Enhanced bulk heterojunction devices prepared by thermal and solvent vapor annealing processes

Abstract

A method for manufacturing a bulk heterojunction organic photovoltaic cell through a combination of thermal annealing and solvent vapor annealing is described. In an effort to improve the crystalline properties of a photoactive material, a bulk heterojunction film may be prepared by a known method, e.g., spin coating, and then exposed to one or more vaporized solvents and thermally annealed.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] The applicant claims priority to U.S. provisional application No. 61 / 322,039 filed on April 8, 2010, and U.S. provisional application No. 61 / 393,646 filed on October 15, 2010 (both incorporated herein by reference in their entirety).

[0003] Declaration on Federally Funded Research

[0004] The subject of protection of this Subject Matter was created with the support of the U.S. government under Contract No. DE-FG36-08GO18022 granted by the National Renewable Energy Laboratory under the U.S. Department of Energy. The said government holds certain rights in the subject matter of protection of this Subject Matter.

[0005] Joint research agreement

[0006] The subject matter of protection of this invention was created by, on behalf of, and / or in connection with one or more of the following entities pursuant to an industry-academia joint research agreement: the University of Michigan and Global Photonic Energy Corporation. The said agreement was in effect from the date the claimed invention was made and prior thereto, and the claimed invention was made as a result of activities undertaken within the scope of said agreement.

[0007] Field of disclosure

[0008] The present disclosure generally relates to a method for manufacturing a bulk heterojunction organic photovoltaic cell using a thermal annealing process and a solvent vapor annealing process. More specifically, the present disclosure relates to increasing the mesoscopic order and crystallinity of an organic thin film by exposing the bulk heterojunction to a vaporized solvent as well as to a combination of thermal annealing and solvent vapor annealing. Background Technology

[0009] Optoelectronic devices rely on the optical and electronic properties of materials to electronically generate or detect electromagnetic radiation, or to generate electricity from ambient electromagnetic radiation.

[0010] Photosensitive optoelectronic devices convert electromagnetic radiation into electricity. Solar cells, also referred to as photovoltaic (PV) devices, are a type of photosensitive optoelectronic device specifically used to generate power. PV devices capable of generating electrical energy from light sources other than sunlight can be used, for example, to drive power-consuming loads to provide lighting or heating, or to power electronic networks or devices, such as calculators, radios, computers, or remote monitoring or communication devices. These applications often involve the charging of batteries or other energy storage devices to ensure that operation continues when direct lighting from the sun or other light sources is unavailable, or to balance the power output of the PV device with the requirements of the specific application. As used herein, the term "resistive load" refers to any power-consuming or storage circuit, device, device, or system.

[0011] Another type of photosensitive optoelectronic device is a photoconductor cell. In this function, a signal detection network monitors the resistance of the device to detect changes caused by the absorption of light.

[0012] Another type of photosensitive optoelectronic device is a photodetector. In operation, the photodetector is used in conjunction with a current detection circuit capable of having an applied bias voltage and measuring the current generated when the photodetector is exposed to electromagnetic radiation. The detection circuit described herein can provide a bias voltage to the photodetector and measure the electronic response of the photodetector to electromagnetic radiation.

[0013] These three classes of photosensitive optoelectronic devices can be characterized by whether a rectifying junction, as defined below, is present, and whether the device is operated by an externally applied voltage, also known as a bias or bias voltage. Photoconductor cells do not have a rectifying junction and are normally operated by bias. PV devices have one or more rectifying junctions and are not operated by bias. Photodetectors have one or more rectifying junctions and are typically operated by bias, but are not always operated by bias. Generally, photovoltaic cells provide power to a circuit, device, or device, but do not provide a signal or current for controlling a detection network, or an output of information from said detection network. In contrast, photodetectors or photoconductors provide a signal or current for controlling a detection network, or an output of information from said detection network, but do not provide power to the network, device, or device.

