EP2067188A1 - Organic photodiode and method for producing it - Google Patents

Organic photodiode and method for producing it

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Publication number
EP2067188A1
EP2067188A1 EP07765356A EP07765356A EP2067188A1 EP 2067188 A1 EP2067188 A1 EP 2067188A1 EP 07765356 A EP07765356 A EP 07765356A EP 07765356 A EP07765356 A EP 07765356A EP 2067188 A1 EP2067188 A1 EP 2067188A1
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EP
European Patent Office
Prior art keywords
layer
organic
anode
blend
cathode
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Ceased
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EP07765356A
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German (de)
French (fr)
Inventor
Jens FÜRST
Debora Henseler
Oliver Rudolph
Edgar Zaus
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Siemens AG
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Siemens AG
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Publication of EP2067188A1 publication Critical patent/EP2067188A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
    • H10K85/211—Fullerenes, e.g. C60
    • H10K85/215—Fullerenes, e.g. C60 comprising substituents, e.g. PCBM
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/549—Organic PV cells

Definitions

  • the present invention relates to an organic photodiode according to the preamble of claim 1 and a method for the production thereof according to the preamble of claim 4.
  • Photodiodes based on organic semiconductor materials offer the possibility of producing pixelated flat detectors with high quantum efficiencies (50 to 85%) in the visible region of the spectrum.
  • the thin organic layer systems used in this case can be produced inexpensively using known production methods, such as spin coating, doctor blades or printing methods, thus enabling a price advantage, especially for larger-area devices.
  • Promising applications of such organic detector arrays can be found, for example, in US Pat. in the medical image recognition as X-ray flat detectors, since here the light of a scintillator tator harsh is typically detected on relatively large areas of at least a few centimeters. This is described for example in US 2003/0025084.
  • the organic photodiodes consist e.g. from a vertical layer system: Au electrode / P3HT-PCBMBlend / Ca-Ag electrode.
  • the blend of the two components P3HT (absorber and hole transport component) and PCBM (electron acceptor and transport component) acts as a so-called "bulk heterojunction", ie the charge carriers are separated at the interfaces of the two materials form the entire layer volume.
  • a disadvantage of such detector arrays with large, unstructured organic semiconductor layers is that the dark current is significantly higher, especially when using polymeric materials (such as P3HT-PCBM blend) than, for example, in the case of inorganic flat-panel detectors.
  • Typical dun Current flows of the organic photodiodes at a bias voltage of -5V are in the range of 10 ⁇ 2 to 10 ⁇ 3 mA / cm 2 , while typical currents for detectors based on amorphous silicon are below 10 ⁇ 5 mA / cm 2 .
  • a low dark current is particularly important when such as e.g. For X-ray detectors, a high dynamic range must be covered, i. although very low light intensities above the noise level must be detected. Although a dark current contribution can basically be subtracted from the signal, it always leads to a noise contribution, which limits the dynamic range in measurements with low x-ray doses.
  • Amorphous silicon-based flat-plate detectors employing a very low dark current of less than 10 -6 mA / cm 2 are used.
  • organic photodiodes are either single-layer systems with a BuIk heterojunction blend between an anode (ITO, gold, palladium, platinum, etc.) and a cathode (eg Ca, Ba, Mg, LIF, etc. followed by covering layer of Ag or Al) or two-layer systems in which an additional hole transport layer (typically Pe-dot: PSS or Pani: PSS) or electron blocker layer is applied between the blend and the anode.
  • the organic materials are usually applied by spin coating or knife coating.
  • Claim 1 wherein the concentrations of the components of the bulk heterojunction blend are changed in the direction of the distance of the two electrodes such that near the anode there is a higher concentration of the hole transport components and that there is a higher concentration of the electron transport component near the cathode.
  • the concentrations of the constituents are changed such that a layer of the hole transport components alone is arranged between the anode and bulk heterojunction blend and a layer of the electron transport component alone is arranged between cathode and bulk heterojunction blend.
