Patent Description:
Conventionally, there has been known an organic thin-film solar cell of "normal type" that includes a light-transmissive electrode layer, a hole transport layer, an organic semiconductor layer, an electron transport layer and a collector electrode layer in this order.

In addition, in recent years, there has been proposed an organic thin-film solar cell of "inverted type" that includes a light-transmissive electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector electrode layer in this order for the sake of improvement in durability and other properties (see Patent Literature <NUM>).

Patent Literature <NUM> describes perovskite solar cells (PSCs) with a composite mesoporous TiO<NUM>-In<NUM>O<NUM> electron transport layer.

Patent Literature <NUM> describes a simple, one-step, solution-based method for fabricating high quality indium-doped titanium oxide electron transport layers.

As described above, an organic thin-film solar cell includes, for instance, a light-transmissive electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector electrode layer in this order.

Such an organic thin-film solar cell is required to demonstrate excellent output characteristics when used in an actual living environment.

In Patent Literature <NUM>, a titanium oxide layer to serve as an electron transport layer is formed using a sol-gel process. A titanium oxide layer formed using a sol-gel process becomes amorphous and includes oxygen deficiency, whereby the electron transfer resistance is perhaps reduced.

However, the present inventors found, through a study, that an organic thin-film solar cell in which an electron transfer layer was formed using a sol-gel process had insufficient output characteristics in some cases.

Moreover, in recent years, it has been proposed to replace glass windows used in, for example, houses and vehicles with an organic thin-film solar cell having good transparency. In this case, a titanium oxide layer serving as an electron transport layer is required to have excellent transparency.

Accordingly, an object of the present invention is to provide a laminate that serves as a light-transmissive electrode layer and an electron transport layer of an inverted type organic thin-film solar cell including the light-transmissive electrode layer, the electron transport layer, an organic semiconductor layer, a hole transport layer and a collector electrode layer in this order, and that enables to obtain an organic thin-film solar cell having excellent output characteristics and transparency.

Another object of the present invention is to provide a new method for producing the laminate.

The present inventors found, through an earnest study, that employing the configuration described below enables the achievement of the above-mentioned objects, and the invention has been completed.

Specifically, the present invention provides the following [<NUM>] to [<NUM>].

The present invention makes it possible to provide a laminate that serves as a light-transmissive electrode layer and an electron transport layer of an organic thin-film solar cell including the light-transmissive electrode layer, the electron transport layer, an organic semiconductor layer, a hole transport layer and a collector electrode layer in this order, and that enables to obtain an organic thin-film solar cell having excellent output characteristics and transparency.

The present invention also makes it possible to provide a new method for producing the laminate.

First, an organic thin-film solar cell <NUM> is described with reference to <FIG>.

<FIG> is a cross-sectional view schematically showing the organic thin-film solar cell <NUM>. The organic thin-film solar cell <NUM> includes, for instance, a light-transmissive electrode layer <NUM>, an electron transport layer <NUM>, an organic semiconductor layer <NUM>, a hole transport layer <NUM> and a collector electrode layer <NUM> in this order.

The thickness of the light-transmissive electrode layer <NUM> is consistent with the thickness of a member <NUM> (see <FIG>) which will be described later.

The thickness of the electron transport layer <NUM> is consistent with the thickness of a titanium oxide layer <NUM> (see <FIG>) which will be described later.

The thicknesses of the organic semiconductor layer <NUM>, the hole transport layer <NUM> and the collector electrode layer <NUM> are suitably set.

A preferable example of the light-transmissive electrode layer <NUM> is a conductive metal oxide film such as an ITO (Indium Tin Oxide) film. The light-transmissive electrode layer <NUM> may be disposed on a transparent substrate such as a glass substrate or a resin film.

An example of the electron transport layer <NUM> is a titanium oxide layer containing titanium oxide (TiO<NUM>) that is an n-type semiconductor.

An example of the organic semiconductor layer <NUM> is a layer containing poly-<NUM>-hexylthiophene (P3HT) that is a polythiophene derivative and [<NUM>,<NUM>]-phenyl-C<NUM>-butyric acid methyl ester (PCBM) that is a fullerene derivative.

The mass ratio between P3HT and PCBM (P3HT:PCBM) is preferably <NUM>:<NUM> to <NUM>:<NUM> and more preferably <NUM>:<NUM> to <NUM>:<NUM>.