[0014] Traditionally, photosensitive optoelectronic devices have been constructed from a number of inorganic semiconductors, e.g., crystalline, polycrystalline, and amorphous silicon, gallium arsenide, cadmium telluride, etc. Here, the term "semiconductor" refers to a material capable of conducting electricity when charge carriers are induced by thermal or electromagnetic excitation. The term "photoconductivity" generally relates to a process in which electromagnetic radiation energy is absorbed and converted into excitation energy for electric charge carriers, thereby enabling said carriers to conduct (i.e., transport) electric charge within the material. The terms "photoconductor" and "photoconductive material" are used herein to refer to semiconductor materials selected for their property of absorbing electromagnetic radiation to generate electric charge carriers.

[0015] PV devices can be characterized by an efficiency capable of converting incident solar power into useful electrical power. Devices using crystalline or amorphous silicon have been the most widely applied commercially, with some achieving efficiencies of over 23%. However, efficient crystalline-based devices, particularly those with large surface areas, are difficult and expensive to manufacture due to inherent problems in producing large crystals that do not exhibit significant efficiency degradation defects. On the other hand, high-efficiency amorphous silicon devices still have stability issues. Currently, commercially available amorphous silicon cells stabilize at efficiencies of 4% to 8%.

[0016] PV devices can be optimized to generate maximum power under standard illumination conditions (i.e., standard test conditions of 1000 W / m², AM1.5 spectral illuminance) for the maximum value of photocurrent multiplied by photovoltage. Under standard illumination conditions, the power conversion efficiency of such cells depends on the following three parameters: (1) current under zero bias, i.e., short-circuit current I SC , in amperes (2) Photovoltage under open circuit conditions, i.e., open circuit voltage V OC , in volts, and (3) fill factor, i.e., ff.

[0017] A PV device generates a current produced by light when the device is connected across a load and irradiated by light. When a PV device is irradiated under an infinite load, its maximum possible voltage is V, or V in the open circuit. OC It generates. When a PV element is irradiated by its short-circuited electrical contact, its maximum possible current, i.e., I short-circuit or I SCIt generates. When a PV device is actually used to generate power, it is connected to a finite resistive load, and the power output is given by the product of current and voltage, i.e., I x V. The maximum total power generated by the PV device is I SC and V OC The product of, that is, I SC x V OC It cannot essentially exceed . When the load value is optimized for maximum power extraction, the current and voltage are I, respectively. 최대 and V 최대 It has a value.

[0018] The numerical value of the advantage for the PV device is the fill factor defined below, i.e., ff:

[0019] [Mathematical Formula 1]

[0020] ff = {I 최대 V 최대} / {I SC V OC}

[0021] In the above equation, I SC and V OC Since it is never obtained simultaneously during actual use, ff is always less than 1. Nevertheless, as ff approaches 1, the device has a lower series or internal resistance, thereby obtaining a higher percentage of I under optimal conditions. SC and V OC Delivers the product of to the load. P inc If α is the power incident on the device, then η is the power efficiency of the device P can be calculated by the following mathematical formula:

[0022] [Mathematical Formula 2]

[0023] η P = ff*(I SC *V OC ) / P inc

[0024] A conventional method for generating an internally generated electric field that occupies a significant volume of a semiconductor is to juxtapose two layers of appropriately selected conductivity, particularly regarding their molecular quantum energy state distributions. The interface between these two materials is referred to as a photovoltaic junction. In traditional semiconductor theory, materials intended to form a PV junction have generally been designated as n-type or p-type materials. Here, n-type indicates that the majority of carrier types are electrons. This can be considered a material having many electrons in a relatively free energy state. p-type indicates that the majority of carrier types are holes. Such materials have many holes in a relatively free energy state. The concentration of background types—that is, the majority of carriers not generated by light—depends primarily on accidental doping by defects or impurities. The type and concentration of impurities determine the value of the Fermi energy or level within the difference between the conduction band minimum energy and the valence band maximum energy. Fermi energy is a characteristic of the statistical occupation of molecular quantum energy states, represented by the energy value at which the occupancy probability is 1 / 2. A Fermi energy close to the conduction band minimum energy implies that electrons are the dominant carriers. A Fermi energy close to the valence band maximum energy implies that holes are the dominant carriers. Therefore, Fermi energy is a primary characteristic of traditional semiconductors, and a circular PV junction is traditionally a pn interface.

