EP4305682A1

EP4305682A1 - Optoelectronic component and method for a spectrally selective detection of electromagnetic radiation

Info

Publication number: EP4305682A1
Application number: EP22714161.1A
Authority: EP
Inventors: Jonas KUBLITSKI; Axel Fischer; Donato SPOLTORE; Karl Leo; Yazhong WANG; Louis Conrad WINKLER; Johannes BENDUHN
Original assignee: Senorics GmbH
Current assignee: Senorics GmbH
Priority date: 2021-03-12
Filing date: 2022-03-11
Publication date: 2024-01-17
Also published as: DE102021106049A1; US20240159593A1; WO2022189629A1

Abstract

By directly exciting optical transitions in the intermolecular CT state, the wavelength range which can be detected by organic photodetectors can be expanded into the NIR or IR range, and the EQE is low even when using resonance effects by arranging the photoactive layer in an optical microcavity. The invention relates to an optoelectronic component (1, 1', 1'', 1''') and to a corresponding detection method in which the concentration of the donor compound in the photoactive layer (2) or the concentration of the acceptor compound in the photoactive layer (2) is so low that the compound with a low concentration provides trap conditions for the corresponding charge carriers (81), said conditions producing a photo-induced accumulation of the charge carriers (81) paired with the compound with a low concentration in a region of the photoactive layer (2) facing the first electrode (31) so that charge carriers (82) paired with the highly concentrated compound are injected into the photoactive layer (2) from the first electrode (31), whereby the charge carrier locations are predominantly in the component (1, 1', 1'', 1'''). In particular, the EQE increase achieved in this manner is advantageous in that the detectable wavelength range can be expanded to higher wavelengths by means of the invention.

Description

Optoelectronic component and method for spectrally selective detection of electromagnetic radiation

The invention relates to an optoelectronic component for the spectrally selective detection of electromagnetic radiation, having a first and a second electrode which are spaced apart and to which an electrical voltage can be applied, and a photoactive layer which is a mixed layer containing a donor compound and an acceptor - Compound comprises, wherein the energy equivalent of a wavelength to be detected of the electromagnetic radiation corresponds to the energy to be expended for direct excitation of an intermolecular charge transfer state at an interface between the donor compound and the acceptor compound, wherein the photoactive layer is arranged in an optical microcavity , which is arranged between the first and the second electrode and formed from two spaced mirror surfaces, wherein the distance between the mirror surfaces is designed to each other so that in the microcavity a standing wave for a simple lling wave of electromagnetic radiation is generated with the wavelength to be detected, as well as the associated method.

To measure requirements z. B. in intelligent vehicles or devices, optoelectronic components in the form of highly sensitive and fast photodetectors are in demand. Photodetectors for the spectrally selective detection of an electromagnetic wave are optoelectronic components that are used for the qualitative and quantitative detection of electromagnetic waves with predefined, specific wavelengths or photons with predefined, specific energies, with the waves irradiating the photodetector, hereinafter referred to as “incident” waves generally a large number of different wavelengths or the incident photons generally have a large number of different energies.

In the following, no distinction is made between the wave image and the photon image of electromagnetic radiation and the associated terms are essentially used synonymously.

A photodetector has a photoactive layer in which electromagnetic radiation is converted into charge carrier pairs, the charge carriers being negatively charged electrons and positively charged holes. Organic photodetectors typically have a photoactive layer that contains an electron donor compound (donor compound or donor for short, D), ie a material that emits electrons and holes or holes, and an electron acceptor compound (acceptor compound or acceptor, A for short), i.e. a material that accepts electrons. The separation of the charge carrier pairs, which is necessary to generate an electrical signal, can take place at the interface between donor and acceptor. After the separation of a charge carrier pair, the holes in the donor and the electrons in the acceptor are transported to the electrodes. In this sense, the holes are understood below as the charge carriers assigned to the donor compound and the electrons as the charge carriers assigned to the acceptor compound.

Using the photomultiplication effect to improve the external quantum efficiency (EQE) of a photodetector is one of the most important approaches to achieve highly sensitive photodetection. The EQE denotes the wavelength-dependent ratio of the number of incident photons and the charge carriers removed from the component. It can be understood as a kind of wavelength-dependent efficiency.

The near-infrared wavelength range (NIR range) between approx. 780 and 3000 nm, which stimulates molecular vibrations in particular, is particularly interesting for many measurement tasks.

The functioning of inorganic avalanche photodiodes used as highly sensitive photodetectors, e.g. B. based on Si in the NIR range for wavelengths up to about 1000 nm or based on InGaAs in the NIR range for wavelengths from about 1000 to 1700 nm, is based on the fact that an additional highly p- or n-doped Layer the space charge distribution is modeled in such a way that a high field strength area can be generated by means of a large voltage in the reverse direction, which acts as a multiplication zone for the charge carriers generated by irradiation. These are accelerated in the multiplication zone so that impact ionization of the crystal lattice takes place, resulting in internal signal amplification.

The photomultiplication effect (PM effect) can also be used in organic photodetectors (OPD), so that small photocurrents can be amplified with PM-OPD without additional external circuit components. However, the PM effect is based here on increased injection of a first type of charge carrier, i.e. electrons or holes (holes), favored by an energy band bending resulting from an accumulation of the opposite, second type of charge carrier, i.e. holes or electrons, in the vicinity of the injecting electrode results. The electric field caused by the accumulated, second type of charge carriers in the vicinity of the injecting electrode bends the relevant energy bands in such a way that the tunneling probability of the first type of charge carriers increases sharply due to the injection barrier and/or the conductivity for the first type of charge carrier. An accumulation of the second type of charge carrier can, for. B. be caused by missing percolation paths for this type of charge carrier and / or by trap states for this type of charge carrier. An overview of the state of the art regarding organic PM-OPD is given by Shi, L, et al. Recent Progress in Photomultiplication Type Organic Photodetectors. Nanomaterials 2018, 8, 713, and Miao, J., et al. Recent Progress on Photomultiplication Type Organic Photodetectors. Laser & Photonics Rev. 2019, 13, 1800204.

