Organic Photovoltaic Device Including an Ionic Liquid Interfacial Layer and Method for Manufacturing the Same

Abstract

The present invention relates to an organic photovoltaic device comprising an ionic liquid interface layer and a method for manufacturing the same. The organic photovoltaic device of the present invention may comprise a bottom electrode, an electron transport layer comprising zinc oxide (ZnO), an imidazolium-based ionic liquid interface layer, a photoactive layer, a hole transport layer, and a top electrode. The imidazolium-based ionic liquid interface layer can passivate surface defects of the electron transport layer and form an interface dipole to improve energy level alignment. Accordingly, charge recombination can be suppressed and charge extraction efficiency improved, and the photoelectric conversion efficiency and long-term stability of the organic photovoltaic device can be improved.

Description

Technology Field

[0001] The present invention relates to an organic photovoltaic device, and more specifically, to an inverted organic solar cell with improved photovoltaic conversion efficiency and stability by improving the interface characteristics of an electron transport layer (ETL), and a method for manufacturing the same. Background Technology

[0002] Organic solar cells (OSCs) are attracting attention as next-generation photovoltaic devices due to their advantages, such as low-cost manufacturing using solution processes, lightweight properties, flexibility, and the ability to be scaled up to large areas.

[0003] In particular, power conversion efficiency (PCE) has been significantly improved recently with the development of non-fullerene acceptors (NFAs), and inverted organic solar cells based on this are being widely studied as a structure capable of simultaneously achieving excellent device stability and high efficiency.

[0004] In general, in inverted organic solar cells, the electron transport layer (ETL) formed on the indium tin oxide (ITO) electrode significantly influences charge extraction characteristics and device stability. Zinc oxide (ZnO) is widely used as the electron transport layer due to its high electron mobility, excellent light transmittance, and compatibility with solution processes.

[0005] However, ZnO contains surface defects such as oxygen vacancies and interstitial zinc, which can act as charge traps, leading to increased charge recombination and reduced charge extraction efficiency. Additionally, since ZnO has photocatalytic properties, contact with a photoactive layer containing non-fullerene acceptors can cause photodegradation of the photoactive layer under prolonged light irradiation conditions, thereby reducing the long-term stability of the device.

[0006] To address these issues, various techniques have been proposed to modify the surface of the electron transport layer or introduce an interlayer; however, there is a continuously increasing demand for effective interface control technologies capable of simultaneously improving charge extraction characteristics and long-term stability.

[0007] Therefore, there is a need to develop a new interface modification technology that can effectively control the interface characteristics between the electron transport layer and the photoactive layer to suppress charge recombination and simultaneously improve charge extraction efficiency and long-term operational stability. Prior art literature

[0008] Korean Patent Publication No. 10-2146610 (Published Aug. 21, 2020) The problem to be solved

[0009] The present invention aims to provide an organic optoelectronic device capable of improving the interface characteristics between an electron transport layer and a photoactive layer.

[0010] In addition, the present invention aims to provide an organic optoelectronic device capable of suppressing charge recombination and improving charge extraction efficiency by effectively passivating surface defects of an electron transport layer containing zinc oxide (ZnO).

[0011] In addition, the present invention aims to provide an organic optoelectronic device capable of improving photoelectric conversion efficiency by improving energy level alignment between the electron transport layer and the photoactive layer and inducing the formation of an ohmic contact.

[0012] In addition, the present invention aims to provide an organic optoelectronic device capable of improving long-term operational stability by suppressing photodegradation of the photoactive layer caused by the photocatalytic activity of the electron transport layer.

[0013] In addition, the present invention aims to provide an organic optoelectronic device applicable to various photoactive layer systems containing non-fullerene acceptors, exhibiting excellent photoelectric conversion efficiency and stability.

[0014] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0015] In order to solve the above problem, according to one aspect of the present invention,

[0016] Lower electrode;

[0017] An electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode above;

[0018] An imidazolium-based ionic liquid interface layer formed on the electron transport layer above;

[0019] A photoactive layer formed on the above ionic liquid interface layer;

[0020] A hole transport layer formed on the above photoactive layer; and

[0021] Characterized by including an upper electrode formed on the hole transport layer above.

[0022] An organic photovoltaic device comprising an ionic liquid interface layer is provided.

[0023] In one embodiment of the present invention, the lower electrode is characterized by comprising indium tin oxide (ITO).

[0024] In one embodiment of the present invention, the lower electrode is formed on a substrate, and the substrate is characterized by comprising one or more materials selected from the group consisting of glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), and polycarbonate (PC).

[0025] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by comprising a compound of the following chemical formula 1:

[0026] [Chemical Formula 1]

[0027]

[0028] In the above formula,

[0029] R is C1 to C 10 It is an alkoxy group or a hydroxyl group of

[0030] R1 is C1 to C 10 It is an alkyl group of, and

[0031] X - is a halide anion, and

[0032] n is an integer from 1 to 6.

[0033] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by comprising 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the following formula 2:

[0034] [Chemical Formula 2]

[0035]

[0036] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by forming an interface dipole to improve energy level alignment between the electron transport layer and the photoactive layer.

[0037] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by passivating surface defects of the electron transport layer to suppress charge recombination.

[0038] In one embodiment of the present invention, the surface defect is characterized by comprising at least one of oxygen vacancies and interstitial zinc.

[0039] In one embodiment of the present invention, the photoactive layer is characterized by comprising a non-fullerene acceptor.

[0040] In one embodiment of the present invention, the non-fullerene receptor is characterized by being one or more selected from the group consisting of Y6, Y6-BO, Y6-HU, ITIC, IT-4F, IDTBR, IDIC, IEICO, N3, N2200, L8-BO, and BTP-eC9.

