JPH01154573A - Photoelectric converter - Google Patents

Abstract

PURPOSE:To obtain a photoelectric converter which exhibits a high optical current and has a large area inexpensively by adding specific diaminocarbazole derivative to an optically active layer. CONSTITUTION:An optically active layer contains at least diaminocarbazole derivative represented by a formula I. Thus, its optical current is largely increased. As a result, its photoelectric conversion efficiency is raised. In the formula I, R1 to R5 are halogen, and substituted or nonsubstituted alkyl group, substituted or nonsubstituted alkyl group, which may be the same or different. This photoelectric converter is composed by sandwiching, for example, a photoconductive organic semiconductor and the layer 2 containing the above compound between a front electrode 1 and a back electrode 4. Since light is incident from the front electrode, the electrode 1 is light transmittive. Both the front and back electrodes may be solely employed, or may be provided with a support or a protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a photoelectric conversion element (organic solar cell) using an organic photoconductor, and is applied to optical sensors, image sensors, etc.

[Prior Art] Many attempts have been made to produce photoelectric conversion elements using inorganic semiconductors. The goal is a) high conversion rate and b)
It is a low-priced photoelectric conversion element.

Single crystal Si, polycrystalline Si, Cd55CdTe.

Attempts have been made to put GaAs, amorphous Si, etc. into practical use, but it is difficult to say that all of these satisfy the goal b).

In order to improve this drawback, attempts have been made in recent years to fabricate photoelectric conversion elements using organic semiconductors. Examples of the organic semiconductor layers used are as follows.

(a) Merocyanine dye layer coated with a spinner (JP-A-51-122389, JP-A-53-131782, and K. Ghosh, "Journal of Applied Physics (J. , Ap
pl, Phys, )JS, 5982.1978) (b)
Laminated with a 5-electron layer such as a phthalocyanine vaporized layer or obalene and an electron acceptor layer such as pyrylium dye (
JP-A-54-27787, JP-A-60-201672, and “Journal of Applied Physics J” by R. O. Loutfy.
, Appl.

Phys, ) J 52. 5218.1981) (c) Eutectic complex layer formed from pyrylium dye and polycarbonate (JP-A-54-27387) (d) Layer in which metal-free phthalocyanine is dispersed in a binder (JP-A-55-1999)
9497) (e) Laminated layer of n-type silicon and p-type doped polyacetylene thin film: JP-A-55-H0182, JP-A-55-H3879, and B.R. Wennberger. applied,
Physics, Letters (Appl, Phys, Lett,) 38. 555.
1981) (to) Vacuum steamed merocyanine dye layer (
(Japanese Patent Application Laid-Open No. 56-35477) These organic semiconductors are prepared by coating a solution of these organic semiconductors alone or together with a suitable binder dissolved or dispersed in a medium on a substrate, or by vacuum evaporating at low temperature, and then applying a separate layer on top of the solution. By providing a conductive layer, a large-area device can be obtained at low cost, but the conversion efficiency was too low to be put to practical use.

[Purpose] The present invention has been made to solve the above-mentioned conventional drawbacks, and is inexpensive, easy to manufacture in a large area, flexible, and suitable for use with organic materials. The purpose of this invention is to provide a photoelectric conversion element that has high conversion efficiency and matches the spectral distribution of sunlight and indoor light compared to conventional photoelectric conversion elements.

[Structure] In order to achieve the above object, the present invention provides an organic semiconductor capable of generating optical carriers in the visible light region when used alone or with an appropriate binder [said (a) to (a).
As a result of intensive research to improve the drawbacks of By containing the photocurrent, the photocurrent increases significantly, and as a result,
This is based on the discovery that photoelectric conversion efficiency increases.

General formula However, in the above general formula, RI to R5 are hydrogen,
A substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, which may be the same or different.

The photoelectric conversion element of the present invention has, for example, a structure in which a photoactive layer (I) containing a photoconductive organic semiconductor and the above compound is sandwiched between two electrodes (front electrode, back electrode).

Since light enters from the front electrode side, the front electrode is transparent.

Both the front and back electrodes may be used alone or may be provided with a support or a protective layer. 1st
Examples of these are shown in FIG.

The front electrode and the back electrode are connected to an external circuit through lead wires, etc., and used for actual use.

