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JP2004210605

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DESCRIPTION JP2004210605
A light absorption layer such as a dye and a p-type charge transport layer such as an electrolytic
solution, in addition to smooth transfer and transfer of electrons and holes, low internal
resistance and recombination probability, and high conversion efficiency And a high aspect ratio
zinc oxide needle-like crystal to be used for the n-type charge transport layer of the photoelectric
conversion device. A zinc oxide needle-like crystal (11) containing copper or copper-containing
compound 13 at its tip portion, having a length to diameter ratio of 10 or more and a diameter of
5 nm or more and 500 nm or less. A transparent oxide semiconductor layer 16 as an n-type
charge transport layer and zinc oxide needle crystals 11, a light absorbing layer 18 and a p-type
charge transport on a transparent conductive material layer 15 formed on a transparent
substrate 14 The photoelectric conversion apparatus which laminatedly formed the layer 17 in
order. [Selected figure] Figure 1
Zinc oxide needle crystals
TECHNICAL FIELD The present invention relates to a zinc oxide needle crystal and a zinc oxide
needle crystal structure, a method for producing them, and a photoelectric conversion device
using them. [0002] Zinc oxide, which has long been attracting attention as a substance having a
wide variety of uses, has long been used as a pigment, paint, printing ink, cosmetics, medicine,
dental material, etc. or as a raw material for producing them In recent years, it is used for
electrophotography photosensitizers, semiconductor lasers, UV-cut materials, photocatalysts,
sensors, surface elasticity, taking advantage of its semiconductivity, light semiconductivity,
piezoelectricity, luminescent properties and interfacial properties. It is used in a wide field as a
wave filter, a camera exposure meter, a photoelectric conversion device or the like, or a raw
material for producing them. In general, a zinc oxide film can be produced by various methods
such as a sputtering method, a vapor deposition method, a CVD method, and an electrodeposition
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method. For example, Japanese Patent Application Laid-Open No. 2001-206800 (Patent
Document 1) discloses a structure having high temperature non-oxidizable metals gold, silver,
platinum and rhodium at the tip of a zinc oxide needle crystal and a method for producing the
same. There is a report on [0005] On the other hand, Gratzel et al. Reported that the dye and the
semiconductor electrode were further improved to obtain performance equivalent to that of a
silicon solar cell [J. Am. Chem. Soc. 115 (1993) 6382 (Non-Patent Document 1), U.S. Patent
No. 5,350,644 (Patent Document 2)]. Here, a ruthenium based dye is used as the dye, and
anatase type porous titanium oxide (TiO 2) fine particles are used as the semiconductor
electrode. さらに、GratzelらはJ. Electrochem. Soc. Chem., 148 (2001)
C 498 (Non-patent Document 2) also reports that semiconductor electrodes of zinc oxide fine
particles were produced using an electrodeposition method. In order for a Gratzel type cell using
fine particles for such a semiconductor electrode to replace a silicon solar cell, it is necessary to
have higher energy conversion efficiency, higher short circuit current, open circuit voltage, form
factor and durability than ever before. It will be [Patent Document 1] JP-A-2001-206800 [Patent
Document 2] US Patent No. 5350644 [Non-patent Document 1] J. Am. Chem. Soc. 115
(1993) 6382 Non-Patent Document 2 J. Electrochem. Soc. However, with the composition and
preparation technology of zinc oxide needle crystals described in the above-mentioned
document, high temperature and relatively difficult to obtain and handle. Only oxidizing metals
could be used.
In addition, when a semiconductor film made of the fine particle film, which is the abovementioned conventional method, is used in a gratzel type cell, there are problems of grain
boundaries, penetration of electrolytes and so forth, and adhesion with a substrate. It was
difficult to secure sufficient photocurrent. SUMMARY OF THE INVENTION The present invention
has been made in view of the above problems, and the transfer and transfer of electrons and
holes are smooth, the internal resistance and recombination probability are low, and the
conversion efficiency is high. In addition to the above, to provide a photoelectric conversion
device having a good contact with a light absorption layer such as a dye or a p-type charge
transport layer such as an electrolytic solution and a high mass transfer rate, and an n-type
photoelectric conversion device To provide a zinc oxide needle crystal having a large aspect ratio
used in a charge transport layer and a zinc oxide needle crystal structure in which a plurality of
zinc oxide needles are disposed on a substrate, and further, to use these zinc oxide needles It is
an object of the present invention to provide a method for easily and inexpensively producing
diamond crystals and zinc oxide needle crystals. That is, according to the present invention, the
following means for solving the problems are provided. 【0011】 1. Zinc oxide needle
crystals comprising a copper or a compound containing copper at at least one tip portion. 【
0012】 2. 3. Zinc oxide needle crystals according to 1 above, characterized in that the ratio
of length to diameter is 10 or more. 【0013】 3. 3. The zinc oxide needle-like crystal as
described in 2 above, which has a diameter of 5 nm to 10 μm. 【0014】 4. 3. The zinc
oxide needle-like crystal as described in 2 above, which has a diameter of 5 nm or more and 500
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nm or less. 【0015】 5. The plurality of zinc oxide needle crystals described in any of the
above 1 to 4 are disposed on the surface of the base with the one tip end side as the end side and
the other tip end side as the base end side The zinc oxide needle crystal structure characterized
by the above. 【0016】 6. The zinc oxide needle-like crystal structure according to the
above 5, wherein the surface of the substrate is formed of a conductive material layer or an oxide
semiconductor layer formed on the surface of the conductive material layer. 【0017】 7.
