JP2003282934A - Rapid response photoelectric current multiplying device formed of mixed thin film of heterologous organic semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the optical response speed of multiplied photoelectric current. <P>SOLUTION: A photoelectric current multiplying layer 1 is an codeposition film added with 30 vol.% of copper phthalocyanine which has a thickness of 500 nm. The photoelectric current multiplying layer 1 is sandwiched between a translucent gold evaporation film electrode 2 and an ITO electrode 3 which are provided on both faces of the photoelectric current multiplying layer 1. When voltage is applied from a power supply 4 via both electrodes 2 and 3 and light is irradiated on the photoelectric current multiplying layer 1 via one electrode 2, the multiplied photoelectric current is caused to flow at a rapid optical response speed between the electrodes 2 and 3. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurrent multiplying device, and more particularly to a photocurrent multiplying device utilizing the photocurrent multiplying phenomenon of a photoconductive organic semiconductor, and an organic electroluminescent (organic EL) layer. The present invention relates to a photocurrent multiplying device including a light-to-light conversion element for obtaining light-to-light converted light.
The photocurrent multiplying element can be used in, for example, a photo sensor.

[0002]

2. Description of the Related Art Conventionally, a photocurrent multiplying device utilizing a photocurrent multiplying phenomenon by a photoconductive organic semiconductor utilizes a photocurrent amplifying effect at an organic / metal interface. Generally, a photocurrent multiplying device has a sandwich type cell structure in which a photoconductive organic semiconductor layer or a laminate of an organic electroluminescent layer is sandwiched between two metal electrodes. The photoconductive organic semiconductor layer is highly purified by refining.
A single vapor-deposited thin film of a class of organic semiconductors was used.

As a concrete example, a photocurrent multiplying device (for example, M. Hir) using a vapor-deposited thin film of perylene pigment is used.
amoto, T. Imahigashi, and M. Yokoyama, Applied Phy
sicsLetters, 64, 187 (1994).), Photocurrent multiplication device using a single vapor-deposited thin film of quinacridone pigment (M. Hiram
oto, S. Kawase, and M. Yokoyama, Japanese Journal
of Applied Physics, 35, L349 (1996).), a photocurrent multiplication device using a single vapor-deposited thin film of a naphthalene derivative (for example, T. Katsume, M. Hiramoto, and M. Yokoyam).
a, Applied Physics Letters, 69, 3722 (1996).) and the like have all reported photocurrent multiplication devices using a single vapor-deposited thin film of a photoconductive organic semiconductor.

Further, there has been reported a light-to-light conversion element for performing wavelength conversion and light amplification of light by integrating and integrating an organic electroluminescent film with a photocurrent multiplication layer made of a photoconductive organic semiconductor (T. Katsume, M. Hiramoto, and M. Yokoyama, Appl. Ph
ys. Lett., 64, 2546 (1994), and M. Hiramoto, T. Kat.
sume, and M. Yokoyama, Opt. Rev., 1, 82 (1994)). Again, the photocurrent multiplication layer is a single vapor deposited thin film of photoconductive organic semiconductor.

[0005]

In the above-described conventional photocurrent multiplication device using a single vapor-deposited thin film, the multiplication factor (the ratio of the number of electrons due to the multiplication photocurrent flowing through the device to the number of incident photons) is larger than 1. It has the potential to be applied to amplification type optical sensing devices such as avalanche photodiodes. However, it takes a time of the order of seconds for the response of the photomultiplied photocurrent to light irradiation start (light on) and light irradiation stop (light off), that is, the photoresponse speed of the multiplied photocurrent is very slow. Therefore, it has been an obstacle when applying the photocurrent multiplying device as a photosensor.

The same problem occurs in a light-to-light conversion device using a photoconductive organic semiconductor with a single vapor-deposited thin film. The present invention is directed to a photocurrent multiplying device including both a photocurrent multiplying element and a photo-photo conversion element as an element. The purpose is to increase the light response speed.