The photoactive layer need not be a single layer; examples of two layers are shown in FIGS. 1-3(b), respectively. This photoactive layer (If) may be a layer that generates charges by light like the photoactive layer (1), or may be a layer that efficiently transfers the charges generated in the photoactive layer (1). In the example of FIG. 1(b), the photoactive layer (1) is drawn on the front electrode side, but it goes without saying that the photoactive layer (n) may be on the front electrode side. The photoactive layer (1) may also be a multilayer consisting of different photoconductive organic materials.

The present invention relates to the photoactive layer (I).

The photoactive layer (I) is a layer that generates holes and electrons when irradiated with light. This requires the presence of an electric field within the layer, either by applying an external voltage between the front and back electrodes or by using metals with different work functions for the front and back electrodes. or a photoactive layer (
1) is the front or back electrode or photoactive layer (n)
When joined, each other's Fermi level (or Shi!
Due to the difference in the μ function), thermal carriers move and a junction barrier is formed, which is achieved without an external voltage.

The photoactive layer (1) is a layer containing a diaminocarbazole derivative represented by the general formula (A). This layer contains, as another essential component, a photoconductive organic semiconductor that absorbs visible light.

It may also contain a suitable binder if necessary.

The inventors have discovered that when such diaminocarbazole derivatives exist, the amount of photocurrent generated in the photoactive layer (1) upon irradiation with light increases dramatically compared to the case where such diaminocarbazole derivatives do not exist, thereby increasing the conversion efficiency. Ta.

Here, a photoconversion element is one that generates an electromotive force or current, or both, when light is irradiated without applying an external voltage between the front and back electrodes in Figure 1, and that generates a large amount of electromotive force or current when an external voltage is applied. This is an element from which photocurrent can be extracted.

As described above, the photoactive layer (1) is a layer containing as essential components the diaminocarbazole derivative represented by the general formula (A) and a photoconductive organic semiconductor that absorbs visible light.

The diaminocarbazole derivative represented by the general formula (A) has a high ability to uniformly dissolve with other organic semiconductors and binders in the layer without crystallizing, and also has a low ionization potential among organic compounds and a positive Pore mobility is also high.

Here, the composition of each component in the photoactive layer (1) is: diaminocarbazole derivative 5 to 50 wt%; photoconductive organic semiconductor having absorption in the visual field 30 to 90 wt%; binder 0 to 50 wt%;
Preferably 10 to 40 wt% and 40 to 70 wL, respectively.
%, 10 to 40 wL%.

As the proportion of the diaminocarbazole derivative decreases, the effect of adding the same compound becomes weaker, and as the proportion of the diaminocarbazole derivative increases, the concentration of the light-absorbing photoconductive organic semiconductor becomes relatively low, thereby reducing the amount of light absorbed. becomes smaller.

When the proportion of the photoconductive organic semiconductor becomes low, the amount of light absorbed becomes small, and when the proportion becomes high, the concentration of the diaminocarbazole derivative becomes relatively low, and the effect of addition becomes weak.

When the amount of binder is small, the probability that the diaminocarbazole derivative crystallizes increases, and when it is large, the generation of photocharge,
The amount of moving parts is reduced, reducing efficiency.

The thickness of the photoactive layer is suitably 0.01 to 10 μm.

The optimum film W varies depending on the type of photoconductive organic semiconductor and resin used, but is preferably 0.05 to 3 μl. If it is thin, the amount of light absorbed will be small, and the probability of pinholes occurring between the front and back electrodes will increase.

When the thickness becomes thicker, the distance for one of the generated holes and electrons to reach the electrode becomes longer, increasing the probability that they will be deactivated on the way, and reducing efficiency.

For the aqueous layer, mix the above organic semiconductor with a resin if necessary in a suitable medium, and if the above organic semiconductor is a pigment, grind the pigment using a method such as a ball mill to create a uniform slurry. After dissolving the pigment in a solvent such as the like, a diaminocarbazole derivative is added, and these are coated on the back electrode or the back electrode on the support, or the front electrode on the support.

The photoactive layer formed in this manner has a slightly increased open circuit voltage (Voc) and a significantly increased short circuit current (Jsc) compared to the case without the diaminocarbazole derivative.

The conversion efficiency (η) is expressed by the following formula, η-t o , V o
It is determined by c x J s c X f fPin (Pin: incident light energy, ff: fill factor).

The device of the present invention provides higher conversion efficiency than that without the addition of diaminocarbazole derivatives. The reason for this is that since the diaminocarbazole derivative has a low ionization potential as an organic substance, holes among the photocharges generated in the photoconductive organic semiconductor due to light absorption are easily injected into the diaminocarbazole derivative. Furthermore, the compound also has high hole mobility. For this reason, it is considered that the probability of recombination of holes and electrons is lowered and the efficiency of hole transfer is increased compared to the system without addition.

