Photoelectric conversion element

Abstract

To provide a photoelectric conversion element capable of preventing electron capturing by a dangling bond of a surface terminal and highly efficiently transporting an electron generated in an organic semiconductor layer to an inorganic semiconductor layer.SOLUTION: A photoelectric conversion element in the present invention comprises a pair of electrodes and a power generation layer laminated with an organic semiconductor layer and an inorganic semiconductor layer. The pair of electrodes holds the power generation layer. The organic semiconductor layer contains an organic semiconductor including a photoactive region generating an exciton. The inorganic semiconductor layer contains an inorganic semiconductor formed of a plurality of materials with different grating constants and including a dissociation region which dissociates an electric charge of the exciton by an electric field where a distorted grating is generated. An energy ranking relationship between the organic semiconductor in the photoactive region and the inorganic semiconductor in the dissociation region meets a prescribed relationship, and the inorganic semiconductor is linked to a termination material having charge transportability via the dangling bond at a surface termination of the inorganic semiconductor layer, so an electron generated in the organic semiconductor layer can be highly efficiently transported to the inorganic semiconductor layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a photoelectric conversion element, and more particularly to a photoelectric conversion element using an organic semiconductor and an inorganic semiconductor. [Background technology]

[0002] Photoelectric conversion elements having an organic semiconductor layer and an inorganic semiconductor layer are promising as next-generation solar cell materials because the semiconductor layer can be formed into a film by coating, making them easy to fabricate, and they can achieve high power generation efficiency.

[0003] When the inorganic semiconductor layer is formed of an inorganic material having piezoelectric properties, the crystal lattice can be distorted by pressure or the like to generate an electric field, which can dissociate electrons from excitons generated in the organic semiconductor layer, thereby improving the photoelectric conversion efficiency.

[0004] Patent Document 1 discloses a photoelectric conversion element in which fine irregularities are formed at the interface between an organic semiconductor layer that generates excitons and an inorganic semiconductor layer that has a dissociation region that dissociates the electrons and holes of the excitons, thereby increasing the contact interface between the inorganic semiconductor layer and the organic semiconductor layer and improving the photoelectric conversion efficiency. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 042579 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] However, when fine irregularities are formed on the surface of the inorganic semiconductor layer, dangling bonds occupied by unpaired electrons that are not involved in the bonds of the inorganic semiconductor are generated on the surface, and some electrons are captured by the dangling bonds and are not transported to the inorganic semiconductor layer, making it impossible to expect an improvement in photoelectric conversion efficiency that would accompany an expansion of the contact interface.

[0007] The present invention has been made in consideration of the problems associated with the conventional techniques, and an object of the present invention is to provide a photoelectric conversion element that can prevent electron capture by dangling bonds and transport electrons generated in an organic semiconductor layer to an inorganic semiconductor layer with high efficiency. [Means for solving the problem]

[0008] As a result of intensive research into achieving the above-mentioned object, the present inventors discovered that the above-mentioned object can be achieved by binding a terminal material having charge transport properties to a dangling bond of an inorganic semiconductor, and thus completed the present invention.

[0009] That is, the photoelectric conversion element of the present invention comprises a pair of electrodes and a power generation layer in which an organic semiconductor layer and an inorganic semiconductor layer are laminated, and the power generation layer is sandwiched between the pair of electrodes. The organic semiconductor layer contains an organic semiconductor having a photoactive region that generates excitons, the inorganic semiconductor layer contains an inorganic semiconductor formed of a plurality of materials having different lattice constants and having a dissociation region that dissociates the charge of the exciton by an electric field generated by distortion of the lattice, the relationship between the energy levels of the organic semiconductor in the photoactive region and the inorganic semiconductor in the dissociation region satisfies the following formulas (1) and (2), and at the surface termination of the inorganic semiconductor layer, the inorganic semiconductor is bonded to a termination material having a charge transport property via its dangling bond, The terminal material and the organic semiconductor are electrically connected via intermolecular interactions. Characterized by: E LUMO > E C ...Equation (1) E HOMO > E V ...Equation (2) However, in formula (1) and formula (2), E LUMO represents the energy level of the lowest unoccupied molecular orbital of an organic semiconductor, E HOMO represents the energy level of the highest occupied molecular orbital of an organic semiconductor, E Crepresents the energy level at the bottom of the conduction band of an inorganic semiconductor, E V represents the energy level at the top of the valence band of an inorganic semiconductor. Effect of the Invention

