SOLID-STATE COMPONENT

Description

[0001] The invention relates to a solid-state component according to the preamble of claim 1, which responds to electromagnetic radiation and, depending on the embodiment, can be used as a (thermo)photovoltaic element, as a photoelectric sensor, as a photocatalyst, or as an electricity storage device.

[0002] A solid-state component according to the preamble of claim 1 is known per se from DE 10 2016 015 581 A1. In this known solid-state component, a further n-type semiconductor material is applied to the anode by a wet-chemical process, the band gap of which is smaller than the band gap of the n-type semiconductor material contacted with the cathode. The electron-conducting contact between the two semiconductor materials in the electrode gap forms an n-isotypic heterojunction.

[0003] Further solid-state elements for at least one of the above-mentioned fields of application are known from EW McFarland, J. Tang, "A photovoltaic device structure based on internal electron emission", Nature, Vol. 421, 2003 as well as from DE 10 2005 028 859 A1 and DE 10 2014 002 092 A1.

[0004] The solid-state component according to the invention is defined by the features of claim 1. It comprises a cathode K (from which electrons emerge) and an anode A (into which these electrons enter). Opposing surfaces of the cathode K and the anode A define an electrode gap EZR. A semiconductor material HL and a coating material BM are located in the electrode gap EZR. The semiconductor material HL is designed as an n-type semiconductor nHL and contacts the cathode K and, preferably, also the coating material BM. The coating material BM contacts the anode A and, preferably, also the n-type semiconductor nHL.

[0005] According to the invention, the materials used have the following energy positions related to vacuum: i) the work function Φ K of the cathode K is larger than the work function Φ A of the anode A (Φ K > Φ A ), ii) the band gap E gHL of the n-type semiconductor nHL is larger than 2.0 eV (E gnHL > 2 eV) and its Fermi energy E FnHL is larger than or (essentially) equal to the work function Φ K of the cathode K (E FnHL ≥ Φ K ), and iii) the work function of the coating material BM is smaller than the work function of the anode A (Φ BM < Φ A ) or the coating material BM has a negative electron affinity (NEA).

[0006] There is electron-conducting contact between the cathode K, the n-type semiconductor material nHL, the coating material BM and the anode A, and areas of the cathode (K) and the anode (A) that are not in contact with the n-type semiconductor material (nHL) or with the coating material (BM) can be connected to one another or - during operation of the solid-state element - are connected to form an electrical circuit via current collectors and, if necessary, a consumer.

[0007] Preferred embodiments of the invention are explained in the subclaims.

[0008] Embodiments of the invention are described in more detail below with reference to a drawing. In the drawings: Fig. 1 shows a schematic representation of a solid-state component with a cathode K, a semiconductor material HL in the form of an n-type semiconductor nHL, a coating material BM and an anode A, as well as the vacuum-related energy positions (in eV) of these components in the non-contacted state, and Fig. 2 shows a band diagram of the materials used for the cathode K, the n-type semiconductor nHL, the coating material BM and the anode A in electron-conducting contact, under short-circuit conditions and the effect of electromagnetic energy hv on the cathode K.

[0009] Corresponding parts, sizes and structures are always provided with the same reference numerals in all figures.

[0010] Fig. 1 shows schematically the arrangement of the components of a solid-state device, namely a cathode K, a semiconductor material HL in the form of an n-type semiconductor nHL, a coating material BM and an anode A to each other. In Fig. 1 The above-mentioned energy positions (in eV) of these components in the non-contacted state, relative to vacuum, are also shown schematically. The opposing surfaces of the cathode K and the anode A define an interelectrode gap EZR.

[0011] The cathode K and the anode A are made of electron-conducting materials, which can be present either in elemental form or as alloys. The electrode materials are selected so that the difference between the work function Φ K of the cathode K and the work function Φ A of the anode A is as large as possible.

[0012] Non-limiting examples of suitable cathode materials are Gold Au (Φ Au 4.8 - 5.4 eV), selenium Se (Φ Se 5.11 eV), platinum Pt (Φ Pt 5.32 - 5.66 eV), nickel Ni (Φ Ni 5.0 eV) and electron-conducting carbon C, e.g. graphite (Φ graphite 4.7 eV).

[0013] Non-limiting examples of electron-conducting carbon C include activated carbon cloth, graphite (in the form of particles, textile fabrics or foils), fullerenes, graphene, and carbon nanotubes.

