needle-shaped crystal is a square such as a hexagon. In the case of, the ratio of the length of the needle crystal to the minimum length passing through the center of gravity of the cut surface is referred to.

As the mixed crystal, those having a large energy gap are preferable, and specifically those having an energy gap of 3 eV or more are preferable. Electron accepting type (n
Examples of the (type) crystal include TiO ₂ , ZnO, SnO ₂
And the like, and examples of the electron donating (p-type) crystal include NiO and CuI.

As a method for producing such a mixed crystal,
There is a method of applying and firing the mixed crystal powder in the same manner as in the above Graetzel type cell. In this case, the needle-like crystals overlap with the substrate 14 in parallel as shown in FIG.
1 (b), it is preferable that one end of the needle-shaped crystal is formed in a direction perpendicular to the substrate 14 in a state where one end of the needle-shaped crystal is bonded to the transparent electrode 15. The angle between the axial direction of the needle-shaped crystal and the main surface of the substrate is preferably 60 ° or more.
゜ is more preferable. In addition, semiconductor crystal 1
No. 8 includes a method of applying in a state of being mixed in advance, and a method of applying one or more kinds of semiconductor crystals in advance so as to apply again. At this time, fine particles having a diameter of the semiconductor crystal 18 of 100 nm or less, preferably 20 nm or less are preferable.

There is also a method of growing a needle-like crystal on a substrate, and this method is roughly classified into two types. One is to supply crystal components from outside,
Examples include a CVD method, a PVD method, and an electrodeposition method. As another method, there is a method in which a component on a substrate is reacted to grow a needle crystal.

[0045] As the former, for example, after forming a metal layer on the substrate 41 as shown in FIG. 5 (a), TiO ₂ and Zn
Needle crystal is grown on a metal layer by using an open-air CVD method using O or the like, and then a semiconductor crystal 18 such as TiO ₂ or ZnO is deposited. Alternatively, as shown in FIG. A method of growing a needle-like crystal on itself using an open-to-air CVD method, and then applying a different semiconductor crystal.

As the latter, for example, as shown in FIG. 5A, a metal layer such as Ti or Zn is formed on a substrate and then oxidized to grow a needle-like crystal. As shown, there is a method of oxidizing the metal substrate itself to grow needle crystals.

In particular, as a method of controlling the diameter and the growth direction of the needle-like crystal, there is a method of growing a needle-like crystal from nanoholes which become micropores as shown in FIG. Specifically, the metal layer 42 or the metal substrate 44 of the acicular crystal component
Is provided thereon, and an aluminum layer is provided thereon in a thickness of about 0.1 to several μm, and the upper aluminum layer is anodized to form a nanohole layer 43 serving as a fine pore layer. In this anodic oxidation, oxalic acid, phosphoric acid, sulfuric acid, or the like is used, and the distance between nanoholes can be controlled by the anodic oxidation voltage. The nanohole diameter can be controlled by etching with a phosphoric acid solution or the like after anodic oxidation. When the alumina nanoholes are prepared and then deoxidized in an atmosphere such as oxygen or water vapor, the underlying metal of the alumina nanoholes is oxidized, and the semiconductor needle-like crystals 17 can grow through the nanoholes.

In the latter method for producing needle-like crystals by oxidation, oxidation conditions are generally an important factor in determining the diameter and length of the needle-like crystals.

After controlling the diameter and the growth direction of the needle-shaped crystal, the needle-shaped crystal 17 is immersed in a gel solution using a different kind of semiconductor crystal, so that the surface of the semiconductor needle-shaped crystal 17 as shown in FIG. A structure in which the semiconductor crystal 18 exists can be adopted. As a result, a semiconductor crystal having a large roughness factor can be manufactured even when the diameter and length of the needle-shaped crystal are insufficient, and a semiconductor mixed crystal in which the influence of a grain boundary on movement of electrons or holes is small. Can do things. <Regarding Light Absorbing Layer> Various semiconductors and dyes can be used as the light absorbing layer of the photoelectric conversion device of the present invention. The semiconductor is preferably an i-type amorphous semiconductor having a large light absorption coefficient or a direct transition semiconductor. As the dye, organic dyes such as metal complex dyes and / or polymethine dyes, perylene dyes, rose bengal, Santalin dyes, and cyanine dyes, and natural dyes are preferable. The dye preferably has an appropriate bonding group to the surface of the semiconductor fine particles. Preferred linking groups include COOH groups, cyano groups, PO ₃ H ₂ groups, or chelating groups having π conductivity, such as oximes, dioximes, hydroxyquinolines, salicylates and α-keto enolates. Among them, COOH group, PO
_{The 3} H ₂ group is particularly preferred. When the dye used in the present invention is a metal complex dye, the ruthenium complex dye @Ru (dcbpy)
₂ (SCN) ₂ , (dcbpy = 2,2-bipyridine (bipyr
idine) -4,4'-dicarboxylic acid
d)) Although｝ etc. can be used, it is important that the oxidized and reduced forms are stable.