The organic semiconductor layer <NUM> as above may further contain additives such as a conductive material and a dye.

Examples of the conductive material include conductive materials of polyacetylene type, polypyrrole type, polythiophene type, polyparaphenylene type, polyparaphenylene vinylene type, polythienylene vinylene type, poly(<NUM>,<NUM>-ethylenedioxythiophene) type, polyfluorene type, polyaniline type, and polyacene type (except PEDOT/PSS to be described later).

Examples of the dye include dyes of cyanine type, merocyanine type, phthalocyanine type, naphthalocyanine type, azo type, quinone type, quinoisin type, quinacridone type, squarylium type, triphenylmethane type, xanthene type, porphyrin type, perylene type, and indigo type.

The additive content is preferably <NUM> to <NUM> parts by mass and more preferably <NUM> to <NUM> parts by mass with respect to <NUM> parts by mass in total of P3HT and PCBM.

Examples of materials for the hole transport layer <NUM> include PEDOT/PSS, V<NUM>O<NUM>, and MoO<NUM>, with PEDOT/PSS being preferred.

PEDOT/PSS is a high molecular compound having PEDOT (poly(<NUM>,<NUM>-ethylenedioxythiophene)) and PSS (polystyrene sulfonate) combined together, and is sometimes referred to as "PEDOT:PSS.

Examples of the collector electrode layer <NUM> include an Au electrode layer, an Ag electrode layer, an Al electrode layer, and a Ca electrode layer, and of these, an Au electrode layer is preferred.

Next, a laminate <NUM> that serves as the light-transmissive electrode layer <NUM> and the electron transport layer <NUM> of the organic thin-film solar cell <NUM> (see <FIG>) is described with reference to <FIG>.

<FIG> is a cross-sectional view schematically showing the laminate <NUM>. The laminate <NUM> includes the member <NUM> that serves as the light-transmissive electrode layer <NUM> (see <FIG>) and the titanium oxide layer <NUM> that is disposed on the member <NUM> and serves as the electron transport layer <NUM> (see <FIG>).

The member <NUM> serving as the light-transmissive electrode layer <NUM> (see <FIG>) is preferably a member having electrical conductivity and more preferably a member containing indium oxide.

In the case of being a member containing indium oxide, the member <NUM> is even more preferably a member containing indium tin oxide (ITO) and particularly preferably an ITO film.

The member <NUM> may be disposed on a transparent substrate such as a glass substrate or a resin film.

The thickness of the member <NUM> that is for example an ITO film is appropriately set in accordance with the resulting organic thin-film solar cell <NUM> (see <FIG>) and is preferably not less than <NUM>, more preferably not less than <NUM>, and even more preferably not less than <NUM>. At the same time, the thickness is preferably not more than <NUM>, more preferably not more than <NUM>, and even more preferably not more than <NUM>.

The thickness of the member <NUM> is a value determined by forming a cross section of the member <NUM> with a focused ion beam and measuring the formed cross section with a scanning electron microscope.

The titanium oxide layer <NUM> is a layer containing titanium oxide.

The titanium oxide layer <NUM> further contains indium oxide and metallic indium, which will be described later.

The titanium oxide layer <NUM> has a thickness of not less than <NUM>. When the thickness of the titanium oxide layer <NUM> is within the foregoing range, current leakage caused by a defect in the titanium oxide layer <NUM> hardly occurs, whereby the organic thin-film solar cell <NUM> using the laminate <NUM> has excellent output characteristics.

The thickness of the titanium oxide layer <NUM> is preferably not less than <NUM>, more preferably not less than <NUM> and even more preferably not less than <NUM> because this leads to further excellent output characteristics.

On the other hand, the titanium oxide layer <NUM> has a thickness of not more than <NUM>. When the thickness of the titanium oxide layer <NUM> is within the foregoing range, an increase in resistance is suppressed, whereby the organic thin-film solar cell <NUM> has excellent output characteristics. The transparency of the titanium oxide layer <NUM> is also excellent. Further, the current application time to be described later can be shortened, whereby the productivity of the laminate <NUM> is also excellent.

The thickness of the titanium oxide layer <NUM> is preferably not more than <NUM>, more preferably not more than <NUM> and even more preferably not more than <NUM> because this leads to further excellent output characteristics, transparency and productivity.

The thickness of the titanium oxide layer <NUM> is determined as follows.