  • the present invention solves the problem of high dark currents by inserting one or two additional layers between the two electrodes and the bulk heterojunction blend (such as P3HT-PCBM blend) which efficiently reduces the dark current caused by injection.
  • the bulk heterojunction blend such as P3HT-PCBM blend
  • P3HT hole transport component alone
  • PCBM electron transport component alone
  • an additional electron blocking layer is applied directly to the anode.
  • Claim 4 relates to a method for producing a photodetector according to the present invention, wherein the organic layers are applied by means of a spraying process.
  • FIG. 1 shows a standard layer system of an organic photodiode according to the prior art
  • FIG. 2 shows a sketch of the associated potential level diagram in the case of a negative bias.
  • Photodetektorbauteils with additional P3HT and PCBM interlayers according to the present invention and
  • Figure 4 is a layer diagram of a photodiode according to the present invention.
  • FIG. 1 shows a standard layer system of an organic photodiode 1 according to the prior art.
  • carrier 2 On here also shown carrier 2, a substrate 3 is applied.
  • the anode 6 made of gold and above it the Buick Heterojunction 4, which consists of a polymer and a fullerene derivative.
  • the cathode 5 Above it is the cathode 5 (Ca / Al).
  • FIG. 2 shows a sketch of the associated potential level diagram for the case of a negative bias voltage for the photodiode according to FIG. 1.
  • the bulk heterojunction consists of a blend of the fullerene derivative PCBM and the polythiophene P3HT in the active layer.
  • the active layer consists of a blend of two materials. Therefore, the HOMO and LUMO levels of the two components are drawn in parallel.
  • FIG. 3 shows a potential level diagram, but for the device structure according to the invention with the additional layers (P3HT and PCBM) consisting of hole or electron transport component.
  • P3HT and PCBM additional layers
  • the injection of electrons at the anode is reduced by the higher energy barrier between the anode and LUMO of the hole conductor component versus that between anode and LUMO of the electron conductor component (e.g., 2 eV for Au / P3HT instead of 1.4 eV for Au / PCBM).
  • the injection of holes at the cathode is reduced by the higher energy barrier between the cathode and HOMO of the electron conductor component over that between Cathode and HOMO of the hole-guiding component (eg 3.2 eV for Ca / PCBM instead of 2.9 eV for Ca / P3HT).
  • FIG. 3 arrows show the two undesired processes, electron injection at the anode and hole injection at the anode, which contribute to the dark current and are reduced by the intermediate layers.
  • a spraying technique is used for the application of the organic layers.
  • the drying process is much faster when applying the layer than with the conventional methods spin coating and doctoring, so that the mixing of the organic materials is largely suppressed and a defined layer structure is made possible.
  • the polymer solution is atomized by means of a fine nozzle (diameter -0.3 mm).
  • a suitable spraying system is the spray gun HP-101 from Sogolee, which is operated at a suitable pressure of 1-2 bar.
  • the lateral extent of the droplets on the layer is on the order of 10 ⁇ m.
  • the dark currents of organic photon could todetektorpixeln of 1.8 x 10 -3 mA / cm 2 to 4 x 10 ⁇ 4 mA / cm 2 can be reduced (each at -5V bias voltage ).
  • the thickness of the P3HT-PCBM blend layer was 300 nm.
  • a hole transport layer was applied between the Au electrode and the first organic layer. Without this additional hole transport layer, the dark currents are higher overall and the influence of the separately sprayed individual layers less.
  • the advantage of the organic semiconductor layer system applied according to the invention with the spraying technique and the organic photodiodes produced therewith is the reduced dark current, which results in a significantly higher sensitivity for low intensities and thus a higher dynamic range. This improvement could allow the commercial use of organic photodiodes in flat panel X-ray detectors.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Nanotechnology (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Electromagnetism (AREA)
  • Light Receiving Elements (AREA)

Abstract

The present invention relates to an organic photodetector having an organic photoactive layer as bulk-heterojunction blend between two electrodes, wherein the concentrations of the constituents of the bulk-heterojunction blend are changed in the direction of the spacing of the two electrodes in such a way that there is a higher concentration of the hole transport components near the anode and that there is a higher concentration of the electron transport component near the cathode. This is done by applying the respective components as interlayers. This is effected by means of a spraying method.