[0007]

In the fast response photocurrent multiplying device of the present invention, a photocurrent multiplying layer containing a photoconductive organic semiconductor is irradiated with light while a voltage is applied to the photocurrent multiplying layer. In the photocurrent multiplying device that obtains photoirradiation induced current with a quantum yield multiplied by the above, the photoconductive organic semiconductor of the photocurrent multiplying layer is a mixture of an electron transporting organic semiconductor and a hole transporting organic semiconductor. And the ratio of the other organic semiconductor to the one organic semiconductor is in the range of 20 vol% to 50 vol%. According to the present invention, it is possible to realize a high-speed response photocurrent multiplication device that can be practically used as an amplification type photosensor.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As an electron transporting organic semiconductor,
Fullerene (C60), naphthalene derivative (NTCDA
(Naphthalenetetracarboxylic anhydride), etc., C7
0, perylene pigments and their derivatives (various types of derivatives having different substituents on the nitrogen atom are known, for example, t
There are -BuPh-PTC, PhEt-PTC and the like, and also Im-PTC having a high photoelectric conversion ability. ) And the like. Figure 2 shows the main ones of these organic semiconductors.
Shown in.

Examples of hole transporting organic semiconductors include phthalocyanine pigments and their derivatives (metal phthalocyanines (MPc) such as copper phthalocyanine (CuPc) having various metals at the center, H ₂ Pc having no metal, and various other materials around it). A quinacridone pigment (DQ), an acene such as anthracene or perylene, and a hole transporting agent such as a triphenyl diamine derivative (TPD). The main ones of these organic semiconductors are also shown in FIG.

Since the photocurrent multiplication phenomenon is observed only in the crystalline organic semiconductor film, the crystallinity of one organic semiconductor is lost by adding a large amount of the other organic semiconductor to one organic semiconductor. In the case of an amorphous film, the multiplication phenomenon itself does not occur. Co-evaporation can be used as an example of the manufacturing method, but in the case of co-evaporation, it has been found that when a high concentration of different materials is added, amorphization of the film occurs at a considerable rate. For example, in the system shown in one example, even if 30% of CuPc was added to C60, C60 did not become amorphous, and a multiplication factor similar to that of C60 alone could be observed. However, even in this system, when 50% is added (C60: CuPc = 50: 50), multiplication itself does not occur.

Further, when the amount of addition of one organic semiconductor to the other organic semiconductor is small, the speed-up effect becomes insufficient. For example, in the system shown in one example, when the amount of CuPc added to C60 was as small as 10%, the speed-up effect was insufficient.

Therefore, the other organic semiconductor added to one organic semiconductor needs to be a material that can be added at a high concentration of 20 to 50% without destroying the crystallinity of the one organic semiconductor. The effect of the present invention cannot be generally observed with a very small amount of addition of several percent or less, which is called doping.

The first form of the photocurrent multiplication layer is a vapor deposition film. The vapor-deposited film is produced by a co-evaporation technique in which an electron-transporting organic semiconductor and a hole-transporting organic semiconductor are simultaneously vapor-deposited or a method in which an organic semiconductor in which an electron-transporting organic semiconductor and a hole-transporting organic semiconductor are premixed is used as a vapor deposition source. can do. The thickness of the vapor deposition film is preferably 0.3 to 5.0 μm. When the film thickness is smaller than this range, pin poles are generated and reliability deteriorates.

As the organic electroluminescent layer constituting the light-to-light conversion element, aluminum-quinolinol complex (Alq ₃ ), 3,
Examples include vapor deposited films of 4,9,10-perylenetetracarboxylic 3,4: 9,10-bis (phenylethylimide). The thickness of the organic electroluminescent layer is 0.05 to 0.1 μm.
Is appropriate.