[0041] In one embodiment of the present invention, the hole transport layer is molybdenum oxide (MoO₂). x ), vanadium oxide (V2O5), tungsten oxide (WO3), nickel oxide (NiO x It is characterized by including ), PEDOT, PTAA, Spiro-OMeTAD, or a combination thereof.

[0042] In one embodiment of the present invention, the upper electrode is characterized by comprising one or more selected from the group consisting of Ag, Au, Al, and Cu.

[0043] In one embodiment of the present invention, the organic photovoltaic device is characterized as being an inverted structure organic solar cell.

[0044] In one embodiment of the present invention, the organic photovoltaic device is characterized by maintaining at least 70% of the initial photovoltaic conversion efficiency after 1,000 hours of continuous light irradiation.

[0045] In addition, according to another aspect of the present invention,

[0046] Lower electrode;

[0047] An electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode above; and

[0048] An imidazolium-based ionic liquid interface layer formed on the electron transport layer above;

[0049] Characterized by including,

[0050] An electron transport structure comprising an ionic liquid interface layer is provided.

[0051] In one embodiment of the present invention, the lower electrode is characterized by comprising indium tin oxide (ITO).

[0052] In one embodiment of the present invention, the lower electrode is formed on a substrate, and the substrate is characterized by comprising one or more materials selected from the group consisting of glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), and polycarbonate (PC).

[0053] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by comprising a compound of Formula 1.

[0054] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer is characterized by comprising 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of Formula 2.

[0055] In addition, according to another aspect of the present invention,

[0056] A step of forming an electron transport layer containing zinc oxide (ZnO) on a lower electrode;

[0057] A step of forming an imidazolium-based ionic liquid interface layer on the electron transport layer;

[0058] A step of forming a photoactive layer on the ionic liquid interface layer; and

[0059] A step of forming a hole transport layer and an upper electrode on the above photoactive layer;

[0060] Characterized by including,

[0061] A method for manufacturing an organic photovoltaic device comprising an ionic liquid interface layer is provided.

[0062] In one embodiment of the present invention, the ionic liquid interface layer is characterized by being formed by spin-coating an ionic liquid solution.

[0063] In one embodiment of the present invention, the ionic liquid is characterized by comprising a compound of Formula 1.

[0064] In one embodiment of the present invention, the ionic liquid is characterized by comprising 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the formula 2.

[0065] In one embodiment of the present invention, the method is further characterized by including a step of heat treating at 50 to 150 ℃ after forming the ionic liquid interface layer.

[0066] In addition, according to another aspect of the present invention,

[0067] An organic solar cell comprising the above electron transport structure is provided. Effects of the invention

[0068] According to the present invention, the surface characteristics and interface characteristics of the electron transport layer can be effectively controlled by forming an imidazolium-based ionic liquid interface layer between the electron transport layer and the photoactive layer.

[0069] In addition, according to the present invention, an interfacial dipole is formed by an imidazolium-based ionic liquid interface layer, which can improve the alignment of energy levels between the electron transport layer and the photoactive layer, and accordingly, the charge extraction efficiency and photoelectric conversion efficiency can be improved.

[0070] In addition, according to the present invention, the imidazolium-based ionic liquid interface layer can suppress charge recombination caused by charge traps by passivating surface defects of the electron transport layer, thereby improving the electrical characteristics of the device.

[0071] In addition, according to the present invention, the imidazolium-based ionic liquid interface layer acts as a protective layer between the electron transport layer and the photoactive layer to suppress photodegradation of the photoactive layer, thereby improving the long-term operational stability of the organic optoelectronic device.

[0072] In addition, according to the present invention, it is applicable to various photoactive layer systems containing non-fullerene receptors and can realize excellent photoelectric conversion efficiency and stability, so it can be usefully utilized in various organic optoelectronic device fields.

[0073] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0074] FIG. 1 is a diagram showing the schematic structure of an organic photovoltaic device including an ionic liquid interface layer according to the present invention. FIG. 2 is a diagram showing the structure of an inverted organic solar cell according to one embodiment of the present invention, the chemical structure of MTMI-Cl, XPS analysis results, UPS analysis results, and optical characteristics. FIG. 3 is a diagram showing the results of an evaluation of the electrical characteristics of an organic solar cell including a ZnO / MTMI-Cl interface layer according to one embodiment of the present invention. FIG. 4 is a diagram showing the change in device stability and the photodegradation characteristics of the photoactive layer according to the light irradiation time of an organic solar cell according to one embodiment of the present invention. FIG. 5 is an AFM image showing the surface morphology and surface characteristics after photodegradation of ZnO and ZnO / MTMI-Cl structures according to one embodiment of the present invention. FIG. 6 is a diagram showing the results of evaluating photoelectric properties and long-term stability in various non-fullerene receptor systems according to one embodiment of the present invention. Specific details for implementing the invention

[0075] Preferred embodiments according to the present invention will be described in detail below with reference to the attached drawings.

[0076] The advantages and features of the present invention and the method for achieving them will become clear by referring to the embodiments described in detail below together with the accompanying drawings.

[0077] However, the present invention is not limited by the embodiments disclosed below but may be implemented in various different forms, and these embodiments are provided merely to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0078] In addition, in describing the present invention, if it is determined that related known technologies, etc., may obscure the essence of the present invention, a detailed explanation thereof will be omitted.

[0079] The present invention will be described in detail below.

[0080] The present invention relates to an organic photovoltaic device comprising an ionic liquid interface layer, and,

[0081] Lower electrode;

[0082] An electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode above;

[0083] An imidazolium-based ionic liquid interface layer formed on the electron transport layer above;

[0084] A photoactive layer formed on the above ionic liquid interface layer;

[0085] A hole transport layer formed on the above photoactive layer; and

[0086] It is characterized by including an upper electrode formed on the hole transport layer above.