[0025] The term "rectification" specifically indicates that an interface exhibits asymmetric conductivity characteristics, that is, the interface preferably supports electron charge transport in one direction. Rectification is normally associated with the intrinsic electric field occurring at the junction between appropriately selected materials.

[0026] Conventional inorganic semiconductor PV cells use a pn junction to establish an internal field. Early organic thin-film cells, such as those reported in the literature (Tang, Appl. Phys Lett. 48, 183 (1986)), contain a heterojunction similar to the one used in conventional inorganic PV cells. However, it is now recognized that, in addition to establishing a pn-type junction, the energy level offset of the heterojunction also plays an important role.

[0027] Energy level offset at organic DA junctions is considered important for the operation of organic PV devices due to the fundamental nature of the photogeneration process in organic materials. Upon optical excitation of organic materials, localized Frenkel or charge-carrying excitons are generated. For electrical detection or current generation to occur, the coupled excitons must dissociate into their constituent electrons and holes. While this process can be induced by an intrinsic electric field, the efficiency in an electric field (F ~ 10) typically found in organic devices 6 The V / cm value is low. The most efficient exciton dissociation in organic materials occurs at the donor-acceptor (DA) interface. At this interface, a donor material with a low ionization potential forms a heterojunction with an acceptor material with high electron affinity. Depending on the alignment of energy levels between the donor and acceptor materials, exciton dissociation at this interface can be energetically favorable, potentially generating free electron polarons in the acceptor material and free hole polarons in the donor material.

[0028] Organic PV cells offer many potential advantages over traditional silicon-based devices. Organic PV cells are lightweight and can be deposited on economical and inexpensive substrates, such as flexible plastic foils. However, organic PV devices typically exhibit a relatively low external quantum efficiency (the efficiency of converting electromagnetic radiation into electricity) of approximately 1% or less. This is thought to be partly due to the secondary nature of the intrinsic photoconductive process; that is, carrier generation requires exciton generation, diffusion, and ionization or collection. An efficiency η exists associated with each of these processes. The subscripts can be used as follows: P for power efficiency, EXT for external quantum efficiency, A for light absorption, ED for diffusion, CC for collection, and INT for internal quantum efficiency. The use of this notation is as follows:

[0029] η P ~η EXT = η A *η ED *η CC

[0030] η EXT = η A *η INT

[0031] Diffusion length of female reporters (L D Since ) is typically much shorter than the optical absorption length (~500Δ) (L D ~50Δ), a balance is required between the use of thick (and therefore resistive) batteries with multiple or highly folded interfaces and the use of thin batteries with low optical absorption efficiency.

[0032] Several methods for fabricating bulk heterojunction (BHJ) devices include phase separation during rotational coating of a polymer, phase separation from a donor-acceptor mixture induced by high-temperature annealing of a small molecular weight organic layer, and controlled growth of a small molecular weight organic layer by organic vapor phase deposition.

[0033] One challenge for efficient bulk heterojunction solar cells is to generate a maximized interface between the donor and acceptor materials within the photoactive layer to ensure efficient exciton dissociation, while keeping the typical dimensions of phase separation within the exciton diffusion range and the continuous path for the transport of charge carriers to the electrode. To realize an ideal material system and blend structure for efficient solar cells, it may be desirable to manipulate the donor-acceptor blend morphology and crystallinity through one or more annealing processes, such as thermal annealing and solvent vapor annealing.

[0034] The spin-cast process provides a simple and convenient method for fabricating homogeneous thin films, but the solvent can evaporate rapidly during the process, and phase separation of intimately mixed donor and acceptor materials can be suppressed. Since organic materials can form amorphous, crystalline, or semicrystalline structures during casting from solution, different evaporation times for different solvents can affect the dynamic assembly process of organic molecules. Consequently, this can determine the microstructure and morphology of the active layer, as well as the potential for resulting changes in carrier transport properties and device performance. Therefore, since thin films obtained from spin coating typically do not exist in their thermodynamic equilibrium state, thermodynamic forces cause the thin film to reorganize toward a stable equilibrium state. This evolution can be accelerated by rising temperatures or solvent vapor pressure.