In the light-to-light conversion element, a carrier transport layer (hole transport layer or electron transport layer) may be provided between the organic electroluminescent layer and the electrode. As the carrier transport layer, triphenyl diamine derivative (TPD) such as N, N-diphenyl-N, N-bis (4-methylphenyl) -4,4-diamine, 3,5-dimethyl-3,5 -Ditertiary butyl-
4,4-Diphenoquinone, 2- (4-biphenyl) -5-
Examples include vapor deposition films of (4-tertiary butylphenyl) -1,3,4-oxadiazole, N, N, N, N-tetra- (m-toluyl) -m-phenylenediamine and the like. The suitable thickness of the carrier transport layer is 0.05 to 0.1 μm.

As the electrode film provided on the side where light transparency is required as the electrode, a vapor deposition film of gold or other metal or a sputtering film can be used in addition to an ITO (indium tin oxide) transparent electrode. The electrode film may be formed on a glass substrate, or may be formed on a laminate with a photocurrent multiplication layer or an organic electroluminescent layer by a vapor deposition method or a sputtering method.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. In this example, a single vapor-deposited film of C60 and C60 obtained by adding 30 vol% of copper phthalocyanine (CuPc) to C60.
-CuPc co-deposited film (C60: CuPc = 70: 30)
The characteristics were compared.

First, FIG. 2 shows a sectional view of a cell of a high-speed response photocurrent multiplying device targeted by the present invention. Reference numeral 1 is a photocurrent multiplying layer, which is a co-deposited film in which 30 vol% of copper phthalocyanine is added to C60 in this embodiment. As a comparative example, one in which the photocurrent multiplication layer 1 was a C60 single vapor deposition film was also prepared. The film thickness of the photocurrent multiplication layer 1 is 500 nm. The photocurrent multiplication layer 1 is sandwiched between the metal electrodes 2 and 3 provided on both surfaces thereof. The electrode 3 is vapor-deposited on the transparent glass substrate 5. At least the electrode film on the incident side of the electrodes 2 and 3 is transparent or semitransparent to incident light. Here, an ITO (indium tin oxide) film that operates as a transparent electrode is used as the electrode 2, and a semi-transparent gold vapor deposition film (film thickness 20 nm) is used as the electrode 2. Reference numeral 4 is a power source for applying a voltage to the cell. FIG. 3 shows the chemical structural formulas of C60 and copper phthalocyanine.

When the present invention is applied to a light-to-light conversion element, an organic electroluminescent layer is laminated and integrated on the photocurrent multiplication layer 1. The cell characteristics are evaluated by applying a voltage so that the gold electrode 2 becomes negative with respect to the ITO electrode 3,
0nm monochromatic light irradiation, photo-response characteristics of multiplication photocurrent,
The applied voltage dependence of the multiplication factor (the ratio of the number of electrons due to the multiplied photocurrent flowing through the cell to the number of incident photons) and the dependence of the multiplied photocurrent on the irradiation light intensity were measured.

FIG. 4A shows a response profile of a multiplication photocurrent in a cell prepared by using a C60 single vapor deposition film as a comparative example, and FIG. 4B shows a C60-CuPc co-evaporation film (C60: CuPc =) as an example. 70:30) shows a response profile of a multiplied photocurrent in a cell manufactured by using (70:30). The horizontal axis represents time (seconds) and the vertical axis represents current density (Current dens
ity). The measurement conditions were an applied voltage of 10 V and Au electrode 2
Is applied to the ITO electrode 3 with a negative voltage, 560n
m monochromatic light is radiated from the Au electrode 2 side, light intensity 30 μW /
It was made to be equal in both cells in cm ² .

The multiplication factor is 10 times in the former case and 15 times in the latter case, which can be considered to be almost the same. It has been confirmed that multiplication under this condition occurs at the interface between the Au electrode 2 and the photocurrent multiplication layer 1 of C60.