[0014] Non-limiting examples of suitable anode materials are Magnesium Mg (Φ Mg 3.7 eV), barium Ba (Φ Ba 1.8 - 2.52 eV), cesium Cs (Φ Cs 1.7 - 2.14 eV), calcium Ca (Φ Ca 2.87 eV) and aluminum Al (Φ Al 4.0 - 4.2 eV).

[0015] Depending on the design and application area of the solid-state component, the surfaces of the cathode K and the anode A forming the electrode gap EZR can be congruent or (in the mathematical sense) similar and can be dimensioned, for example, in the range of square micrometers or even square meters.

[0016] The contact surfaces of cathode K or anode A with the semiconductor material nHL or coating material BM located in the interelectrode space EZR are as large as possible. The thicknesses of cathode K and anode A vary depending on the design and application: When designed as a photovoltaic element, for example, a thin, nanometer-thick cathode K made of (leaf) gold is used. When designed as a (thermo)photovoltaic element, the cathode K is, for example, a micrometer- or millimeter-thick graphite foil or is formed from nanometer- or micrometer-sized graphite particles. When designed as an energy storage device, the dimensions of the (porous) electrodes are in the decimetre or liter range.

[0017] Suitable n-type semiconductor materials nHL that satisfy the conditions E gnHL > 2 eV and E FnHL > FK can be found, for example, in the works of Shiyou Chen and Lin-Wang Wang, Chem. Mater., 2012, 24 (18), pp. 3659-3666 or by J. Robertson and B. Falabretti, Electronic Structure of Transparent Conducting Oxides, pp. 27-50 in Handbook of Transparent Conductors, Springer, DOI 10.1007 / 978-1-4419-1638-9). If graphite (with Φ graphite approx. 4.7 eV) is used as cathode K, these are, as non-limiting examples, ZnO, PbO, FeTiO 3 , Ba-TiO 3 , CuWO 3 , BiFe 2 O 3 , SnO 2 , TiO 2 , WO 3 , Fe 2 O 3 , In 2 O 3 and Ga 2 O 3 .

[0018] The surface of the anode A facing the electrode gap EZR is coated with a coating material BM whose work function Φ BM is even lower than the work function Φ A of the anode A (Φ BM < Φ A ). According to the invention, alkali oxides, alkaline earth oxides, rare earth oxides, rare earth sulfides, or binary or ternary compounds consisting of these are used for this purpose. According to literature, e.g., VS Fomenko and GV Samsonov (ed.), Handbook of Thermionic Properties, ISBN: 978-1-4684-7293-6, their work functions Φ are in the range of 0.5 - 3.3 eV. Such compounds have been used to date for coating cathode materials of photodetectors, vacuum tubes, thermionic emitters, LEDs, etc., in order to Exitof electrons from the cathode material. In this case, it is assumed that they facilitate the entry of electrons into the anode material A. In addition to the aforementioned coating material BM, whose work function is below the reference value of vacuum, compounds with a work function above vacuum are also used. These are compounds with negative electron affinity (NEA). One example is hexagonal boron nitride (hBN).

[0019] The component according to the invention is created by electron-conductive contacting of the materials described above with each other. Fig. 2 shows the mutual energetic relationships of the cathode K, the n-type semiconductor material nHL, the coating material BM and the anode A from Fig. 1In the short-circuited state: An interface K / nHL formed between the cathode K and the n-type semiconductor material nHL forms a "Schottky contact with electron accumulation" (marked with ⊕). An interface nHL / BM formed between the n-type semiconductor material nHL and the coating material BM is also assumed to exhibit electron accumulation ⊕. In contrast, an interface BM / A formed between the coating material BM and the anode A is more likely to be tunneled through by electrons (shown with a dashed line). These interfaces are not energetic barriers for electrons: Even at room temperature and in the dark, they can leave the energetically lower cathode K and enter the energetically higher anode A – as evidenced by a continuous increase in the open terminal voltage Voc, see Example 1.