First, on a given portion of the titanium oxide layer <NUM>, measurement of narrow-range photoelectron spectra of Ti3s and In3d by means of an X-ray photoelectron spectroscope (XPS device) and sputtering using argon ions (Ar+) are repeatedly carried out under the conditions stated below. By this process, element compositional proportions (unit: at%) in the depth direction of sputtering in the titanium oxide layer <NUM> are obtained. A relative sensitivity factor method is adopted for determination of the element compositional proportions. As the relative sensitivity factors for the peak areas of narrow-range photoelectron spectra, Ti3s: <NUM> and In3d: <NUM> are used. A distance from the uppermost surface of the titanium oxide layer <NUM>, which is the measurement starting position, to the depth position where the element compositional proportion of titanium (Ti) is <NUM>/<NUM> of the maximum value is defined as the thickness of the titanium oxide layer <NUM>.

The titanium oxide layer <NUM> contains indium oxide.

The atomic ratio (InOx/Ti) of the titanium oxide layer <NUM> is not less than <NUM> and not more than <NUM>, where the elemental titanium content is represented by "Ti" and the indium oxide content "InOx.

The titanium oxide layer <NUM> as above is obtained by a method to be described later, and in this case, presumably, many In<NUM>+'s are present and much oxygen deficiency is introduced as compared with a titanium oxide layer formed using a conventional sol-gel process (for example, see Patent Literature <NUM>). Excess electrons are generated due to the oxygen deficiency, and a part of the electrons contributes to electrical conductivity as carriers.

Thus, the organic thin-film solar cell <NUM> using the laminate <NUM> having the titanium oxide layer <NUM> has excellent output characteristics.

However, any other mechanisms than the foregoing are also regarded as being within the scope of the invention.

The atomic ratio (InOx/Ti) is preferably not less than <NUM>, more preferably not less than <NUM>, further preferably more than <NUM> and particularly preferably not less than <NUM> because this leads to more excellent output characteristics.

For the upper limit value, the atomic ratio (InOx/Ti) is preferably not more than <NUM>, more preferably not more than <NUM>, and further preferably not more than <NUM>.

The titanium oxide layer <NUM> further contains metallic indium.

The atomic ratio (InM/Ti) is not more than <NUM>, where the elemental titanium content is represented by "Ti" and the metallic indium content "InM. " With this constitution, the transparency of the titanium oxide layer <NUM> (electron transport layer <NUM>) is excellent.

The atomic ratio (InM/Ti) is preferably not more than <NUM>, and further preferably not more than <NUM> because this leads to more excellent transparency.

For the lower limit value, the atomic ratio (InM/Ti) is preferably not less than <NUM>.

The atomic ratios (InOx/Ti) and (InM/Ti) are determined as follows.

First, the measurement using an XPS device is carried out on the titanium oxide layer <NUM> in the same manner as described above. Next, the obtained narrow-range photoelectron spectrum of In3d is subjected to peak separation to be divided into a metal component and an oxide component. More precisely, in the peak separation, function fitting is carried out using software, i.e., MultiPak (Ver.

To oxides, a Gaussian-Lorentzian function is applied. To metal components, an asymmetric function (tail length: <NUM> ± <NUM>, tail scale: <NUM> ± <NUM>) is applied.

Note that indium oxide and metallic indium have peak positions close to each other. To cope with it, having the following ranges, and with the peak heights, the half-widths and the Gaussian function ratios being used as variable parameters, convergence calculation is carried out such that a residual sum of squares with respect to the actually measured spectrum becomes minimum.

Element compositional proportions (unit: at%) of titanium (Ti), indium oxide and metallic indium are integrated over a portion from the uppermost surface of the titanium oxide layer <NUM> to the depth position where the element compositional proportion of titanium (Ti) is <NUM>/<NUM> of the maximum value, thereby obtaining their integration values.

Each of the integration value of indium oxide (InOx) and the integration value of metallic indium (InM) is divided by the integration value of titanium (Ti). In this manner, the atomic ratios (InOx/Ti) and (InM/Ti) are obtained.

In order to produce the above-mentioned laminate <NUM>, the member <NUM> is subjected to cathode polarization and then to anode polarization in a treatment solution containing a Ti component. For the counter electrode, an insoluble electrode such as a platinum electrode is suitable. The cathode polarization and the anode polarization of the member <NUM> are performed in, for example, an electrolytic treatment tank.

