JPH0427170A - Photovoltaic element - Google Patents

Abstract

PURPOSE:To improve light absorption rate in an optically active layer by using light multiple reflection from a rear electrode by laminating an electron acceptive organic layer and an electron donative organic layer to be rectified and bonded thereto between a light transmission front electrode and the rear electrode having light reflecting capacity, and further providing an organic layer having different main light absorption wavelength band from the acceptive or donative organic layer on the rear electrode side from the continuous two layers. CONSTITUTION:A laminate of an electron acceptive organic layer and an electron donative organic layer 1 for forming an optically active layer is included between a transparent electrode and a rear electrode having a light reflecting capacity, and an electron donative organic layer 2 having different essential light absorption band from that of the layer 1 is provided on a back surface electrode side. With this structure, JSC is particularly improved as compared with a configuration of the mere laminate of the acceptive layer 1. Further, the layer 1 has an optimum range of the JSC in a thick region for sufficiently transmitting a light with respect to the rise of the JSC, and the higher the light reflectivity of the rear electrode is, the higher of JSC is.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photovoltaic element useful also as a light sensor and the like.

[Prior Art] Many studies have been conducted on photovoltaic elements using organic substances as active materials. The purpose is to develop an inexpensive, non-toxic photovoltaic device, which is difficult to achieve with single-crystal, polycrystalline, or amorphous Si.

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

l) Schottky junction or MIS type junction A type that utilizes the internal electric field of a metal/semiconductor junction. Merocyanine dyes, phthalocyanine pigments, etc. have been reported as organic semiconductor materials.

78 polishing V/e for Al/merocyanine/Ag elements
Conversion efficiency of 0.7% (Voc-1
, 2V% J Se-1,8mA/e12, fT-
0,25) have been reported. [A, ni, Ghos
h et al. J, Appl, Phys, 49°5982 (19
78)] Among the organic semiconductors used in this type of device, those with high conversion efficiency are limited to p-type. Therefore, electrode materials with low work functions such as AI, In, and Mg are used. These are easily oxidized.

2) Hetero pn junction using an n-type inorganic semiconductor/p-type organic semiconductor junction A type that utilizes the internal electric field generated when an n-type inorganic semiconductor/p-type organic semiconductor is joined. CdS, Z as n-type material
nO etc. are used. Merocyanine dyes, phthalocyanines, etc. have been reported as p-type organic semiconductor materials.

ITO/electrodeposited CdS/chlorinated aluminum chlorophthalocyanine/75a1cfl12 for Au element
Conversion efficiency was 0.22% (V oc −
0,69V, Jsc -0,89mA/cm2
IT -0,29) is the best [A, Hor et al. AI
)I)1. Phys.

Lett, 42.15 (1983)].

3) Using the electric field generated when an electron-accepting organic substance and an electron-donating organic substance are joined using an organic/organic heterojunction.

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

ITO/copper phthalocyanine/perylene pigment/Ag element was irradiated with 75 mW/c112 am M-2 light with a conversion efficiency of 0.95% (V oc -0.45V % J s
c-24mA7cm2, fr-0,85) has been reported [C, TangAppl, Phys, Lett,
, 48, 183 (198B)], this value is the highest among photovoltaic elements using organic materials. In addition, in Japanese Patent Publication No. 62-4871 by the same inventor, the conversion efficiency of 1% (V oc -0
,44V, J se -3,0mA/cm2fT-
0,6) have been reported.

The conversion efficiency of photovoltaic devices using organic materials is lower than those using inorganic semiconductors. The biggest factor contributing to this is the low short-circuit photocurrent (JSc). A device with a conversion efficiency of 5% requires a J sc of at least 10 mA/cm 2 for white light irradiation of 75 mV/c 2 . The aforementioned Js
c is much lower than that. This is due to low quantum efficiency and narrow spectral sensitivity wavelength range. It is desirable that the spectral sensitivity wavelength extends from 400 nm to as long as possible, but in many conventional examples it is limited to a specific wavelength range.

Furthermore, there are many cases where rr is small. It is said that one of the reasons for the low rr is that the quantum efficiency of organic semiconductors rapidly decreases in low electric fields. Therefore, a configuration that generates a strong internal electric field that does not cause such a decrease is preferable for improving rr. Furthermore, an element configuration that allows generated charges to smoothly reach the electrode without an energy barrier increases rr. Achieving these goals will also improve VOC, but
In the past, there were many cases in which sufficient consideration was not given to these points.