Moreover, of course, even when a voltage is applied from the outside, a large photocurrent can be extracted, and therefore it is used as a photoelectric conversion element with excellent sensitivity.

Specific examples of the diaminocarbazole derivatives used in the present invention include those with the following structures.

For the front electrode layer and its support: Nialuminum, lead, zinc, tantalum, nickel, titanium, cobalt,
Translucent metals such as niobium, copper, Hastelloy C1 gold, platinum, silver, and palladium, and metal oxides such as tin oxide and ITO can be used as the front electrode, and glass and transparent plastic films can be used as the support. .

Regarding the back electrode and its support: Most metals can be used as the back electrode.

Glass or transparent plastic film is used as the support.

Regarding the photoactive layer (I[): This layer either a) contains other charge-generating organic semiconductors to cover the low sensitivity wavelength range of the pigments used in the photoactive layer (I), or b) contains a photoactive layer. (I) A layer that forms a junction barrier between the photoactive layer (C) and a layer that effectively moves holes and electrons generated in the photoactive layer (1).

Among these, for layer a), a compound having a color tone that corrects that of (1) among the exemplified compounds for photoactive layer (1) described later is highly effective, and it is formed by coating in the same manner as photoactive layer (1). be done.

The layer b) is formed by dispersing fine particles of zinc oxide, titanium oxide, cadmium sulfide, selenium crystals, lead oxide, etc. in an adhesive resin.

The layer C) is formed by mixing the additive of the photoactive layer (I) or an electron donor with an even lower Ip value with a suitable resin.

The light-absorbing keratotic semiconductor used as an essential component of the present invention includes azo pigments such as disazo pigments and trisazo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, aromatic polycyclic boron pigments, and indigo pigments. , thioindigo pigments, and dyes such as triphenylmethane dyes, cyanine dyes, and merocyanine dyes.

Examples of resins used as binders include polyester resins, polycarbonate resins, polyamide resins, polyurethane resins, epoxy resins, alkyd resins, phenolic resins, melamine resins, acrylic resins, cellulose resins, vinyl acetate resins, vinyl chloride resins, and vinylidene chloride. Resin, vinylidene fluoride resin, butyral resin, polyvinylcarbazole resin, polystyrene resin, polyimide resin, polyacrylonitrile resin, vinyl chloride-vinyl acetate copolymer, vinylidene chloride-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene -butadiene copolymer, ethyl cellulose, etc.

Next, structural examples of the photoelectric conversion element of the present invention will be explained with reference to the schematic diagrams shown in FIGS. 1 to 3. Figure b shows an example in which a second photoactive layer is added to supplement the photoactive layer shown in figure a.

In the figure, ■ is a translucent front electrode, 2 is a photoactive layer (I),
3 is a photoactive layer (n), 4 is a back electrode, 5 is a front electrode support, and 6 is a back electrode support. It should be understood that these structures can be varied in various ways depending on the application.

Examples will be shown below to explain the present invention more specifically, but the present invention is not limited thereto.

Example 1 0.8g of azo pigment with the following structure and butyral resin (UC
After ball milling 8 g of a 5% tetrahydrofuran solution from Company C (9XYHL) for 3 days, the dispersion was further diluted with tetrahydrofuran to prepare a 1.5 wL% pigment dispersion.

To this pigment dispersion, an additive (compound N
After adding o and 3) and stirring, a coating liquid was prepared.

This coating solution is indium-doped tin oxide (hereinafter referred to as I).
2101 by dipping a glass substrate provided with
The substrate was pulled up at a speed of 11/sec to form a coating film on the ITO substrate.

On top of this, semi-transparent aluminum was vacuum-steamed so that the transmittance at 580n1 was about 5.1%, and then ITO
A thin copper wire was connected to the aluminum using silver paste.

This sample is irradiated with 580 nm monochromatic light from the AI electrode side (reaching the pigment dispersion film).
The current-voltage characteristics were measured by applying a ramp wave swept at a rate of Bmv/sec to the picture electrode while applying a ramp wave to the picture electrode. As a result, Voc=0.92V Jsc-69.7nA/cd rr-0.20.

The photoelectric conversion characteristic (η') at 580 μm after correcting the transmittance of the electrode was 0.82796.