Comparing the two results of FIG. 4, the response is clearly faster when the C60-CuPc co-deposited film is used as compared with the case where the C60 single film is used as the photocurrent multiplication layer 1 (a). You can see that

The 90% response time (time required to reach 90% of the saturation value of the multiplication photocurrent) when the light is turned on is 1 second in the photocurrent multiplication layer of the C60 single film, whereas C60
In the photocurrent multiplication layer of the -CuPc co-deposited film, the photocurrent multiplication layer rises at the time resolution limit of this measurement system (the time interval between each point of the response profile) of 0.2 seconds or less, and is in the order of milliseconds (ms). I found that I was responding.

90% response time when light is off (time required to return to 90% of current level before light irradiation)
Is 13 seconds in the photocurrent multiplication layer of the C60 single film, whereas in the photocurrent multiplication layer of the C60-CuPc co-deposited film, the time resolution limit of the measurement system (at each point of the response profile The time interval is 0.2 seconds or less. As described above, we succeeded in making the response of the photomultiplied photocurrent both on and off for the first time to the millisecond order.

FIG. 5A shows the result of measuring the response speed of a cell using a C60-CuPc co-deposited film (C60: CuPc = 70: 30) with a higher time resolution using an oscilloscope. . An LED having a wavelength of 560 nm is used as a light source, and ON / OFF of light is controlled by a function generator. Note that (b) in FIG. 5 shows the shape of the irradiated periodic optical pulse (pulse width: 100 ms). Applied voltage 14V, irradiation light intensity 250μW / c
m ² . The multiplication factor is 15 times. It was found that the rising response speed was 8 ms and the falling response speed was 15 ms. Therefore, an operation using an optical pulse of 40 Hz or higher is possible.

The response profile is very reproducible,
When the light was turned off, it returned to the dark current level before light irradiation with good reproduction. The resolution of this measurement (time interval of each point of the profile) is 100 μs, but the multiplied photocurrent completely follows the rising response of the LED and is 100 μs.
It can be seen that it has started within (one time interval). As described above, by adding 30% of CuPc to C60, the response speed of the multiplication photocurrent could be increased about 1000 times without lowering the multiplication factor.

FIG. 6 shows a C60-CuPc co-deposited film (C6
0: CuPc = 70: 30) 90% of the response speed of the cell using Rise time (Rise time (milliseconds)) and the applied voltage (Applied v) of the multiplication rate
oltage (V)) dependence is shown. White circles represent the response speed, and black corners represent the multiplication factor. The light intensity is 250 μW / cm ² . It can be seen that as the applied voltage increases, the multiplication factor increases to nearly 30 times, and at the same time, the response speed also rapidly increases. At an applied voltage of 20 V, the fastest response of 90% response speed of 3 milliseconds could be observed.

The response profile when the applied voltage is 20 V is shown in FIG. The horizontal axis represents time (milliseconds), and the vertical axis represents current (μA). It can be clearly read that the 90% response speed is 3 milliseconds. FIG. 8 shows a rising response profile when the irradiation light intensity is changed from 15 to 250 μW / cm ² at an applied voltage of 11V. The horizontal axis represents time (milliseconds), and the vertical axis represents current (μA).

In FIG. 9, the result of FIG. 8 is increased by 90%.
The dependence of the response speed and the multiplication photoelectric flow rate on the irradiation light intensity is summarized as follows.
I have The horizontal axis is the light intensity (μW / c
m²)), The vertical axis on the left is the rise response speed (Rise time
(Milliseconds)), the vertical axis on the right is the multiplication photoelectric flow rate (Multiplied
 photocurrent (μA)). White circle stands up
The response speed and the black angle represent the multiplication photoelectric flow rate. Irradiation light intensity is 25
0 to 15 μW / cm ²90% response speed even if weakened
If it ’s almost 10 to 15 ms and it ’s almost late,
There wasn't. Also, the multiplication photoelectric flow rate is almost proportional to the light intensity.
I found that it was an example relationship.