Additionally, in the reported organic photovoltaic devices,
Many electrode materials also have problems in terms of chemical stability.

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

1) Schottky junction or MIS type junction Voc can be made large, but since metal material is used as the electrode,
The light transmittance of the electrode becomes low. The actual light transmittance is at best 30%, usually around 10%. Also, these materials have poor oxidation resistance. Therefore, with this element form, it cannot be expected to produce high conversion efficiency and stable characteristics.

2) Inorganic semiconductor/organic semiconductor heteropn junction Since charge generation is mainly performed in the organic layer, the spectral sensitivity is limited. Typically, the organic layer is formed from a single material, but 40
This is because there is currently no organic semiconductor that has strong optical absorption from 0 to, for example, 800 square meters. Therefore, with this device configuration, the problems of light transmittance of the light incident electrode and stability of the electrode can be overcome, but high conversion efficiency cannot be expected because the spectral sensitivity region is narrow.

3) Organic/organic heteropn junction Compared to the above two types of configurations, this is currently the most desirable one. Since light can be irradiated from a transparent electrode and photocharges can be generated using two types of materials, spectral sensitivity can also be expanded. In fact, according to the report by Taug mentioned above, 450
Perylene pigment at ~550nm, 550-700rv
This shows that an electric charge is generated in the copper phthalocyanine.

Furthermore, the fact that rr is larger than other element configurations is presumed to indicate that the generated internal electric field is large. However, Taug
Even with his technology, it was difficult to reliably achieve a conversion efficiency of over 1%. As a result of investigation, it was found that this is because the organic layer (hereinafter referred to as photoactive layer) that actually contributes to photocurrent generation is very thin, at 100 to 300 mm, and therefore the light absorption of the device is insufficient. The thickness of the organic layer necessary for photocurrent generation is approximately the same as that of the photoactive layer; if it is thicker than this, light will simply be absorbed in vain. However, since the photoactive layer is thin, if the thickness of the organic layer is set to this level, electrical short circuits due to pinholes cannot be ignored, making it difficult to fabricate a good device.

[Problems to be Solved by the Invention] An object of the present invention is to prevent deterioration of device performance due to pinholes in an organic/organic pn type photovoltaic device, and to
By suppressing the thickness of the organic layer that forms the bond to about the thickness of the photoactive layer, multiple reflections of light from the back electrode can be used to improve the light absorption efficiency in the photoactive layer, resulting in an organic photovoltaic device. The objective is to provide an element that provides high conversion efficiency.

[Means for solving the problem] In order to achieve the above object, a highly transparent electrode is placed on the incident side of an organic/organic hetero pn junction type photovoltaic element, and a highly reflective material is used. By providing an organic layer on the back electrode side that has a different light absorption wavelength range from the organic layer that forms the pn junction, it prevents deterioration of device performance due to pinholes and reduces the thickness of the organic layer that forms the pn junction. By suppressing the thickness to about the thickness of the photoactive layer, multiple reflections of light from the back electrode are used to improve the light absorption efficiency in the photoactive layer, resulting in a conversion of over 1%, which is high for an organic photovoltaic device. We have found that efficiency can be achieved.

The device configuration, materials used, manufacturing method, etc. in the present invention will be explained below.

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

The feature of this device structure is that it includes a stack of an electron-accepting organic material layer and an electron-donating organic material layer (L), which form a photoactive layer, between a transparent electrode and a back electrode having light-reflecting ability. An electron-donating organic layer (2), which has a different main light absorption region from layer (1), is provided on the back electrode side. It has been found that with this configuration, J sc is particularly improved compared to a configuration in which an electron-accepting organic layer and an electron-donating organic layer (1) are simply laminated.

This effect was found to be due to an improvement in the quantum yield in the spectral sensitivity wavelength region of the electron-donating organic layer (1). Furthermore, for an increase in Jsc, the electron donating organic layer (1) has an optimal thickness in a region where light can pass through sufficiently, and the higher the light reflectance of the back electrode, the higher the Jsc. Do you get it. These results suggested that the thickness of the photoactive layer in the electron-donating organic layer (1) is so thin that short circuits would be noticeable in the absence of the electron-donating organic layer (2).

Therefore, the electron-donating organic layer (
It is considered that the combination of 2) and a back electrode with high light reflectivity improved the Jsc by increasing the light absorption efficiency of the electron-donating organic layer (1) by utilizing the reflection of the back electrode.