[0020] How it works: Electromagnetic radiation acting on the cathode K with sufficiently high energy excites electrons in the bulk of the cathode material - directly or indirectly via phonons and plasmons - to such an extent that they are able to leave the cathode material and enter the conduction band of the n-type semiconductor material nHL, which is (easily) possible due to the electron accumulation ⊕ existing at the K / nHL interface. If the electrons still have sufficient (kinetic) energy, they pass across the nHL / BM interface into the bulk of the coating material BM, in order to pass across the BM / A interface into the volume of the anode A, which has a higher energy. Since the n-type semiconductor material nHL has a band gap E gHL of more than 2 eV, no recombination with holes from the valence band occurs.

[0021] To operate the solid-state component, n-type semiconductor-free portions of the cathode K and coating-material-free portions of the anode A are connected to form an electrical circuit by one or more electrical conductors and, if applicable, an electrical load connected in between. The electrical conductor(s) mentioned and any load present form an outer part of the circuit—not belonging to the solid-state component according to the invention. In this operating state of the solid-state component, sufficiently "hot" electrons are capable of performing electrical work, as they flow from the energetically higher anode A back to the cathode K via the outer part of the circuit. Thus, the component is also suitable, among other things, as a (thermo)photovoltaic cell for converting thermal energy into electrical energy.

[0022] For the respective electron-conducting contacting of the materials used, well-known (semiconductor) technologies such as spin coating, (electrostatic) fixation of (nano)crystals, sputtering, atomic layer deposition (ALD), epitaxy, chemical vapor deposition (CVD), physical vapor deposition (PVD), chemical bath deposition (CBD) or (electro)chemical methods can be used.

[0023] Parameters such as contact conditions (temperature, pressure, gas atmosphere, air humidity, pH of solutions), stoichiometric composition of the electrode and / or semiconductor materials, their roughness, their position in the thermoelectric or electrochemical series, formation of (dipole) layers, crystal size, crystal face orientation, crystallinity, water of crystallization (proportion), type and extent of lattice defects, type and extent of doping, lattice adaptation, layer morphology, thickness of the applied layer(s), their porosity, etc., are familiar to the person skilled in the art, can be varied within a wide range and can be optimized (on the basis of test results obtained). Example 1:

[0024] Materials used: The material for the cathode K is graphite with a work function Φ K of 4.7 eV. The material for the anode A is magnesium with a work function Φ A of 3.7 eV. The coating material BM for the anode A is barium oxide with a work function Φ BM of 1.9 eV. The n-type semiconductor material nHL is tin(IV) oxide SnO 2 .

[0025] According to the literature, an energy position of the conduction band LB of 5.1 eV, a Fermi energy E FSnO2 of 5.3 eV, an energy position of the valence band VB of 8.6 eV and a band gap E gSnO2 of 3.5 eV are assumed.

[0026] Manufacturing of the component: I) Electron-conducting contacting of the cathode K with the n-type semiconductor material nHL

[0027] An activated carbon cloth (FLEXSORB FM30K) from Chemviron Cloth Division, Tyne & Wear (UK) is completely covered with a solution of approximately 2.0% (w / v) Sn(II)Cl 2 *2H 2 O in a 70% (v / v) 2-propanol solution in water for 5 hours. After removing excess solution, one side of the moist cloth is exposed to an ammonia atmosphere for approximately 12 hours. The cloth is then dried for several hours at approximately 50°C. The resulting silvery-lustrous layer consists of (cassiterite) crystals of tin(IV) oxide SnO 2 . II) Electron-conductive contacting of the anode A with the coating material BM

[0028] An approximately 17 mm long section of a 20 x 3.2 x 0.3 mm magnesium strip is immersed in 1 N hydrochloric acid for approximately 2 seconds, which removes the adhering oxide layer with the evolution of hydrogen. After drying with a soft paper towel, approximately 10 µl of a saturated, approximately 90°C aqueous barium oxide solution is applied with a pipette to the acid-exposed section. The strip is then heat-treated, treated side up, on a glassy carbon plate placed on a Bunsen burner for approximately 30 minutes at an estimated temperature of approximately 900°C. The resulting gray layer is barium oxide (BaO). III) Assembly into a solid-state component

[0029] The untreated side of anode A, prepared as per II), is fixed to a self-adhesive tape (Tesafilm ®< ). The silvery-shiny side of cathode K, prepared as per I), is fixed congruently to the anode A in such a way that the end not treated with hydrochloric acid and approximately 2 mm of the gray BaO layer are left out, resulting in an electron-conducting contact surface of anode A measuring approximately 15 x 3.2 mm. A 0.1 mm thick copper wire is fixed to the activated carbon cloth using adhesive tape (Tesafilm ®< ) as the cathodic current collector; the end of the magnesium strip not contacted with hydrochloric acid serves as the anodic current collector, with the oxide layer present here being mechanically removed.