Also, the potential of the excited electrons in the light absorbing layer,
That is, the potential of the dye that has been photoexcited (LUMO potential of the dye) and the conduction charge potential in the semiconductor are higher than the electron acceptance potential of the electron-accepting charge transport layer (such as the conduction charge potential of an n-type semiconductor), and the photoexcitation in the light absorption layer Is required to be lower than the electron donating potential of the electron donating type charge transfer layer (such as the valence charge potential of the p-type semiconductor and the potential potential of the redox couple). It is also important to lower the probability of recombination of excited electrons and holes near the light absorption layer in order to increase the photoelectric conversion efficiency. <Charge transport layer (counter electrode to mixed crystal)> When an n-type mixed crystal is used, it is necessary to form a hole transport layer with a light absorbing layer interposed therebetween. For this hole transport layer, a redox system can be used as in a wet solar cell. Even when redox is used, not only a simple solution system but also a method of using carbon powder as a holding material or gelling an electrolyte is available.
There is also a method using a molten salt or an ion conductive polymer. Further, as a method of transporting electrons (holes), an electropolymerized organic polymer or p such as CuI, CuSCN, NiO, etc.
A type semiconductor can also be used. Conversely, when a p-type mixed crystal is used, n-type semiconductors such as ZnO and Ti
O ₂ and SnO ₂ can be used.

Since the transport layer needs to penetrate between the mixed crystals, it is suitable to use a permeation method that can be used for a liquid or a polymer, a plating method or a CVD method that can be used for a solid transport layer. <Electrode> An electrode is provided adjacent to the charge transport layer and the semiconductor needle crystal layer. The electrodes may be provided on the outer front surface of these layers or may be provided partially. If the charge transport layer is not solid, it is better to provide an electrode on the front surface from the viewpoint of holding the charge transport layer. It is preferable to provide a catalyst such as Pt or C on the surface of the electrode adjacent to the charge transport layer, for example, in order to efficiently reduce the redox couple.

As the electrode on the light incident side, a transparent electrode made of indium-tin composite oxide, tin oxide doped with fluorine, or the like is suitably used. When the resistance of the layer (charge transport layer or semiconductor mixed crystal layer) in contact with the electrode on the light incident side is sufficiently low, it is possible to provide a partial electrode, for example, a finger electrode, as the electrode on the light incident side.

The electrodes not on the light incident side are Cu, A
A metal electrode made of g, Al, or the like is preferably used. <Regarding Substrate> The material and thickness of the substrate can be appropriately designed according to the durability required for the photovoltaic device.
As the substrate on the light incident side, a glass substrate, a plastic substrate, or the like is suitably used as long as it is translucent. As a substrate that does not become the light incident side, a metal substrate, a ceramic substrate, or the like can be used as appropriate. On the surface of the substrate on the light incident side,
It is preferable to provide an antireflection film made of SiO ₂ or the like.

It should be noted that the above-mentioned electrode may also serve as a substrate so that a substrate separate from the electrode may not be provided. <Seal> Although not shown, it is preferable that the photoelectric conversion device of the present invention seal at least a portion other than the substrate from the viewpoint of improving weather resistance. An adhesive or a resin can be used as the sealing material. When the light incident side is sealed, the sealing material is preferably light-transmitting.

[0055]

The present invention will be further described below with reference to examples. [Embodiment 1] In this embodiment, an example in which a rutile-type acicular crystal powder is used for an electron-accepting electron-transporting layer to fabricate a photoelectric conversion device will be described with reference to FIGS.