Preparing a zinc oxide needle-like crystal containing copper or a compound containing copper at
at least one tip portion, providing a substrate on which a thin layer of copper or a compound
containing copper is formed on at least a part of the surface; A raw material comprising at least
zinc or a compound containing zinc is vaporized by heating at a first temperature, and a material
containing zinc vaporized from the raw material is attached to the surface of the substrate heated
to a second temperature. A process for producing zinc oxide needle crystals, comprising the steps
of
【0018】 8. In a method of producing zinc oxide needle crystals containing a copper or a
compound containing copper at at least one tip site, the method comprising the steps of:
preparing a substrate for forming zinc oxide needle crystals; Or a material containing a
compound containing copper is vaporized by heating at a first temperature, and a material
containing zinc and copper vaporized from the material is attached to the surface of the substrate
heated to a second temperature And manufacturing the zinc oxide needle crystals. 【0019】
9. A zinc oxide needle crystal structure is prepared, wherein a plurality of zinc oxide needle
crystals are placed on the surface of a substrate, and said zinc oxide needle crystals each contain
copper or a compound containing copper at least at one end. In the method, the method
comprises the steps of: preparing a substrate on which a thin layer of a compound containing
copper or copper is formed on at least a part of the surface; and evaporating a raw material
comprising at least zinc or a compound containing zinc at a first temperature. And D. attaching a
material containing zinc vaporized from the raw material to the surface of the substrate heated to
the second temperature. 【0020】 10. A zinc oxide needle crystal structure is prepared,
wherein a plurality of zinc oxide needle crystals are placed on the surface of a substrate, and said
zinc oxide needle crystals each contain copper or a compound containing copper at least at one
end. In the method, the step of preparing the substrate forming zinc oxide needle crystals, and
vaporization of a raw material comprising at least zinc or a compound containing zinc and a
compound containing copper or copper at a first temperature And depositing a material
containing zinc and copper vaporized from the raw material on the surface of the substrate
heated to a second temperature. 【0021】 11. A photoelectric conversion device in which
an n-type charge transport layer, a light absorption layer, and a p-type charge transport layer are
sequentially stacked on a conductive material layer formed on a substrate, the n-type charge
transport A photoelectric conversion device characterized in that the layer contains at least zinc
oxide needle crystals, and the zinc oxide needle crystals contain copper or a compound
containing copper at at least one tip. 【0022】 12. 12. The photoelectric conversion
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device according to the above 11, wherein the substrate and the conductive material layer are
transparent. 【0023】 13. The n-type charge transport layer includes an oxide
semiconductor layer together with the zinc oxide needle crystals, and the oxide semiconductor
layer is formed on the surface of the conductive material layer. The photoelectric conversion
apparatus in any one of 11-12.
【0024】 14. The photoelectric conversion device according to the above 13, wherein the
oxide semiconductor layer is transparent. 【0025】 15. 11. The photoelectric conversion
device according to any of 11 to 14, wherein the light absorption layer is formed on the surface
of the zinc oxide needle crystals. 【0026】 16. 12. The photoelectric conversion device
according to any one of 11 to 15, wherein the zinc oxide needle crystals have a ratio of length to
diameter of 10 or more. 【0027】 17. 17. The photoelectric conversion device according
to the above 16, wherein the zinc oxide needle crystals have a diameter of 5 nm to 10 μm. 【
0028】 18. The photoelectric conversion device according to the above 16, wherein the
zinc oxide needle crystals have a diameter of 5 nm or more and 500 nm or less. BEST MODE FOR
CARRYING OUT THE INVENTION Embodiments of the present invention will be described below
with reference to the drawings as needed. The main feature of the zinc oxide needle crystals and
the zinc oxide needle crystal structures according to the present invention and the method for
producing them is a zinc oxide needle with a high aspect ratio containing copper or a compound
containing copper at its tip. It is to manufacture a zinc oxide needle-like crystal structure in
which a plurality of crystals and the zinc oxide needle-like crystals are disposed on a substrate
using a vapor phase growth method. In addition, the main feature of the photoelectric conversion
device according to the present invention is that a zinc oxide needle-like crystal having a large
aspect ratio, containing copper or a compound containing copper in the tip portion, is made to
have the tip end side. It is to be disposed on the surface to constitute an n-type charge transport
layer. The zinc oxide needle crystals and zinc oxide needle crystal structures, the method for
producing them, and the photoelectric conversion device using them will be described below.
