JP2935998B2 - Photovoltaic element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photovoltaic element useful for an optical sensor or the like.

[Prior Art] Many photovoltaic devices using an organic material as an active material have been studied. The purpose is to develop an inexpensive and non-toxic photovoltaic device that is difficult to achieve with single crystal, polycrystalline, or amorphous Si.

Since the photovoltaic element is an element that converts light energy into electric energy (voltage × current), the conversion efficiency is a main evaluation target. The generation of a photocurrent requires the presence of an internal electric field, and several element configurations are known as methods for generating the internal electric field. The best data of conversion efficiency in each of the known configurations when an organic material is used as the active material is as follows.

1) Schottky junction or MIS junction An internal electric field generated by metal / semiconductor junction.
Merocyanine dyes, phthalocyanine pigments and the like have been reported as organic semiconductor materials.

Irradiation of white light of 78 mW / cm ^{2 on} the Al / merocyanine / Ag device yields a conversion efficiency of 0.7% (Voc = 1.2 V, Jsc = 1.8 mA / cm ² , ff =
0.25) has been reported. [AKGhosh et al. J. Appl. Phys. 4
9, 5982 (1978)] that convert organic semiconductor used in the device of this type efficiency is high is limited to p-type. Therefore, an electrode material having a low work function, such as Al, In, or Mg, is used. These are easily oxidized.

2) Hetero pn junction using n-type inorganic semiconductor / p-type organic semiconductor junction An internal electric field generated when an n-type inorganic semiconductor / p-type organic semiconductor is bonded. CdS, ZnO, or the like is used as the n-type material. Merocyanine dyes, phthalocyanines and the like have been reported as p-type organic semiconductor materials.

ITO / electrodeposition CdS / chlorinated aluminum chloro phthalocyanine / Au element conversion AM-2 light irradiation of 75 mW / cm ² on the efficiency
The best is 0.22% (Voc = 0.69V, Jsc = 0.89mA / cm ² , ff = 0.29) [A. Hor et al. Appl. Phys. Lett., 42 , 15 (198
3)].

3) A device utilizing an organic / organic hetero junction A device utilizing an electric field generated when an electron-accepting organic substance and an electron-donating organic substance are joined.

As the former organic substances, dyes such as malachite green, methyl violet and pyrylium, flavanthrone and condensed polycyclic aromatic compounds such as perylene pigments have been reported.
As the latter examples, phthalocyanine pigments, merocyanine dyes and the like have been reported.

Conversion efficiency of 0.95% (Voc = 0.4) with 75 mW / cm ² AM-2 light irradiation for ITO / copper phthalocyanine / perylene pigment / Ag device
5 V, Jsc = 2.3 mA / cm ² , ff = 0.65) have been reported [C.
Tang Appl. Phys. Lett., 48 , 183 (1986)]. This value is the highest in a photovoltaic device using an organic substance. or,
Japanese Patent Publication No. 62-4871 by the same inventor discloses that the conversion efficiency of 1% (Voc = 0.44V,
Jsc = 3.0 mA / cm ² , ff = 0.6).

The conversion efficiency of a photovoltaic element using an organic substance is lower than that using an inorganic semiconductor. The biggest factor for this is the low short-circuit photocurrent (Jsc). For a device with a conversion efficiency of 5%, at least 10 mA / cm ² for 75 mW / cm ² of white light irradiation
Jsc is required. The aforementioned Jsc is much lower. This is due to low quantum efficiency and narrow spectral sensitivity wavelength range. It is desirable that the spectral sensitivity wavelength be as wide as possible from 400 nm to as long as possible, but many of the conventional examples are limited to a specific wavelength range.

In many cases, ff is small. It is said that one of the causes of the low ff is that the quantum efficiency exhibited by the organic semiconductor rapidly decreases at a low electric field. Therefore, a configuration in which a strong internal electric field that does not cause such a decrease is generated is preferable for improving ff. Further, an element configuration in which generated charges can smoothly reach the electrodes without an energy barrier increases ff.
These achievements can also improve Voc, but there have been many cases where sufficient consideration has not been given to these points in the past.

In addition, many of the organic photovoltaic devices reported have problems in terms of the chemical stability of the electrode material.

 The above-mentioned prior art is viewed from the above viewpoint.

1) The Schottky junction or the MIS type junction Voc can be large, but since the metal material is used for the electrode, the light transmittance of the electrode is low. The actual light transmittance is at best 30%, usually around 10%. Also, these materials have poor oxidation resistance. Therefore, it is impossible to produce high conversion efficiency and stable characteristics in this element form.