3 g (gram) of rutile-type TiO ₂ needle-like crystals having a diameter of 200 to 300 nm and a length of about 10 times the diameter and 3 g of anatase-type TiO ₂ microcrystals (P25) having a particle size of about 20 nm were added to 10 mL of water ( Milliliter), 0.2 mL of acetylacetone, and 0.2 mL of Triton-X (registered trademark; manufactured by Union Carbide Co.) to form a slurry. This slurry is mixed with conductive glass (F-doped Sn).
O ₂ , 10Ω / □) on a spacer with a thickness of about 5
0 μm, 1 cm square was applied. And 100 oxygen gas
Firing was performed at 450 ° C. for 1 hour while flowing at a flow rate of mL / min (sccm).

The thickness of the TiO ₂ needle crystal layer after firing is about 1
It was 0 μm. The pigment is Ru, reported by Graetzel et al.
The complex Ru ((bipy) (COOH) ₂ ) ₂ (S
CN) ₂ was used. The dye was dissolved in distilled ethanol, and a TiO ₂ electrode was immersed in the ethanol for 120 minutes to allow the dye to be adsorbed on the electrode, and then taken out and dried at 80 ° C. In addition, platinum was added on conductive glass (F-doped SnO ₂ , 10Ω / □).
A counter electrode formed by sputtering to a thickness of nm was used, and the redox pair used was I ⁻ / I ₃ ⁻ . The solute was tetrapropylammonium iodide (0.46
mol / L) and iodine (0.06 mol / L), and the solvent used was a mixture of ethylene carbonate (80 vol%) and acetonitrile (acetonitrile) (20 vol%). This mixed solution was dropped on conductive glass with TiO ₂ and sandwiched between counter electrodes to form a cell.

A cell was similarly assembled using only P25 as a comparative example.

Then, xenon lamp light of 500 W equipped with an ultraviolet cut filter was irradiated from the conductive glass side with TiO ₂ or the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open potential and the fill factor of the cell of the present invention were about 5% higher than those of the cell of the present invention. This is considered to be because the internal resistance of the electron-accepting charge transport layer was reduced by using the mixed crystal. [Example 2] An experiment similar to that of Example 1 was performed using a ZnO needle crystal and a SnO ₂ needle crystal instead of TiO ₂ needle crystals.

At this time, the ZnO needle-like crystal is in the form of a tetrapod, having a diameter of about 1 μm, a length of about 5 times the diameter, and
The nO ₂ needle crystal had a diameter of about 0.5 μm and a length of about 10 times the diameter. The same evaluation as in Example 1 was performed with the same manufacturing method as in Example 1. As a result, compared to the comparative examples (apparatus using ZnO powder and apparatus using SnO ₂ powder), in each apparatus, when light was irradiated from the conductive glass side with the mixed crystal layer, the open potential and fill Both factors were about 3% larger, and when light was irradiated from the counter electrode side, both the open potential and the fill factor were 5% or more. This is considered to be because the internal resistance of the electron-accepting charge transport layer was reduced by using the mixed crystal. [Embodiment 3] In this embodiment, an example in which a semiconductor material is manufactured by oxidizing a metal material will be described with reference to FIGS.

A Ti base metal layer 42 is formed on a quartz substrate 41
A substrate having a thickness of μm and a substrate of a Ti plate 44 are prepared, and the respective Ti surfaces are slightly anodized at 40 V in 0.3 mol / L of oxalic acid. These substrates were fired at 700 ° C. for 10 hours while flowing He gas containing 10 ppm of oxygen at 100 mL / min (sccm). T after firing
Rutile-type TiO ₂ needle-like crystals grew from the substrate on the i-base and the surface of the Ti substrate as shown in FIGS. 5 (a) and 5 (b). The diameter of the needle-like TiO ₂ crystal was 0.1 to 2 μm, and the length was 10 to 100 times the length. The anatase type TiO ₂ microcrystal (P
25) 3 g of water 40 mL, acetylacetone 0.2 m
L, mixed with 0.2 mL of Triton-X, immersed in a slurry solution, and further oxygen was added at 100 mL / min.
The firing was performed at 450 ° C. for 1 hour while flowing (sccm). Then, a dye was adsorbed on the surface of the needle-shaped crystal in the same manner as in Example 1. Then, conductive glass (F-doped SnO ₂ ,
A counter electrode having a thickness of about 1 nm made of graphite on 10Ω / □) was used, and I ⁻ / I ₃ ⁻ was used as a redox pair.
As in Example 1, the solute was also tetrapropylammonium iodide (0.46 mol /
L), iodine (0.06 mol / L), and a solvent used were a mixture of ethylene carbonate (80 vol%) and acetonitrile (acetonitrile) (20 vol%). This mixed solution was dropped on conductive glass with TiO ₂ and sandwiched between counter electrodes to form a cell.