More particularly, first, current is applied with the member <NUM>, such as an ITO film, being used as the cathode. Consequently, the titanium oxide layer <NUM> is formed on the member <NUM>. It is presumed that through this cathode polarization, metallic indium is deposited inside the titanium oxide layer <NUM> and at the interface between the titanium oxide layer <NUM> and the member <NUM> such as an ITO film.

It is presumed that the titanium oxide layer <NUM> is formed as follows. First, upon generation of hydrogen, the pH increases at the surface of the member <NUM>. As a result, when the Ti component in the treatment solution is hexafluorotitanic acid and/or its salt for instance, hexafluorotitanic acid ions in the treatment solution generate titanium hydroxide while being defluorinated. It is likely that this titanium hydroxide adheres to the surface of the member <NUM>, and through subsequent washing and dehydration condensation by drying or the like, the titanium oxide layer <NUM> is formed. However, any other mechanisms than the foregoing are also regarded as being within the scope of the invention.

Current is then applied using the member <NUM> as the anode. In this manner, metallic indium deposited in the titanium oxide layer <NUM> is oxidized to improve the transparency.

As described above, the member <NUM> is preferably a member having electrical conductivity, e.g., a conductive metal oxide film such as an ITO film.

The member <NUM> may be disposed on a transparent substrate such as a glass substrate or a resin film, as described above. In this case, the transparent substrate having the member <NUM> (e.g., an ITO film-bearing glass substrate) is subjected to cathode polarization and then to anode polarization. In this case, the resulting laminate also includes this transparent substrate.

The treatment solution contains a Ti component (Ti compound) for supplying Ti (elemental titanium) to the titanium oxide layer <NUM> to be formed.

As the Ti component, preferred is at least one selected from the group consisting of hexafluorotitanic acid (H<NUM>TiF<NUM>), potassium hexafluorotitanate (K<NUM>TiF<NUM>), sodium hexafluorotitanate (Na<NUM>TiF<NUM>), ammonium hexafluorotitanate ((NH<NUM>)<NUM>TiF<NUM>), ammonium titanyl oxalate ((NH<NUM>)<NUM>[TiO(C<NUM>O<NUM>)<NUM>]), potassium titanyl oxalate dihydrate (K<NUM>[TiO(C<NUM>O<NUM>)<NUM>]•<NUM><NUM>O), titanium sulfate (Ti(SO<NUM>)<NUM>), and titanium lactate (Ti(OH)<NUM>[OCH(CH<NUM>)COOH]<NUM>).

Of these, hexafluorotitanic acid and/or its salts (potassium hexafluorotitanate, sodium hexafluorotitanate, ammonium hexafluorotitanate) are preferred for the sake of stability of the treatment solution, availability, and other factors.

The Ti content of the treatment solution is preferably not less than <NUM> mol/L, more preferably not less than <NUM> mol/L, and even more preferably not less than <NUM> mol/L.

At the same time, the Ti content of the treatment solution is preferably not more than <NUM> mol/L, more preferably not more than <NUM> mol/L, even more preferably not more than <NUM> mol/L, particularly preferably not more than <NUM> mol/L, and most preferably not more than <NUM> mol/L.

Water is used as a solvent of the treatment solution.

The pH of the treatment solution is not particularly limited and is for example <NUM> to <NUM>. Known acid components (e.g., phosphoric acid, sulfuric acid) or alkaline components (e.g., sodium hydroxide, ammonia water) may be used for pH adjustment.

The treatment solution may optionally contain a surfactant such as sodium lauryl sulfate or acetylenic glycol. The treatment solution may also contain condensed phosphate such as pyrophosphate for the sake of stability of deposition behavior over time.

The treatment solution has a temperature preferably of <NUM> to <NUM> and more preferably of <NUM> to <NUM>.

The treatment solution may further contain a conduction aid.

Exemplary conduction aids include: sulfates such as potassium sulfate, sodium sulfate, magnesium sulfate and calcium sulfate; nitrates such as potassium nitrate, sodium nitrate, magnesium nitrate and calcium nitrate; and chloride salts such as potassium chloride, sodium chloride, magnesium chloride and calcium chloride.

The conduction aid content of the treatment solution is preferably <NUM> to <NUM> mol/L and more preferably <NUM> to <NUM> mol/L.

The current density during cathode polarization is preferably not less than <NUM> A/dm<NUM>, more preferably not less than <NUM> A/dm<NUM>, and even more preferably not less than <NUM> A/dm<NUM>.