2) Inorganic semiconductor / organic semiconductor hetero pn junction Since charge generation is mainly performed in an organic layer, spectral sensitivity is limited. Usually, the organic layer is formed from a single material, but there is currently no organic semiconductor having strong light absorption from 400 to 800 nm. Therefore, this device configuration can solve the problems of the light transmittance of the light incident electrode and the stability of the electrode, but cannot achieve high conversion efficiency because the spectral sensitivity region is narrow.

3) Organic / organic hetero pn junction Compared to the above two configurations, it is currently the most desirable. Since light irradiation from the transparent electrode can be performed and photocharge can be generated by using two kinds of materials, spectral sensitivity can be broadened. In fact, the report by Tang mentioned earlier was 450-550
It can be seen that charges are generated by the perylene pigment at nm and copper phthalocyanine at 550-700 nm. Also, the fact that ff is larger than other element configurations is presumed that the generated internal electric field is large. However, Tang's technology has the following disadvantages:

First, since the thickness of the organic layer is small (the patent describes that 300 to 500 ° is desirable), the probability of pinholes is high. In our experiments, there is a relatively high probability of a short circuit between the two electrodes, possibly due to a pinhole. The electrode area in Tang's paper is 0.1 cm ^2, and improving the yield will be a major issue if the area is actually used (1 cm ² or more is required).

The second is the problem of the electrode material. In his invention, the electrodes need to be in ohmic contact with each organic material. The aforementioned paper states that the organic layer lowers Voc in the inverted device configuration. This is presumed to be due to impaired ohmic contact. However, in a configuration that achieves ohmic contact, the stability of the metal material becomes a problem. This is because a metal that can make such contact with an electron-accepting organic substance needs to have a low work function. In fact, during the patent
In, Ag, Sn, and Al are exemplified. These are all easily oxidized.

[Problems to be Solved by the Invention] An object of the present invention is to use an electrode having high translucency on the incident side, use an electrode material having high stability, and achieve high conversion as an organic photovoltaic device. An object is to provide a device that provides efficiency.

[Means for Solving the Problems] In order to achieve the above object, as a result of intensive studies, it has been found that an n-type inorganic semiconductor layer, an electron-accepting organic material layer, an electron In a photovoltaic device including a portion in which a donor organic material layer is stacked in this order, a substance forming an electron-accepting organic material layer may be a perinone pigment and / or
Alternatively, it has been found that the object can be achieved by using a perylene pigment. Hereinafter, the device configuration, materials used, production method, and the like in the present invention will be described.

One embodiment of the photovoltaic element of the present invention is as shown in FIG.

Here, the support may be on the back electrode side. In addition, the order of the electron accepting layer and the electron donating layer may be reversed. In this case, the n-type inorganic semiconductor layer is located on the back electrode side and does not have to be porous. However, the preferred embodiment is preferred. Therefore, the configuration of the embodiment shown in the upper diagram will be described below.

The feature of this element structure is the presence of an n-type inorganic semiconductor layer.
With the n-type inorganic semiconductor layer, improvement of conversion efficiency (1) and reduction of short circuit (2) are achieved by improvement of Voc, Jsc, and ff. It is not clear exactly why such an effect occurs, but the following may be considered.

1) Improvement of conversion efficiency a) As the transparent electrode, a material having a low Fermi level, such as ITO, is usually used. Therefore, when there is no n-type inorganic semiconductor layer, a Schottky junction is formed between the electron-accepting organic substance and the transparent electrode. This junction acts as an energy barrier when electrons move from the electron-accepting organic layer to the transparent electrode. When the n-type inorganic semiconductor layer is present,
The contact between the transparent electrode / n-type inorganic semiconductor layer and the n-type inorganic semiconductor layer / electron-accepting organic material layer achieves ohmic contact, respectively, and the movement of electrons becomes smooth.

b) Since the probability of a short circuit can be reduced, the organic layer can be made thinner, leading to an improvement in quantum efficiency.

c) Electrons are supplied from the n-type inorganic semiconductor layer to the electron-accepting organic layer in the dark, and the internal electric field generated at the interface between the electron-accepting organic layer and the electron-donating organic layer is strengthened.

2) Reduction of short circuit a) Step at the edge of the transparent electrode layer (1000 when ITO is used)
(Normally about Å or more) becomes gentle due to the presence of the n-type inorganic semiconductor layer, and the probability of short-circuiting between both electrodes at this portion is reduced.

b) For example, even if a pinhole exists in the electron-accepting organic material layer, the electron-donating organic material layer in contact therewith forms a pn junction with the n-type inorganic semiconductor layer, thereby eliminating the effect of the pinhole in the electron-accepting organic material layer. It becomes a form to make it. The same effect is produced between the back electrode and the electron-accepting organic layer when a pinhole exists in the electron-donating organic layer. For this reason, a short circuit is hardly observed.