A cell was similarly assembled using P25 as a comparative example.

In the same manner as in Example 1, a 500 W xenon lamp light equipped with an ultraviolet cut filter was irradiated from the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open potential and the fill factor of the cell of the present invention were both higher by about 10%. This is considered to be due to the fact that the internal resistance of the electron-accepting charge transport layer was reduced by using the needle-like crystals. Embodiment 4 In this embodiment, an example in which a metal material is oxidized to form a semiconductor needle crystal from nanoholes will be described with reference to FIGS.

A Ti base metal layer 42 is formed on a quartz substrate 41
A substrate having a thickness of μm and a substrate of the Ti plate 44 were prepared, and 0.5 μm of Al was formed on each Ti surface. Then, the Al layer was anodized at 40 V in oxalic acid 0.3 mol / L, and then immersed in phosphoric acid 5 wt.% For 40 minutes. A large number of nanoholes having a diameter of about 50 nm were opened at intervals of about 100 nm in the alumina layer 43 anodized by this treatment. 100 mL / min of He gas containing 10 ppm of oxygen
(Sccm) while flowing these substrates at 700 ° C. for 1 hour.
The firing was performed for 0 hours. Rutile-type TiO ₂ needle-like crystals 17 were grown from the alumina nanoholes on the surface of the Ti base and the surface of the Ti substrate after firing, as shown in FIGS. 4A and 4B. The diameter of the TiO ₂ needle crystal is 0.02 to
The length was 0.05 μm, and the length was 20 to 500 times the length. The substrate is made of anatase TiO having a particle size of about 20 nm.
( ₂ ) 3 g of microcrystals (P25) are mixed with 40 mL of water, 0.2 mL of acetylacetone, and 0.2 mL of Triton-X to be immersed in a slurry solution, and oxygen is further added to 100 mL.
Calcination was performed at 450 ° C. for 1 hour while flowing at a flow rate of / min (sccm).

In the same manner as in Example 1, a dye was adsorbed on the surface of the needle crystal. Then, the conductive glass (F-doped S
A counter electrode in which graphite was formed to a thickness of about 1 nm on nO ₂ , 10Ω / □) was used, and I ⁻ / I ₃ ⁻ was used as a redox pair. As in Example 1, the solute was tetrapropylammonium iodide (0.
46mol / L) and iodine (0.06mol / L), solvent is ethylene carbonate (80vol)
%) And acetonitrile (acetonitrile) (20 vol.
%). This mixed solution was dropped on conductive glass with TiO ₂ and sandwiched between counter electrodes to form a cell.

A cell was similarly assembled using P25 as a comparative example.

Then, in the same manner as in Example 1, a 500 W xenon lamp light equipped with an ultraviolet cut filter was irradiated from the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open cell potential and the fill factor of the cell of the present invention were both higher by about 5%. This is considered to be due to the fact that the internal resistance of the electron-accepting charge transport layer was reduced by using the needle-like crystals. [Embodiment 5] In this embodiment, an example in which a semiconductor needle crystal is manufactured by using an open-air CVD method will be described with reference to FIGS.