CN 1 09935699 A shows an organic PM-OPD whose layer structure comprises a transparent substrate, an anode, an anode modification layer, a photoactive layer and a cathode. The photoactive layer is a mixed layer containing a donor compound, e.g. B. P3HT, PBDB-T or PDPP3T, and an acceptor compound, e.g. B. PCBM. A range between 1:100 and 1:5 is given for the donor:acceptor mixing ratio. The anode modification layer is a hole transport or electron blocking layer (HTL or EBL), e.g. B. from PVC, Poly-TPD, ZnO or PEDOT:PSS. The PM-OPD described is suitable for a wavelength range between 300 and 800 nm.

Approaches such as that disclosed in CN 1 08807683 A exist to advance into the NIR wavelength range. In the PM-OPD described here, the photoactive layer contains an acceptor compound, e.g. B. PCBM, in which a thin film of an absorbing in the NIR range up to about 900 nm donor compound is embedded. In this case, the optical excitation of the donor by absorption of a photon is accompanied by the formation of a Frenkel exciton, i.e. a strongly localized bound charge carrier pair.

On the other hand, the detectable spectral range can be expanded by using the absorption of a photon with direct excitation of an intermolecular charge transfer state (CT state) at an interface between a donor and an acceptor compound. The donor and the acceptor compound do not necessarily have to absorb in the NIR region, ie the band gap between the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) of both the donor and the acceptor compound do not necessarily have to correspond to an energy equivalent in the NIR range. Rather, the energy of a photon that can be absorbed via the CT state essentially corresponds to the difference between the energetically higher HOMO of one compound and the energetically lower LUMO of the other compound. In a mixed layer of a donor compound and an acceptor compound, lower-energy photons, i.e. photons with longer wavelengths, are absorbed at the interfaces between a molecule of the donor compound and a molecule of the acceptor compound than by a molecule of the donor compound or by a molecule of the acceptor compound . Typically, the energy ECT that can be absorbed via the CT state can also be somewhat lower than the above-mentioned difference between the energetically higher HOMO of one compound and the energetically lower LUMO of the other compound, since the charge carriers assigned to the compounds are located at the interface tighten and are thus bound a little more strongly. Furthermore, it is observed that intermolecular CT states can generally also accept photons with an energy lower than the difference mentioned above. For these transitions in particular, however, the absorption cross section is so small that conventional components have so far not focused on their use. An overview of the physics of intermolecular CT states is given e.g. B. Vandewal, K. Interfacial Charge Transfer States in Condensed Phase Systems. Annual Review of Physical Chemistry 2016, 67, 113-133.

EP 3 152 785 B1 discloses an OPD in which intermolecular CT states can be used to detect electromagnetic waves with wavelengths in the NIR or IR range (CT-OPD). In the CT-OPD, the photoactive mixed layer consists of a donor and an acceptor compound between two mirror surfaces, e.g. B. two electrodes with facing reflective surfaces arranged, whereby an optical microcavity is formed. A complex sequence of material layers, hereinafter referred to as "layer structure", can be arranged in the microcavity of the CT-OPD. B. can be 50 nm, z. B. filter layers for specific wavelength ranges, charge carrier transport layers, charge carrier blocking layers, optically transparent spacer layers, etc., may have.

For electromagnetic waves with a wavelength that satisfies the resonance condition of the optical microcavity, standing waves form in the microcavity. The EGE of the CT-OPD is narrow-band for such a wavelength and significantly increased. Typically, the resonance condition of an optical cavity designed as a Fabry-Perot cavity is met if the optical length nL is: nL = (7v\i COS a)/2, where n is the effective refractive index over the physical length L of the cavity, which, neglecting the penetration depth of the electromagnetic field into the material containing the mirror surfaces, corresponds to the distance between the mirror surfaces, / the order of the standing wave that forms, L the wavelength of the incident wave wave and a denote the angle of incidence of the incident wave with respect to a direction parallel to the physical length L of the cavity. If the cavity is irradiated parallel to the physical length L (er = 0), the resonance condition is met if the optical path length of the cavity is an integer multiple of half the wavelength of the incident wave.

Actually, incident waves with wavelengths located in a range around the wavelength for which the above-mentioned resonance condition applies are amplified by the cavity. In comparison with a layer structure corresponding to the layer structure of the CT-OPD, which is not arranged in a microcavity, the EQE of the CT-OPD is increased if the optical path length between the mirror surfaces of the microcavity is 25% to 75% of the wavelength of the incident wave amounts to. In the following, the term "resonance wave" is used for those waves in which resonance effects occur in the microcavity. Advantageously, the wavelengths for which resonance occurs can be varied by varying the distance between the mirror surfaces.

However, despite the significant increase in EQE by embedding the mixed photoactive layer in a microcavity, the EQE of the CT-OPD is still low compared to the EQE of OPDs that exploit the intramolecular excitation of the donor or the acceptor via its band gap per se. Furthermore, an extension of the detectable wavelength range to longer wavelengths is desirable for many measurement tasks.

The object of the invention is therefore to overcome the disadvantages of the prior art and to specify an optoelectronic component and an associated method which are particularly well suited for detecting electromagnetic radiation (electromagnetic waves) with wavelengths in the NIR range.