[0087] FIG. 1 is a diagram showing the schematic structure of an organic photovoltaic device (100) including an ionic liquid interface layer according to the present invention.

[0088] Referring to FIG. 1, an organic photovoltaic device (100) according to the present invention may include a lower electrode (10), an electron transport layer (20), an ionic liquid interface layer (30), a photoactive layer (40), a hole transport layer (50), and an upper electrode (60).

[0089] Below, each component is described in detail.

[0090] lower electrode (10)

[0091] The lower electrode above can function as an electrode for collecting electrons and may include, for example, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), or a combination thereof.

[0092] The lower electrode may be formed on a substrate. The substrate may include glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polycarbonate (PC), or a combination thereof.

[0093] Electron transport layer (20)

[0094] The electron transport layer can selectively collect electrons generated in the photoactive layer and transfer them to the bottom electrode, and can reduce charge recombination by suppressing the movement of holes. In addition, the electron transport layer can improve charge extraction efficiency by improving energy level alignment between the photoactive layer and the bottom electrode.

[0095] The electron transport layer may include a metal oxide, an organic semiconductor material, or a combination thereof, and may include, for example, zinc oxide (ZnO), titanium dioxide (TiO2), tin oxide (SnO2), indium oxide (In2O3), tungsten oxide (WO3), or a combination thereof.

[0096] In one embodiment of the present invention, the electron transport layer may comprise zinc oxide (ZnO). Since zinc oxide has excellent electron mobility, high light transmittance, and solution process suitability, it can be advantageously used as an electron transport layer for inverted organic solar cells. In addition, the zinc oxide may contain surface defects such as oxygen vacancies and interstitial zinc, and the imidazolium-based ionic liquid interface layer described below may passivate said surface defects to suppress charge recombination.

[0097] ionic liquid interface layer (30)

[0098] The above ionic liquid interface layer may be formed between the electron transport layer and the photoactive layer. The above ionic liquid interface layer may be formed as an independent layer distinct from the electron transport layer, and may be coated or laminated on the electron transport layer to modify the surface characteristics of the electron transport layer and the interface characteristics between the electron transport layer and the photoactive layer.

[0099] In addition, the ionic liquid interface layer can function as an interlayer that modifies the surface of the electron transport layer. Accordingly, the ionic liquid interface layer can improve charge extraction efficiency and device stability by controlling the interface characteristics between the electron transport layer and the photoactive layer.

[0100] The above ionic liquid interface layer can form an interfacial dipole to improve energy level alignment between the electron transport layer and the photoactive layer, and can improve charge extraction efficiency.

[0101] In addition, the ionic liquid interface layer can suppress charge recombination by passivating surface defects of the electron transport layer. In one embodiment, the surface defects may include oxygen vacancies, interstitial zinc, or a combination thereof.

[0102] In one embodiment of the present invention, the ionic liquid interface layer may include an imidazolium-based compound of the following chemical formula 1.

[0103] [Chemical Formula 1]

[0104]

[0105] In the above formula,

[0106] R is C1 to C 10 It is an alkoxy group or a hydroxyl group of

[0107] R1 is C1 to C 10 It is an alkyl group of, and

[0108] X - is a halide anion, and

[0109] n is an integer from 1 to 6.

[0110] The above imidazolium-based compound can provide excellent ionic conductivity and interfacial dipole formation ability through imidazolium cations, and can improve bonding strength with the surface of the electron transport layer through substituents containing silyl groups or hydroxyl groups. In addition, the above imidazolium-based compound can effectively passivate surface defects of the electron transport layer to reduce charge recombination and improve charge extraction characteristics.

[0111] In particular, the silane group of the imidazolium-based compound can induce passivation of the surface defects by forming a Zn-O bond with zinc oxide (ZnO) contained in the electron transport layer. Additionally, the imidazolium cation can form an interfacial dipole to improve energy level alignment between the electron transport layer and the photoactive layer.

[0112] In one embodiment of the present invention, the ionic liquid interface layer may comprise 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the following formula 2.

[0113] [Chemical Formula 2]

[0114]

[0115] Photoactive layer (40)

[0116] The above photoactive layer may be a layer that absorbs light incident from the outside to generate excitons, and separates the generated excitons into charges to generate electrons and holes. Additionally, the above photoactive layer may transfer the generated electrons to an electron transport layer and transfer the holes to a hole transport layer.

[0117] The above photoactive layer may include a non-fullerene acceptor as a donor material and an acceptor material. The donor material can transfer electrons generated by light absorption to the non-fullerene acceptor, and the non-fullerene acceptor can accept the electrons to induce charge separation.

[0118] The above donor material is not particularly limited and may include, for example, PM6, PM7, PTB7, PTB7-Th, PBDB-T, PBDB-TF, P3HT, D18, J71, J52, PffBT4T-2OD, PCDTBT, or a combination thereof, but it is preferable to use PM6.

[0119] The above-mentioned non-fullerene receptor can provide excellent light absorption characteristics, energy level regulation characteristics, and charge transport characteristics, and may include, for example, Y6, Y6-BO, Y6-HU, ITIC, IT-4F, IDTBR, IDIC, IEICO, N3, N2200, L8-BO, BTP-eC9, or a combination thereof.

[0120] In one embodiment of the present invention, the photoactive layer may include PM6:Y6-BO or PM6:Y6-HU.