The C60-CuPc co-deposited film (C
The cell using (60: CuPc = 70: 30) has a response speed reaching millisecond for both light-on and light-off, the multiplication photoelectric flow is proportional to the light intensity, and the dark current level is stable. Therefore, the photocurrent response has very good reproducibility and is very suitable for optical sensing. It can be said that this element performance demonstrates the possibility of an amplification type photo sensor utilizing the photocurrent multiplication phenomenon.

The multiplication factor at present is about 30 times, but in the cell using the C60 single vapor deposition film, by reducing the film thickness of the photocurrent multiplication layer from the current 500 nm to 350 nm, about 1000 times. It has been confirmed that the multiplication factor can be increased, and a multiplication factor of about 1000 times can be realized even in the case of a cell using a C60-CuPc co-deposited film.

FIG. 10 shows the energy structure of the C60 / Au interface during multiplication. The multiplying photocurrent is caused by a large amount of electrons being tunnel-injected from the Au electrode into the C60 layer by accumulating photogenerated holes at the C60 / Au interface and concentrating a high electric field at the interface.

FIG. 11 shows a schematic view of the C60-CuPc / Au interface. It is known that the vapor-deposited Au electrode is an aggregate of ultra-fine particles of 20 nm, and photo-generated holes are accumulated in a space between the C60-CuPc co-deposited film and the Au particles to concentrate the electric field on the interface. And cause electron injection from the electrode (structure trap model). Where CuP
When c is added at a high concentration such as 30%, C6
A CuPc connected route is formed in the 0 film.

The cause of the high-speed response will be described with reference to FIGS. First, regarding the rise at the time of turning on the light, the photocarrier generation quantum yield (the normal (primary) photocurrent quantum yield before secondary multiplication electron injection occurs)
12 is remarkably sensitized by mixing C60 and CuPc as shown in FIG. 12, and is 20% with C60 alone at an applied voltage of 6 V, whereas C60-
It has been actually measured that the CuPc co-deposited film (C60: CuPc = 70: 30) has reached 60%. In FIG. 12, the horizontal axis represents applied voltage (V), and the vertical axis represents Quantum efficiency of primary photocurrent.
(%)). Therefore, it can be estimated that it is close to the upper limit of 100% in the high voltage region close to 20 V in which the device of the example is operated. Also, CuPc, which has a hole-transporting property, can efficiently generate photogenerated holes in a C60-CuPc co-deposited film / A.
Provide a route to transport to the u interface (Figure 11). Due to these two effects, C60-CuPc co-deposited film / A
Due to the increased number of photogenerated holes supplied to the u interface, enough holes accumulate enough to cause electron injection, resulting in a multiplication photocurrent of 10 as shown in FIG.
It is considered that it started up within 0 μs.

On the other hand, to explain the speeding up of the fall at the time of turning off the light, the holes accumulated at the C60-CuPc co-deposited film / Au interface pass through the CuPc route newly formed by adding about 30% CuPc. It can be considered that the Au electrode was quickly released to the Au electrode (Fig. 1
1).

From the above, the speeding up of the rising up to 3 ms increases both the accumulation rate of holes in the structure trap at the interface and the release rate of holes from the structure trap due to the addition of CuPc. Equilibrium is now achieved very quickly (on the order of milliseconds), and the amount of hole accumulation at the interface is constant on the order of milliseconds, so (equilibrium between hole accumulation and release processes is If the above condition is achieved, the number of holes existing in the trap will be constant), and it can be rationalized if the multiplication photocurrent determined by the number of holes at the interface reaches a saturation value in the order of milliseconds. On the contrary, in the device with a very slow photo-response speed, the multiplication photocurrent reaches a constant saturation value because both the hole supply rate and the release rate to the structure trap at the organic / metal interface are very slow. It can be said that it took tens of seconds to reach it.