The object is achieved by an optoelectronic component for the spectrally selective detection of electromagnetic radiation according to claim 1 and an associated method according to claim 9. Developments of the invention are specified in the subordinate claims. The optoelectronic component according to the invention for the spectrally selective detection of electromagnetic radiation has at least: a first and a second electrode which are spaced apart from one another and to which an electrical voltage can be applied, a photoactive layer which is a mixed layer containing a donor compound and an acceptor Compound comprises, wherein the energy equivalent of a wavelength to be detected of the electromagnetic radiation corresponds to the energy to be expended for the direct excitation of an intermolecular charge transfer state at an interface between the donor compound and the acceptor compound, the photoactive layer being arranged in an optical microcavity, which is arranged between the first and the second electrode and is formed from two mirror surfaces spaced apart from one another, the distance between the mirror surfaces being configured such that a standing wave is incident in the microcavity nde wave of electromagnetic radiation with the wavelength to be detected is generated, the concentration of the donor compound at least in a region of the photoactive layer facing the first electrode or the concentration of the acceptor compound in at least one region of the photoactive layer facing the first electrode is small that the low concentration compound provides trap states for its associated charge carriers, which cause a photo-induced accumulation of charge carriers associated with the low concentration compound in the region of the photoactive layer facing the first electrode, so that charge carriers associated with the high concentration compound are separated from the first Electrode are injected into the photoactive layer, whereby this type of charge carrier predominates in the component. These charge carriers assigned to the highly concentrated compound are transported to the second electrode.

The charge carriers assigned to the highly concentrated compound are referred to below as "main charge carriers"; the charge carriers assigned to the low-concentration compound as "non-main charge carriers". is e.g. For example, if the photoactive layer is formed in such a way that the concentration of the acceptor molecules is low in the sense explained above, holes are the main charge carriers and electrons are the non-main charge carriers. The optoelectronic component according to the invention can be described as spectrally selective in that, due to the arrangement of the photoactive layer in the microcavity, the EQE for those incident waves that are resonant waves is particularly amplified. The wavelength of the resonance waves can be predetermined by choosing the distance between the mirror surfaces. The distance between the mirror surfaces is set in such a way that the resonance condition for a specific wavelength λ* is met. This wavelength λ* is referred to as the "wavelength to be detected". As explained above, the EQE is ultimately increased in a wavelength range around the wavelength to be detected. The energy equivalent of the wavelength to be detected corresponds to the energy of a photon which is absorbed with direct excitation of an intermolecular CT state at an interface between the donor compound and the acceptor compound in the photoactive layer.

The incident waves can be emitted by an illumination system assigned to the optoelectronic component according to the invention.

A mirror surface can be a reflective surface of an electrode. The microcavity is preferably formed by the spaced-apart, opposite surfaces of the two electrodes of the optoelectronic component, with the mentioned surfaces of the two electrodes being reflective in this case. The mirror surfaces have a high reflectivity, at least for the wavelength to be detected.

The opposite mirror surfaces are preferably arranged plane-parallel to one another.

The first and the second electrode of the optoelectronic component, one of the two electrodes acting as a cathode and the other of the two electrodes acting as an anode, are designed in such a way that an electrical DC voltage can be applied between them. The voltage is preferably directed in such a way that the non-main charge carriers accumulate in a region of the photoactive layer facing the first electrode and are essentially not injected into the photoactive layer, while the main charge carriers are injected from the first electrode into the photoactive layer. The positive pole of the voltage is preferably applied to a first electrode functioning as a cathode, so that holes are injected as main charge carriers from the cathode into the photoactive layer, while the negative pole is to be applied to the second electrode, which then functions as an anode. Such Voltage with preferred polarity is hereinafter referred to as "reverse voltage" or "reverse-bias voltage".

One of the two electrodes can be formed in such a way that the optoelectronic component can be illuminated by this electrode. For example, the second electrode can be made transparent at least for the wavelength to be detected. If the electrode through which the illumination is to take place has a reflective surface that represents a mirror surface of the microcavity, the electrode can be designed to be partially transparent at least for the wavelength to be detected, so that at least the wavelength to be detected can be transmitted through the electrode , but is also reflected by the reflective surface of the electrode.

An optoelectronic component according to the invention can be connected to a readout unit for reading out, preferably also for further processing, electrical signals that are generated by the optoelectronic component.

At least one of the electrodes can be multi-piece, i. H. from electrode segments arranged in an array-like manner. Different electrode segments can be assigned different wavelengths to be detected. The electrical signals are then expediently read out in such a way that the electrical signals that can be picked up from different electrode segments can be discriminated, e.g. B. in that each electrode segment is connected to a separate readout unit.

The photoactive layer of the optoelectronic component according to the invention comprises a mixed layer in which a donor compound (D) and an acceptor compound (A) are mixed (frequently referred to in the literature as “D:A blend”). The mixed layer represents a mixed heterojunction (bulk heterojunction).

At the interface between a molecule of the donor compound and a molecule of the acceptor compound, an intermolecular CT state (also referred to as an “interchromophoric” CT state) can be photoinduced directly. In contrast to the excitation of donor or acceptor by absorption of a photon with energies greater than or equal to the energy gap between the HOMO and LUMO of the respective compound, the intermolecular CT state is already excited by a photon with an energy essentially equal to the energy difference between the highest HOMO and corresponds to, or even be lower than, the lowest LUMO of the material combination D:A. In the case of the known CT-OPD, a volume ratio D:A is preferably selected for the mixed layer, at which the interface between the two compounds in the mixed layer is at its maximum. For the typical material combination ZnPc:C ₆ o, this is the case with a volume ratio of 1:1 or a mass fraction of 50% for both the donor and the acceptor compound, based on the total mass of the mixed layer.