[0121] The transport layer (50)

[0122] The hole transport layer described above can selectively collect holes generated in the photoactive layer and transfer them to the upper electrode. Additionally, the hole transport layer can suppress the movement of electrons to reduce charge recombination and improve energy level alignment between the photoactive layer and the upper electrode.

[0123] The hole transport layer may comprise a metal oxide, an organic semiconductor material, or a combination thereof, for example, molybdenum oxide (MoO₂). x ), vanadium oxide (V2O5), tungsten oxide (WO3), nickel oxide (NiO x It may include ), PEDOT, PTAA, Spiro-OMeTAD, or a combination thereof.

[0124] In one embodiment of the present invention, the hole transport layer is molybdenum oxide (MoO₂). x It may include ). The molybdenum oxide can effectively collect holes from the photoactive layer and transfer them to the top electrode, and can improve energy level alignment with the photoactive layer through a high work function.

[0125] upper electrode (60)

[0126] The upper electrode described above can perform the function of collecting holes delivered from the hole transport layer and delivering them to an external circuit. In addition, the upper electrode can contribute to improving the electrical characteristics and photoelectric conversion efficiency of the organic optoelectronic device by efficiently collecting charges generated in the photoactive layer.

[0127] The upper electrode may include a metal or a metal alloy, for example, Ag, Au, Al, Cu, or a combination thereof.

[0128] In one embodiment of the present invention, the upper electrode may include Ag. The Ag electrode has excellent electrical conductivity and can provide good electrical contact characteristics with the hole transport layer.

[0129] In one embodiment of the present invention, the organic photovoltaic device (100) may be an inverted organic solar cell.

[0130] The above-described inverted organic solar cell may have a structure in which an electron transport layer is disposed on the lower electrode side and a hole transport layer is disposed on the upper electrode side. This inverted structure can provide superior device stability compared to a conventional organic solar cell and may be advantageous for improving charge collection efficiency.

[0131] In one embodiment of the present invention, the inverted organic solar cell may include a stacked structure of a substrate / bottom electrode / electron transport layer / ionic liquid interface layer / photoactive layer / hole transport layer / top electrode.

[0132] In addition, the imidazolium-based ionic liquid interface layer of the present invention is formed between the electron transport layer and the photoactive layer to improve interface characteristics and enhance charge extraction efficiency and long-term stability.

[0133] In addition, the present invention relates to an electron transport structure comprising an ionic liquid interface layer, wherein

[0134] Lower electrode;

[0135] An electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode above; and

[0136] An imidazolium-based ionic liquid interface layer formed on the electron transport layer above;

[0137] It is characterized by including

[0138] The above electron transport structure can be applied to the electron transport layer portion of an organic optoelectronic device and can improve the interface characteristics between the electron transport layer and the photoactive layer.

[0139] In addition, the imidazolium-based ionic liquid interface layer can reduce charge recombination and improve charge extraction efficiency by passivating surface defects of the electron transport layer and forming an interface dipole.

[0140] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer may be formed on the electron transport layer and may improve energy level alignment at the interface with the photoactive layer subsequently formed.

[0141] In addition, the present invention relates to a method for manufacturing an organic photovoltaic device comprising an ionic liquid interface layer, wherein

[0142] A step of forming an electron transport layer containing zinc oxide (ZnO) on a lower electrode;

[0143] A step of forming an imidazolium-based ionic liquid interface layer on the electron transport layer;

[0144] A step of forming a photoactive layer on the ionic liquid interface layer; and

[0145] A step of forming a hole transport layer and an upper electrode on the above photoactive layer;

[0146] It is characterized by including

[0147] The imidazolium-based ionic liquid interface layer described above is formed on the electron transport layer to passivate surface defects of the electron transport layer and improve interfacial characteristics between the electron transport layer and the photoactive layer. In addition, the imidazolium-based ionic liquid interface layer can improve charge extraction efficiency and device stability by forming an interfacial dipole to improve energy level alignment.

[0148] In one embodiment of the present invention, the imidazolium-based ionic liquid interface layer may be introduced after the formation of the electron transport layer and before the formation of the photoactive layer. The ionic liquid interface layer may be formed as an ultrathin layer on the surface of the electron transport layer and can control the interface characteristics between the electron transport layer and the photoactive layer.

[0149] Additionally, the ionic liquid interface layer can be formed through a solution process, specifically by spin-coating an ionic liquid solution. The ionic liquid solution may include methanol, ethanol, or a mixed solvent thereof.

[0150] In addition, the method may further include a step of heat treating at 50 to 150 ℃ after forming the ionic liquid interface layer. The heat treatment can contribute to the stable formation of the ionic liquid interface layer and the improvement of the bonding strength with the electron transport layer.

[0151] In addition, the present invention relates to an organic solar cell comprising the electron transport structure.

[0152] The above organic solar cell may further include the photoactive layer, hole transport layer, top electrode, etc. described above.

[0153] The above organic solar cell may be an inverted structure organic solar cell.

[0154] The present invention will be explained in more detail below through examples. However, the following examples are intended to explain the invention more specifically and do not limit the scope of the invention. The following examples may be appropriately modified or changed by those skilled in the art within the scope of the invention.

[0155] <Example>

[0156] 1. Fabrication of Inverted Structure Organic Solar Cells

[0157] A ZnO electron transport layer (ETL) was prepared using a conventional sol-gel method. Subsequently, to further control optical and electrical properties, an ultrathin layer of MTMI-Cl was spin-coated onto the ZnO surface using methanol as a solvent, thereby fabricating an inverted organic solar cell (inverted OSC) structure (Fig. 2a).