At the same time, the current density during cathode polarization is preferably not more than <NUM> A/dm<NUM>, more preferably not more than <NUM> A/dm<NUM>, and even more preferably not more than <NUM> A/dm<NUM>.

The current application time is suitably set to obtain a desired thickness of the titanium oxide layer <NUM>.

The current density during anode polarization is preferably not less than <NUM> A/dm<NUM>, more preferably not less than <NUM> A/dm<NUM>, and even more preferably not less than <NUM> A/dm<NUM>.

At the same time, the current density during anode polarization is preferably not more than <NUM> A/dm<NUM>, more preferably not more than <NUM> A/dm<NUM>, and even more preferably not more than <NUM> A/dm<NUM>.

The current application time is suitably specified to oxidize the metallic indium (In→In<NUM>+) deposited, for example, inside the titanium oxide layer <NUM>.

Cathode polarization and/or anode polarization may be followed by washing with water.

The water washing method is not particularly limited, and one exemplary method is immersion in water after cathode polarization and/or anode polarization. Washing with water is performed in, for example, a water washing tank to be described later. The temperature of water (water temperature) for use in washing is preferably <NUM> to <NUM>.

The washing time is preferably more than <NUM> seconds and preferably <NUM> to <NUM> seconds.

Further, drying may replace or follow the washing with water. The temperature and the method of drying are not particularly limited, and a drying process using a typical drier or electric furnace may be employed for example. The drying temperature is preferably not higher than <NUM>.

As a method of producing the laminate <NUM>, a batch type or a continuous type is preferable.

This method is appropriately selected according to, for example, a type or a shape of a transparent substrate (glass substrate or a resin film) on which the member <NUM> is disposed.

For example, when the member <NUM> is disposed on a glass substrate (that is, when a glass substrate with the member <NUM> is used), the batch type production is preferable.

In this case, for example, a washing treatment tank, an electrolytic treatment tank, and a water washing tank may be prepared, and the glass substrate with the member <NUM> may be immersed and treated in each tank.

The cathode polarization and the anode polarization may be carried out in one electrolytic treatment tank or in two separate electrolytic treatment tanks.

In addition, for example, when the member <NUM> is disposed on a resin film wound in a roll form (that is, when a resin film with the member <NUM> is used), the continuous type production is preferred for the sake of productivity.

In this case, for example, a washing treatment tank, an electrolytic treatment tank, a water washing tank, and a drying device are disposed between a tension reel for unwinding and a tension reel for winding, and rolls are appropriately provided so that the resin film with the member <NUM> is continuously passed through the respective tanks.

The cathode polarization and the anode polarization may be carried out in one electrolytic treatment tank or in two separate electrolytic treatment tanks. In the latter case, a water washing tank may be further provided between the two electrolytic treatment tanks.

The organic thin-film solar cell <NUM> including the light-transmissive electrode layer <NUM>, the electron transport layer <NUM>, the organic semiconductor layer <NUM>, the hole transport layer <NUM> and the collector electrode layer <NUM> in this order is produced using the above-described laminate <NUM>.

For instance, layers serving as the organic semiconductor layer <NUM>, the hole transport layer <NUM> and the collector electrode layer <NUM> are sequentially formed on the titanium oxide layer <NUM> in the laminate <NUM>.

The organic semiconductor layer <NUM> is formed by, for example, spin-coating a solution having P3HT and PCBM dissolved therein onto the titanium oxide layer <NUM> serving as the electron transport layer <NUM>, followed by drying. Examples of a solvent of the solution include <NUM>,<NUM>-dichlorotoluene, chloroform, chlorobenzene, and a mixture of two or more thereof.

The hole transport layer <NUM> is formed by, for example, spin-coating an aqueous dispersion of PEDOT/PSS onto the organic semiconductor layer <NUM>, followed by drying.

The collector electrode layer <NUM> is formed by, for example, vapor-depositing metal such as Au onto the hole transport layer <NUM>.

The methods for forming the respective layers are not limited to the foregoing methods, and known methods may be suitably used.

The invention is specifically described below with reference to Examples. However, the present invention should not be construed as being limited to the following examples.

Prepared was an ITO film-bearing glass substrate (sheet resistance: <NUM>Ω/sq, manufactured by Ideal Star Inc. ) having an ITO (Indium Tin Oxide) film laminated on one surface of a glass substrate (<NUM> x <NUM>, thickness: <NUM>, alkali-free glass) by sputtering. The thickness of the ITO film was <NUM>. This ITO film-bearing glass substrate was used as a transparent substrate having a member serving as the light-transmissive electrode layer.