[0035] In organic semiconductor materials, post-annealing can enhance charge carrier transport by increasing meso-order and crystallinity that may spontaneously arise from the maximization of intermolecular π-π stacking. Generally, the performance of bulk solar cells can be optimized by controlling the nanometer form of the active layer. For small molecule bulk solar cells, the thermal annealing process DPP(TBFu)2 / PC is used to increase charge-carrier transport and improve carrier collection. 70 It can be investigated in the BM system.

[0036] Alternatively, solvent vapor annealing can be useful for controlling and optimizing the active layer morphology. Here, the atmosphere is rapidly saturated with solvent, allowing the film formation reaction to be further extended. This additional film formation can induce improved interpenetration of donor / acceptor domains and increased order within the donor domain, similar to thermal annealing. Therefore, there remains a need to further develop the control and optimization of the active layer morphology. The applicant describes herein a solvent vapor annealing process that not only meets this need but can also be utilized to fabricate bulk heterojunction devices with enhanced performance characteristics. Furthermore, the applicant provides a combination of thermal annealing and solvent vapor annealing that yields a bulk heterojunction device with an optimized active layer morphology and enhanced performance characteristics.

[0037] outline

[0038] A method for manufacturing a bulk heterojunction organic photosensitive device is disclosed, comprising the step of exposing to some thermal annealing process and / or solvent vapor annealing process. In one embodiment, the method for manufacturing a photosensitive device comprises the following steps:

[0039] A step of providing a structure comprising one or more electrodes and a bulk heterojunction, wherein the bulk heterojunction comprises one or more first photoactive materials and one or more second photoactive materials;

[0040] A step of providing one or more solvents;

[0041] A step of vaporizing at least a portion of the above solvent; and

[0042] A step of exposing at least a portion of the above structure to a vaporized solvent, wherein the exposure to the vaporized solvent increases the crystallinity of one or more of the first photoactive material and the second photoactive material.

[0043] In some embodiments, the method further comprises the step of thermally annealing the structure. In some embodiments, the thermal annealing step occurs after at least a portion of the structure has been exposed to a vaporized solvent.

[0044] In another embodiment, a method for improving the crystallinity of a bulk heterojunction comprising one or more first organic photoactive materials and one or more second organic photoactive materials in a photosensitive device is described. In one embodiment, the method comprises the step of exposing at least a portion of the bulk heterojunction to a vaporized solvent, wherein the photosensitive device exhibits one or more of the following characteristics compared to a device not exposed to the vaporized solvent:

[0045] Increased charging rate (FF);

[0046] Increased external quantum efficiency (EQE); and

[0047] Increased current density versus voltage (JV).

[0048] In some embodiments, the method further comprises the step of thermally annealing the structure. In some embodiments, the thermal annealing step occurs after at least a portion of the structure has been exposed to a vaporized solvent. Brief explanation of the drawing