If the electron-donating organic layer (2) is not provided, the electron-donating organic layer (1) must be provided to have a thickness greater than that of the photoactive layer in order to prevent deterioration of device performance due to short circuits.

In this case, the remaining light transmitted through the photoactive layer is not used for photocurrent generation and is simply wasted and absorbed. Therefore, it is understood that the light utilization efficiency is improved when the electron-donating organic material layer is multilayered.

Another more preferable embodiment of this element is the configuration shown in FIG. The feature of this structure is that a light-transmitting n-type inorganic semiconductor layer is inserted. The presence of the n-type inorganic semiconductor layer achieves improved conversion efficiency and reduced short circuits by improving VocSJ SC,rr.

As another embodiment, a structure in which electron-accepting organic material layers are multilayered as shown in FIG. 3 can also be used.

Here, a photocurrent is generated at the interface between the electron-donating organic layer and the electron-accepting organic layer (1). The reason why the photocurrent is improved compared to the two-layer structure is due to the same reason as explained in FIG. 1.

Next, various materials, manufacturing methods, etc. used in the photovoltaic device of the present invention will be explained.

As the transparent insulating support used in the present invention, glass, plastic film, etc. are used.

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

The n-type semiconductor layer used in the present invention includes zinc oxide, zinc oxide doped with a trivalent metal, CdS, titanium oxide, amorphous silicon doped with phosphorus, and preferably zinc oxide, CdS, and the like. Thickness is 10~10000
People are preferred.

Electron-accepting organic layer (1) used in the present invention (
As for 2), perylene pigment Pig+gent Red (hereinafter referred to as PR) 179°PR190, PR149, PR189
, PR123゜Plgment Brown 2B etc. Plgment Orange 43
．． Anthraquinone pigments such as PR194 PR188, P
R177, VatYellow 4, quinone-containing yellow pigments such as flavanthrone, dyes such as crystal violet, methyl violet, malachite green, fluorenone, 2.4.7-
trinitrofluorenone, tetracyanoquinodimethane,
Examples include acceptor compounds such as tetracyanoethylene. These films are formed by vapor deposition, spin code, or dipping. Vapor deposition is preferred for thinning and uniformity.

The film thickness is preferably 100 to 3000×.

Electron-accepting organic substances (1) and (2) preferred in the present invention
) combinations include perylene pigments (main absorption band in the visible light region is 450-700nrA)/perinone pigments (400-550nr+m), perylene pigments/flavanthrone (400-550nrA), perylene pigments/
Examples include acceptor compound (400 to 500 nm), perinone pigment/acceptor compound, crystal violet (500 to B50na+)/perylene pigment, and anthraquinone pigment (450 to fi00 nm)/acceptor compound.

The appropriate film thickness for the electron-accepting organic layer (1) is 30 to 300 layers. As the thickness increases, no increase in Jsc is observed, and
When the layer becomes thinner, the light absorption efficiency of the layer decreases, and J sc decreases. The appropriate film thickness for the electron-accepting organic layer (2) is 5
It is 0-3000X.

Electron-donating organic layer (1) used in the present invention (
2) is a phthalocyanine pigment (the central metal is Cu).
5ZnSCO% Nis Pb, Pt.

Divalent metals such as Fe5Mg, trivalent metal phthalocyanines coordinated with halogen atoms such as metal-free phthalocyanine, aluminum chlorophthalocyanine, indium chlorophthalocyanine, and gallium chlorophthalocyanine, and other oxygen-coordinated phthalocyanines such as vanadyl phthalocyanine and titanyl phthalocyanine. Phthalocyanine) Indigo, thioindigo pigments (PigmentBlu
e6B, Pigment Violet 3B, etc.), quinacridone pigments (Pigment Violet 1
9. Pigment Red 122, etc.), dyes such as merocyanine compounds, cyanine compounds, squalium compounds, charge transfer agents used in organic electrophotographic photoreceptors (hydrazone compounds, pyrazoline compounds, triphenylmethane compounds, triphenylamine compounds, etc.), electrical conductivity electron-donating compounds used in organic charge transfer complexes (tetrathiofulvalene, tetraphenyltetrathioflavalene, etc.), conductive polymers (polypyrrole, polythiophene,
polyaniline, etc.).