<Regarding n-Type Zinc Oxide Needle-Like Crystal> The zinc oxide needle-like crystal according
to the present invention is, for example, one shown by reference numeral 11 in FIG. The needlelike crystals are so-called whiskers, and are composed of needle-like single crystals having no
defects or needle-like crystals containing a screw dislocation or the like. Furthermore, as shown
in (a), (b) and (c) in FIG. 3, needle-like crystals are those in which a large number of needle-like
crystals have grown from one point including tetrapod-like, dendritic And those formed from one
or more crystals grown in a polygonal shape. Needle-like crystals are in the form of cylinders and
cones, cones having a flat end or having a large tip, or cylinders having a pointed tip or having a
large tip, etc. Including all
In addition, triangular pyramids, quadrangular pyramids, hexagonal pyramids, other polygonal
pyramids or those with flat or large polygonal pyramid tips, triangular prisms, quadrangular
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prisms, hexagonal prisms, and many others These include prismatic columns, triangular prisms
with pointed or enlarged tips, square prisms, hexagonal columns, other polygonal columns and
those with enlarged tips, and further, these shapes are broken into lines. The connected shape is
also included. Further, the aspect ratio of zinc oxide needle crystals used in the photoelectric
conversion device of the present invention is preferably 10 or more, particularly preferably 100
or more, and the minimum length (diameter) passing through the center of gravity of the
transverse cut face of needle crystals 10 μm or less, particularly 500 nm or less is preferable,
and 100 nm or less is more preferable. The diameter of the needle crystals is preferably 5 nm or
more. Here, the aspect ratio means the ratio of the length to the diameter when the cross section
of the needle crystal is circular or nearly circular, and the cross section of the needle crystal is a
square such as a hexagon. Is the ratio of the length to the minimum length through the center of
gravity of the cutting plane. As shown in FIG. 1, the zinc oxide needle crystals 11 according to the
present invention contain copper or a compound 13 containing copper at the tip 12 on the end
side. The shape of the distal end portion 12 may be any shape such as a spherical body as shown
in FIG. 2 (a) or a fine particle laminate as shown in FIG. 2 (b). Examples of the copper-containing
compound of the tip portion 12 include cuprous oxide, cupric oxide, and a copper-zinc alloy. The
content of copper or a compound containing copper in the zinc oxide needle crystals is, for
example, 5 to 90% of the ratio (%) of the number of atoms of copper to the total number of atoms
of zinc and copper, for example, at tip portions. is there. The above ratio can be calculated, for
example, by measuring the types and contents of elements constituting the sample using an
energy dispersive X-ray analyzer (EDX). Next, the method for producing the zinc oxide needle
crystals and the zinc oxide needle crystal structure including the same will be described with
reference to FIG. Any material can be applied to the substrate 14 as long as it can withstand the
zinc oxide needle crystal manufacturing process described later. For example, a glass plate, a
semiconductor substrate such as Si, a substrate of an oxide such as MgO or Al 2 O 3, one having
a conductive film formed on the surface thereof, or a metal plate such as stainless steel (SUS) can
be used. When using for the photoelectric conversion apparatus mentioned later, the base ¦
substrate in which the conductive material layer 15 was formed on the board ¦ substrate 14 is
used.
As the conductive material 15, a transparent electrode material made of, for example, indium-tin
complex oxide, tin oxide doped with fluorine, or the like is preferably used. Further, by using the
base having the oxide semiconductor layer 16 formed on the conductive material layer 15, short
circuit with the p-type charge transport layer 17 can be prevented. The oxide semiconductor
layer 16 is preferably made of, for example, zinc oxide, titanium oxide, tin oxide or the like. At
this time, the substrate on the side on which incident light is incident is preferably transparent,
and glass or the like is suitably used. Here, the substrate refers to a structure having a surface for
growing zinc oxide needle crystals. The raw material for producing the zinc oxide needle crystals
of the present invention is at least zinc or a compound containing zinc. Examples of the
compound containing zinc include zinc oxide, zinc sulfide and a copper-zinc alloy. The heating
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temperature of the raw material may be equal to or higher than the melting point of the raw
material, and is, for example, 400 ° C. or higher when zinc is used. As a method of heating the
raw material, methods such as resistance heating method, laser heating method, high frequency
induction heating method and the like can be mentioned. In the present invention, zinc oxide
needle crystals 11 containing copper or copper-containing compound 13 in the tip portion
thereof are produced by the following two methods using the above-mentioned substrate and
raw materials. One is a method of depositing a thin layer of copper or a compound containing
copper on the surface of a substrate and growing zinc oxide needle crystals on the thin layer, and
the other includes at least zinc or zinc. In this method, copper or a compound containing copper
is allowed to coexist in a raw material which is a compound to grow zinc oxide needle crystals on
a substrate. First, the former manufacturing method will be described. Any method may be used
to place a thin layer of copper or a compound containing copper on the surface of the substrate.