[0049] The attached drawings, which are incorporated into and constitute part of this specification, illustrate various embodiments described herein and contribute to explaining the principles of the present invention together with the detailed description. The drawings are not necessarily drawn in a fixed proportion. Fig. 1a shows an SQ:PC cast from chloroform and thermally annealed at various temperatures for 10 minutes. 70 BM(1:6) bulk solar cells, and SQ:PC cast from chloroform and solvent annealed with dichloromethane for various exposure times 70 Shows XRD (X-ray diffraction data) for a BM (1:6) bulk solar cell. FIGS. 1b to 1d are SQ:PC from chloroform, respectively. 70 BM(1:6) bulk solar cell biocast, SQ:PC thermally annealed at 70°C for 10 minutes 70 BM(1:6) bulk solar cells, and SQ:PC solvent annealed with dichloromethane for 12 minutes 70 Shows the RMS (Root Mean Square) roughness for a BM (1:6) bulk solar cell. Fig. 2a shows SQ:PC cast from chloroform and thermally annealed at various temperatures. 70 Shows FF versus power intensity for BM(1:6) bulk solar cells. FIG. 2b shows an SQ:PC cast from chloroform and solvent annealed with dichloromethane for various exposure times. 70 Shows FF versus power intensity for BM(1:6) bulk solar cells. FIG. 2c shows SQ:PC cast from 1,2-dichlorobenzene and solvent annealed with dichloromethane for various exposure times. 70 Shows FF versus power intensity for BM(1:6) bulk solar cells. Fig. 3a shows SQ:PC cast from 1,2-dichlorobenzene and solvent annealed with dichloromethane for various exposure times.70 Shows the EQE for BM(1:6) bulk solar cells. Figure 3b shows the JV for a bulk heterojunction device cast from 1,2-dichlorobenzene and solvent annealed with dichloromethane for various exposure times. FIG. 3c shows η for a bulk heterojunction device cast from 1,2-dichlorobenzene and solvent annealed with dichloromethane for various exposure times. Ρ Shows high power intensity. Figure 4 shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 Shows XRD for BM(1:6) bulk solar cells. Figures 5a to 5c show the RMS of a bulk heterojunction device cast from DCB, a bulk heterojunction device solvent annealed with dichloromethane for 12 minutes, and a bulk heterojunction device solvent annealed with dichloromethane for 30 minutes, respectively. Fig. 6a shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 Shows the absorption coefficient for a BM(1:6) bulk solar cell. Fig. 6b shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 Shows PL (photoluminescence) intensity for a BM (1:6) bulk solar cell (see legend in Fig. 6a). Fig. 6c shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 Shows the EQE for a BM(1:6) bulk solar cell (see legend in Fig. 6a). Fig. 6d shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 This shows current density versus V (voltage) for a BM (1:6) bulk solar cell (see legend in Fig. 6a). Fig. 7a shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 η for BM(1:6) bulk solar cells Ρ Shows high power intensity. Fig. 7b shows an SQ:PC cast from DCB and solvent annealed with dichloromethane for various exposure times. 70 Shows FF versus power intensity for BM(1:6) bulk solar cells. Fig. 8a shows several SQ:C thermally annealed for 20 minutes at various temperatures. 60 Shows XRD (X-ray diffraction) data for a planar cell. Fig. 8b is the planar SQ:C tested in Fig. 8a. 60 Shows the EQE for the device. Figure 9a shows the planar SQ:C tested in Figure 8a. 60 η for the element Ρ Shows high power intensity. Fig. 9b is the planar SQ:C tested in Fig. 8. 60 Shows the FF versus power intensity for the device. Fig. 10a shows several SQ:PCs cast from DCB and thermally annealed at various temperatures for 10 minutes. 70 Shows XPS (X-ray photoelectron spectroscopy) measurements for a BM (1:6) bulk heterojunction device. FIG. 10b is the SQ:PC described in FIG. 10a 70 Shows AFM (atomic force microscope) measurements of a BM (1:6) bulk heterojunction device. Figure 11a shows the SQ:PC tested in Figure 10a. 70 η for BM(1:6) bulk heterojunction devices Ρ Shows high power intensity. Fig. 11b is the SQ:PC tested in Fig. 10a 70 Shows the FF versus power intensity for a BM(1:6) bulk heterojunction device. Figure 12a is SQ:PC from DCB70 Shows the RMS (roughness measurement system) of a BM (1:6) bulk heterojunction device casting. FIG. 12b is an SQ:PC thermally annealed at 70°C after being cast from DCB. 70 Shows the RMS roughness of a BM (1:6) bulk heterojunction device. FIG. 12c is an SQ:PC cast from DCB, solvent vapor annealed with dichloromethane for 30 minutes, and thermally annealed at 50°C. 70 Shows the RMS roughness of a BM (1:6) bulk heterojunction device. FIG. 12d is an SQ:PC thermally annealed at 110°C after being cast from DCB. 70 Shows the RMS roughness of a BM (1:6) bulk heterojunction device. FIG. 12e shows an SQ:PC cast from DCB, solvent vapor annealed with dichloromethane for various times, and thermally annealed at 50°C. 70 XRD data of a BM(1:6) bulk heterojunction device is shown. FIG. 13a shows an SQ:PC cast from DCB, solvent vapor annealed with dichloromethane for various times, and thermally annealed at 50°C. 70 η for BM(1:6) bulk heterojunction devices Ρ Shows high power intensity. Figure 13b is the SQ:PC tested in Figure 13a. 70 Shows the FF versus power intensity for a BM(1:6) bulk heterojunction device. Figure 14 shows the SQ:PC tested in Figure 13a. 70 Shows the EQE for a BM(1:6) bulk heterojunction device. Fig. 15 shows cast and thermally annealed SQ / C at various temperatures. 60 Flat cell, cast and thermally annealed SQ:PC at various temperatures 70BM(1:6) bulk cells, and SQ:PC cast and DCM solvent annealed for 2, 6, 8, and 12 minutes at 1 degree of sun illumination. 70 η of BM(1:6) bulk battery Ρ Shows an overview. Specific details for implementing the invention