Comparative Example 1 A pigment dispersion film was prepared in the same manner as in Example 1 except that the additives in Example 1 were not added, and the transmittance at 580 cm was 7.
Translucent aluminum was vacuum-deposited to a concentration of 7% and used as a sample. When monochromatic light of 580 .mu.m was incident on this sample from the ITO electrode side CPin'-1,6 .mu.v/cm.sup.2)L, the photoelectric conversion characteristics were measured in the same manner as in Example 1, and the following results were obtained.

Voc=0.74V Jsc-2,50n^/ cd f'f'-0,22 η' 0.026% Example 2 Example 1 except that the azo pigment in Example 1 was changed to one with the following structure. A pigment dispersion was prepared in the same manner as above, and the additive (compound No. 3) was similarly dissolved and applied.
Translucent aluminum (A1) was vacuum-deposited to give a sample.

When monochromatic light of 58On11 was incident on this sample from the Al electrode side (Pin' -1, 8 μw/cd) L, and the photoelectric conversion characteristics were measured in the same manner as in Example 1, the following results were obtained.

Voc=0.85V Jsc-34,7nA/cd 0.13 η--0.230% Comparative Example 2 A pigment dispersion film was prepared in the same manner as in Example 2 except that the additive in Example 2 was not added. The transmittance of the prepared 5B0nml is 7.
, 2% of translucent aluminum was vacuum-deposited and used as a sample.

Monochromatic light of 560 μm is incident on this sample from the AI main electrode (P
When the photoelectric conversion characteristics were measured in the same manner as in Example 1, the following results were obtained.

Voc-0,61V Jsc-4,80nA/cd f'l'-0,20 η--0,035% Example 3 Same as Example 1 except that the additive in Example 1 was changed to compound No. 2. Samples containing additives were similarly prepared.

Monochromatic light of 580 r+m was incident on this sample from the Al electrode side (Pin' = 1.55 μv/cd) L, and the photoelectric conversion characteristics were determined in the same manner as in Example 1, and the following results were obtained.

Voc-0,88V Jsc-18,lnA/cj 1'f'-0,23 η'' -0,21% Example 4 Same as Example 1 except that the additive in Example 1 was changed to compound No. 4. Samples containing additives were similarly prepared.

Monochromatic light of 580 μm is incident on this sample from the A1 electrode side (
When the photoelectric conversion characteristics were measured in the same manner as in Example 1, the following results were obtained.

Voc=0.90V Jsc-68,3n^/ cd f'f-0,20 η'-〇, 77% Example 5 Same as Example 1 except that the azo pigment in Example 1 was changed to β-type copper phthalocyanine. Samples containing additives were similarly prepared.

[i20nmO7l1 color light was incident on this sample from the Al electrode side (PIn'=1.5 μv/ant) L, and the photoelectric conversion characteristics were determined in the same manner as in Example 1, and the following results were obtained.

VocJ, 94V Jsc-21, 8nA/ci 1'r-0,22 η--0.30% Comparative Example 3 A sample was prepared in the same manner as in Example 5 except that no additives were added, and it was exposed to monochromatic light of 620 nm. is incident from the AI electrode (Pin
When the photoelectric conversion characteristics were measured in the same manner using 1.5μν/cd), the following results were obtained.

Voc-0,72V Jsc-10,4nA/cd fl'-0,26 η=-0,13% [Effect] As described above, according to the present invention, diaminocarbazole derivatives are added to the photoactive layer. By doing so, it is possible to achieve a photoelectric conversion element that exhibits a high photocurrent, is inexpensive, and has a large area.

For this reason, conventionally, alone or in combination with a binder,
Photoconductive organic semiconductors, which were previously unusable due to their low photocurrent, can now be used effectively, expanding the range of materials to choose from.

[Brief explanation of the drawing]

FIGS. 1a to 3 are schematic diagrams showing cross sections of the photoelectric conversion element of the present invention. ■...Transparent front electrode, 2...Photoactive layer (1)
, 3... Photoactive layer (II), 4... Back electrode, 5...
...Front electrode support, 6...Back electrode support.

Claims (1)

[Scope of Claims] A photoelectric conversion element having a translucent front electrode, a photoactive layer, and a back electrode, wherein the photoactive layer at least comprises:
A photoelectric conversion element characterized by containing a diaminocarbazole derivative represented by the following general formula. General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ However, in the above general formula, R_1 to R_5 are hydrogen, substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, and they may be the same or different. You can.