Description

Beschreibungdescription
Organische Photodiode und Verfahren zu deren HerstellungOrganic photodiode and process for its production
Die vorliegende Erfindung betrifft eine organische Photodiode nach dem Oberbegriff des Anspruchs 1 und ein Verfahren zu deren Herstellung nach dem Oberbegriff des Anspruchs 4.The present invention relates to an organic photodiode according to the preamble of claim 1 and a method for the production thereof according to the preamble of claim 4.
Photodioden auf der Basis von organischen Halbleitermateri- alien bieten die Möglichkeit, pixelierte Flachdetektoren mit hohen Quanteneffizienzen (50 bis 85%) im sichtbaren Bereich des Spektrums herzustellen. Die hierbei eingesetzten dünnen organischen Schichtsysteme können mit bekannten Herstellungsverfahren wie Spin-Coating, Rakeln oder Druckver- fahren kostengünstig hergestellt werden und ermöglichen so einen Preisvorteil, vor allem für größerflächige Devices. Vielversprechende Anwendungen solcher organischer Detektor- arrays finden sich z.B. in der medizinischen Bilderkennung als Röntgen-Flachdetektoren, da hier das Licht einer Szin- tillatorschicht typischerweise auf relativ großen Flächen von mindestens einigen Zentimetern detektiert wird. Dies ist beispielsweise beschrieben in US 2003/0025084.Photodiodes based on organic semiconductor materials offer the possibility of producing pixelated flat detectors with high quantum efficiencies (50 to 85%) in the visible region of the spectrum. The thin organic layer systems used in this case can be produced inexpensively using known production methods, such as spin coating, doctor blades or printing methods, thus enabling a price advantage, especially for larger-area devices. Promising applications of such organic detector arrays can be found, for example, in US Pat. in the medical image recognition as X-ray flat detectors, since here the light of a scintillator tatorschicht is typically detected on relatively large areas of at least a few centimeters. This is described for example in US 2003/0025084.
Die organischen Photodioden bestehen z.B. aus einem verti- kalen Schichtsystem: Au-Elektrode / P3HT-PCBMBlend / Ca-Ag- Elektrode. Der Blend aus den beiden Komponenten P3HT (Absorber- und Lochtransportkomponente) und PCBM (Elektronenakzeptor und -transportkomponente) wirkt hierbei als so genannte „Bulk Heterojunction" , d.h. die Trennung der La- dungsträger erfolgt an den Grenzflächen der beiden Materialien, die sich innerhalb des gesamten Schichtvolumens ausbilden .The organic photodiodes consist e.g. from a vertical layer system: Au electrode / P3HT-PCBMBlend / Ca-Ag electrode. The blend of the two components P3HT (absorber and hole transport component) and PCBM (electron acceptor and transport component) acts as a so-called "bulk heterojunction", ie the charge carriers are separated at the interfaces of the two materials form the entire layer volume.
Ein Nachteil solcher Detektor-Arrays mit großflächigen, un- strukturierten organischen Halbleiterschichten besteht darin, dass der Dunkelstrom vor allem bei Verwendung polymerer Materialen (wie z.B. P3HT-PCBM-Blend) deutlich höher ist als z.B. bei anorganischen Flachdetektoren. Typische Dun- kelströme der organischen Photodioden bei einer Biasspan- nung von -5V liegen im Bereich von 10~2 bis 10~3 mA/cm2, typische Ströme für Detektoren auf Basis von amorphem Silizium liegen dagegen unterhalb von 10~5 mA/cm2.A disadvantage of such detector arrays with large, unstructured organic semiconductor layers is that the dark current is significantly higher, especially when using polymeric materials (such as P3HT-PCBM blend) than, for example, in the case of inorganic flat-panel detectors. Typical dun Current flows of the organic photodiodes at a bias voltage of -5V are in the range of 10 ~ 2 to 10 ~ 3 mA / cm 2 , while typical currents for detectors based on amorphous silicon are below 10 ~ 5 mA / cm 2 .
