JP2008091694A - Organic semiconductor photodetector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photodetector which achieves accurate wavelength identification capability and simple layer structure by utilizing a rapid change of the absorptivity at specific wavelength found in an organic semiconductor thin film without use of external wavelength selection element for wavelength detection and by steepening a change in the photoelectric signal. <P>SOLUTION: In the organic semiconductor photodetector where a bottom electrode, an organic semiconductor thin film and a top electrode are sequentially stacked on a substrate, the wavelength characteristics (solid line) of the photoelectric signal actually obtained from the photodetector have steeper rate of change against the wavelength than those (dotted line) of the photoelectric signal intensity which is calculated from the optical absorptivity of the organic semiconductor thin film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides an organic semiconductor having a characteristic in which the change in photoelectric signal intensity with respect to the change in wavelength changes sharper than the change in wavelength characteristic of the photoelectric signal intensity calculated from the absorptance of the organic semiconductor light-absorbing thin film used. The present invention relates to a photodetector.

A photodetector is used for light detection, and a photodetector is used for a spectroscopic analyzer, a refractive index measuring device, and the like. As a photodetector, for example, Patent Documents 1 and 2 describe an organic semiconductor photodetector using an organic photosemiconductor layer in an electrode / organic matter / electrode structure.
JP 2003-101060 A JP-T-2002-502129

  A conventional photodetector is a source that measures the intensity of light using photoelectric conversion that converts light into an electrical signal, and does not have a sufficient function for identifying wavelengths that are important in spectroscopic applications. For this reason, the detector itself does not have a wavelength detection function, and a wavelength change element is converted into light intensity by combining a wavelength selective element such as a spectroscope, a prism, and a wavelength filter to detect the wavelength. It was. In particular, in order to detect the peak of a specific wavelength with accuracy in the order of nm, the wavelength selection element is also enlarged, and the apparatus for measuring the wavelength has become large and expensive.

  Therefore, the present invention does not use an external wavelength selection element for wavelength detection, utilizes a rapid change in the absorption rate at a specific wavelength of the organic semiconductor thin film, and further makes the photoelectric signal change sharp, It is an object of the present invention to provide a photodetector having a simple layer structure having a function of accurately identifying a wavelength.

  The present invention relates to an organic semiconductor photodetector in which a lower electrode, an organic semiconductor thin film, and an upper electrode are sequentially laminated on a substrate, wherein the organic semiconductor thin film has a wavelength characteristic of a photoelectric signal actually obtained from the photodetector. It is characterized in that the change with respect to the wavelength is sharper than the wavelength characteristic of the photoelectric signal intensity calculated from the light absorption rate.

In the present invention, the photoelectric signal intensity V (λ) is calculated from the light absorptance of the organic semiconductor thin film by the following equation.
V (λ) = RE (1- (1-A (λ)) ^T )
However,
A (λ): Absorption rate per unit thickness of thin film as a function of wavelength E: Incident light energy T: Thin film thickness R: Conversion efficiency of absorbed light energy into voltage

  In general, V (λ) is substantially proportional to A (λ), and there is a positive correlation between them even when they are not proportional.

  The change in the absorptance with respect to the wavelength of the organic semiconductor thin film has a sharp peak that increases and decreases with the maximum value while the wavelength changes from 10 to 50 nm. The photoelectric signal of the photodetector using this has a light absorption. It changes more steeply than the wavelength characteristic of the photoelectric signal intensity calculated from the rate. For some elements, the photoelectric signal intensity changes from increasing to decreasing or decreasing to increasing in a wavelength region where the photoelectric signal intensity calculated from the absorption rate increases or decreases uniformly. As a result, the wavelength characteristic of the photoelectric signal actually changes more sharply than the curve of the photoelectric signal intensity vs. wavelength characteristic calculated from the light absorption rate. Furthermore, despite the fact that the wavelength characteristic of the photoelectric signal intensity calculated from the optical absorptance is a non-zero wavelength region, the signal intensity becomes 0 as a result of the photoelectric signal inversion, and the change in wavelength is extremely high. Acts as a sensitive detector. The photoelectric signal is reversed between positive and negative before and after the wavelength. Moreover, for example, a cyanine dye can be used as the material of the organic semiconductor thin film.