[0037]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a quantum is multiplied by irradiating a photocurrent multiplication layer containing a photoconductive organic semiconductor with light while applying a voltage to the photocurrent multiplication layer. In a photocurrent multiplication device that obtains photoirradiation-induced current at a yield, the photoconductive organic semiconductor of the photocurrent multiplication layer is a mixture of an electron transporting organic semiconductor and a hole transporting organic semiconductor,
The ratio of one organic semiconductor to the other organic semiconductor is 2
Since it is set in the range of 0 vol% to 50 vol%, the photoresponse speed of the multiplied photocurrent can be improved, and a photocurrent multiplication device applicable as a practical amplification type photosensor can be realized.

[Brief description of drawings]

FIG. 1 is a chemical formula showing some of the organic semiconductors used in the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of the fast response photocurrent multiplying device of the present invention.

FIG. 3 is a chemical formula of C60 and CuPc.

4A is a response profile of a multiplication photocurrent in a cell prepared by using a C60 single vapor deposition film as a comparative example, and FIG. 4B is a C60-CuPc co-evaporation film (C60: Cu).
It is a figure which shows the response profile of the multiplication photocurrent in the cell of one Example produced using Pc = 70: 30.

FIG. 5A is a C60-CuPc co-deposited film (C60:
CuPc = 70: 30), the response profile of the cell of the same example manufactured with higher time resolution,
(B) is the waveform of the irradiated periodic light pulse light.

FIG. 6 is a diagram showing applied voltage dependency of 90% rising response speed and multiplication factor of the cell of the example.

FIG. 7 is a diagram showing a response profile of 90% response observed at an applied voltage of 20 V in the cell of the example.

FIG. 8 shows an irradiation light intensity of 15 to 250 in the cell of the embodiment.
It is a figure which shows the rising response profile when changing to (micro | micron | mu) W / cm < ² >.

FIG. 9 is a diagram showing irradiation light intensity dependence of rising response speed and multiplication photoelectric flow rate in the cell of the example.

FIG. 10 is an energy structure diagram of a C60 / Au interface at the time of multiplication in the example.

FIG. 11 is a schematic view of a C60-CuPc co-deposited film / Au interface in the example.

FIG. 12 is a diagram showing an applied voltage dependency of a primary photocarrier generation quantum yield in a cell manufactured using a C60-CuPc co-deposited film and a cell manufactured using a C60 single-deposited film.

[Explanation of symbols]

1 Photocurrent multiplication layer 2 Gold evaporated film electrode 3 ITO electrode 4 power supply

Claims (6)

[Claims] 1. A photoirradiation induced current is obtained with a multiplied quantum yield by irradiating the photocurrent multiplication layer with light while applying a voltage to the photocurrent multiplication layer containing a photoconductive organic semiconductor. In the photocurrent multiplying device, the photoconductive organic semiconductor of the photocurrent multiplying layer is a mixture of an electron transporting organic semiconductor and a hole transporting organic semiconductor, and the ratio of one organic semiconductor to the other organic semiconductor is 20.
High-speed response photocurrent multiplication deheiss characterized by being in the range of vol% to 50 vol%. 2. An organic electroluminescent layer is integrally laminated on the photocurrent multiplying layer, and the photoelectron multiplying layer is irradiated with light to emit light-to-light converted light from the organic electroluminescent layer. A high-speed response photocurrent multiplication device according to claim 1. 3. The fast response photocurrent multiplying device according to claim 1, wherein the photocurrent multiplying layer is a co-deposited film of the electron transporting organic semiconductor and the hole transporting organic semiconductor. 4. The fast response according to claim 1, wherein the electron transporting organic semiconductor is at least one selected from the group consisting of fullerenes, naphthalene derivatives, C70, and perylene pigments and their derivatives. Photocurrent multiplication device. 5. The hole transporting organic semiconductor is at least one selected from the group consisting of a phthalocyanine pigment and its derivative, a quinacridone pigment, an acene, and a hole transporting agent. Fast response photocurrent multiplication device. 6. The photocurrent multiplication layer is a co-deposited thin film of fullerene and copper phthalocyanine, and copper phthalocyanine is added to fullerene in a range of 20 vol% to 50 vol%. Fast response photocurrent multiplication device.