[0050] definition

[0051] As used herein, the term “organic” includes polymeric materials and small molecule organic materials that can be used in the fabrication of organic optoelectronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecule” can actually be quite large. Small molecules may contain repeating units under certain conditions. For example, using long-chain alkyl groups as substituents does not exclude molecules from the class of “small molecules.” Small molecules may be introduced into the polymer, for example, as pendant groups on the polymer backbone or as part of said backbone. Small molecules may also act as the core portion of a dendrimer, which consists of a series of chemical shells built on a moiety. The core portion of the dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule.” Generally, small molecules have a defined chemical formula with the same molecular weight for each molecule, whereas polymers have a defined chemical formula with a molecular weight that may vary for each molecule. As used herein, “organic” includes, but is not limited to, metal complexes of hydrocarbyl and hydrocarbyl ligands substituted with heteroatoms.

[0052] Methods and processes utilizing solvent annealing, specifically solvent vapor annealing and thermal annealing, during the fabrication of bulk heterojunction organic photovoltaic cells are described herein. The form and phase separation of organic materials can be important in that they enable both charge separation and collection. The solvent vapor annealing process described herein may be useful for exhibiting a templating effect (this effect causes the organic material to self-assemble to form ordered aggregates) on one or more organic photoactive materials comprising bulk heterojunctions. The nanoform and crystallinity of the organic material may depend on the type and duration of the solvent. In some embodiments, the solvent vapor annealing and / or thermal annealing process described herein may increase the crystalline characteristics of one or more organic materials comprising bulk heterojunction blends that are biomolecules exhibiting primarily amorphous properties.

[0053] In one embodiment, a method for manufacturing a photosensitive element is described, comprising the following steps:

[0054] A step of providing a structure comprising one or more electrodes and a bulk heterojunction, wherein the bulk heterojunction comprises one or more first organic photoactive materials and one or more second organic photoactive materials;

[0055] A step of providing one or more solvents;

[0056] A step of vaporizing at least a portion of the above solvent; and

[0057] A step of exposing at least a portion of the above structure to a vaporized solvent, wherein the exposure increases the crystallinity of one or more of the first organic photoactive material and the second organic photoactive material.

[0058] In some embodiments, the method further comprises the step of thermally annealing the structure. In some embodiments, the thermal annealing step occurs after at least a portion of the structure has been exposed to a vaporized solvent.

[0059] In some embodiments, the structure may be manufactured by depositing one or more first organic photoactive materials and one or more second organic photoactive materials on the first electrode. After the annealing process is completed, the second electrode may be patterned on the bulk heterojunction.

[0060] Electrodes, e.g., anodes and cathodes, may be composed of metals or "metal substitutes." Here, the term "metal" is used to encompass both materials composed of elementally pure metals and metal alloys composed of two or more elementally pure metals. The term "metal substitute" refers to a material that is not a metal within the ordinary definition but exhibits metal-like properties, e.g., conductivity. Metal substitutes include, for example, doped wide-bandgap semiconductors, degenerate semiconductors, conductive oxides, and conductive polymers.