An Al base metal layer 42 is formed on a quartz substrate 41
A substrate on which a film having a thickness of μm was formed and a substrate having an Al plate 44 were prepared, and each was placed on a substrate heating table 76 of a CVD apparatus. Then, solid bis (acetylacetonato) zinc (II) was put in the raw material vaporizer 73, and heated at 115 ° C. to vaporize. It was carried by nitrogen and sprayed from a nozzle 74 onto a heated Al substrate 75. On the Al base after the treatment and on the surface of the Al substrate, needle-like ZnO crystals are shown from the substrate in FIG.
It grew as shown in (b). This ZnO The diameter of the needle-like crystal was about 1 μm, and the length was 10 to 100 times the length. The substrate was treated with 3 g of rutile TiO ₂ needle-like crystals and anatase TiO ₂ microcrystals (P2
5) 3 g of water 40 mL, acetylacetone 0.2 mL,
It was immersed in a slurry-like solution mixed with 0.2 mL of Triton-X, and oxygen was further added at 100 mL / min (sc).
cm) while flowing at 450 ° C. for 1 hour. Then, a dye was adsorbed on the surface of the needle-shaped crystal in the same manner as in Example 1. Then, conductive glass (F-doped SnO ₂ , 10Ω)
/ □), a counter electrode having a thickness of about 1 nm formed of graphite was used, and I ⁻ / I ₃ ⁻ was used as a redox pair. As in Example 1, the solute was tetrapropylammonium iodide (0.46 mol / L) and iodine (0.06 mol / L), and the solvents were ethylene carbonate (80 vol%) and acetonitrile (80 vol%). acetonitrile) (20 vol%). This mixed solution is ZnO On the conductive substrate with
A cell was sandwiched between the opposite electrodes.

As a comparative example, a cell was similarly assembled using a heat-treated ZnO powder having a particle size of about 1 μm as a main component.

Then, in the same manner as in Example 1, a xenon lamp light of 500 W equipped with an ultraviolet cut filter was irradiated from the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open potential and the fill factor of the cell of the present invention were higher by about 7%. This is considered to be due to the fact that the internal resistance of the electron-accepting charge transport layer was reduced by using the needle-like crystals. [Embodiment 6] In this embodiment, an example in which a semiconductor needle crystal is manufactured by using an open-to-air CVD method will be described with reference to FIGS.

F-doped SnO ₂ on the substrate glass 44
42 coated with conductive glass (F-doped SnO ₂ , 10
Ω / □) was prepared and placed on the substrate heating table 76 of the CVD apparatus. Then, solid bis (acetylacetonato) zinc (II) was put in the raw material vaporizer 73, and heated at 115 ° C. to vaporize. It was carried by nitrogen and sprayed from a nozzle 74 onto a heated conductive glass substrate 75. On the surface of the conductive glass after the treatment, ZnO needle-like crystals
It grew as shown in FIG. This ZnO The diameter of the needle-like crystal was 1 μm, and the length was 10 to 100 times the length. The substrate is made of 3 g of rutile-type TiO ₂ needle crystals and anatase-type TiO ₂ microcrystals having a particle size of about 20 nm (P25).
3 g was mixed with 40 mL of water, 0.2 mL of acetylacetone, and 0.2 mL of Triton-X, immersed in a slurry solution, and oxygen was further added at 100 mL / min (scc
m) Baking was performed at 450 ° C. for 1 hour while flowing. Then, a dye was adsorbed on the surface of the needle-shaped crystal in the same manner as in Example 1.
Then, conductive glass (F-doped SnO ₂ , 10Ω /
□) A counter electrode having a thickness of about 1 nm made of graphite was used thereon, and CuI was used as a p-type semiconductor. CuI is
It was dissolved in anhydrous acetonitrile and deposited on the interface of the mesoscopic ZnO film supporting the dye. The solid-state solar cell was fabricated by superposing the solid electrode thus adjusted on a counter electrode.

As a comparative example, a cell was similarly assembled using a heat-treated ZnO powder having a particle size of about 1 μm as a main component.

Then, in the same manner as in Example 1, a 500 W xenon lamp light equipped with an ultraviolet cut filter was irradiated from the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open potential and the fill factor of the cell of the present invention were higher by about 7%. This is considered to be due to the fact that the internal resistance of the electron-accepting charge transport layer was reduced by using the needle-like crystals. [Embodiment 7] In this embodiment, an example in which a photoelectric conversion device is manufactured using rutile-type acicular crystal powder for an electron-accepting electron-transporting layer will be described with reference to FIGS.