[0010] According to the present invention, a terminal material having charge transport properties is bonded to the dangling bonds of an inorganic semiconductor, so that a photoelectric conversion element can be provided that can transport electrons generated in the organic semiconductor layer to the inorganic semiconductor layer with high efficiency. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a photoelectric conversion element. [Diagram 2] FIG. 2 is a diagram illustrating the energy levels at the interface between a photoactive region and a dissociation region. [Diagram 3] FIG. 1 is a diagram illustrating the energy levels when a dangling bond is present at the interface between a photoactive region and a dissociation region. [Figure 4] FIG. 4 is a schematic cross-sectional view showing another example of the configuration of a photoelectric conversion element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The photoelectric conversion element of the present invention will now be described in detail. As shown in FIG. 1, the photoelectric conversion element includes a pair of electrodes and a power generation layer in which an organic semiconductor layer and an inorganic semiconductor layer are laminated, and the power generation layer is sandwiched between the pair of electrodes.

[0013] The organic semiconductor layer contains an organic semiconductor having a photoactive region that generates excitons, and the inorganic semiconductor layer contains an inorganic semiconductor having a dissociation region that dissociates the charge of the excitons generated in the photoactive region. The inorganic semiconductor is formed of a plurality of materials having different lattice constants and also has properties as a piezoelectric body.

[0014] In this photoelectric conversion element, the energy level relationship between the organic semiconductor in the photoactive region and the inorganic semiconductor in the dissociation region satisfies the following formulas (1) and (2). E LUMO > E C ...Equation (1) E HOMO > E V ...Equation (2) However, in formula (1) and formula (2), E LUMO represents the energy level of the lowest unoccupied molecular orbital of an organic semiconductor, E HOMO represents the energy level of the highest occupied molecular orbital of an organic semiconductor. E C represents the energy level at the bottom of the conduction band of an inorganic semiconductor, E V represents the energy level at the top of the valence band of an inorganic semiconductor.

[0015] In this photoelectric conversion element, light absorption causes electrons in the highest occupied molecular orbital of the organic semiconductor to move to the lowest unoccupied molecular orbital, generating bound excitons in which electrons and holes are paired by Coulomb force. As a result of the diffusion of these bound excitons, some of the bound excitons reach the interface between the photoactive region and the dissociation region.

[0016] The bound excitons that reach the interface are separated into negative charges (electrons) and positive charges (holes), and photoelectric conversion is performed by extracting these charge carriers to an external circuit.

[0017] Here, the relationship between the energy levels of the photoactive region and the dissociation region will be described taking as an example a case where the photoactive region is a donor (p-type) and the dissociation region is an acceptor (n-type). The horizontal axis of FIG. 2 represents the distance from the interface between the photoactive region and the dissociation region, and the vertical axis represents the energy level.

[0018] The lowest unoccupied molecular orbital (E LUMO The energy level of the conduction band minimum of inorganic semiconductors with dissociation regions (EC ) of the organic semiconductor, HOMO The energy level of the valence band (E V ) higher.

[0019] When a bound exciton, which is a pair of an electron and a hole generated in the photoactive region, reaches the interface between the photoactive region and the dissociation region, E LUMO The energy level of E C Since the energy level of the electron is higher than that of the electron transporter, the electron moves into the dissociation region.

[0020] However, E HOMO The energy level of E V Since the energy level of the electron is sufficiently higher than that of the electrons, an energy barrier is formed against the electrons, so that the electrons do not move to the dissociation region.

[0021] Even if the electrons of the bound excitons move to the dissociation region, the holes remain in the photoactive region, and the organic semiconductor and the inorganic semiconductor are stabilized in a state similar to that of a charge-transfer complex electrostatically attracted to each other at their interface. Therefore, it is generally difficult to transport the electrons and holes away from the interface between the photoactive region and the dissociation region.

[0022] In the photoelectric conversion element of Patent Document 1, since the inorganic semiconductor having a dissociation region has the properties of a piezoelectric body, an electric field is generated by the polarization due to the lattice distortion of the crystal, that is, the so-called piezoelectric effect, and the E C The energy level of decreases with increasing distance from the interface.