A laminate serving as the light-transmissive electrode layer and the electron transport layer was produced using the prepared ITO film-bearing glass substrate (the transparent substrate having the member serving as the light-transmissive electrode layer) in the following manner.

First, prepared was a treatment solution containing <NUM> mol/L of potassium hexafluorotitanate (K<NUM>TiF<NUM>) and <NUM> mol/L of potassium sulfate (K<NUM>SO<NUM>) and having the pH adjusted to <NUM> by use of potassium hydroxide (hereinafter simply called "treatment solution").

Next, the prepared ITO film-bearing glass substrate was immersed in a cleaning solution having Semiclean M-<NUM> (manufactured by Yokohama Oils & Fats Industry Co. ) diluted by <NUM> times with ion exchanged water, and subjected to ultrasonic cleaning for <NUM> minutes. Thereafter, the ITO film-bearing glass substrate was taken out from the cleaning solution, immersed in ion exchanged water, and subjected to ultrasonic cleaning for <NUM> minutes.

The cleaned ITO film-bearing glass substrate was immersed in the prepared treatment solution (solution temperature: <NUM>). The ITO film-bearing glass substrate was subjected to cathode polarization and then to anode polarization in the treatment solution under the relevant conditions shown in Table <NUM> below. Then, the ITO film-bearing glass substrate was immersed in a water bath at <NUM> for <NUM> seconds for washing with water, followed by drying by a blower at room temperature. Thus, a titanium oxide layer serving as the electron transport layer was formed on the ITO film of the ITO film-bearing glass substrate. The ITO film-bearing glass substrate having the titanium oxide layer formed thereon (a laminate serving as the light-transmissive electrode layer and the electron transport layer) was produced in this manner.

First, <NUM> mmol of titanium tetraisopropoxide was added to <NUM> of <NUM>-methoxyethanol, and the mixture was cooled in an ice bath for <NUM> minutes. Subsequently, <NUM> mmol of acetylacetone was added thereto, and the mixture was stirred in an ice bath for <NUM> minutes to thereby obtain a mixed solution. The obtained mixed solution was heated at <NUM> for <NUM> hours and then refluxed for <NUM> hour. Finally, the mixed solution was cooled to room temperature, thereby obtaining a titanium oxide precursor solution. The atmosphere in each step was a nitrogen atmosphere.

Next, the titanium oxide precursor solution was spin-coated on the ITO film of the ITO film-bearing glass substrate, which had been cleaned, under the conditions of a rotational speed of <NUM> rpm and a rotational time of <NUM> seconds to form a coating. Thereafter, the resultant was left in air to hydrolyze a titanium oxide precursor in the coating. Then, heating treatment at <NUM> for <NUM> hour was carried out to obtain a titanium oxide layer with a thickness of <NUM>.

A laminate (comparative laminate) thus produced was used for No. <NUM> to be described later.

The thickness of the titanium oxide layer, and the atomic ratio (InOx/Ti) and the atomic ratio (InM/Ti) were obtained in the above-described manners.

The visible light transmittance (unit: %) of the produced laminate was measured under the following conditions. With a larger visible light transmittance value, the transparency can be rated as more excellent.

In the following manner, an organic thin-film solar cell having a photoelectric conversion area of <NUM> x <NUM>, that is, <NUM><NUM> was produced using the produced laminate.

A mixed solution was obtained by mixing <NUM>,<NUM>-dichlorotoluene and chloroform at a volume ratio of <NUM>:<NUM>. Into this mixed solution, P3HT (manufactured by Aldrich) and PCBM (manufactured by Frontier Carbon Corporation) were dissolved at a mass ratio of <NUM>:<NUM> such that the total concentration was <NUM> mass%.

The thus-obtained mixed solution was spin-coated onto the titanium oxide layer under the conditions of <NUM> rpm and <NUM> seconds and dried at room temperature for about <NUM> minutes, thereby obtaining an organic semiconductor layer with a thickness of <NUM>.