Electron-donating organic layer (1) used in the present invention/(
The combination of 2) is a phthalocyanine pigment (550~
850nm)/quinacridone pigment (450-800nm)
s), cyanine compound (600-800ns)/quinacridone pigment, squalium compound (550-800ns)
s) /quinacridone pigment, phthalocyanine pigment/
Charge transfer agent (400-500rv), phthalocyanine pigment/electron donating compound (400-500rv), phthalocyanine pigment/conductive polymer (400-5501 layer), quinacridone pigment/charge transfer agent, quinacridone pigment/ Examples include indigo (500 to 700n*).

These layers are formed by methods such as vapor deposition, spin code, dipping, and electrolytic polymerization. Among these, vapor deposition is preferable for making the film thin and uniform.

The appropriate film thickness for the electron-donating organic layer (1) is 30 to 300 layers. As the thickness increases, no increase in Jsc is observed, and
When the layer becomes thinner, the light absorption rate of the layer decreases, and J sc decreases. The appropriate film thickness for the electron-donating organic layer (2) is 5
It is 0-3000X.

If the electron-donating organic layer is not a multilayer, the film thickness is 100
~3000 people is preferred.

In addition, the back electrode used in the present invention is Au, Pt.
s Ni, Pd5Cu, Cr, Ag.

Metals such as AI, Tis Mo, Nb, and Ta, and alloys such as stainless steel, Hastelloy, and nichrome are used.

These exhibit high light reflectance over all visible light or over a significant portion of the visible light range. These may themselves be substrates or may be provided by vapor deposition or sputtering. In the latter case,
The film thickness is preferably 50 to 3000 people.

[Example] EXAMPLES The present invention will be explained in more detail by way of Examples below.

Example 1 Well-washed ITO glass (manufactured by Matsuzaki Vacuum, 3°Ω/mouth)
Zinc oxide was deposited on the substrate to a thickness of about 1500.t by RF magnetocolo sputtering at a substrate temperature of 250''C using argon as an introduced gas.

Approximately 400% of perylenetetracarboxylic acid methylimide (PL-ME), an electron-accepting substance, is applied on top of it by vacuum evaporation.
The thickness of aluminum chlorophthalocyanine (AICIPc) was varied, and then 2,9-dimethylquinacridone (QA-ME) was applied to a thickness of about 300 mm, and gold was vacuum deposited thereon. The area between ITO and gold was 0.25c+a'. Lead wires were attached to the two electrodes using silver paste.

The two electrodes of this device were short-circuited, monochromatic light was irradiated in the intestine region from 460 to 800 nm, and the photocurrent spectrum was measured. As shown in FIG. 4, the photocurrent based on the AlClPc layer for 600 to 800 ns increased as the thickness of the AlClPc layer became thinner.

This is achieved by thinning the AlClPc layer and combining it with a QA-ME layer with a different light absorption wavelength range.
This is because the light utilization efficiency of the layer has increased. Also, from the plot of the internal quantum yield of 720n■ shown in Figure 5, AlC
The thickness of the photoactive layer of the lPc layer was found to be as thin as approximately 150 nm.

Example 2 The conversion efficiency was measured by applying a voltage swept at BmV/s while irradiating the ITO side of the element of Example 1 with 751Ue Kasumi 2 white light, and the results shown in Figure 6 were obtained. Ta.

It was found that corresponding to the increase in internal quantum yield of 600 to 8G0nii in Example 1, the J sc of white light irradiation also increased, thereby improving the conversion efficiency. At a film thickness around 100 A, a conversion efficiency of over 1% was obtained. Furthermore, PL-
300 ME, 120 AlClPc, QA-M
In a device with E as 300 people, V oc-0.48V,
J5c-8,5sA/cs2, fT=0.49, and a conversion efficiency of 1.1% h< was obtained. This value is large for an organic photovoltaic device.

Comparative Example 1.2 Example 1 (7) A device was manufactured in the same manner as in Example 1 except that the number of AlClPc layers was 150 and 400, and the QA-ME layer was not provided, and the conversion efficiency was determined in the same manner as in Example 2. was measured. As a result, 150 elements were short-circuited, and 40
02 element: VOC-0,43V% J 5c-2
, 44 mA/es2, fl'-0.46, and the conversion efficiency was 0.65%.

Example 3 A device was produced in the same manner as in Example 1, except that QA-ME in Example 1 was replaced with a pyrazoline compound having the following structure, and the film thickness was changed to 200. Short-circuit the two electrodes of this element,
740na+ with a strength of 30μw/e112 from the ITO side
When we irradiated it with monochromatic light and observed the photocurrent, we found that 4.
A short circuit photocurrent of 4 μA/Cm2 was obtained.