Surprisingly, with the optoelectronic component according to the invention, however, a volume ratio D:A that is significantly different from 1:1 proves to be advantageous. Either the concentration or the mass fraction of the acceptor compound is so low, at least in a region of the mixed layer facing the first electrode, that the acceptor molecules act as electron traps, or the concentration or mass fraction of the donor compound is in at least one of the The area of the mixed layer facing the first electrode is so small that the donor molecules act as hole traps. A “trap” or “trap condition” is a location or an energetic condition that restricts the movement of a charge carrier through the solid.

The effect resulting from the low concentration of one of the compounds in the mixed layer is explained below using the example of a low concentration of the acceptor compound. The person skilled in the art can readily transfer the explanation to an embodiment of the component according to the invention with a low concentration of the donor compound.

The cause of the effect of the low-concentration acceptor molecules as electron traps is the energetic difference between the LUMO of the acceptor and the LUMO of the donor, with the LUMO of the acceptor being lower in energy than the LUMO of the donor. Due to the low concentration of the acceptor compound, at least in the region of the mixed layer close to the cathode, there are accordingly only very few percolation paths for electrons. If the optoelectronic component is illuminated so that charge carrier pairs are formed by photo-induced excitation of CT states, application of a blocking voltage between cathode and anode results in an accumulation of electrons in the area of the mixed layer close to the cathode. The electric field resulting from the increased charge density causes the energy bands to bend in the region of the mixed layer close to the cathode, which means that the opposite charge carriers, in this case the holes, can tunnel from the cathode through the injection barrier. Holes are therefore injected from the cathode into the donor phase of the mixed layer, so that the number of holes in the component increases the number of electrons exceeds. The injected holes are then transported to the anode together with the photo-induced holes.

That such a low concentration of one of the compounds of the mixed layer also proves to be advantageous in a CT-OPD is surprising in that the mentioned low concentration, which is required for the PM effect, reduces the number of CT states, whereby there is a trade-off between increased EQE from the PM effect at low concentration and increased absorption from a larger number of CT states at higher concentration (maximizing the contact area of donor and acceptor).

In order to utilize the advantageous effect described in the optoelectronic component according to the invention, it is in principle sufficient if one of the first electrodes, e.g. B. the cathode, area of the photoactive layer facing a sufficiently low concentration of a compound, z. B. the acceptor compound. In the sense of this description, the area of the photoactive layer facing the first electrode is the area of the photoactive layer that adjoins the first electrode, although this can also be indirect, for example via one or more between the photoactive layer and the layers arranged in the first electrode.

It is therefore not necessary for the entire photoactive layer to have such a low concentration of the compound in question. The area facing the first electrode can have a thickness, ie an extension essentially perpendicular to the surface of the first electrode, which is significantly less than the thickness of the photoactive layer, e.g. B. at most 10% of the thickness of the photoactive layer. Typically, the thickness of the area facing the first electrode can be between 5 and 10 nm. The concentration of the low-concentration compound may increase from the region facing the first electrode in a direction towards the surface of the second electrode in the photoactive layer, e.g. B. until a volume ratio D:A is reached, at which the interface between the two compounds in the photoactive layer is maximal, in order to increase the absorption cross section for the direct excitation of intermolecular CT states. Preferably, the photoactive layer has a volume ratio D:A in a region in which the standing wave forming for the wavelength to be detected in the optical microcavity of the optoelectronic component according to the invention has a spatial intensity maximum, in which the absorption cross section for the direct excitation of intermolecular CT states as high as possible, particularly preferably maximum. The increase in the concentration of the low-concentration compound from a region of the photoactive layer facing the first electrode at least up to a region of the photoactive layer which is different from the region facing the first electrode and is arranged closer to the second electrode than this can be in any desired way continuously, e.g. B. linear, or discontinuous, z. B. stepped, take place. However, the entire photoactive layer can also be designed with the low concentration of one of the compounds according to the invention, i.e. in such a way that the concentration of the donor compound or the concentration of the acceptor compound is so low that the low-concentration compound traps states for the compounds assigned to it Charge carrier provides.

The optoelectronic component according to the invention is the first CT-OPD utilizing the PM effect. The optoelectronic component according to the invention shows that, unexpectedly, the generation of very few charge carriers, as is the case here due to the small absorption cross section of the CT states, is sufficient to trigger the PM effect.

In order to achieve an amplification effect by arranging the photoactive layer in a microcavity, it is beneficial if the optical losses in the photoactive layer are small enough to allow constructive interference of the waves reflected between the mirror surfaces. As a result, amplification is to be expected in particular for optical transitions with a small absorption cross section, such as the CT transition. An excessive increase in the EQE in this sense due to the PM effect can therefore have a negative effect on the detection behavior of a CT-OPD. One goal of utilizing the PM effect in the optoelectronic component according to the invention is therefore not primarily to increase the EQE above 100%. Rather, the EQE can advantageously be increased in wavelength ranges with an intrinsically particularly small EQE. As a result, the detection range of the component according to the invention can be extended to higher wavelengths, at which the EQE in known CT-OPD was too small to trigger a detectable signal. The optoelectronic component according to the invention can thus advantageously expand the wavelength range of the electromagnetic radiation that can be detected by means of the component to higher wavelengths while the EQE remains essentially the same.

The EQE of the optoelectronic component can be increased by a suitable increase in the blocking voltage between the cathode and anode, that is to say the first and second electrodes, of the optoelectronic component. If no voltage is applied between the first and the second electrode of the optoelectronic component, no PM effect is observed.

The low concentration of one of the compounds of the mixed layer, which is necessary for exploiting the PM effect in the optoelectronic component according to the invention, can be controlled particularly advantageously in the case of vacuum-processed small molecule layers. The same applies to an optionally present concentration gradient in the photoactive layer.