[0158] Specifically, a patterned indium tin oxide (ITO) coated glass substrate was ultrasonically cleaned for 15 minutes each using detergent, deionized water, acetone, and isopropanol (IPA). After drying the substrate, UV-ozone treatment was performed for 20 minutes to improve surface wettability and remove organic residues. Next, a ZnO precursor solution was spin-coated onto the ITO substrate to form a ZnO electron transport layer, and the substrate was heat-treated at 200 °C for 30 minutes in an air atmosphere. Subsequently, an ionic liquid solution of MTMI-Cl dissolved in methanol was spin-coated onto the ZnO electron transport layer to form an ionic liquid interface layer, and the substrate was heat-treated at 110 °C for 10 minutes. The substrate with the ionic liquid interface layer formed thereon was then moved to a glove box under a nitrogen atmosphere, and a photoactive layer was formed. A composition for forming a photoactive layer was prepared by dissolving 5 mg of PM6 and 6 mg of Y6-BO6 in 1 mL of o-xylene, and a photoactive layer was formed by spin coating. Subsequently, MoO2 was applied as a hole transport layer on the photoactive layer. x A was formed, and an Ag electrode was sequentially formed on top of it. The above MoO x Ag and Ag were deposited to thicknesses of 10 nm and 100 nm, respectively, by thermal evaporation under high vacuum conditions after defining the active region using a shadow mask.

[0159] Finally, glass / ITO / ZnO / MTMI-Cl / photoactive layer / MoO x An inverted organic solar cell having a / Ag structure was fabricated. The effective area of ​​the fabricated organic solar cell was 0.09 cm².

[0160] The chemical structures of PM6, the polymer donor used in the present invention, and Y6-BO, the non-fullerene acceptor, are shown in Fig. 2a. Additionally, the chemical structure and dipole moment of MTMI-Cl calculated using density functional theory (DFT) are shown in Fig. 2a. MTMI-Cl exhibited a relatively high dipole moment of 8.23 ​​D, which suggests strong intramolecular charge-transfer characteristics.

[0161] The strong intrinsic dipole moment of MTMI-Cl enables the formation of an interfacial dipole, which can facilitate charge extraction and charge transport at the interface between the electron transport layer and the photoactive layer. Interfacial charge dynamics were investigated by analyzing the electrostatic potential (ESP) distribution obtained from the DFT-optimized structures of PM6, Y6-BO, and MTMI-Cl.

[0162] PM6 exhibited electron-rich surface characteristics, particularly along the π-conjugated backbone, with predominantly negative ESP values. In contrast, Y6-BO exhibited electron-deficient characteristics, with positive ESP regions near the central fused-ring core and terminal unit. This complementary distribution provides an intermolecular electric field formed from the donor (PM6) toward the acceptor (Y6-BO), which facilitates the separation of excitons and directional electron transfer at the donor / acceptor (D / A) interface.

[0163] In addition, MTMI-Cl exhibits strong ESP asymmetry, where electron-rich trimethoxysilyl groups interact with ZnO, while positively charged imidazolium portions are exposed toward the photoactive layer. This dipole structure not only alters the local electric field at the ZnO / photoactive layer interface but also promotes efficient electron extraction and suppresses interfacial recombination, ultimately improving device performance.

[0164] Ultraviolet photoelectron spectroscopy (UPS) was performed to confirm the formation of interfacial dipoles and energy-level alignment at the electron transport layer (PM6 interface). UPS analysis results confirmed that when MTMI-Cl was introduced into the ZnO electron transport layer, the secondary electron cutoff shifted from 17.38 eV to 17.30 eV (Fig. 2c). This shift in the vacuum level suggests that interfacial dipoles were formed by MTMI-Cl.

[0165] Accordingly, the work function (WF) of the reference sample ITO / ZnO substrate was calculated to be 3.92 eV, whereas the introduction of MTMI-Cl showed a significant change in the work function, decreasing to 3.84 eV. This decrease in work function is believed to be mainly due to the formation of interfacial dipoles induced by imidazolium functional groups present within the ionic liquid structure. These dipoles are aligned outward from the ZnO surface, effectively altering interfacial energetics and promoting electron extraction within the device.

[0166] The work function change observed in the ZnO / MTMI-Cl-based electron transport layer helps remove the Schottky barrier and improves energy level alignment with the acceptor material, Y6-BO. This change transitions the cathode / photoactive layer interface from an equilibrium state to an ohmic contact state, reducing voltage loss and suppressing charge accumulation and recombination.

[0167] After the formation of the photoactive layer, a phenomenon was observed in which the absorption spectrum of non-fullerene receptors (NFA) shifted slightly toward the long wavelength direction (red-shift) (Fig. 2d), which suggests that MTMI-Cl affects the molecular aggregation of non-fullerene receptors.

[0168] <Comparative Example>

[0169] 1. Fabrication of inverted organic solar cells without MTMI-Cl introduction

[0170] An inverted structure organic solar cell was manufactured in the same manner as in the above example, except for the step of forming an ionic liquid interface layer.

[0171] Specifically, a ZnO electron transport layer formed on an ITO substrate was heat-treated at 200°C for 30 minutes, and then the substrate was moved to a glove box under a nitrogen atmosphere to form a photoactive layer. Subsequently, MoO on the photoactive layer x and Ag electrodes were formed sequentially.

[0172] Finally, glass / ITO / ZnO / photoactive layer / MoO x An inverted organic solar cell having a / Ag structure was fabricated. The effective area of ​​the fabricated organic solar cell was 0.09 cm².

[0173] <Experimental Example>

[0174] 1. XPS Analysis

[0175] To confirm the mechanism for removing the light-soaking effect and improving device performance in ZnO / MTMI-Cl-based structures, the surface chemical state of ZnO before and after MTMI-Cl modification was analyzed using X-ray photoelectron spectroscopy (XPS).