Ein niedriger Dunkelstrom ist insbesondere dann wichtig, wenn wie z.B. bei Röntgendetektoren ein hoher Dynamikbereich abgedeckt werden muss, d.h. wenn auch sehr geringe Lichtintensitäten über dem Rauschlevel detektiert werden müssen. Ein Dunkelstrombeitrag kann zwar grundsätzlich vom Signal subtrahiert werden, führt aber immer zu einem Rauschbeitrag, der bei Messungen mit niedrigen Röntgendosen den Dynamikbereich limitiert.A low dark current is particularly important when such as e.g. For X-ray detectors, a high dynamic range must be covered, i. although very low light intensities above the noise level must be detected. Although a dark current contribution can basically be subtracted from the signal, it always leads to a noise contribution, which limits the dynamic range in measurements with low x-ray doses.
Bisher werden daher kommerziell anorganische Röntgen-So far, commercial inorganic X-ray
Flachdetektoren auf der Basis von amorphem Silizium eingesetzt, die einen sehr geringen Dunkelstrom von weniger als 10~6 mA/cm2 aufweisen.Amorphous silicon-based flat-plate detectors employing a very low dark current of less than 10 -6 mA / cm 2 are used.
Stand der Technik für effiziente organische Photodioden sind entweder Einschichtsysteme mit einem BuIk Heterojunction Blend zwischen einer Anode (ITO, Gold, Palladium, Platin, etc.) und einer Kathode (z.B. Ca, Ba, Mg, LIF, etc. mit anschließender Deckschicht aus Ag oder Al) oder Zweischicht- Systeme, bei denen zwischen dem Blend und der Anode noch eine zusätzliche Lochtransporterschicht (typischerweise Pe- dot:PSS oder Pani:PSS) oder Elektronenblockerschicht aufgebracht ist. Die organischen Materialien werden üblicherweise mittels Spin Coating oder Rakeln aufgebracht. Bei diesen Verfahren besteht bei der Herstellung von Mehrschichtsystemen die Problematik, dass beim Aufbringen einer organischen Schicht auf eine bereits vorhandene organische Schicht, das Lösungsmittel des aufzubringenden Materials die vorhandene Schicht an- oder auflöst mit der Folge einer Durchmischung der Materialien. Bisher sind in der Literatur keine polymerbasierten Photodetektor-Systeme mit ausreichend niedrigen Dunkelstrom-Niveaus bekannt. Der vorliegenden Erfindung liegt das Problem zu Grunde, organische Photodioden hinsichtlich deren Einsatzmöglichkeiten zu verbessern.State of the art for efficient organic photodiodes are either single-layer systems with a BuIk heterojunction blend between an anode (ITO, gold, palladium, platinum, etc.) and a cathode (eg Ca, Ba, Mg, LIF, etc. followed by covering layer of Ag or Al) or two-layer systems in which an additional hole transport layer (typically Pe-dot: PSS or Pani: PSS) or electron blocker layer is applied between the blend and the anode. The organic materials are usually applied by spin coating or knife coating. In the case of these methods, in the production of multilayer systems there is the problem that when applying an organic layer to an already existing organic layer, the solvent of the material to be applied on or dissolves the existing layer, with the result of a thorough mixing of the materials. So far, no polymer-based photodetector systems with sufficiently low dark current levels are known in the literature. The present invention is based on the problem of improving organic photodiodes with regard to their possible uses.
Diese Aufgabe wird nach der vorliegenden Erfindung gemäßThis object is according to the present invention according to
Anspruch 1 gelöst, indem die Konzentrationen der Bestandteile der Bulk-Heterojunction-Blend in Richtung des Abstandes der beiden Elektroden geändert werden derart, dass nahe der Anode eine höhere Konzentration der Lochtransportkomponenten besteht und dass nahe der Kathode eine höhere Konzentration der Elektronentransportkomponente besteht.Claim 1, wherein the concentrations of the components of the bulk heterojunction blend are changed in the direction of the distance of the two electrodes such that near the anode there is a higher concentration of the hole transport components and that there is a higher concentration of the electron transport component near the cathode.