For example, a vapor deposition method or a plating method may be used. As a material to be
used for the thin layer, copper is most preferably used, of which various manufacturing methods
are known and easy to handle, but it is not limited thereto. For example, copper oxide or copperzinc alloy may be used. Good. At this time, the thickness of the thin layer made of copper or the
like is preferably 200 nm or less, particularly preferably 100 nm or less, and more preferably 1
nm or more. The thin layer may completely cover the entire surface of the substrate but may
partially cover it. The substrate on which the thin layer of copper or a compound containing
copper is formed is held in a furnace. Then, zinc or a compound containing zinc, which is a raw
material of the zinc oxide needle crystals 11, is put in a crucible or the like and heated in the
same furnace.
Under these conditions, zinc oxide needle crystals can be formed on the substrate. Further, the
detailed description will be made with reference to FIG. 5 (a). When the crucible 105 which is a
resistance heating body is connected to the electrode 106 disposed in the reaction vessel 107
and the crucible is heated by applying a current, the raw material 104 in the crucible is
vaporized and the substrate holder disposed oppositely The device is designed such that a thin
layer of copper or a compound containing copper attached to 102 can be attached to the surface
of the substrate (substrate) 101 formed on the surface. Further, the gas is introduced from the
gas introduction line 108 at the lower part of the reaction vessel, rises in the reaction vessel and
is exhausted from the gas exhaust line 109 at the upper part of the reaction vessel. A substrate
heater 103 is provided on the back of the substrate holder 102 in order to keep the substrate
101 at an appropriate temperature. In order to grow zinc oxide needle crystals on a substrate,
first, a carrier gas and an oxidizing gas are introduced from a gas introduction line to maintain
the inside of the reaction vessel 107 in an oxidizing atmosphere and an appropriate pressure. At
this time, the carrier gas is preferably He, Ar, nitrogen or the like which is an inert gas, and
oxygen is preferable as the oxidizing gas. In some cases, air or water can also be used as the
oxidizing gas. The pressure in the reaction vessel 107 is usually about 100 to 100,000 Pa, but is
not limited thereto. Next, the substrate temperature is set by the substrate heater 103 to a
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temperature suitable for producing zinc oxide needle crystals. For that purpose, although not
shown, it is preferable to place a thermocouple for temperature measurement in the vicinity of
the substrate. The substrate temperature also depends on the pressure, but is generally about
400 to 1000.degree. Then, a current is supplied through the electrode 106 to heat the crucible
105 containing the raw material 104. Although a crucible obtained by bonding an alumina
crucible to a tungsten wire is usually used for this crucible, other ones can of course be used. It is
preferable to place a thermocouple near the crucible so that the temperature of the crucible can
also be controlled. The crucible 105 is heated to an appropriate temperature, and when the raw
material 104 is vaporized, the raw material vapor adheres to the surface of the base on which a
thin layer of copper or a compound containing copper is formed on the surface to grow zinc
oxide needle crystals. . Generally, the oxidation of the raw material proceeds in the process from
the vaporization to the deposition, but at which point the oxidation proceeds depends on the
pressure, the oxygen concentration, the temperature and the like. In these reaction mechanisms,
copper or a compound containing copper on the substrate is in the form of nanoscale droplets,
and when zinc oxide is supplied thereto, zinc oxide initially dissolves in copper, It is considered
that this is a VLS (Vapor Liquid Solid) growth mechanism in which it becomes impossible to
dissolve in due course and precipitation of zinc oxide starts.
Next, the latter production method will be described. An optional substrate is prepared, and the
substrate is held in a furnace (reaction vessel). Then, a mixture of zinc or a compound containing
zinc as a raw material of zinc oxide needle crystals 11 with a compound containing copper or
copper (for example, copper oxide, copper-zinc alloy) is put as a raw material in a crucible etc.