[0176] In the O 1s spectrum, the low binding energy component corresponds to lattice oxygen, and the high binding energy peak is attributed to defects associated with oxygen vacancies (Fig. 2b). In the present invention, following MTMI-Cl modification, the main lattice oxygen peak shifted from 528.3 eV to 528.1 eV, and the defect-related oxygen peak shifted from 529.7 eV to 529.5 eV, with each shifting by approximately 0.2 eV. Additionally, it was confirmed that the relative area corresponding to oxygen vacancy defects decreased in the ZnO / MTMI-Cl thin film compared to untreated ZnO.

[0177] These results indicate that MTMI-Cl contributes to the elimination of the light-soaking effect by effectively passivating surface trap states containing interstitial Zn and oxygen vacancies.

[0178] 2. Evaluation of Current Density-Voltage (JV) Characteristics

[0179] For PM6-based inverted organic solar cells with and without the introduction of MTMI-Cl on the ZnO electron transport layer, under AM 1.5G light irradiation conditions (100 mW·cm²) - The current density-voltage (JV) characteristics were evaluated in 2) (Fig. 3a).

[0180] The device of the comparative example without MTMI-Cl introduced has an open-circuit voltage (VOC) of 0.82 V and a short-circuit current density (JSC) of 25.55 mA·cm² -It showed a fill factor (FF) of 75.72% and a photoelectric conversion efficiency (PCE) of 15.93%.

[0181] On the other hand, the device of the embodiment comprising a ZnO electron transport layer modified with MTMI-Cl under optimized conditions exhibited a VOC of 0.84 V and a JSC of 26.26 mA·cm². - It showed 2 and FF 78.37%, and the photoelectric conversion efficiency was significantly improved to 17.44% (Table 1).

[0182] Active layer ETL V OC [V] J SC [mA cm -2 ] FF [%] PCE max (PCE avg ) a [%] PM6:Y6-BO ZnO 0.82 25.55 75.72 15.93 (15.74±0.17) a ZnO / MTMI-Cl 0.84 26.26 78.37 17.44 (17.29±0.15) a

[0183] a Average PCEs in bracket are based on over 15 devices.

[0184] These results demonstrate the excellent interfacial engineering properties provided by MTMI-Cl and prove its potential as a general-purpose interlayer for improving OSC performance.

[0185] In addition, as a result of the external quantum efficiency (EQE) spectrum, the device of the example containing the ZnO / MTMI-Cl bilayer exhibited an enhanced photocurrent response across the 400 to 850 nm wavelength range compared to the device of the comparative example (Fig. 3b).

[0186] These enhanced photoresponse characteristics are consistent with the high JSC and EQE integral values ​​observed in the JV results, once again confirming that MTMI-Cl is effective in charge extraction and improving overall photoelectric conversion efficiency.

[0187] To evaluate charge transport characteristics and leakage current behavior with and without MTMI-Cl modification, JV characteristics under dark conditions were compared (Fig. 3c).

[0188] It was confirmed that the device of the example containing a ZnO / MTMI-Cl bilayer exhibited a significant reduction in leakage current under reverse bias conditions and an increase in the rectification ratio. This implies that electron selectivity was improved and charge leakage paths were reduced.

[0189] To understand the recombination mechanism in greater depth, changes in VOCs and JSCs under different photointensity conditions were analyzed (Figs. 3d and 3e).

[0190] In the relationship between VOC and photovoltaic intensity, the slope value n represents the degree of trap-assisted recombination, and a value of 2kTq -1 The closer it is to , the greater the influence of the trap. Here, k represents the Boltzmann constant, T represents the absolute temperature, and q represents the elementary charge.

[0191] In the case of the ZnO device of the comparative example, the value of n is 1.18 kTq -1 However, in the case of the MTMI-Cl modified device, 1.06kTq -1 It was confirmed that trap-assisted recombination was inhibited as it decreased.

[0192] In addition, the slope α value in the relationship between JSC and light intensity indicates the degree of bimolecular recombination, and a value closer to 1 means less loss.

[0193] The α value of the ZnO device in the comparative example was 0.97, but in the case of the MTMI-Cl modified device in the example, it was close to 0.99, confirming that bimolecular recombination was also effectively suppressed by interface modification.

[0194] These results clearly demonstrate that both trap-assisted recombination and bimolecular recombination are effectively reduced by introducing an MTMI-Cl layer onto the ZnO surface. Enhanced charge selectivity and reduced interfacial recombination loss contribute significantly to the improvement of charge extraction efficiency and overall device performance in PM6-based OSCs.

[0195] 3. Evaluation of Charge Extraction Efficiency

[0196] To analyze the charge extraction efficiency in more detail, the photocurrent density (Jph) was analyzed according to the effective voltage (Veff) (Fig. 3f).

[0197] In the high Veff region where charge collection is assumed to be complete, the charge collection probability Pdiss was calculated using the saturation current density (Jsat) with the relationship Pdiss = Jph / Jsat.

[0198] Under short-circuit conditions, Pdiss increased from 96.5% of the comparative example device to 98.5% of the example MTMI-Cl modified device. This means that the charge carrier extraction behavior was improved by the introduction of MTMI-Cl, which consequently leads to improved JSC and FF characteristics.

[0199] To analyze charge extraction behavior and recombination characteristics, transient photovoltage (TPV) and transient photocurrent (TPC) measurements were performed (Figs. 3g and 3h).

[0200] The device including the ZnO / MTMI-Cl interface layer of the example exhibited a longer carrier lifetime of 3.06 μs compared to 2.18 μs of the device of the comparative example, which means that charge recombination was reduced.

[0201] In addition, the device of the example exhibited a shorter charge extraction time of 0.64 μs compared to 0.72 μs of the device of the comparative example.