The diameter is 200 to 300 nm and the length is
Rutile type TiO which is about 10 times_Two6 g of needle-like crystals are added to water 10
mL, acetylacetone 0.2 mL, Triton-X0.
It was mixed with 2 mL to make a slurry. Make this slurry conductive
Glass (F-doped SnO)_Two, 10Ω / □)
It was applied to a thickness of about 50 μm and 1 cm square using a laser.
Then, flow oxygen gas at 100 mL / min (sccm).
While firing at 450 ° C. for 1 hour. TiO after firing
_TwoThe thickness of the needle-like crystal layer was about 10 μm. The board
With anatase TiO having a particle size of about 20 nm._TwoMicrocrystal (P
25) 3 g of water 40 mL, acetylacetone 0.2 m
L, mixed with 0.2 mL of Triton-X to form a slurry
Immerse in the solution and further add oxygen at 100 mL / min
Baking at 450 ° C for 1 hour while flowing (sccm)
Was. In the same manner as in Example 1, the dye was absorbed on the surface of the needle-shaped crystal.
I wore it. Then, the conductive glass (F-doped SnO)_Two,
10 Ω / □) on top of about 1 nm thick graphite
Using the counter electrode, I ^-/ I_Three ^-Was used.
The solute was also tetrapropylammonium iodide as in Example 1.
Boride (tetrapropylammonium iodide) (0.46mol /
L) and iodine (0.06mol / L), solvent is ethylene carb
Nart (ethylene carbonate) (80 vol%) and Ase
Mixed solution of tonitrile (acetonitrile) (20 vol%)
Was used. This mixed solution is TiO_TwoWith conductive glass drops
The cell was sandwiched by the opposite electrodes.

A cell was similarly assembled using only P25 as a comparative example.

Then, a xenon lamp light of 500 W equipped with an ultraviolet cut filter was irradiated from the conductive glass side with TiO ₂ or the counter electrode side. Then, the value of the photocurrent due to the photoelectric conversion reaction generated at this time was measured. As a result of the measurement, the open potential and the fill factor of the cell of the present invention were about 3% higher than those of the cell of the present invention. This is considered to be due to the fact that the internal resistance of the electron-accepting charge transport layer was reduced by using the needle-like crystals.

[0077]

As described above, according to the present invention, it is possible to provide a photoelectric conversion device in which transfer and movement of electrons and holes are performed smoothly, internal resistance and recombination probability are low, and conversion efficiency is high. it can.

Further, according to the present invention, it is possible to provide a photoelectric conversion device having a semiconductor electrode in which a light absorbing layer of a dye or the like or a charge transporting layer of an electrolyte or the like is quickly permeated or moved.

Further, according to the present invention, a photoelectric conversion device having a high open-circuit voltage can be provided.

Further, according to the present invention, a method for manufacturing a photoelectric conversion device having the above characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a photoelectric conversion device of the present invention.

FIG. 2 is a cross-sectional view showing a configuration example of light irradiation, a transparent electrode, and a mixed crystal layer of the present invention.

FIG. 3 is a cross-sectional view showing a bonded state of a mixed crystal of the present invention.

FIG. 4 is a cross-sectional view showing a mixed crystal from nanoholes according to the present invention.

FIG. 5 is a cross-sectional view showing a mixed crystal from the substrate of the present invention.

FIG. 6 is a sectional view showing a conventional Graetzel type cell.

FIG. 7 is a simplified view of an open-to-atmosphere type CVD apparatus.

FIG. 8 is a view showing a structure of a needle crystal.

FIG. 9 is a cross-sectional view showing a cell using a needle crystal and a mixed crystal.

FIG. 10 is a cross-sectional view showing an embodiment of a mixed crystal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Substrate with an electrode 11 Absorption layer modified semiconductor mixed crystal layer 12 Charge transport layer 13 Substrate with an electrode 14 Glass substrate 15 Transparent electrode layer 16 Light absorption layer 17 Semiconductor needle crystal 18 Semiconductor crystal 21 Glass with a transparent electrode 22 Electrode 41 Substrate 42 Underlayer Electrode layer 43 Nanohole layer 44 Base electrode 61 Anatase type TiO ₂ fine particles 62 Light absorbing layer 63 Electrolytic solution 64 Glass 65 Transparent electrode layer (anode) 66 Transparent electrode layer (cathode) 71 Nitrogen cylinder 72 Flow meter 73 Raw material vaporizer 74 Nozzle 75 Substrate 76 Substrate heating table

Claims (22)