Another advantage of the present configuration is the use of a highly stable back electrode. This is because ohmic contact is required between the electron donating organic material layer and the back electrode. An electrode material satisfying this condition has a large work function and is a material having high stability.

It has been found that when a perinone-based pigment and / or a perylene-based pigment are used as the electron-accepting material, the effects of the above-described device configuration can be sufficiently obtained, and high conversion efficiency can be obtained as an organic photovoltaic device. This is a perinone pigment and / or
Or, a perylene pigment has a low ionization potential among organic substances, and generates an internal electric field strong enough to generate a photocharge with an electron donating organic substance layer, has excellent photoconductivity, and has an electron transfer ability. Is high, and the light absorption wavelength region is on the long wavelength side of 600 nm or more, so that the light absorption of the electron-donating organic material layer such as phthalocyanine can be well separated and the spectral sensitivity of the entire device can be widened. For reasons.

The perinone pigment used as the electron-accepting organic substance in the present invention is represented by the following general formulas (1) to (3).

(In the formula, X represents 0 or NR, and the substituent R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group.) (In the formula, X represents a substituted or unsubstituted aryl ring.) (In the formula, X represents a substituted or unsubstituted aryl ring.) Examples of the perinone pigment represented by the general formulas (1), (2) and (3) include the following exemplified compounds.

Further, the perylene pigment used in the present invention is represented by the following general formulas (1) to (3).

(In the formula, X represents 0 or NR, and this substituent, R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group.) (In the formula, X represents a substituted or unsubstituted aryl ring.) (In the formula, X represents a substituted or unsubstituted aryl ring.) Examples of the perylene compounds represented by the general formulas (1) to (3) include the following exemplary compounds.

These perinone and / or perylene pigment layers are deposited,
The film is formed by a method such as spin coating and dipping.
Among them, vapor deposition is preferable for thinning and uniforming. The film thickness is
100-3000Å.

Further, as the transparent insulating support used in the present invention, glass, plastic film or the like is used.

As the transparent electrode used in the present invention, indium tin oxide (ITO), tin oxide, indium oxide and the like are used. The preferred thickness is between 100 and 1000 mm.

As the n-type semiconductor layer used in the present invention, zinc oxide, CdS, titanium oxide, amorphous silicon doped with phosphorus, and the like, such as zinc oxide and CdS, are preferable. The thickness is preferably from 10 to 10,000 mm.

As the electron donating organic material used in the present invention, a phthalocyanine pigment (the center metal of which is Cu, Zn, Co, Ni, P
b, Pt, Fe, Mg, etc., divalent ones, metal-free phthalocyanine, aluminum chlorophthalocyanine, indium chlorophthalocyanine, trivalent metal phthalocyanine to which a halogen atom is coordinated, such as gallium chlorophthalocyanine, other vanadyl phthalocyanine, titanyl phthalocyanine, etc. Phthalocyanine to which oxygen is coordinated); Indigo and thioindigo pigments (Pigment Blue 66.Pi
gment Violet 36); quinacridone pigments (Pigment V
iolet 19, Pigment Red 122, etc.); dyes such as merocyanine compounds, cyanine compounds, and squarium compounds; these are formed into films by methods such as vapor deposition, spin coating, and dipping. Among them, vapor deposition is preferable for thinning and uniforming. The film thickness is 100-3000Å.

Further, as the back electrode used in the present invention, Au, P
A metal having a high work function such as t, Ni, Pd, Cu, Cr, and Ag is used, and Au is particularly stable and preferable. The film thickness is preferably 50 to 3000 °.

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 A well-washed ITO glass (Matsuzaki Vacuum, 30Ω / □) was used at a substrate temperature of about 300 ° C. and argon was used as an introduction gas.
Zinc oxide was provided in a thickness of about 1300 mm by C magnetron sputtering. On top of this, a perinone pigment of Exemplified Compound No. 7, which is an electron-accepting substance, is deposited in a thickness of about 500 mm by a vacuum evaporation method, and then aluminum chlorophthalocyanine (AlClPc)
It was provided with a thickness of about 400 mm, and gold was vacuum-deposited thereon. ITO
And the area made of gold was 0.25 cm ² . Lead wires were attached to the two electrodes with silver paste.

While irradiating 75 mW / cm ² of white light to the ITO side of this device and applying a voltage swept at 6 mV / s and measuring the conversion efficiency, Voc = 0.53 V, Jsc = 0.45 mA / cm ² , ff = 0.28, and a conversion efficiency of 0.088% was obtained. This value is great for an organic photovoltaic device.