Heat with. The same apparatus as the former manufacturing method can be used, and the vapor
of zinc or the compound containing zinc which is the heated raw material and the vapor of the
compound containing copper or the compound containing copper simultaneously deposit on the
surface of the substrate, the former It is considered to grow zinc oxide needle crystals in the
same manner as in the manufacturing method. In the former method of the above two
manufacturing methods, in the case where a thin layer of copper or a compound containing
copper does not remain after growth of a required zinc oxide needle crystal is adopted. Even if
light is incident from the substrate side, there is no influence of the thin layer on light
transmission, so the zinc oxide needle crystal structure manufactured under this condition is
applied to a photoelectric conversion device described later in which light is incident from the
substrate side. There is no problem. In addition, in the former method, in the case of adopting a
condition in which a thin layer of copper or a compound containing copper remains after
growing the required zinc oxide needle crystals, when light is made incident from the substrate
side Since the layer affects light transmission to some extent, this point is taken into
consideration when applying the zinc oxide needle-like crystal structure manufactured under this
condition to a photoelectric conversion device of the type in which light is incident from the
substrate side. It is preferable to do. Further, in the latter method of the above two manufacturing
methods, since a thin layer of copper or a compound containing copper as in the former method
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is not used, the zinc oxide needle crystal structure manufactured by this method is used. There is
no problem when applied to the later-described photoelectric conversion device in which light is
incident from the substrate side. Thus, the two production methods can be properly used
according to the usage forms of the zinc oxide needle crystals and the zinc oxide needle crystal
structure. Further, as shown in FIG. 5B, it is also possible to use a configuration in which the
substrate is placed downstream of the raw material with respect to the flow of introduced gas.
<Regarding Configuration of Photoelectric Conversion Device> The configuration of the
photoelectric conversion device of the present invention using a zinc oxide needle crystal will be
described. First, a conventional Gratzel type photoelectric conversion device will be described.
FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a photochemical
cell using a conventional Gratzel type dye-sensitized semiconductor electrode (herein referred to
as a Gratzel type cell).
In FIG. 4, reference numeral 44 is a glass substrate, 45 is a transparent electrode layer formed on
the surface, 41 is an anatase type TiO 2 fine particle layer, and from a porous joined body in
which titanium oxide fine particles are joined. It is made. Reference numeral 42 denotes a
pigment bonded to the surface of the titanium oxide fine particle, which acts as a light absorbing
layer. The principle of operation of this Gratzel type cell will be described. Light is made incident
from the left side of FIG. Then, the electrons in the dye forming the light absorption layer 42 are
excited by the incident light, and move to the conduction band of titanium oxide. The dye which
loses the electron and is in the oxidation state rapidly receives the electron from the p-type
charge transport layer 43, for example, the iodine ion of the electrolyte, is reduced and returns to
the original state. The electrons injected into the anatase-type TiO 2 particle layer 41 move
between the titanium oxide particles by a mechanism such as hopping conduction and reach the
transparent electrode layer (anode) 45. In addition, the iodine ion that has been supplied to the
dye and is in the oxidized state (I3 <->) receives the electron from the transparent electrode layer
(cathode) 46, is reduced, and returns to the original state (I <->). As can be inferred from the
above principle of operation, the energy level of electrons in the excited state of the dye must be
higher than the conduction band of TiO 2 in order to efficiently separate and move the electrons
and holes generated by the dye. It is necessary that the energy level of holes in the dye be lower
than the redox level. In the dye-sensitized cell such as the above-mentioned Gratzel cell, the light
absorption rate of the dye 1 layer is not sufficient, so the surface area is increased to increase the
substantial light absorption amount. In the method of enlarging the surface, although the method
of dispersing and bonding fine particles like the above-mentioned Gratzel type cell is simple,
there is a problem that the movement of electrons is not sufficiently efficient. For example, when
light is incident from the side of the anode transparent electrode 45 on which the anatase type
TiO 2 fine particle layer 41 is provided in the above-mentioned Gratzel type cell and when light is
incident from the glass substrate 44 on the cathode transparent electrode 46 side, The former
often has better photoelectric conversion efficiency. This is not merely a difference in the amount
of light absorption by the dye, but the probability that electrons excited by light absorption move
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the anatase type TiO 2 particle layer 41 and reach the anode transparent electrode 45 is as the
light excitation position is separated from the transparent electrode It suggests that it will
decline. That is, it is suggested that sufficiently efficient electron transfer is not achieved in the
Gratzel type cell having many grain boundaries.