[0030] The resulting component is then placed between two glass slides, with the upper slide being sized to accommodate the leads of a multimeter connected to the above-mentioned current collector. Electron-conductive contact between cathode K and anode A is achieved by pressing the two slides together and securing them with clamps. To further increase the component's handling and stability, it can be encased in an optically clear 2K epoxy potting compound, leaving the current collectors out, and then cured.

[0031] The component produced in this way is integrated into an electrical circuit by connecting the (cathode) copper wire to the positive pole of a multimeter and the free end of the (anodic) magnesium strip to the negative pole.

[0032] When measuring the short-circuit current Isc at room temperature and in room light, values of around 5 µA / cm 2< are found consistently. In sunlight, values of around 2,000 µA / cm 2< are achieved when the focal spot of a magnifying glass is directed onto the cathode K. If the open terminal voltage Voc is measured immediately after such an Isc measurement, Voc values of around 0.7 volts are found. Even at room temperature and in the dark, the Voc value then rises to around 1.8 volts within around eight hours. If an Isc measurement is taken at maximum Voc value, initial current values of 400 µA / cm 2< are found, which then continuously drop to values of around 20 µA / cm 2< within around 20 minutes. The component is therefore suitable as an energy storage device, also in the form of a self-charging capacitor.

[0033] The open terminal voltage Voc of the component (encapsulated in epoxy) remains constant at approximately 1.8 volts over months, which is also reflected in the lack of corrosion of anode A.

[0034] The above-mentioned dimensions of cathode K and anode A are retained for the following examples. Example 2:

[0035] TiO2 is used as the n-type semiconductor (nHL). Energy positions: conduction band LB 4.6 eV; Fermi energy E FTiO2 5.3 eV; valence band VB 7.8 eV; and band gap E gTiO2 3.7 eV. The activated carbon cloth (cathode K) is impregnated with a 1% (v / v) solution of titanium(IV) ethylate in 2-propanol and dried for several days at 90°C. Anode A and coating material BM are as in Example 1. Contacting of the activated carbon cloth (whitened due to TiO2 formation) with BaO-coated anode A and assembly as described in Example 1. Measurement results as in Example 1. Example 3:

[0036] Fe2O3 is used as the n-type semiconductor (nHL). Energy positions: conduction band LB 5.0 eV; Fermi energy E FFe2O3 5.3 eV; valence band VB 7.3 eV and band gap E gFe2O3 2.3 eV. Anode A and coating material BM as in Example 1. Approximately 10 µl of an aqueous, saturated solution of Fe(III) nitrate are applied to the BaO coating surface. Initially, drying takes place at room temperature, followed by heat treatment as in Example 1. Contacting with unmodified activated carbon cloth (cathode K) and assembly as in Example 1. Measurement results as in Example 1. Example 4:

[0037] Calcium oxide (CaO) is used as the coating material (BM). The anode, which is also made of magnesium, is cleaned as in Example 1. Approximately 10 µl of an aqueous, saturated solution of calcium nitrate (Ca(NO 3 ) 2 ) is applied to the cleaned magnesium surface, followed by heat treatment at approximately 900°C. Approximately 10 µl of an aqueous, saturated solution of Fe(III) nitrate is then applied to the CaO coating surface to form the semiconductor layer consisting of Fe 2 O 3 (analogous to Example 3). Initially, the coating is dried at room temperature and then heated as in Example 1. Contact with untreated activated carbon cloth and assembly as in Example 1. Measurement results are as in Example 1. Example 5:

[0038] Strontium oxide SrO is used as the coating material BM. Anode A, also made of magnesium, is cleaned as in Example 1. Approximately 10 µl of an aqueous, saturated solution of strontium nitrate Sr(NO 3 ) 2 is applied to the cleaned magnesium surface, followed by heat treatment at approximately 900°C. Approximately 10 µl of an aqueous, saturated solution of Fe(III) nitrate is then applied to the SrO coating surface to form the semiconductor layer consisting of Fe 2 O 3 (analogous to Example 3). First, dry at room temperature and then heat as in Example 1. Contact with untreated activated carbon cloth (cathode K) and assemble as in Example 1. Measurement results as in Example 1. Example 6:

[0039] Caesium oxide Cs2O is used as the coating material BM. Clean the anode A, which is also made of magnesium, as in Example 1. Dissolve a spatula tip of caesium iodide CsI in approximately 10 ml of diluted KOH. Apply 10 µl to the cleaned magnesium surface, followed by heat treatment at approximately 900°C. Then, apply approximately 10 µl of an aqueous, saturated solution of Fe(III) nitrate to the coating surface with Cs2O to form the semiconductor layer consisting of Fe2O3 (analogous to Example 3). First, dry at room temperature and then heat as in Example 1. Contact with untreated activated carbon cloth and assembly as in Example 1. Measurement results as in Example 1. Example 7:

[0040] Hexagonal boron nitride (hBN) is used as the coating material (BM). Anode A, also made of magnesium, is cleaned as in Example 1. Disperse a spatula tip of hBN in approximately 10 ml of ethyl acetate. Apply 10 µl of the dispersion to the cleaned magnesium surface. After evaporating the ethyl acetate, heat treat at approximately 900°C for 30 minutes. Then, apply approximately 10 µl of an aqueous, saturated solution of Fe(III) nitrate to the hBN coating surface to form the Fe2O3 semiconductor layer (analogous to Example 3). First, dry at room temperature and then heat as in Example 1. Contact with untreated activated carbon cloth and assemble as in Example 1. Measurement results as in Example 1.

[0041] In summary, in the solid-state component, opposing asymmetric electrodes, namely the cathode K and the anode A, are connected to each other in an electron-conductive manner by means of a semiconductor material HL and a coating material BM in such a way that an open terminal voltage Voc of approximately 1.8 volts or even more is achieved by acting electromagnetic radiation.

Claims

1. Solid-state component for use as (thermo) photovoltaic element, as photoelectric sensor, as photocatalyst, or as power storage means, comprising - a cathode (K) exposable to electromagnetic radiation, - an anode (A), - an electrode gap (EZR) formed by opposing surfaces of cathode (K) and anode (A), - a semiconductor material (HL) in the electrode gap (EZR) and - a coating material (BM) in the electrode gap (EZR), where an electron flow between cathode (K) and anode (A) is achieved in that - the work function (ΦK) of the material of the cathode (K) is greater than the work function (ΦA) of the material of the anode (A), - the semiconductor material (HL) makes contact with the cathode (K) in the electrode gap (EZR) and is an n-type semiconductor material (nHL) having a bandgap (EgHL) of greater than 2.0 eV and having a Fermi energy position (EFnHL) equal to or greater than the work function (ΦK) of the cathode (K), - the coating material (BM) makes contact with the anode (A) in the electrode gap (EZR), - there is an electron-conducting contact between the cathode (K), the n-type semiconductor material (nHL), the coating material (BM) and the anode (A), and - regions of the cathode (K) and of the anode (A) that are not in contact with the n-type semiconductor material (nHL) or with the coating material (BM) are connectable to one another to form a circuit via current collectors and optionally a load, characterized in that the coating material (BM) has a work function (ΦBM) smaller than the work function of the anode (A), or in that the coating material (BM) has a negative electron affinity (NEA).

2. Solid-state component according to Claim 1, wherein the material of the cathode (K) is electron-conducting carbon.

3. Solid-state component according to Claim 1 or 2, wherein the material of the anode (A) is magnesium or a magnesium alloy.

4. Solid-state component according to any of Claims 1 to 3, wherein the coating material (BM) is an alkali metal oxide, an alkaline earth metal oxide, a rare earth metal oxide, a rare earth metal sulfide or a binary or ternary compound consisting thereof or a material having negative electron affinity.

5. Solid-state component according to any of Claims 1 to 3, wherein the coating material (BM) is barium oxide BaO, calcium oxide CaO, strontium oxide SrO, caesium oxide Cs2O or hexagonal boron nitride hBN.

6. Solid-state component according to any of Claims 1 to 5, wherein the n-type semiconductor material (nHL) is ZnO, Fe2O3, PbO, FeTiO3, BaTiO3, CuWO3, BiFe2O3, SnO2, TiO2, WO3, In2O3 or Ga2O3.