[0023] Therefore, the electrons that have moved to the dissociation region are more likely to move in a direction away from the interface, so that dissociation of the bound exciton between the electron and the hole should be possible efficiently.

[0024] However, at the surface termination of the inorganic semiconductor layer, dangling bonds occupied by unpaired electrons that are not involved in bonding are inevitably present.

[0025] When this dangling bond is present at the surface end of the inorganic semiconductor layer, that is, at the interface between the photoactive region on the dissociation region side and the dissociation region, the energy level of the dangling bond is, as shown in FIG. C Since the interfacial tension is lower than the interface, the electrons that move to the dissociation region are captured by dangling bonds and are not transported in a direction away from the interface, and the photoelectric conversion efficiency does not improve as much as expected.

[0026] The decrease in photoelectric conversion efficiency caused by the dangling bonds becomes more remarkable as the surface of the inorganic semiconductor layer is roughened by etching or the like, and the contact interface between the photoactive region and the dissociation region is increased.

[0027] In the present invention, since the dangling bonds of the inorganic semiconductor are bonded to a terminal material having charge transport properties, the electrons that have moved to the dissociation region are prevented from being captured by the dangling bonds.

[0028] Therefore, even if projections and recesses are formed on the surface of the inorganic semiconductor layer, voltage loss due to surface defects is suppressed, enabling highly efficient photoelectric conversion.

[0029] (terminal material) The above-mentioned terminal material may be any material that has charge transport properties and can bond to the dangling bonds of the inorganic semiconductor. Examples of the terminal material include compounds having a thiol group, such as 4-methylthiophenol and 4-(trifluoromethyl)thiophenol, as well as organic semiconductors having a thiol group, such as Poly(3-hexylthiol thiophene).

[0030] The compound having a thiol group has a molecular structure in which a thiol moiety and an aromatic compound moiety are directly bonded to each other, the thiol moiety bonds to a dangling bond of the inorganic semiconductor, and the aromatic compound moiety faces the organic semiconductor.

[0031] Therefore, the compound having a thiol group itself has charge transport properties due to the π-electron conjugated system of the aromatic compound moiety, and is electrically connected to the organic semiconductor via intermolecular interaction.

[0032] Furthermore, an organic semiconductor having a thiol group has a photoactive region, and the thiol group directly bonds to the dangling bond of the inorganic semiconductor, so that the photoactive region and the dissociation region are electrically connected via this bond.

[0033] Therefore, the electrons of the bound excitons generated in the photoactive region are transported from the photoactive region to the dissociation region through a terminal material, such as the compound having the thiol group or the organic semiconductor having the thiol group, so that deterioration of the electron transport properties at these interfaces can be suppressed, enabling even more efficient photoelectric conversion.

[0034] (Organic Semiconductor) As the organic semiconductor, an organic semiconductor having a photoactive region that can absorb light and generate bound excitons can be used, such as P3HT (Poly-3-hexylthiophene), PTB7, PTB7-Th, PffBT4T-2OD, PffBT4T-C9C13, PBDB-T, and DTS(FBTTh2)2.

[0035] (Inorganic semiconductors) As the inorganic semiconductor, an inorganic semiconductor having a dissociation region that dissociates the charge of an exciton and having piezoelectricity can be used, and the inorganic semiconductor is formed from a plurality of materials having different lattice constants.

[0036] When an inorganic semiconductor is formed from multiple materials with different lattice constants, the atomic arrangement becomes disrupted near the interface where the different materials come into contact, generating strain stress. This creates a stable electric field without being influenced by surrounding factors such as solar radiation or temperature, allowing electrons and holes to dissociate.

[0037] In addition, it is preferable to use materials having similar compositions when combining multiple types of materials. When the materials have similar compositions, an inorganic semiconductor layer having a structure in which multiple types of materials are stacked can be formed, and the direction of the electric field caused by strain can be aligned.

[0038] In addition, the inorganic semiconductor preferably has a higher dielectric constant than the organic semiconductor. If an inorganic semiconductor has a high dielectric constant and is easily polarized, the inorganic semiconductor itself will become polarized, thereby reducing the binding force acting between the electron and hole of the bound exciton. This makes it easier for electrons that have migrated from the photoactive region to move away from the interface, thereby enabling efficient dissociation of the electron and hole of the bound exciton.