[Claims] 1. A photoelectric conversion device comprising at least an electron-accepting type charge transporting layer, an electron-donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. A photoelectric conversion device, wherein any one of the semiconductor layers is a semiconductor layer made of a mixture of two or more different modes or compositions, and at least one of the semiconductor layers is a needle crystal. 2. The photoelectric conversion device according to claim 1, wherein the diameter of the needle-shaped crystal is 1 μm or less. 3. The photoelectric conversion device according to claim 1, wherein, when an aspect ratio is a ratio of a length to a diameter of the acicular crystal, the aspect ratio is 5 or more. 4. The aspect ratio of the length of the needle-shaped crystal to the diameter of the needle-shaped crystal, or the ratio of the length of the needle-shaped crystal to the minimum length passing through the center of gravity of the cross-section of the needle-shaped crystal, 3. The photoelectric conversion device according to claim 1, wherein the aspect ratio is 10 or more. 5. An arrangement in which one end of the needle-like crystal is joined to an electrode provided on a substrate, and an angle between an axial direction of the needle-like crystal and a main surface of the substrate is 60 ° or more. The photoelectric conversion device according to any one of claims 1 to 4, wherein: 6. The photoelectric conversion device according to claim 1, wherein the semiconductor other than the needle-like crystals in the mixture is fine particles having a diameter of 100 nm or less. 7. The photoelectric conversion device according to claim 6, wherein the fine particles are present on a surface of a needle-like crystal. 8. The photoelectric conversion device according to claim 1, wherein a material of the light absorbing layer is a dye. 9. The photoelectric conversion device according to claim 1, wherein the mixture is a metal oxide. 10. The photoelectric conversion device according to claim 9, wherein at least one kind of the mixture is titanium oxide. 11. The photoelectric conversion device according to claim 9, wherein at least one kind of the mixture is zinc oxide. 12. The photoelectric conversion device according to claim 9, wherein at least one kind of the mixture is tin oxide. 13. The photoelectric conversion according to claim 1, wherein a part of the needle-like crystals is present in the fine pores of a microporous layer having a large number of fine pores. apparatus. 14. A method for manufacturing a photoelectric conversion device having at least an electron-accepting type charge transporting layer, an electron-donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. A semiconductor mixture solution composed of a semiconductor mixture having a different aspect or composition as described above is coated on a substrate and baked to form a semiconductor mixed crystal layer on the substrate, and the semiconductor mixed crystal layer is combined with any of the charge transport layers. A method for manufacturing a photoelectric conversion device. 15. A method for manufacturing a photoelectric conversion device, comprising at least an electron-accepting type charge transporting layer, an electron-donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. Forming a needle-shaped crystal semiconductor layer by applying a solution containing the crystallites on a substrate and baking to form a needle-shaped crystal semiconductor layer, and further attaching a simple substance or a mixture having a different form or composition to the needle-shaped crystal to the semiconductor layer, Forming a semiconductor mixed crystal layer on a substrate, wherein the semiconductor mixed crystal layer is any one of the charge transport layers. 16. A method for producing a photoelectric conversion device comprising at least an electron-accepting type charge transporting layer, an electron-donating type charge transporting layer, and a light absorbing layer existing between these charge transporting layers. Growing a needle crystal on the substrate, forming a semiconductor mixed crystal layer on the substrate by attaching a single substance or a mixture having a different form or composition from the needle crystal to the needle crystal, and forming the semiconductor mixed crystal layer on the substrate. A method for manufacturing a photoelectric conversion device, comprising any one of the charge transport layers. 17. The method according to claim 16, further comprising a step of growing the needle-like crystal on the substrate by a CVD method. 18. A step of providing an aluminum layer on the surface of the substrate, a step of forming an alumina microporous layer by anodizing the aluminum layer, and forming a semiconductor needle through the micropores of the alumina microporous layer by a CVD method. The method according to claim 17, further comprising the step of growing a crystal. 19. The method according to claim 16, further comprising the step of growing the needle-like crystals on the substrate by oxidizing the surface of the substrate. 20. A step of providing an aluminum layer on the surface of the substrate, a step of anodizing the aluminum layer to form an alumina microporous layer, and oxidizing at least a portion of the substrate to form the alumina microporous layer. 20. The method of manufacturing a photoelectric conversion device according to claim 19, further comprising a step of growing a semiconductor needle crystal through the fine hole. 21. The method for manufacturing a photoelectric conversion device according to claim 16, wherein a substrate having at least a surface containing any of titanium, zinc, and tin is used as the substrate. 22. The method for manufacturing a photoelectric conversion device according to claim 14, wherein a substrate having an electrode on a surface is used as the substrate.