Various combinations of donor and acceptor compounds are suitable for the photoactive mixed layer of an optoelectronic component according to the invention. A typical combination is, for example, ZnPc (zinc(II) phthalocyanine) as the donor compound and _CO as the acceptor compound. In this case, for example, Obo can be so low in concentration in the mixed layer that the C ₆ O molecules provide trap states for electrons, which cause a photo-induced accumulation of electrons in a region of the mixed layer facing the cathode, so that holes are injected from the cathode into the mixed layer so that holes in the component as charge carriers predominate over electrons.

Other typical D:A combinations that are particularly suitable for the photoactive layer of the optoelectronic component according to the invention are listed below as a non-exhaustive list: TPDP:C6o; MeO-TPD:C6o; m-MTDATA:C6o; pentacenes:C6o; TAPC:C ₆₀ ; ZnPc:HATNA-CI ₆ ; TPDP:HATNA-CI ₆ ; MeO-TPD: HATNA-CI ₆ ; m-MTDATA:HATNACl ₆ ; Pentacene: HATNA-CI ₆ ; TAPC:HATNA-CI ₆ .

In one embodiment of the optoelectronic component according to the invention, the concentration of the donor compound in the mixed layer or the concentration of the acceptor compound is at least in the region of the mixed layer facing the first electrode between 0.1 and 10 percent by weight (wt%), which means that the proportion by mass of the low-concentration compound in this area of the mixed layer, based on the total mass of the mixed layer in this area, is between 0.1 and 10%, the limits included in each case. The mass fraction mentioned is preferably at least 1% by weight and/or at most 5% by weight. A mass fraction of at most 4% by weight, very particularly preferably of at most 3% by weight, including the respective limits, is particularly preferred.

For example, in a mixed layer containing ZnPc as the donor compound and Obo as the acceptor compound, a concentration of 3% by weight of Obo has proven to be particularly advantageous in that both the EQE and the specific defectivity of a Component comprising said mixed layer at least at the wavelength to be detected compared to components with a mixed layer of the composition ZnPc: C ₆ o with (varying in integral steps) lower and higher concentrations of Obo. The specific defectivity can be interpreted as a normalized signal-to-noise ratio, where, in a manner known to those skilled in the art, z. B. the dark current of the component is taken into account.

By utilizing the PM effect, the EQE of an optoelectronic component according to the invention, in particular with a concentration ratio optimized in the above sense, is compared with a conventional CT-OPD, which has a mixed layer of the same donor and acceptor compound as the photoactive layer with a photoinduced excitation of an intermolecular CT state has an optimized concentration ratio, also in the higher NIR wavelength range, in which the EQE of the conventional CT-OPD is small, e.g. B. by a factor between 10 and 100. For some wavelengths to be detected, an optoelectronic component according to the invention, in particular with a concentration ratio optimized in the above sense, can have an EQE of significantly more than 100% (eg 1000%).

In addition to the photoactive layer, an optoelectronic component according to the invention can have further layers which are also arranged between the two electrodes and/or between the mirror surfaces of the microcavity.

In principle, the wavelength to be detected of a CT-OPD can be varied by changing the optical path length between the mirror surfaces, whereby the variation does not have to be via the thickness of the photoactive layer, but via an arrangement of at least one layer that is largely transparent at least for the wavelength to be detected Spacer layer can be done between the mirror surfaces. Embodiments of the optoelectronic component according to the invention can have such an arrangement of optical spacer layers.

In one embodiment of the optoelectronic component according to the invention, a spacer layer that is transparent at least for the wavelength to be detected is arranged between the second electrode and the photoactive mixed layer, so that the mixed layer is arranged closer to the first electrode, i.e. to the charge carrier injecting electrode, than to the second electrode . Advantageously, the charge carrier injection from the first electrode into the photoactive layer can be further intensified with the aid of this embodiment. In a further embodiment of the optoelectronic component according to the invention, at least one first charge carrier blocking layer is arranged between the first electrode and the photoactive layer. Depending on the type of charge carrier to be blocked, the blocking layer can be an electron blocking layer (EBL) or a hole blocking layer (HBL). In the non-illuminated state of the optoelectronic component, the first blocking layer can serve to weaken the transport of the charge carriers (main charge carriers) injected by the first electrode and assigned to the highly concentrated compound to the first electrode. For example, in the case of a photoactive layer with a low concentration of the acceptor compound according to the invention, an HBL can be arranged between the photoactive layer and the first electrode (cathode). The dark current of the component can advantageously be reduced by means of this embodiment. The thickness of the first blocking layer is to be selected in such a way, in particular so small, that an injection of the blocked charge carriers, e.g. in the case of HBL of the holes into the photoactive layer is not prevented.

It is clear to the person skilled in the art that the position of the energy levels that forms in the layer stack is decisive for whether a layer effectively leads to the blocking or to the transport of a specific type of charge carrier.

The first blocking layer for the charge carriers associated with the high-concentration compound can function as a transport layer for the other type of charge carrier associated with the low-concentration compound. Depending on the type of charge carrier to be transported, the transport layer can be an electron transport layer (ETL) or a hole transport layer (HTL). For example, an HBL can act as an ETL.

Such a transport layer arranged between the photoactive layer and the first electrode is to be designed in such a way that the transported charge carriers are not efficiently extracted from the photoactive layer to the first electrode. For example, an HBL placed between the cathode and the mixed layer acts as an ETL, where the ETL is designed such that the mobility of electrons in the ETL is low enough to ensure low extraction of electrons. This condition can e.g. B. be fulfilled in that the ETL is undoped.