[0039] Combinations of such inorganic semiconductors include AlN / AlGaN, AlGaN / GaN, GaN / InGaN, InGaN / InN, AlAs / AlGaAs, AlGaAs / GaAs, GaAs / InGaAs, InGaAs / InAs, AlP / AlGaP, AlGaP / GaP, GaP / GaAsP, GaAsP / GaAs, AlP / AlAsP, AlAsP / AlAs, AlAs / InAlAs, InAlAs / InAs, GaAs / GaAsSb, GaAsSb / GaSb, AlSb / AlGaSb, AlGaSb / GaSb, AlSb / AlInSb, AlInSb / InSb, MgS / MgZnS, MgZnS / ZnS, and MgS / MgSS. Examples of the suitable ZnSe / CuAlS2 / CuAlSSe, CuAlSSe / CuAlSe2, CuAlS2 / CuGaAlS2, CuGaAlS2 / CuGaAlS2, CuGaS2 / CuGaSSe, CuGaSSe / CuGaSe2, CuGaS2 / CuInGaS2, CuInGaS2 / CuInS2, CuInS2 / CuInSSe, CuInSSe / CuInSe2, CuGaSe2 / CuInGaSe2, CuInGaSe2 / CuInSe2, MgSe / MgZnSeTe, and MgZnSeTe / ZnTe can be mentioned.

[0040] The inorganic semiconductor layer containing the inorganic semiconductor preferably has irregularities on the interface side in contact with the organic semiconductor layer. By having irregularities on the interface with the organic semiconductor layer, the contact area with the organic semiconductor layer is increased, enabling highly efficient photoelectric conversion.

[0041] (electrode) The electrode is not particularly limited as long as it can transmit light to the organic semiconductor layer side, but a transparent electrode such as an ITO film is preferably used because light can reach the organic semiconductor even if it is formed on the entire surface of the organic semiconductor. EXAMPLES

[0042] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0043] [Example 1] The surface of one side of an AlGaN / GaN inorganic semiconductor substrate, on which AlGaN had grown uniformly on the GaN surface, was etched in a lattice pattern to form columnar protrusions 1 μm high and 1 × 1 μm square at 1 μm intervals, forming an inorganic semiconductor layer with an uneven surface. The native oxide film on the surface was removed with a hydrogen fluoride (HF) solution, and the inorganic semiconductor layer was obtained by rinsing with water.

[0044] A termination material coating liquid was prepared by dissolving 4-methylthiophenol in a mixed solvent of ethanol and ammonium hydroxide. The inorganic semiconductor layer was then immersed in this termination material coating liquid for 10 hours and then washed with ethanol to form a monomolecular film of 4-methylthiophenol on the surface of the inorganic semiconductor layer.

[0045] When the surface of this inorganic semiconductor layer was analyzed by XPS, it was confirmed that S-Ga bonds were formed and that the dangling bonds of the inorganic semiconductor were bonded to 4-methylthiophenol.

[0046] Next, an ITO (Indium Tin Oxide) film was formed on the other surface of the inorganic semiconductor layer by sputtering and annealed in a temperature range of 150 to 250° C. to form an electrode on the inorganic semiconductor layer.

[0047] Poly(3-hexylthiol thiophene) (brand: Poly(3-hexylthiophene-2,5-diyl), regioregular Electronic grade, product number: 4002-EE, company name: RIEKE METALS) was dissolved in a mixed solvent of ethanol and ammonium hydroxide to prepare an organic semiconductor layer coating liquid.

[0048] The organic semiconductor layer coating liquid was applied by spin coating to one side of the inorganic semiconductor layer having a surface irregularity, and annealed at 150°C to laminate the organic semiconductor layer on the inorganic semiconductor layer to form a power generation layer.

[0049] An ITO (Indium Tin Oxide) film was formed on the organic semiconductor layer by sputtering and annealed at a temperature range of 150 to 250° C. to form electrodes on the organic semiconductor layer, thereby obtaining a photoelectric conversion element having the structure shown in FIG.

[0050] [Example 2] A photoelectric conversion element was obtained in the same manner as in Example 1, except that the terminating material was changed from 4-methylthiophenol to Poly(3-hexylthiol thiophene). When the surface of the inorganic semiconductor layer was analyzed by XPS, it was confirmed that S-Ga bonds were formed and that the dangling bonds of the inorganic semiconductor were bonded to Poly(3-hexylthiol thiophene).