  The semiconductor photodetector of the present invention utilizes the fact that the organic semiconductor thin film to be used has a characteristic in which the wavelength characteristic of the photoelectric signal intensity calculated from the absorptance with respect to the change in wavelength is greatly changed under certain film forming conditions, Furthermore, when a device is formed as a light detection element by stacking under certain conditions, it is possible to obtain the performance that the wavelength characteristic of the actual photoelectric signal intensity changes to absorption, rather than the wavelength characteristic of the photoelectric signal intensity calculated from the absorptance. it can. Because of this performance, it has a more improved wavelength selectivity / modulation change detection function, so that it is possible to accurately detect the wavelength change of light of a specific wavelength.

  Further, in the semiconductor photodetector of the present invention, an organic photodetector having a light receiving surface localized to 1 mm square or less can be manufactured with a laminated structure of only three layers, and an optical device as a microchip photodetector. Therefore, it can be used in various fields such as various types of inspection and analysis such as built-in spectroscope, laser wavelength monitor, refractive index measuring device, micro flow cytometry.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a conceptual diagram illustrating an example of an organic photodiode according to the present invention, and FIG. 2 is a diagram illustrating an example of a molecular structure of a semiconductor thin film material.

  In this embodiment, an organic photodiode (OPD) is formed by laminating an organic semiconductor thin film 3 between a transparent electrode 1 and a metal electrode 2 as shown in FIG. For the semiconductor thin film material 3, a cyanine organic semiconductor dye molecule, for example, a red cyanine dye shown in FIG. 2 (a) or a yellow cyanine dye shown in FIG. 2 (b) is used. Both dye molecules have an advantageous property that they are water-soluble and easy to handle, and are insoluble in the insulating resist used and the organic solvent used in the production process.

  FIG. 3 is a diagram showing an example of an OPD manufacturing process according to the present invention.

  In FIG. 3, the insulating layer 5 is spin-coated on the ITO electrode 1 formed on the glass substrate 4 or the film-like substrate 4, and then the light-receiving surface 6 is formed by patterning, and the organic semiconductor thin film 3 is spin-coated. . Thereafter, an aluminum electrode 2 is deposited. In this way, the OPD is formed by sandwiching the organic semiconductor film 3 between the ITO electrode 1 and the aluminum electrode 2 only at the portion of the light receiving surface 6 where the insulating layer does not exist by patterning. Further, instead of patterning the insulating layer, the OPD can also be manufactured by a method of forming a limited organic semiconductor thin film using ink jet.

  When an OPD is produced on a glass substrate or a film-like substrate 4, a glass with ITO or a substrate coated with ITO on a PET film (300Ω □, PET film thickness 125 μm) is used. After the organic film resist is spin-coated, an insulating film pattern having a light receiving surface 6 on the surface of ITO is formed by pre-annealing, ultraviolet exposure, development, and post-annealing.

  Next, the organic semiconductor thin film 3 is formed by spin coating a cyanine dye film solution. The film thickness is 200 to 300 nm.

  Finally, an aluminum electrode 2 is vapor-deposited on the organic semiconductor thin film using a transmission mask to constitute an OPD.

  FIG. 4 is a graph showing the results of measuring the VI characteristics of red cyanine dye and yellow cyanine dye, which are organic semiconductor dye molecules, using aluminum as a cathode and ITO as an anode.

  As shown in the graph of red cyanine dye in FIG. 4 (a) and the graph of yellow cyanine dye in FIG. 4 (b), the gradual diode characteristics can be confirmed for any organic semiconductor dye molecule, and the Schottky barrier is It can be seen that it has been generated. The impedance at the time of reverse connection was 23.3 kΩ.