Further, in the case where an electrolyte is used also in the p-type charge transport layer 43,
diffusion of ions such as iodine is rate-limiting, and there is a problem that charges can not be
sufficiently transported to increase the current. In addition, even when the p-type charge
transport layer is solidified, it is difficult to sufficiently fill the space between the fine particles
with the p-type charge transport layer material. On the other hand, as schematically shown in
FIG. 1, in the photoelectric conversion device manufactured using the zinc oxide needle crystals
of the present invention, the zinc oxide needle crystals 11 of the present invention are n-type. In
the case of using as the charge transport layer of the above, the zinc oxide needle crystals 11 are
thin and the aspect ratio is large, so that the surface area becomes large even in the single crystal
state. In order to further increase the surface area, it is also effective to deposit a layer of fine
particles on the surface of the needle crystals. As the layer of the fine particles, for example, one
obtained by applying and baking a coated material containing fine particles of an oxide
semiconductor such as titanium oxide, tin oxide, zinc oxide and the like is exemplified. The
present invention is not limited to dye sensitization, and can be widely used in general
photoelectric conversion devices configured to increase the amount of absorbed light by
increasing the surface area because the light absorptivity is not sufficient. In the photoelectric
conversion device according to the present invention, since the zinc oxide needle crystals 11 are
n-type wide gap semiconductors, the zinc oxide needle crystals 11 include p-type wide gap
semiconductors and redox couples with a light absorption layer 18 such as a dye. A p-type
charge transport layer 17 such as an electrolytic solution or a polymer conductor is required. In
the photoelectric conversion device of the present invention, since the air gaps around the zinc
oxide needle crystals 11 are relatively linear, the electrolyte or p-type semiconductor functioning
as the p-type charge transport layer 17 is filled. It is also convenient in the case. That is, in the
case of the electrolytic solution, the diffusion of iodine ions and the like becomes fast, and the
permeation is quick at the time of preparation. Also in the case where the p-type charge
transport layer is a solid such as CuI, it is possible to rapidly fill the depth of the porous n-type
layer during fabrication, which is advantageous because the contact becomes good. When the
zinc oxide needle crystals of the present invention are used in a photoelectric conversion device,
zinc oxide needle crystals having a minimum diameter of 50 nm or less and an aspect ratio of
100 or more are particularly preferable. In the zinc oxide needle crystal structure in which a
plurality of zinc oxide needle crystals are formed on the surface of the substrate, 70% or more of
the needle crystals form an angle of 60 degrees or more with the surface of the substrate. It is
preferable to stand at This is because the needle crystals can be arranged at a high density and
the p-type charge transport layer can easily penetrate.
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In FIG. 1, the base is formed by sequentially providing a conductive material layer 15 which is a
transparent electrode and an oxide semiconductor layer 16 made of, for example, zinc oxide on a
substrate 14. A zinc oxide needle crystal 11 is used as an n-type charge transport layer, and a
light absorption layer 18 is formed on the surface thereof. The light absorption layer 18 is
provided between the zinc oxide needle crystals 11 and the p-type charge transport layer 17.
Comparing the layer of zinc oxide needle crystals of the present invention with the layer of fine
particle crystals as shown in FIG. 4, the zinc oxide needle crystal layer transfers electrons or
holes generated by photoexcitation to the electrode layer. The probability of being scattered by
grain boundaries is reduced. As shown in FIG. 1, in the case where one end (proximal end) of a
zinc oxide needle crystal is configured to be joined to an electrode, a gratzel type using
conventional fine particles in the movement of electrons or holes. Compared to cells, the effect of
grain boundaries is almost eliminated. The irradiation surface of light is determined by which
surface the transparent electrode is used. As shown in FIG. 1, either configuration may be used as
long as absorption and reflection of irradiation light from the n-type charge transport layer side
and from the p-type charge transport layer side to the light absorption layer 18 is small. It is also
possible to use light irradiation from both sides. These configurations also depend on the method
and composition of the charge transport layer to be combined. Various semiconductors and dyes
can be used as the light absorption layer 18 of the photoelectric conversion device of the present
invention. As the semiconductor, an i-type amorphous semiconductor having a large light
absorption coefficient or a direct transition semiconductor is preferable. As the dye, metal
complex dye and / or polymethine dye, perylene dye, rose bengal, eosin Y, mercurochrome,
organic dye such as santarin dye, cyanine dye and the like, and natural dye are preferable. The
dye preferably has a suitable bonding group to the surface of the semiconductor fine particle.
Preferred linking groups include COOH groups, cyano groups, PO3 H2 groups or chelating
groups having π conductivity such as oximes, dioximes, hydroxyquinolines, salicylates and αketo enolates. Among these, COOH group and PO 3 H 2 group are particularly preferable. When
the dye used in the present invention is a metal complex dye, ruthenium complex dye {Ru (dcbpy)
2 (SCN) 2, (dcbpy = 2,2-bipyridine-4,4'-dicarboxylic acid) etc. can be used. It is important that the
oxidant / reductant be stable.