In a further embodiment of the optoelectronic component according to the invention, there is at least a second electrode between the first electrode and the photoactive layer Charge carrier blocking layer is arranged, which, in contrast to the first blocking layer, additionally weakens the transport of the charge carriers associated with the low-concentration compound to the first electrode in relation to an optoelectronic component according to the invention without a second blocking layer and thus leads to an increase in the photo-induced accumulation of the low-concentration Connection associated charge carrier leads. The arrangement of a second blocking layer thus contributes to an increase in the photomultiplication effect in the component.

If the low concentration compound is the acceptor, i.e. electrons are to be accumulated, the second blocking layer is an EBL. In the case of the low-concentration compound donor, the second blocking layer is an HBL. It is clear to the person skilled in the art that the material of the second blocking layer must be selected in such a way that the energy levels, in the case of electrons to be blocked the LUMO, in the case of holes to be blocked the HOMO, in relation to the position of the energy levels of the photoactive layer blocking the desired type of charge carrier effect.

The optoelectronic component according to the invention can have at least a first or at least a second or at least a first and at least a second blocking layer. In the latter case, the second blocking layer is expediently arranged on the photoactive layer and the first blocking layer on the first electrode.

In a further embodiment of the optoelectronic component according to the invention, at least one transport layer for the charge carriers injected by the first electrode and associated with the highly concentrated compound is arranged between the second electrode and the photoactive layer, which transport layer can act as a blocking layer for the charge carriers associated with the low-concentrated compound. to largely prevent the transport of these charge carriers to the second electrode. For example, an HTL can be placed between the photoactive layer and the anode, which acts as an EBL.

Furthermore, an optoelectronic component according to the invention can have optical input filters in order to obtain a narrow-band output signal in the range of the wavelength to be detected.

The optoelectronic component according to the invention can be arranged on a substrate which can be rigid, partially flexible or flexible. In particular, it is expedient to make the substrate transparent at least for the wavelength to be detected in order to to be able to illuminate the optoelectronic component through the substrate. The optoelectronic component can have an encapsulation in order to reduce the effects of harmful environmental influences.

The invention also relates to a method for the spectrally selective detection of electromagnetic radiation, which has at least the following method steps: a. Providing an optoelectronic component according to the invention; b. illuminating the optoelectronic component with an incident wave of electromagnetic radiation having a wavelength to be detected and generating free charge carriers by direct excitation and dissociation of the intermolecular charge transfer state at an interface between donor compound and acceptor compound in the photoactive layer of the optoelectronic component; c. Application of an electrical voltage to the electrodes of the optoelectronic component, the electrical voltage being directed in such a way that the charge carriers associated with the low-concentration compound of its photoactive layer accumulate in a region of the photoactive layer facing the first electrode; i.e. Accumulation associated with the low concentrated compound

charge carriers in a region of the photoactive layer of the optoelectronic component facing the first electrode; e. injecting charge carriers associated with the highly concentrated compound from the first electrode into the photoactive layer of the optoelectronic component; f. Transport of the charge carriers assigned to the highly concentrated compound and of the charge carriers of the same type generated by illumination to the second electrode of the optoelectronic component and generation of an electrical signal.

If the optoelectronic component according to the invention has a low concentration of the acceptor compound in at least one region of the photoactive layer facing the cathode, it occurs when the optoelectronic component is illuminated and a voltage is applied to the electrodes in the reverse direction (positive pole on the cathode, negative pole on the anode) to an accumulation of electrons in the region of the photoactive layer facing the cathode and consequently to the injection of holes from the cathode into the photoactive layer. The additional injected holes are transported to the anode with the photoinduced holes present after dissociation of the charge carrier pairs generated by direct excitation of the intermolecular CT state at an interface between donor compound and acceptor compound in the photoactive layer.

This explanation of the method according to the invention, which is given for the case of a low acceptor compound, can easily be transferred by a person skilled in the art to an embodiment of the component according to the invention with a low concentration of the donor compound.

If the optoelectronic component according to the invention has at least one second blocking layer which is designed to block the non-main charge carriers associated with the low-concentration compound and is arranged between the photoactive layer and the first electrode, these charge carriers accumulate in method step c. additionally at this blocking layer.

In the context of this description, the term "at least one" is used for brevity, which can mean: one, exactly one, several (e.g. exactly two, or more than two), many (e.g. exactly three or more than three), etc. "Several" or "many" does not necessarily mean that there are several or many identical elements, but rather several or many essentially functionally identical elements.

The invention is not limited to the illustrated and described embodiments, but also includes all embodiments that have the same effect within the meaning of the invention. Furthermore, the invention is not limited to the combinations of features specifically described, but can also be defined by any other combination of specific features of all individual features disclosed overall, provided that the individual features are not mutually exclusive, or a specific combination of individual features is not explicitly excluded.

The invention is explained below using exemplary embodiments with reference to figures, without being restricted to these. The

1 shows the layer structure of an optoelectronic component according to the invention in a first embodiment;

1b shows the layer structure of an optoelectronic component according to the invention in a second embodiment;

1c shows the layer structure of an optoelectronic component according to the invention in a third embodiment;

1d shows the layer structure of an optoelectronic component according to the invention in a fourth embodiment;

FIG. 2 shows a schematic energy diagram for the optoelectronic component according to the invention from FIG. 1a;

3 shows the wavelength dependency of the EQE of an optoelectronic component according to the invention for different lengths L of the optical microcavity.

1a-d each show a schematic of the layer structure of an optoelectronic component 1, T, 1", 1'" according to the invention. The optoelectronic component 1, T, 1", 1"" has a photoactive layer 2, which is a mixed layer made of a donor compound, e.g. B. ZnPc, and an acceptor compound, z. B. Obo, wherein the concentration, in terms of mass fraction, of Obo in the mixed layer is much lower than the concentration of ZnPc. For example, the mass fraction of Obo in the mixed layer is 3%. The photoactive layer 2 is arranged between two mirror surfaces 310, 320 located opposite one another at a distance. The mirror surfaces 310, 320 are arranged between two electrodes 31, 32. The layer structure is applied to a substrate 4 .