Es hat sich gezeigt, dass mit einem solchen Aufbau die Dunkelströme deutlich reduziert werden können.It has been shown that with such a structure, the dark currents can be significantly reduced.
Bei der Ausgestaltung nach Anspruch 2 sind die Konzentrationen der Bestandteile derart geändert, dass zwischen Anode und Bulk-Heterojunction-Blend eine Schicht der Lochtransportkomponenten allein angeordnet wird und zwischen Kathode und Bulk-Heterojunction-Blend eine Schicht der Elektronentransportkomponente allein angeordnet wird.In the embodiment according to claim 2, the concentrations of the constituents are changed such that a layer of the hole transport components alone is arranged between the anode and bulk heterojunction blend and a layer of the electron transport component alone is arranged between cathode and bulk heterojunction blend.
Die vorliegende Erfindung löst das Problem der hohen Dunkelströme durch Einfügen einer oder zweier zusätzlicher Schichten zwischen den beiden Elektroden und der Bulk-Heterojunction- Blend (wie z.B. P3HT-PCBM-Blend) , die den durch Injektion verursachten Dunkelstrom effizient reduzieren. Zwischen Anode und Blend wird eine dünne Schicht der Lochtransportkomponente allein (P3HT) eingefügt, zwischen Kathode und Blend eine dün- ne Schicht der Elektronentransportkomponente allein (PCBM) . Es wird also kein zusätzliches Material eingefügt, sondern die Konzentration der beiden Komponenten in vertikaler Richtung variiert.The present invention solves the problem of high dark currents by inserting one or two additional layers between the two electrodes and the bulk heterojunction blend (such as P3HT-PCBM blend) which efficiently reduces the dark current caused by injection. Between the anode and the blend, a thin layer of the hole transport component alone (P3HT) is inserted, between the cathode and the blend a thin layer of the electron transport component alone (PCBM). So no additional material is inserted, but the concentration of the two components varies in the vertical direction.
Es hat sich gezeigt, dass durch diesen Schichtaufbau die Dunkelströme besonders stark reduziert werden können. Bei der Ausgestaltung nach Anspruch 3 ist unmittelbar auf der Anode eine zusätzliche Elektronenblockierschicht aufgebracht.It has been shown that the dark currents can be greatly reduced by this layer structure. In the embodiment according to claim 3, an additional electron blocking layer is applied directly to the anode.
Dadurch werden die Dunkelströme nochmals reduziert.As a result, the dark currents are reduced again.
Anspruch 4 betrifft ein Verfahren zur Herstellung eines Photodetektors nach der vorliegenden Erfindung, wobei die organischen Schichten mittels eines Sprühverfahrens aufgetragen werden .Claim 4 relates to a method for producing a photodetector according to the present invention, wherein the organic layers are applied by means of a spraying process.
Bei dem Sprühverfahren erweist es sich als vorteilhaft, dass der Trocknungsprozess bei dieser Art der Aufbringung wesentlich schneller vonstatten geht. Insbesondere wird damit der Effekt des An- bzw. Auflösens anderer Schichten beim Auftra- gen minimiert, so dass die definierte Trennung der Schichten verbessert wird.In the spraying process, it proves to be advantageous that the drying process is much faster in this type of application. In particular, this minimizes the effect of the application or dissolution of other layers during application, so that the defined separation of the layers is improved.
Gemäß Anspruch 5 hat es sich hinsichtlich der Aufbringung und der Trocknung als vorteilhaft erwiesen, wenn die Tröpfchengröße beim Auftragen etwa 10 μm beträgt.According to claim 5, it has proved to be advantageous in terms of application and drying, when the droplet size during application is about 10 microns.
Ein Ausführungsbeispiel der Erfindung ist in der Zeichnung dargestellt. Es zeigt dabei im Einzelnen:An embodiment of the invention is shown in the drawing. It shows in detail:
Figur 1 zeigt ein Standard-Schichtsystem einer organischen Photodiode nach dem Stand der Technik,FIG. 1 shows a standard layer system of an organic photodiode according to the prior art,
Figur 2 eine Skizze des zugehörigen Potentialniveau- Diagramms für den Fall einer negativen Bias-FIG. 2 shows a sketch of the associated potential level diagram in the case of a negative bias.