The material of these light absorption layers is selected such that the electrochemical reaction of
photoelectric conversion proceeds without any delay. A redox system similar to a wet solar cell
can be used for the p-type charge transport layer. Even in the case of using redox, 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. Furthermore, as a method of transporting electrons (holes), a p-type semiconductor
such as an electric field polymerization organic polymer or CuI, CuSCN, NiO can be used. The
transport layer needs to penetrate between the zinc oxide needle crystals, so for the preparation
thereof, a penetration method which can be used for liquids, polymers, etc., an electrodeposition
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which can be used for a solid transport layer, a CVD method, etc. are suitable. There is. A
conductive material layer 20 is provided adjacent to the p-type charge transport layer 17. The
conductive material layer 20 may be provided on the entire outer surface or on a part of these
layers. If the p-type charge transport layer is not solid, it is better to provide the conductive
material layer 20 on the entire surface of the substrate 19 from the viewpoint of holding the
charge transport layer. For example, a catalyst layer 21 such as Pt or C is preferably provided on
the surface of the conductive material layer 20 adjacent to the p-type charge transport layer 17
in order to efficiently perform reduction of the redox couple, for example. The film thickness of
the catalyst layer 21 may be such that light can not be transmitted when light irradiation is
performed only from the side of the zinc oxide needle crystals in FIG. 1, but from the p-type
charge transport layer side In the case of light irradiation, it is preferable to set the film thickness
by the balance between the catalytic function and the transmitted light. Note that by making the
conductive substance layer 20 also function as a base, a substrate different from the conductive
substance layer 20 may not be provided. In particular, when the p-type charge transport layer 17
is solid, it is preferable to dispose the conductive substance layer 20 such as Au or Ag directly on
top of the p-type charge transport layer 17 and omit the substrate 19. Although not shown, the
wet type of the photoelectric conversion device of the present invention is preferably sealed from
at least a portion other than the substrate from the viewpoint of enhancing the weather
resistance. An adhesive or resin can be used as the sealing material. When the light incident side
is sealed, the sealing material is preferably translucent. EXAMPLES The present invention will be
further described with reference to the following examples. Example 1 An example in which zinc
oxide needle crystals were produced from a thin copper layer formed on the surface of a
substrate using the zinc oxide needle crystal production apparatus shown in FIG. 5A will be
described in detail. .
First, surface-oxidized Zn powder was placed as a raw material 104 in an alumina crucible 105
attached to a tungsten (W) wire, and the W wire was connected to the electrode 106. An alumina
substrate having a thickness of 0.5 mm was used as the substrate, and a substrate in which Cu of
50 nm was formed on the surface was used, and the substrate temperature was set to 450 to
550 ° C. Next, 100 sccm of argon gas mixed with 1% oxygen was flowed in the reaction vessel
and maintained at 30,000 Pa. And the temperature of the crucible was heated to 650-750
degreeC, and the raw material was evaporated gradually for about 30 minutes. As a result of
observing the prepared sample with an FE-SEM (field scanning electron microscope), a large
number of zinc oxide needle crystals having an average diameter of 50 nm and an average length
of 10 μm and having orientation grow on the substrate. Was. Analysis of this tip portion by EDX
confirmed that it contained zinc and copper. The ratio of the number of copper atoms to the total
number of zinc and copper atoms was 10%. The present example showed that good zinc oxide
needle crystals and zinc oxide needle crystal structures can be produced using copper, which is a
very inexpensive raw material as compared with the prior art. Example 2 An example of
producing zinc oxide needle crystals by coexistence of copper in a raw material using the zinc
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oxide needle crystal production apparatus shown in FIG. 5B will be described in detail. First, a
mixture of Zn powder and Cu powder was placed in an alumina crucible 105 as a raw material
104 and placed in the apparatus. A conductive glass (F-doped SnO 2, 10 Ω / □) having a
thickness of 10 mm was used as the substrate, and was placed at 450-550 ° C. during crucible
heating. Next, 100 sccm of argon gas mixed with 2% oxygen was flowed in the reaction vessel
and maintained at 100000 Pa. Then, the temperature of the crucible was brought to 650-750 °
C. by heating the heater 112 and the raw material was gradually evaporated for about 30
minutes. As a result of observing the produced sample with an FE-SEM (field scanning electron
microscope), a large number of zinc oxide needle crystals having an average diameter of 50 nm
and an average length of 10 μm and having orientation grow on the substrate. Was. Analysis of
this tip portion by EDX confirmed that it contained zinc and copper. The ratio of the number of
copper atoms to the total number of zinc and copper atoms was 12%. The present example
shows that good zinc oxide needle crystals and zinc oxide needle crystal structures can be
produced using copper, which is a very inexpensive raw material as compared with the prior art.