Example 2 A device was manufactured in the same manner as in Example 1, except that the electron accepting substance of Example 1 was changed to the perinone pigment of Exemplified Compound No. 8, and the thickness of the AlClPc layer was set to 600 ° and the thickness of the perinone pigment layer was set to 300 °. Was prepared, and the conversion efficiency was measured. As a result, Voc = 0.50V,
Jsc = 0.46 mA / cm ² , ff = 0.28, and a conversion efficiency of 0.086% was obtained.

Example 3 On a well-cleaned ITO glass (Matsuzaki Vacuum, 30Ω / □), at a substrate temperature of about 300 ° C., using argon as an introduced gas, and using a DC magnetron sputtering method, zinc oxide was coated with about 1300 mm of zinc oxide.
The thickness was provided. On top of that, perylenetetracarboxylic acid methylimide (exemplified compound No. 2), which is an electron-accepting substance, is provided in a thickness of about 500 mm by vacuum evaporation, and then aluminum chlorophthalocyanine (AlClPc) is provided in a thickness of about 400 mm. , And gold was vacuum-deposited thereon. The area that ITO and gold make
0.25 cm ² . Lead wires were attached to the two electrodes with silver paste.

While irradiating 75 mW / cm ² white light to the ITO side of this element and applying a voltage swept at 6 mV / s and measuring the conversion efficiency, Voc = 0.43 V, Jsc = 2.44 mA / cm ² , ff was 0.46, and a conversion efficiency of 0.65% was obtained. This value is great for an organic photovoltaic device.

Example 4 A device was manufactured in the same manner as in Example 1 except that the electron accepting substance of Example 3 was changed to the perylene pigment of Exemplified Compound No. 6, and the thickness of the AlClPc layer was changed to 600 ° and the thickness of the perylene pigment layer was changed to 100 °. Was prepared, and the conversion efficiency was measured. As a result, Voc = 0.50V,
Jsc = 0.60 mA / cm ² , ff = 0.45, and a conversion efficiency of 0.18% was obtained.

Example 5 Example 1 was repeated except that the electron accepting substance of Example 3 was changed to the perylene pigment of Exemplified Compound No. 1 and the film thickness was changed to 250 °.
A device was prepared in the same manner as described above, and the conversion efficiency was measured. As a result, Voc = 0.52 V, Jsc = 1.90 mA / cm ² , ff = 0.38, and a conversion efficiency of 0.50% was obtained.

Example 6 A device was prepared in the same manner as in Example 1 except that the electron accepting substance of Example 3 was changed to the perylene pigment of Exemplified Compound No. 10 and the film thickness was set to 500 °, and the conversion efficiency was measured. As a result, Voc = 0.46 V, Jsc = 1.49 mA / cm ² , ff = 0.39, and a conversion efficiency of 0.35% was obtained.

Example 7 Example 1 was repeated except that the electron accepting substance of Example 3 was changed to the perylene pigment of Exemplified Compound No. 8 and the film thickness was set to 300 °.
A device was prepared in the same manner as described above, and the conversion efficiency was measured. As a result, Voc = 0.55 V, Jsc = 0.46 mA / cm ² , ff = 0.26, and a conversion efficiency of 0.09% was obtained.

Example 8 Example 1 was repeated except that the electron accepting substance of Example 3 was changed to the perylene pigment of Exemplified Compound No. 9 and the film thickness was changed to 150 °.
A device was prepared in the same manner as described above, and the conversion efficiency was measured. As a result, Voc = 0.40 V, Jsc = 1.86 mA / cm ² , ff = 0.39, and a conversion efficiency of 0.39% was obtained.

[Effects of the Invention] The effects of the photovoltaic device of the present invention are summarized as follows.

1. Voc, Jsc, ff by a combination of a device configuration using an n-type inorganic semiconductor layer and a perylene pigment and / or a perylene pigment.
And a high conversion efficiency is achieved as an organic photovoltaic device.

2. Stable electrode materials can be used.

[Brief description of the drawings]

 FIG. 1 is a diagram showing an example of a photovoltaic device of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 31/04-31/078 H01L 31/10-31/119

Claims (1)

(57) [Claims] 1. A structure having a portion composed of three consecutive layers of an n-type inorganic semiconductor layer, an electron-accepting organic material layer, and an electron-donating organic material layer between two electrodes, at least one of which is translucent. Wherein the substance forming the electron-accepting organic layer is a perinone-based pigment and / or a perylene-based pigment.