[0202] These results show that MTMI-Cl modification not only improves charge extraction efficiency but also effectively suppresses recombination loss, which is consistent with the results of JSC and FF improvement.

[0203] 4. Long-term operational stability evaluation

[0204] Long-term operational stability is a critical factor that directly affects the industrial and practical applicability of organic solar cells (OSCs), and it is particularly important under full-spectrum light irradiation conditions.

[0205] To evaluate this, the photostability of glass-to-glass encapsulated organic solar cells was evaluated for 1,000 hours under continuous 1 Sun light irradiation conditions in a weathering chamber maintained at 45°C and 65% relative humidity.

[0206] As a result, the organic solar cell containing ZnO / MTMI-Cl exhibited significantly superior photostability compared to the organic solar cell containing only ZnO (Figs. 4a to 4d).

[0207] For example, ZnO / MTMI-Cl-based organic solar cells maintained about 77% of their initial photovoltaic conversion efficiency (PCE), whereas ZnO-based organic solar cells experienced significant performance degradation and were found to maintain only about 58% of their initial performance.

[0208] 5. Evaluation of Photo-Induced Morphological Degradation

[0209] To investigate the effect of photo-induced morphological degradation occurring in the electron transport layer (ETL) on the photoelectric properties of organic solar cells, atomic force microscopy (AFM) analysis was performed (Fig. 5).

[0210] AFM image analysis revealed that the surface morphology of the ZnO thin film and the ZnO / MTMI-Cl thin film were different, with root-mean-square roughness (Rq) values ​​of 1.03 nm and 1.19 nm, respectively. These results suggest that the Rq value is influenced by the MTMI-Cl coating layer.

[0211] After the photodegradation test, changes in surface morphology were observed in the unmodified ZnO thin film, and the Rq value increased to 1.11 nm after light soaking. This implies that photo-induced chemical reactions contribute to morphological degradation.

[0212] On the other hand, the ZnO / MTMI-Cl coated thin film maintained a stable surface morphology even under light stress conditions. Specifically, in the case of the ZnO / MTMI-Cl structure, the Rq value decreased from 1.19 nm to 1.09 nm.

[0213] These results suggest that the MTMI-Cl layer forms a robust protective network, effectively protecting the electron transport layer from morphological degradation.

[0214] Enhanced stability under such light stress is considered to be one of the main reasons why inverted organic solar cells containing a modified interface structure exhibit excellent operational durability.

[0215] 6. Evaluation of Universality for Various Photoactive Layer Systems

[0216] To evaluate whether the MTMI-Cl electron transport layer (ETL) is applicable to various photoactive layer systems, Y6-HU, a non-fullerene acceptor (NFA), was used instead of Y6-BO (Figs. 6a, 6b and Table 2).

[0217] Active layer ETL V OC [V] J SC [mA cm -2 ] FF [%] PCE max (PCE avg ) a [%] PM6:Y6-HU ZnO 0.85 26.20 78.81 17.73 (17.58±0.14) a ZnO / MTMI-Cl 0.86 27.15 79.36 18.74 (18.62±0.12) a

[0218] As a result, the optimized organic solar cell containing an electron transport structure including an MTMI-Cl interface layer consistently exhibited superior performance compared to devices using pristine ZnO, achieving a maximum photoelectric conversion efficiency (PCE) of 18.74%. In all cases, the short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) all showed an improving trend.

[0219] Figure 6c shows the external quantum efficiency (EQE) spectrum and the corresponding integrated JSC value. The integrated JSC value was in very good agreement with the JSC value obtained from the JV measurement, and the difference was only about 5%.

[0220] In particular, PM6-based organic solar cells with MTMI-Cl applied stably exhibited high EQE values ​​across a wide wavelength range, which demonstrates that MTMI-Cl effectively contributes to the performance improvement of inverted organic solar cells.

[0221] In addition, the effect of MTMI-Cl on the long-term operational stability of the organic solar cell produced after operating for 1,000 hours under continuous 1 Sun light irradiation conditions was evaluated (Fig. 6d).

[0222] As a result, the device containing the electron transport layer modified with MTMI-Cl maintained 71.2% of the initial photoelectric conversion efficiency (PCE), exhibiting significantly improved stability.

[0223] On the other hand, devices using untreated ZnO showed significant performance degradation and were found to maintain only 43.7% of their initial photoelectric conversion efficiency.

[0224] The above results clearly show that the MTMI-Cl interlayer plays an important role in improving both the photoelectric conversion efficiency and long-term stability of inverted structure organic solar cells.

[0225] Furthermore, according to the inventors, it was confirmed that among the ionic liquid-based organic solar cells reported to date, a device with a PM6 photoactive layer and an MTMI-Cl modified electron transport layer achieved the highest level of photoelectric conversion efficiency (Fig. 6e).

[0226] Although specific embodiments of an organic photovoltaic device including an ionic liquid interface layer according to the present invention have been described so far, it is obvious that various modifications are possible within the scope of the present invention.