  Next, the spectral characteristics can be measured by making the laser incident using an optical parametric generator / amplifier (OPG + OPA) developed as a light source.

  FIG. 5 is a graph plotting the wavelength response peak value of the photoelectric signal intensity calculated from the measured photoelectric signal and the absorptance. FIG. 5A shows a red cyanine dye, and FIG. 5B shows a yellow cyanine dye. .

  In 5 (a), as a result of measuring the red cyanine dye, the measured photoelectric signal has a bias of 0 V, an input impedance of 10 MΩ, and a signal is obtained from around a wavelength of 440 nm as shown by the solid line. The response peak is maximum at 530 nm. When the input wavelength is longer than 540 nm, the photoelectric signal output V (λ) calculated from the absorptance indicated by the dotted line slightly increases, but the photoelectric signal output attenuates rapidly and shows a more steep change. ing. Further, the photoelectric signal output becomes 0 at 545 nm, and the sign of the signal is reversed before and after that. It was found that the signal had a negative maximum at 550 nm, and the output attenuated to 0 after the wavelength of 555 nm.

  In FIG. 5B, as a result of measuring the yellow cyanine dye, the peak of the photoelectric signal intensity V (λ) calculated from the absorptance indicated by the dotted line is in the vicinity of 465 nm, whereas the peak of the photoelectric signal indicated by the solid line is shown. Is in the vicinity of 454 nm. The signal intensity has a characteristic that it changes suddenly to a negative value when the wavelength is shifted by only 10 nm from the peak.

  The OPD of the present invention provides an organic photodetector having a light receiving surface localized to 1 mm square or less, and can be freely incorporated into a chip. Therefore, the OPD in various fields equipped with a photodetector such as a refractive index measuring device and a wavelength spectroscopic device. It can be used for other devices.

It is a conceptual diagram which shows an example of OPD by this invention. It is a figure which shows the example of the molecular structure of the semiconductor thin film material of this invention. It is a figure which shows an example of the manufacturing process of OPD by this invention. It is a graph which shows the result of having measured the VI characteristic of the organic-semiconductor pigment | dye molecule | numerator red-type cyanine pigment | dye, and yellow-type cyanine pigment | dye. It is the graph which plotted the wavelength response peak value of a red-type cyanine pigment | dye and a yellow-type cyanine pigment | dye.

Explanation of symbols

1: Transparent electrode (ITO)
2: Metal electrode (Al)
3: Organic semiconductor thin film 4: Substrate 5: Insulating layer (organic film resist)
6: Light receiving surface

Claims (4)

In an organic semiconductor photodetector in which a lower electrode and an organic semiconductor thin film / upper electrode are sequentially laminated on a substrate,
The organic signal characterized in that the wavelength characteristic of the photoelectric signal actually obtained from the photodetector has a sharper change with respect to the wavelength than the wavelength characteristic of the photoelectric signal intensity calculated from the light absorption rate of the organic semiconductor thin film. Semiconductor photodetector.   In the wavelength region where the wavelength characteristic of the photoelectric signal intensity calculated from the light absorptance of the organic semiconductor thin film uniformly increases or decreases, the vs. wavelength characteristic of the photoelectric signal actually obtained from the photodetector increases. The organic semiconductor photodetector according to claim 1, wherein the organic semiconductor photodetector has a characteristic that changes from decreasing to increasing or decreasing to increasing.   The photoelectric signal intensity actually obtained from the photodetector is a signal intensity corresponding to zero or zero at a specific wavelength, even though the light absorption rate of the organic semiconductor thin film is not zero. The organic semiconductor photodetector according to claim 1.   4. The organic semiconductor photodetector according to claim 1, wherein the organic semiconductor thin film contains cyanine dye molecules.

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