The first electrode, the top electrode, acts as cathode 31, the second electrode, the bottom electrode, as anode 32. Between cathode 31 and anode 32, a voltage can be applied in the reverse direction, ie the positive pole is connected to the cathode 31 and the Negative pole applied to the anode 32. The electrodes 31, 32 can consist of the same material or of different materials. The electrodes 31, 32 can, for. B. consist of a metal, z. B. silver, aluminum, etc. A typical oxidic material for the anode 32 can be ITO (indium tin oxide). The mirror surfaces 310, 320 can be surfaces of the electrodes 31, 32 designed to be reflective or layers that are separate from the electrodes 31, 32. The illumination system (not shown) for illuminating the optoelectronic component 1, T, 1", "T" can be arranged on the substrate side, so that the illumination of the photoactive layer 2 through the substrate 4, the bottom electrode 32 and the bottom electrode arranged Mirror surface 320 takes place (illumination direction 100). The layers mentioned must therefore be at least partially transparent for the wavelength to be detected by means of the optoelectronic component 1, T, 1", T". The dependence of the wavelength to be detected on the thickness of the individual layers and the materials used can be evaluated using transfer matrix simulations.

The optoelectronic component 1 shown in FIG. 1a can, for. B. have the following layer structure, with the material and the thickness of the layer being given in brackets: substrate 4 (glass, 1.1 mm)—partially transparent bottom electrode 32 with a reflective surface 320 (Ag, 25 nm)—photoactive layer 2 (ZnPc:C ₆ O (3% by weight), 400 nm)—reflective top electrode 31 with a reflective surface 310 (Ag, 100 nm).

The EQE of the optoelectronic component 1 with the layer structure mentioned shows a narrow peak (FWHM approx. 23 nm) at approx. 880 nm.

In addition to the layered structure of the optoelectronic component 1 , the optoelectronic component T shown in FIG. The HBL can be e.g. B. be a 10 nm thick layer consisting of HATNA-CI ₆ , preferably undoped HATNA-CI ₆ to act only weakly electron-conducting.

In addition to the layer structure of the optoelectronic component T, the optoelectronic component 1″ shown in FIG. 1c has a hole transport layer (HTL) 6, which is arranged between the photoactive layer 2 and the bottom electrode/anode 32 with mirror surface 320 and also has an electron-blocking effect . The HTL can be e.g. B. be a 10 nm thick doped layer consisting of MeO-TPD:F ₆ -TCNNQ.

In addition to the layer structure of the optoelectronic component 1", the optoelectronic component T" of FIG. Connection Obo associated charge carriers, in the top electrode / cathode 31 facing area of the photoactive layer 2 is used. The EBL 6 can be e.g. B. be a 10 nm thick layer NTCDA or HAT (CN) ₆ act. FIG. 2 schematically shows an energy diagram for an optoelectronic component with a layer structure as in FIG. 1a under illumination with electromagnetic radiation and with a voltage applied in the reverse direction to the electrodes of the optoelectronic component. By illuminating the optoelectronic component with electromagnetic radiation, a CT state in the photoactive layer of the optoelectronic component can be triggered by a photon whose energy is e.g. B. the difference between the HOMO of the donor compound 73 and the LUMO of the acceptor compound 74 in the photoactive layer, to form a charge carrier pair 80 are excited. After the charge carrier pair has dissociated into free charge carriers, electrons 81 accumulate in the region of the photoactive layer close to the cathode, since there are only a few percolation paths for electrons due to the low concentration of the acceptor compound in the photoactive layer. Due to the electric field created by the enrichment of the electrons 81 in the region of the photoactive layer close to the cathode, the energy levels HOMO of the acceptor compound 72, HOMO of the donor compound 73, LUMO of the acceptor compound 74 and LUMO of the donor compound bend as shown 75. The bending allows holes 82 from the cathode (Fermi level 76) to tunnel through the injection barrier (tunneling action illustrated by arrow 77) and be injected into the photoactive layer. Due to the high donor concentration in the photoactive layer, the injected holes are efficiently transported together with the photo-induced holes 82 to the anode (Fermi level 71).

FIG. 3 shows the dependency of the EQE on the wavelength for four different optoelectronic components, with a voltage in the reverse direction of −10 V being applied to the electrodes of the optoelectronic component in each case. The optoelectronic components differ in the length L of the optical cavity. The EQE of an optoelectronic component according to the invention shows a narrow peak with a maximum at the wavelength / _ec to be detected, for which the resonance condition is met with regard to the selected length of its cavity. The full width at half maximum (FWHM) of the peaks at the wavelengths to be detected is between 20 and 40 nm. Reference sign

1, r, 1”,1 optoelectronic component 100 direction of illumination 2 photoactive layer