Spannung,Tension,
Figur 3 eine Skizze des Potentialniveau-Diagramms eines3 shows a sketch of the potential level diagram of a
Photodetektorbauteils mit zusätzlichen P3HT- und PCBM-Zwischenschichten nach der vorliegenden Erfindung und Figur 4 eine Schichtdarstellung einer Photodiode nach der vorliegenden Erfindung.Photodetektorbauteils with additional P3HT and PCBM interlayers according to the present invention and Figure 4 is a layer diagram of a photodiode according to the present invention.
Figur 1 zeigt ein Standard-Schichtsystem einer organischen Photodiode 1 nach dem Stand der Technik. Auf hier ebenfalls dargestellten Träger 2 ist ein Substrat 3 aufgebracht. Darüber befindet sich die Anode 6 aus Gold sowie darüber die BuIk He- terojunction 4, die aus einem Polymer und einem Fulleren- Derivat besteht. Darüber befindet sich die Kathode 5 (Ca/Al) .FIG. 1 shows a standard layer system of an organic photodiode 1 according to the prior art. On here also shown carrier 2, a substrate 3 is applied. Above it is the anode 6 made of gold and above it the Buick Heterojunction 4, which consists of a polymer and a fullerene derivative. Above it is the cathode 5 (Ca / Al).
Figur 2 zeigt eine Skizze des zugehörigen Potentialniveau- Diagramms für den Fall einer negativen Bias-Spannung für die Photodiode nach Figur 1. Die Bulk-Heterojunction besteht aus einem Blend aus dem Fullerenderivat PCBM und dem Polythiophen P3HT in der aktiven Schicht. In der Darstellung der Figur 2 besteht die aktive Schicht daher aus einem Blend von zwei Materialien. Daher sind die HOMO- und LUMO-Niveaus der beiden Komponenten parallel gezeichnet.FIG. 2 shows a sketch of the associated potential level diagram for the case of a negative bias voltage for the photodiode according to FIG. 1. The bulk heterojunction consists of a blend of the fullerene derivative PCBM and the polythiophene P3HT in the active layer. In the illustration of Figure 2, therefore, the active layer consists of a blend of two materials. Therefore, the HOMO and LUMO levels of the two components are drawn in parallel.
Figur 3 zeigt ein Potentialniveau-Diagramm, aber für den erfindungsgemäßen Device-Aufbau mit den zusätzlichen Schichten (P3HT und PCBM) bestehend aus Loch- bzw. Elektronentransportkomponente .FIG. 3 shows a potential level diagram, but for the device structure according to the invention with the additional layers (P3HT and PCBM) consisting of hole or electron transport component.
Die Injektion von Elektronen durch die Anode und die Injektion von Löchern durch die Kathode wird in diesem Aufbau reduziert, weil unmittelbar an den jeweiligen Elektroden Transportmaterialien der anderen Ladungsträgersorte angrenzen.The injection of electrons through the anode and the injection of holes through the cathode is reduced in this structure, because immediately adjacent to the respective electrodes transport materials of the other charge carrier type.
Die Injektion von Elektronen an der Anode wird reduziert durch die höhere Energiebarriere zwischen Anode und LUMO der Lochleiterkomponente gegenüber der zwischen Anode und LUMO der Elektronenleiterkomponente (z.B. 2 eV für Au/P3HT statt 1.4 eV für Au/PCBM) .The injection of electrons at the anode is reduced by the higher energy barrier between the anode and LUMO of the hole conductor component versus that between anode and LUMO of the electron conductor component (e.g., 2 eV for Au / P3HT instead of 1.4 eV for Au / PCBM).