Example 3 Example of manufacturing zinc oxide needle crystals using the zinc oxide needle
crystal production apparatus shown in FIG. 5 (b) and producing a photoelectric conversion device
using the zinc oxide needles Will be described in detail. First, surface-oxidized Zn powder was
placed as a raw material 104 in an alumina crucible 105 and placed in the apparatus. As a
substrate, one having a 200 nm zinc oxide layer (oxide semiconductor layer) formed on the
surface of a 10 mm thick conductive glass (F-doped SnO 2, 10 Ω / □) is used, and a 30 nm thin
copper layer is formed thereon. I made a film. The temperature of the substrate was set to 450550 ° C. during crucible heating. Next, argon gas mixed with 0.5% of oxygen was flowed in the
reaction vessel at 100 sccm and held at 100000 Pa. Then, the temperature of the crucible was
heated to 650-750 ° C. to evaporate the surface oxidized Zn powder gradually for about 120
minutes. As a result of observing the prepared sample with an FE-SEM (field scanning electron
microscope), a large number of zinc oxide needle crystals having an average diameter of 30 nm
and an average length of 10 μm and having orientation grow on the substrate. Was. Analysis of
this tip portion by EDX confirmed that it contained zinc and copper. The ratio of the number of
copper atoms to the total number of zinc and copper atoms was 8%. The dye of the light
absorption layer used Ru ((dcbpy) (COOH) 2) 2 (SCN) 2 which is a Ru complex. The dye was
dissolved in distilled ethanol, and the zinc oxide needle-like crystal structure was immersed in
this for 24 h to adsorb the dye onto the needle-like crystals and then taken out and dried at 80
° C. In addition, a conductive material layer was formed by sputtering platinum to a thickness of
10 nm on the surface of another conductive glass (F-doped SnO 2, 10 Ω / □), and this was used
as a counter electrode. The redox couple of the p-type charge transport layer was I <-> / I3 <->.
Here, tetrapropylammonium iodide (0.46 mol / L) and iodine (0.06 mol / L) are used as the
solute, and ethylene carbonate (ethylene carbonate) (80 vol%) is used as the solvent. Acetonitrile
(20 vol%) was used. This solution was dropped on a zinc oxide needle crystal structure having a
light absorption layer formed, and sandwiched between counter electrodes to obtain a cell. For
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comparison, an n-type charge transport layer as shown in FIG. 4 was produced using zinc oxide
fine particles having an average diameter of 100 nm, and a cell was similarly assembled using it.
Then, a 500 W xenon lamp light attached with an ultraviolet cut filter was irradiated from the ptype charge transport layer side. In the case of the Example of this invention, the short circuit
current value by the photoelectric conversion reaction which arose at this time was 13 mA / cm
<2>, and the photoelectric conversion efficiency was 7.5%. As compared with the measurement
results using the zinc oxide fine particles, both the short circuit current value and the
photoelectric conversion efficiency of the cell of the present invention were larger by about 10%.
It is believed that this is because the internal resistance of the n-type charge transport layer is
reduced by using the zinc oxide needle crystals. According to this embodiment, a photoelectric
conversion device constructed using zinc oxide needle crystals and zinc oxide needle crystal
structures manufactured using copper, which is a much cheaper raw material than in the prior
art, is conventionally used. It has been shown to have good properties compared to those of As
described above, according to the present invention, a zinc oxide needle crystal having a large
aspect ratio and a zinc oxide needle crystal structure formed by placing a plurality of the zinc
crystal on a substrate are provided. There is provided a method of manufacturing the method
easily and at low cost. Moreover, according to the present invention, in addition to smooth
transfer and transfer of electrons and holes, low internal resistance and recombination
probability, and high conversion efficiency, p-type charge such as a light absorbing layer such as
a dye or an electrolytic solution There is provided a photoelectric conversion device having a
good transfer rate and a good contact with the transport layer. BRIEF DESCRIPTION OF THE
DRAWINGS FIG. 1 is a schematic cross-sectional view showing the configuration of a
photoelectric conversion device manufactured using the zinc oxide needle crystals of the present
invention. FIG. 2 is a schematic view of the tip portion of zinc oxide needle crystals. FIG. 3 is a
schematic view showing types of zinc oxide needle crystals. FIG. 4 is a schematic cross-sectional
view showing the configuration of a conventional Gratzel type cell. FIG. 5 is a schematic view
showing a manufacturing apparatus of zinc oxide needle crystals having a crucible type
resistance heating mechanism and a manufacturing apparatus of zinc oxide needle crystals by
heating a crucible in an annular furnace. [Description of the code] 11: zinc oxide needle crystals
12: tip portion 13: copper or a compound containing copper 14: substrate 15: conductive
substance layer (anode) 16: oxide semiconductor layer 17: p-type charge transport layer 18: light
absorbing layer 19: substrate 20: conductive material layer (cathode) 21: catalyst layer 41:
anatase type TiO 2 fine particles 42: light absorbing layer 43: p type charge transport layer 44:
glass substrate 45: transparent electrode layer ( Anode) 46: transparent electrode layer (cathode)
101: substrate 102: substrate holder 103: substrate heater 104: raw material 105: crucible 106:
electrode 107: reaction vessel 108: gas introduction line 109: gas exhaust line 110: quartz tube
111: quartz tube 111: Reactor 112: Heater
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