[0051] In the photoelectric conversion element of the present invention, since a terminating material is bonded to the dunking bonds on the surface of the inorganic semiconductor layer, it is possible to suppress voltage loss resulting from surface defects in the inorganic semiconductor layer and to suppress deterioration of the electron transport properties at the interface between the organic semiconductor and the inorganic semiconductor. [Explanation of symbols]

[0052] 1 Photoelectric conversion element 2. Power generation layer 3. Organic semiconductor layer 31 Photoactive region 4. Inorganic semiconductor layer 41 Dissociation region 5 Interface 6 Bound excitons 7 electron 8 holes 9 electrodes

Claims

1. A pair of electrodes; a power generation layer in which an organic semiconductor layer and an inorganic semiconductor layer are laminated, A photoelectric conversion element in which the power generation layer is sandwiched between the pair of electrodes, the organic semiconductor layer comprises an organic semiconductor having a photoactive region that generates excitons; the inorganic semiconductor layer is formed of a plurality of materials having different lattice constants, and contains an inorganic semiconductor having a dissociation region in which the charge of the exciton is dissociated by an electric field generated by distortion of the lattice; The energy level relationship between the organic semiconductor in the photoactive region and the inorganic semiconductor in the dissociation region satisfies the following formulas (1) and (2): A photoelectric conversion element characterized in that, at the surface terminal end of the inorganic semiconductor layer, the inorganic semiconductor is bonded to a terminal material having charge transport properties via its dangling bond, and the terminal material and the organic semiconductor are electrically connected via intermolecular interactions. E ＬＵＭＯ > E Ｃ ...Formula (1) E ＨＯＭＯ > E Ｖ ...Formula (2) However, in formula (1) and formula (2), E ＬＵＭＯ represents the energy level of the lowest unoccupied molecular orbital of an organic semiconductor, E ＨＯＭＯ represents the energy level of the highest occupied molecular orbital of an organic semiconductor, E Ｃ represents the energy level at the bottom of the conduction band of an inorganic semiconductor, E Ｖ represents the energy level at the top of the valence band of an inorganic semiconductor.

2. A photoelectric conversion element as described in claim 1, characterized in that the terminal material has a π-electron conjugated system in its molecular structure.

3. A photoelectric conversion element as described in claim 1 or 2, characterized in that the molecular structure of the terminal material has a moiety in which a thiol moiety and an aromatic compound moiety are directly bonded.

4. The photoelectric conversion element described in claim 1, characterized in that the terminal material is an organic semiconductor having a portion having a photoactive region and a terminal portion that bonds to a dangling bond of the inorganic semiconductor.

5. A photoelectric conversion element described in any one of claims 1 to 4, characterized in that electrons of the excitons generated in the organic semiconductor layer are transported to the inorganic semiconductor layer through the terminating material.

6. The inorganic semiconductor may be AlN / AlGaN, AlGaN / GaN, GaN / InGaN, InGaN / InN, AlAs / AlGaAs, AlGaAs / GaAs, GaAs / InGaAs, I nGaAs / InAs, AlP / AlGaP, AlGaP / GaP, GaP / GaAsP, GaAsP / GaAs, AlP / AlAsP, AlAsP / AlAs, AlAs / InAlAs, In AlAs / InAs, GaAs / GaAsSb, GaAsSb / GaSb, AlSb / AlGaSb, AlGaSb / GaSb, AlSb / AlInSb, AlInSb / InSb, MgS / MgZnS, MgZnS / ZnS, MgS / MgSSe, MgSSe / MgSe, ZnS / ZnSSe, ZnSSe / ZnSe, MgSe / MgZnSe, MgZnSe / ZnSe, CuAlS 2 / CuAlSSe, CuAlSSe / CuAlSe 2 , CuAlS 2 / CuGaAlS 2 , CuGaAlS 2 / CuGaAlS 2 , CuGaS 2 / CuGaSSe, CuGaSSe / CuGaSe 2 , CuGaS 2 / CuInGaS 2 , CuInGaS 2 / CuInS 2 , CuInS 2 / CuInSSe, CuInSSe / CuInSe 2 , CuGaSe 2 / CuInGaSe 2 , CuInGaSe 2 / CuInSe 2 6. The photoelectric conversion element according to claim 1, which is at least one combination selected from the group consisting of MgSe / MgZnSeTe, and MgZnSeTe / ZnTe.

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