[0227] Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

[0228] That is, the aforementioned embodiments should be understood as exemplary in all respects and not limiting, and the scope of the invention is defined by the claims set forth below rather than by the detailed description, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the invention. Explanation of the symbols

[0229] 10: Lower electrode 20: Electron transport layer 30: Ionic liquid interface layer 40: Photoactive layer 50: Precision Transport Layer 60: Upper electrode 100: Organic optoelectronic device

Claims

Claim 1 An organic optoelectronic device comprising an ionic liquid interface layer, wherein the lower electrode; an electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode; an imidazolium-based ionic liquid interface layer formed on the electron transport layer; a photoactive layer formed on the ionic liquid interface layer; a hole transport layer formed on the photoactive layer; and an upper electrode formed on the hole transport layer; wherein the imidazolium-based ionic liquid interface layer comprises a compound of the following chemical formula 1: [Chemical Formula 1] In the above formula, R is a C1 to C10 alkoxy or hydroxyl group, R1 is a C1 to C10 alkyl group, X- is a halide anion, and n is an integer from 1 to 6. Claim 2 An organic photovoltaic device comprising an ionic liquid interface layer, wherein, in claim 1, the lower electrode comprises indium tin oxide (ITO). Claim 3 An organic optoelectronic device comprising an ionic liquid interface layer, wherein, in paragraph 2, the lower electrode is formed on a substrate, and the substrate comprises one or more selected from the group consisting of glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), and polycarbonate (PC). Claim 4 delete Claim 5 An organic photovoltaic device comprising an ionic liquid interface layer according to claim 1, wherein the imidazolium-based ionic liquid interface layer comprises 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the following chemical formula 2: [Chemical Formula 2] Claim 6 An organic optoelectronic device comprising an ionic liquid interface layer according to claim 1, wherein the imidazolium-based ionic liquid interface layer forms an interface dipole to improve energy level alignment between the electron transport layer and the photoactive layer. Claim 7 An organic optoelectronic device comprising an ionic liquid interface layer, wherein, in claim 1, the imidazolium-based ionic liquid interface layer passesivates surface defects of the electron transport layer to suppress charge recombination. Claim 8 An organic optoelectronic device comprising an ionic liquid interface layer, wherein, in claim 7, the surface defect comprises at least one of an oxygen vacancy and interstitial zinc. Claim 9 An organic photovoltaic device comprising an ionic liquid interface layer, wherein, in claim 1, the photoactive layer comprises a non-fullerene acceptor. Claim 10 An organic optoelectronic device comprising an ionic liquid interface layer, wherein, in claim 9, the non-fullerene receptor is one or more selected from the group consisting of Y6, Y6-BO, Y6-HU, ITIC, IT-4F, IDTBR, IDIC, IEICO, N3, N2200, L8-BO, and BTP-eC9. Claim 11 In claim 1, the hole transport layer is molybdenum oxide (MoO₂). x ), vanadium oxide (V2O5), tungsten oxide (WO3), nickel oxide (NiO x An organic optoelectronic device comprising an ionic liquid interface layer characterized by including ), PEDOT, PTAA, Spiro-OMeTAD, or a combination thereof. Claim 12 An organic photovoltaic device comprising an ionic liquid interface layer, wherein, in claim 1, the upper electrode comprises one or more selected from the group consisting of Ag, Au, Al, and Cu. Claim 13 An organic photovoltaic device comprising an ionic liquid interface layer, characterized in that, in claim 1, the organic photovoltaic device is an inverted structure organic solar cell. Claim 14 An organic photovoltaic device comprising an ionic liquid interface layer, wherein, in claim 1, the organic photovoltaic device maintains at least 70% of the initial photovoltaic conversion efficiency after 1,000 hours of continuous light irradiation. Claim 15 An electron transport structure comprising an ionic liquid interface layer, wherein the lower electrode; an electron transport layer comprising zinc oxide (ZnO) formed on the lower electrode; and an imidazolium-based ionic liquid interface layer formed on the electron transport layer; wherein the imidazolium-based ionic liquid interface layer comprises a compound of the following chemical formula 1: [Chemical Formula 1] In the above formula, R is a C1 to C10 alkoxy or hydroxyl group, R1 is a C1 to C10 alkyl group, X- is a halide anion, and n is an integer from 1 to 6. Claim 16 An electron transport structure comprising an ionic liquid interface layer, wherein, in claim 15, the lower electrode comprises indium tin oxide (ITO). Claim 17 An electron transport structure comprising an ionic liquid interface layer, wherein, in claim 15, the lower electrode is formed on a substrate, and the substrate comprises one or more selected from the group consisting of glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), and polycarbonate (PC). Claim 18 delete Claim 19 An electron transport structure comprising an ionic liquid interface layer according to claim 15, wherein the imidazolium-based ionic liquid interface layer comprises 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the following chemical formula 2: [Chemical Formula 2] Claim 20 A method for manufacturing an organic optoelectronic device comprising an ionic liquid interface layer, characterized by comprising: a step of forming an electron transport layer comprising zinc oxide (ZnO) on a lower electrode; a step of forming an imidazolium-based ionic liquid interface layer comprising a compound of Chemical Formula 1 on the electron transport layer; a step of forming a photoactive layer on the ionic liquid interface layer; and a step of forming a hole transport layer and an upper electrode on the photoactive layer: [Chemical Formula 1] In the above formula, R is a C1 to C10 alkoxy or hydroxyl group, R1 is a C1 to C10 alkyl group, X- is a halide anion, and n is an integer from 1 to 6. Claim 21 A method for manufacturing an organic photovoltaic device comprising an ionic liquid interface layer, wherein, in claim 20, the ionic liquid interface layer is formed by spin-coating an ionic liquid solution. Claim 22 delete Claim 23 A method for manufacturing an organic photovoltaic device comprising an ionic liquid interface layer according to claim 20, wherein the imidazolium-based ionic liquid interface layer comprises 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (MTMI-Cl) of the following chemical formula 2: [Chemical Formula 2] Claim 24 A method for manufacturing an organic photovoltaic device comprising an ionic liquid interface layer, characterized in that, in claim 20, it further comprises the step of heat treating at 50 to 150 ℃ after forming the ionic liquid interface layer. Claim 25 An organic solar cell comprising an electron transport structure according to any one of paragraphs 15 through 17 and 19.

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