Comparative Example 3 The device of Comparative Example 2 was subjected to the same measurements as in Example 3, and the short-circuit photocurrent value was 2.8 μA/c2.

Example 4 AlClPc of Example 1 was converted into metal-free phthalocyanine (H2
A device was produced in the same manner as in Example 1, except that QA-ME was replaced with PC), the film thickness was changed, and quinacridone (QA) was used instead of QA-ME, and the conversion efficiency was measured in the same manner as in Example 2. As a result H
The thickness of the photoactive layer of the 2PC layer is about 200, and the conversion characteristic at this thickness is V □ (-0,37V s J s
c"" 2.0 mA/cm2, rr-0.51, and a conversion efficiency of 0.5% was obtained.

Comparative Example 4 A device was produced in the same manner as in Example 1 except that the number of H2Pc layers in Example 4 was 300 and the QA layer was not provided, and the conversion efficiency was measured. As a result, VOC-0,37V SJ s
c-1,6aA/am2fT -0,51, and the conversion efficiency was 0.4%.

Example 5 The thickness of the PL-ME layer of Example 1 was 500, and AlC
A device was fabricated in the same manner as in Example 1, except that lPc was changed to titanyl phthalocyanine (TiOPc) and the film thickness was changed to 120, and the conversion efficiency was determined by /IPI in the same manner as in Example 2. As a result, V oc-0,5V s J sc-2
, 8+nA/cm' ff -0.48, and a conversion efficiency of 0.8% was obtained.

Comparative Example 5 A device was produced in the same manner as in Example 5 except that the number of TioPc layers was 300 and the QA layer was not provided, and the conversion efficiency was measured. As a result, Voc=0.5V, J
sc-1.7 mA/cm2, ff-0.46, and the conversion efficiency was 0.52%.

Example 6 A device was produced in the same manner as in Example 5 except that the zinc oxide layer of Example 4 was not provided, and the conversion efficiency was measured. As a result, V
oc-0,42V s J sc = 2.1mA/cm
', f'r-0-4B and Nari conversion efficiency of 0.5496 were obtained.

Comparative Example 6 A device was produced in the same manner as in Example 6 except that the number of TioPc layers in Example 6 was 300 and the QA layer was not provided, and the conversion efficiency was measured. As a result, Voc-0,46V SJ
SC-1, 6 mA/cm 2 , ff 0.41, and the conversion efficiency was 0.4%.

Example 7 PL-ME of Example 3 was added to the following compound, AlClPc
A device was produced in the same manner as in Example 3 except that QA was used and the thickness was 200. The conversion efficiency of this element was measured in the same manner as in Example 2. As a result, Voc-0,5
0V, Jsc-1, 46mA/cm', ff'
= 0.53, and a conversion efficiency of 0.52% was obtained.

+Mixture Comparative Example 7 A device was produced in the same manner as in Example 7, except that the number of QA layers in Example 7 was 300, and the QA layer was not provided, and the conversion efficiency was measured. As a result, voc-0,53V, J sc-0
, 93 mA/cs', fT-0.57, and the conversion efficiency was 0.37%.

Example 8 For the device of Example 2 in which the AlClPc layer was 120X, after Au was deposited on the back electrode, Ag was further deposited, and the conversion efficiency was measured. As a result, V □(-0,50V s
J sc-3,911IA/cm', ff'-0,
46, which was a conversion efficiency of 1.2%.

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

1. High conversion efficiency can be achieved as an organic photovoltaic device due to the device configuration in which the organic material layers are multilayered and light reflection from the back electrode can be utilized.

[Brief explanation of the drawing]

1 to 3 are diagrams illustrating configuration examples of the photovoltaic device of the present invention, and FIG. 4 is a photovoltaic device of Example 1 in which two electrodes are short-circuited, and monochromatic light in the region of 460 to 800 ns is emitted. Fig. 5 is a diagram explaining the relationship between the internal quantum yield and the thickness of the AlClPc layer in the same photovoltaic element, and Fig. 6 shows the conversion efficiency in Example 2. The figure which shows the measurement result of.

Claims (1)

[Claims] An electron-accepting organic material layer and an electron-donating organic material layer capable of rectification bonding to the layer are laminated between a light-transmitting front electrode and a back electrode having light-reflecting ability. 1. A photovoltaic element, further comprising an electron-accepting organic material layer or an electron-donating organic material layer having a main light absorption wavelength region different from that of the electron-accepting organic material layer or the electron-donating organic material layer.