Ebenso wird die Injektion von Löchern an der Kathode reduziert durch die höhere Energiebarriere zwischen Kathode und HOMO der Elektronenleiterkomponente gegenüber der zwischen Kathode und HOMO der Löcherleitkomponente (z.B. 3.2 eV für Ca/PCBM statt 2.9 eV für Ca/P3HT) .Likewise, the injection of holes at the cathode is reduced by the higher energy barrier between the cathode and HOMO of the electron conductor component over that between Cathode and HOMO of the hole-guiding component (eg 3.2 eV for Ca / PCBM instead of 2.9 eV for Ca / P3HT).
In Figur 3 sind mit Pfeilen die beiden unerwünschten Prozes- se, Elektroneninjektion an der Anode und Lochinjektion an der Anode, gezeigt, die zum Dunkelstrom beitragen und durch die Zwischenschichten reduziert werden.In FIG. 3, arrows show the two undesired processes, electron injection at the anode and hole injection at the anode, which contribute to the dark current and are reduced by the intermediate layers.
Für die Realisierung des in Figur 4 dargestellten Device- Aufbaus wird für das Auftragen der organischen Schichten eine Sprüh-Technik eingesetzt. Der Trocknungsprozess ist beim Aufbringen der Schicht wesentlich schneller als bei den konventionellen Methoden Spin Coating und Rakeln, so dass die Durchmischung der organischen Materialien weitgehend unter- bleibt und ein definierter Schichtaufbau ermöglicht wird. Bei der Sprüh-Technik wird die Polymerlösung mittels eine feinen Düse (Durchmesser -0.3 mm) zerstäubt. Ein geeignetes Sprühsystem ist die Sprühpistole HP-101 der Firma Sogolee, die mit einem geeigneten Druck von 1-2 bar betrieben wird. Die late- rale Ausdehnung der Tröpfchen auf der Schicht liegt in der Größenordnung 10 μm.For the realization of the device structure shown in FIG. 4, a spraying technique is used for the application of the organic layers. The drying process is much faster when applying the layer than with the conventional methods spin coating and doctoring, so that the mixing of the organic materials is largely suppressed and a defined layer structure is made possible. In the spraying technique, the polymer solution is atomized by means of a fine nozzle (diameter -0.3 mm). A suitable spraying system is the spray gun HP-101 from Sogolee, which is operated at a suitable pressure of 1-2 bar. The lateral extent of the droplets on the layer is on the order of 10 μm.
Mit einer 100 nm P3HT-Zwischenschicht und einer 100 nm PCBM- Zwischenschicht konnten die Dunkelströme von organischen Pho- todetektorpixeln von 1.8 x 10~3 mA/cm2 auf 4 x 10~4 mA/cm2 reduziert werden (jeweils bei -5V Biasspannung) . Die Dicke der P3HT-PCBM-Blend-Schicht betrug 300 nm. der Bei diesen Devices wurde zusätzlich zu den in Abb. 4 dargestellten Schichten zwischen Au-Elektrode und der ersten organischen Schicht eine Lochtransporterschicht aufgebracht. Ohne diese zusätzliche Lochtransportschicht sind die Dunkelströme insgesamt höher und der Einfluss der separat gesprühten Einzelschichten geringer .With a 100 nm P3HT intermediate layer and a 100 nm PCBM intermediate layer, the dark currents of organic photon could todetektorpixeln of 1.8 x 10 -3 mA / cm 2 to 4 x 10 ~ 4 mA / cm 2 can be reduced (each at -5V bias voltage ). The thickness of the P3HT-PCBM blend layer was 300 nm. In these devices, in addition to the layers shown in FIG. 4, a hole transport layer was applied between the Au electrode and the first organic layer. Without this additional hole transport layer, the dark currents are higher overall and the influence of the separately sprayed individual layers less.