31 Top electrode, cathode 310 Mirror surface arranged on the top electrode

32 bottom electrode, anode 320 Mirror surface arranged on the bottom electrode

4 substrate

5 HBL

6 HTL 7 EBL

71 Fermi level of bottom electrode/anode

72 HOMO of the acceptor compound

73 HOMO of the donor compound

74 LUMO of the acceptor compound

75 LUMO of the donor compound

76 Fermi level of top electrode/cathode

77 Arrow showing the injection of holes from the

Cathode into the photoactive layer

80 pairs of carriers

81 electron

82 Hole injected into the photoactive layer

Claims

patent claims

1. Optoelectronic component (1, 1', 1", V") for the spectrally selective detection of electromagnetic radiation, having a first (31) and a second electrode (32) which are spaced apart and to which an electrical voltage can be applied, a photoactive layer (2) comprising a mixed layer containing a donor compound and an acceptor compound, the energy equivalent of a wavelength to be detected of the electromagnetic radiation being one for direct excitation of the intermolecular charge transfer state at an interface between the donor compound and corresponds to the energy to be used for the acceptor compound, the photoactive layer (2) being arranged in an optical microcavity which is arranged between the first (31) and the second electrode (32) and is formed from two mirror surfaces (310, 320) spaced apart from one another , The distance between the mirror surfaces (310, 320) being designed to one another in such a way that in the microcavi tät a standing wave is generated for an incident wave of the electromagnetic radiation with the wavelength to be detected, characterized in that the concentration of the donor compound at least in a region of the photoactive layer (2) facing the first electrode (31) or the concentration of the acceptor compound is so low, at least in a region of the photoactive layer (2) facing the first electrode (31), that the low-concentration compound provides trap states for the charge carriers assigned to it, which cause a photo-induced accumulation of the charge carriers (81 ) in a region of the photoactive layer (2) facing the first electrode (31), so that charge carriers (82) associated with the highly concentrated compound are injected from the first electrode (31) into the photoactive layer, whereby these

Type of charge carrier in the component (1, 1', 1", V") predominates.

2. Optoelectronic component (1, 1', 1", V") according to claim 1, characterized in that the concentration of the donor compound in the entire photoactive layer (2) or the concentration of the acceptor compound in the entire photoactive layer (2) is so low that the low-concentration compound provides trap states for the charge carriers associated with it, which cause a photo-induced accumulation of the charge carriers (81) associated with the low-concentration compound in a region of the photoactive layer (2) facing the first electrode (31) cause so that the highly concentrated compound associated charge carriers (82) are injected from the first electrode (31) into the photoactive layer, as a result of which this type of charge carrier predominates in the component (1, 1', 1").

3. Optoelectronic component according to claim 1, characterized in that the concentration of the low-concentration compound from the area of the photoactive layer (2) facing the first electrode (31) to at least one area of the photoactive layer that differs from the area facing the first electrode (2) increases in the direction of the second electrode (32), it being possible for the concentration to increase continuously or discontinuously.

4. Optoelectronic component (1, 1′, 1″T″) according to one of claims 1 to 3, characterized in that the concentration of the donor compound is at least in the area of the photoactive layer (2) or the area facing the first electrode Concentration of the acceptor compound at least in the area of the photoactive layer (2) facing the first electrode between 1 and 10% by weight, preferably between 1 and 5% by weight, particularly preferably between 1 and 4% by weight, very particularly preferably between 1 and 3 % by weight.

5. Optoelectronic component according to one of the preceding claims, characterized in that an optically transparent spacer layer is arranged between the second electrode (32) and the photoactive layer (2), so that the photoactive layer (2) is closer to the first electrode (31 ) than on the second electrode (32).

6. Optoelectronic component (1', 1", T") according to one of the preceding claims, characterized in that between the first electrode (31) and the photoactive layer (2) at least one first blocking layer (5) is arranged, wherein the first blocking layer (5) in the non-illuminated state of the optoelectronic component (1', 1", T") the transport of the charge carriers (82) injected by the first electrode (31) and assigned to the highly concentrated compound of the photoactive layer (2) to the first electrode (31) weakens.

7. Optoelectronic component (1"') according to one of the preceding claims, characterized in that at least one second blocking layer (7) is arranged between the first electrode (31) and the photoactive layer (2), the second blocking layer (7) the transport of the low-level compound at least weakens the charge carriers (81) assigned to the photoactive layer (2) to the first electrode (31) and causes the photo-induced accumulation of the charge carriers (81) assigned to the low-concentration compound on the second blocking layer (7).

8. Optoelectronic component (1", 1"') according to one of the preceding claims, characterized in that between the second electrode (32) and the photoactive layer (2) there is at least one transport layer (6) for the transport layer (6) from the first electrode (31 ) injected charge carriers (82) associated with the highly concentrated compound of the photoactive layer (2), which acts as a blocking layer for the charge carriers (81) associated with the low-concentrated compound of the photoactive layer.

9. Method for the spectrally selective detection of electromagnetic radiation, having at least the following method steps: a. Providing an optoelectronic component (1, T, 1", "T") according to one of Claims 1 to 8; b. Illumination of the optoelectronic component (1, T, 1", "T") with an incident wave of electromagnetic radiation with a wavelength to be detected and generation of free charge carriers by direct excitation and dissociation of the intermolecular charge transfer state at an interface between donor compound and acceptor compound in the photoactive layer (2) of the optoelectronic component (1, T, 1", T"); c. Application of an electrical voltage to the electrodes (31, 32) of the optoelectronic component (1, T, 1", "T"), the electrical voltage being directed in such a way that the charge carriers (81) associated with the low-concentration compound are in one of the pile up the region of the photoactive layer (2) facing the first electrode (31); i.e. Accumulation of charge carriers (81) associated with the low-concentration compound of the photoactive layer (2) in a region of the photoactive layer (2) of the optoelectronic component (1, T, 1", T") facing the first electrode (31); e. Injection of charge carriers (82) assigned to the highly concentrated compound of the photoactive layer (2) from the first electrode (31) into the photoactive layer (2) of the optoelectronic component (1, T, 1", T"); f. Transport of the injected charge carriers (82) assigned to the highly concentrated compound of the photoactive layer and the charge carriers of the same type generated by illumination to the second electrode (32) of the optoelectronic component (1, T, 1", T") and generation of a readable one electrical signal.