Prepared was a nonionic surfactant (manufactured by Aldrich) containing <NUM> mass% of polyoxyethylene tridecyl ether (C<NUM>H<NUM>(OCH<NUM>CH<NUM>)<NUM>OH) and <NUM> mass% of xylene and having water and isopropanol as solvents. This nonionic surfactant in an amount of <NUM> parts by mass was mixed to <NUM> parts by mass of <NUM> mass% aqueous PEDOT/PSS dispersion (manufactured by Aldrich) to obtain a PTE-containing aqueous PEDOT/PSS dispersion.

The PTE-containing aqueous PEDOT/PSS dispersion was heated to <NUM> to <NUM>, spin-coated onto the organic semiconductor layer under the conditions of <NUM> rpm and <NUM> seconds, and then naturally dried at room temperature, thereby forming a hole transport layer with a thickness of <NUM>.

An Au electrode layer (collector electrode layer) was formed on the hole transport layer by vacuum deposition to have a thickness of about <NUM>.

More specifically, a shadow mask corresponding to an electrode shape of <NUM> x <NUM> and the glass substrate on which the layers up to the hole transport layer had been formed were placed in a chamber. The pressure in the chamber was reduced using a rotary pump and a turbomolecular pump to achieve a pressure of not higher than <NUM> x <NUM>-<NUM> Pa in the chamber. A gold wire was subjected to resistance heating in the chamber to form, via the shadow mask, a film of gold with a thickness of <NUM> on the hole transport layer. The film formation rate was set to <NUM> to <NUM>/min, and the pressure during the film formation was not higher than <NUM> x <NUM>-<NUM> Pa.

The thus-obtained glass substrate on whose one surface the ITO film (light-transmissive electrode layer), the titanium oxide layer (electron transport layer), the organic semiconductor layer, the hole transport layer and the collector electrode layer had been formed was heated at <NUM> for <NUM> minutes and further held at <NUM> for <NUM> hour. Thereafter, atmospheric sealing was made. Thus, an organic thin-film solar cell was produced.

The following evaluation was conducted with the produced organic thin-film solar cell.

The organic thin-film solar cell was irradiated, from its ITO film side, with artificial sunlight having a spectrum distribution of AM <NUM> (IEC standard <NUM>-<NUM>) and a light intensity of <NUM> mW/cm<NUM> by use of a solar simulator (XES-<NUM>, manufactured by SAN-EI Electric Co. In this state, a photocurrent-voltage profile of the organic thin-film solar cell was measured with a linear sweep voltammetry (LSV) measurement device (HZ-<NUM>, manufactured by Hokuto Denko Corporation). The maximum output was determined based on the obtained profile and evaluated according to the following criteria. With a larger maximum output value, the output characteristics can be rated as more excellent.

As shown in Table <NUM> above, No. <NUM> to No. <NUM> having atomic ratios (InOx/Ti) of not less than <NUM> and not more than <NUM> had better output characteristics than those of No. <NUM> that did not satisfy this range.

Comparing among No. <NUM> to No. <NUM>, No. <NUM> and No. <NUM> having larger values of atomic ratios (InOx/Ti) had more excellent output characteristics than those of No. <NUM> to No. <NUM> and No. <NUM>.

In addition, No. <NUM> to No. <NUM> having atomic ratios (InM/Ti) of less than <NUM> had higher visible-light transmittance values and better transparencies than those of No. <NUM> that did not satisfy this range.

Claim 1:
A laminate (<NUM>) suitable as a light-transmissive electrode layer (<NUM>) and as an electron transport layer (<NUM>) of an organic thin-film solar cell (<NUM>), which organic thin-film solar cell (<NUM>) includes the light-transmissive electrode layer (<NUM>), the electron transport layer (<NUM>), an organic semiconductor layer (<NUM>), a hole transport layer (<NUM>) and a collector electrode layer (<NUM>) in this order, the laminate (<NUM>) comprising:
a member (<NUM>) that serves as the light-transmissive electrode layer (<NUM>); and
a titanium oxide layer (<NUM>) that is disposed on the member (<NUM>) serving as the light-transmissive electrode layer (<NUM>) and serves as the electron transport layer (<NUM>),
wherein the titanium oxide layer (<NUM>) has a thickness of not less than <NUM> and not more than <NUM>,
characterized in that the titanium oxide layer (<NUM>) contains indium oxide and metallic indium, InOx/Ti is not less than <NUM> and not more than <NUM> in atomic ratio, and InM/Ti is not more than <NUM> in atomic ratio, where an elemental titanium content is represented by Ti, an indium oxide content is represented by InOx, and a metallic indium content is represented by InM.