Das Aufbringen von organischen Schichten mittels Sprühen wurde bereits in der Publikation von T. Ishikawa und Mitarbeitern demonstriert (Appl. Phys . Lett. 84, 2424 (2004)). Auch die Verwendung von Schichten unterschiedlicher Konzentration der jeweiligen Komponenten wurde von S. Heutz und Mitarbeitern untersucht (SoI. Energy Mater. SoI. Cells 83, 229 (2004)), allerdings nicht im Hinblick auf Reduzierung des Dunkelstroms sondern zur Effizienzsteigerung von organischen Solarzellen. Zudem bestanden die in dieser Publikation untersuchtenThe application of organic layers by spraying has already been demonstrated in the publication by T. Ishikawa and coworkers (Appl. Phys. Lett., 84, 2424 (2004)). Also, the use of layers of different concentration of The respective components were investigated by S. Heutz and co-workers (SoI, Energy Mater, SoI, Cells 83, 229 (2004)), but not with regard to reducing the dark current, but rather to increase the efficiency of organic solar cells. In addition, those studied in this publication existed
Schichten aus Small Molecules, die mittels Aufdampfen aufgebracht werden, so dass hier nicht das Problem der Durchmischung besteht. Durch die Sprüh-Technik ist ein definierter Schichtaufbau auch mit Polymeren in Lösung möglich.Layers of Small Molecules, which are applied by vapor deposition, so that there is no problem of mixing here. Due to the spray technique, a defined layer structure is also possible with polymers in solution.
Der Vorteil des erfindungsgemäß mit Sprüh-Technik aufgebrachten organischen Halbleiter-Schichtensystems und den damit hergestellten organischen Photodioden liegt in dem reduzierten Dunkelstrom, der eine deutlich höhere Empfindlichkeit für niedrige Intensitäten und damit einen höheren Dynamikbereich zur Folge hat. Diese Verbesserung könnte die kommerzielle Verwendung von organischen Photodioden in Röntgen- Flachdetektoren ermöglichen. The advantage of the organic semiconductor layer system applied according to the invention with the spraying technique and the organic photodiodes produced therewith is the reduced dark current, which results in a significantly higher sensitivity for low intensities and thus a higher dynamic range. This improvement could allow the commercial use of organic photodiodes in flat panel X-ray detectors.

Claims

Patentansprüche claims
1. Organischer Photodetektor, der zwischen zwei Elektroden eine organische photoaktive Schicht als Bulk-Heterojunction- Blend aufweist, dadurch gekennzeichnet, dass die Konzentrationen der Bestandteile der Bulk-Heterojunction-Blend in Richtung des Abstandes der beiden Elektroden geändert werden derart, dass nahe der Anode eine höhere Konzentration der Lochtransportkomponenten besteht und dass nahe der Kathode eine höhere Konzentration der Elektronentransportkomponente besteht.1. An organic photodetector comprising an organic photoactive layer between two electrodes as a bulk heterojunction blend, characterized in that the concentrations of the constituents of the bulk heterojunction blend in the direction of the distance of the two electrodes are changed such that close to the anode there is a higher concentration of the hole transporting components and that there is a higher concentration of the electron transporting component near the cathode.
2. Photodetektor nach Anspruch 1, dadurch gekennzeichnet, dass die Konzentrationen der Bestand- teile derart geändert sind, dass zwischen Anode und Bulk- Heterojunction-Blend eine Schicht der Lochtransportkomponenten allein angeordnet wird und zwischen Kathode und Bulk- Heterojunction-Blend eine Schicht der Elektronentransportkomponente allein angeordnet wird.2. Photodetector according to claim 1, characterized in that the concentrations of the constituents are changed such that between anode and bulk heterojunction blend one layer of the hole transport components alone is arranged and between cathode and bulk heterojunction blend a layer of the electron transport component is arranged alone.
3. Photodetektor nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass unmittelbar auf der Anode eine zusätzliche Elektronenblockierschicht aufgebracht ist.3. Photodetector according to claim 1 or 2, characterized in that directly on the anode, an additional electron blocking layer is applied.
4. Verfahren zur Herstellung eines Photodetektors nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass die organischen Schichten mittels eines Sprühverfahrens aufgetragen werden.4. A method for producing a photodetector according to any one of claims 1 to 3, characterized in that the organic layers are applied by means of a spraying process.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass die Tröpfchengröße beim Auftragen etwa 10 μm beträgt. 5. The method according to claim 4, characterized in that the droplet size during application is about 10 microns.
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