[0061] The term “cathode” is used in the following manner. In a single unit of a non-stacked PV device without a PV device or a stacked PV device that exists under ambient radiation and is connected to a resistive load and an externally applied voltage, electrons move from the photoconductive material to the cathode. Similarly, the term “anode” is used herein to refer to holes moving from the photoconductive material to the anode in correspondence with electrons moving in the opposite manner in a PV device existing under illumination. It will be recognized that, as the terms are used herein, the anode and cathode may be electrodes or charge transfer layers.

[0062] The electrode may comprise a single layer or multiple layers ("compound" electrodes) and may be transparent, translucent, or opaque. Examples of electrodes and electrode materials include, but are not limited to, the electrodes and electrode materials disclosed in U.S. Patent No. 6,352,777 (Bulovic et al.) and U.S. Patent No. 6,420,031 (Parthasarathy, et al.) (each of which is incorporated herein by reference for the disclosure of features of each thereof). As used herein, a layer is referred to as "transparent" if it transmits at least 50% of the surrounding electromagnetic radiation at the relevant wavelength.

[0063] In one embodiment, the first electrode may include an interface layer comprising molybdenum oxide (MoOx). MoOx is an exemplary interface layer in organic PV cells that is thought to contribute to reducing dark current and increasing open circuit voltage (Li, N. et al. Open circuit voltage enhancement due to reduced dark current in small molecule photovoltaic cells, Appl. Phys. Lett., 94, 023307, Jan. 2009).

[0064] In some embodiments, the first organic photoactive material may include a donor-type material. Non-limiting examples of the first organic photoactive material that may be used herein include subphthalocyanine (SubPc), copper phthalocyanine (CuPc), chloroaluminum phthalocyanine (CIAIPc), tin phthalocyanine (SnPc), pentacene, tetracene, didenoperylene (DIP), and squaraine (SQ).

[0065] In some embodiments, the second organic photoactive material may comprise a receptor-type material. Non-limiting examples of the second organic photoactive material that may be used herein include C 60 , C 70 , [6,6]-phenyl C70 Methyl butyric acid ester (PC 70 BM), 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI) and hexadecafluorophthalocyanine (F 16 There is CuPc)

[0066] In another embodiment, a blocking layer may be included, for example, between the bulk heterojunction and the second electrode. Examples of exciton blocking layers (EBLs) are described in U.S. Patents No. 6,451,415 and 7,230,269 (Forrest et al.) (these are incorporated herein by reference for their disclosures regarding EBLs). Further background information on EBLs may be found in the literature (Peumans et al., "Efficient photon harvesting at high optical intensities in ultrathin organic double-heterostructure photovoltaic diodes," Applied Physics Letters 76, 2650-52 (2000)) (this literature is also incorporated herein by reference). EBLs are thought to reduce quenching by preventing excitons from migrating out of the donor and / or acceptor material. Non-limiting examples of exciton blocking layers that may be used herein include vasocuproin (BCP), vasophenanthroline (BPhen), 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI), 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi), tris(acetylacetonato)ruthenium(III) (RuAcaca3) and aluminum(III)phenolate (Alq2OPH).

[0067] Examples of the second electrode that may be used in the present invention include metal substitutes, non-metallic materials, or metallic materials selected from, for example, Ag, Au, and Al.

[0068] It is recognized that the first electrode may comprise a conductive oxide selected from, for example, indium tin oxide (ITO), tin oxide (TO), gallium indium tin oxide (GITO), zinc oxide (ZO), and zinc indium tin oxide (ZITO), and that the transparent conductive polymer comprises polyaniline (PANI). In one embodiment, the bulk heterojunction organic photovoltaic cell is ITO / MoO3 / SQ:PC 70 BM / LiF / Al; and ITO / MoO3 / SQ:PC 70 BM / C 60 Includes / BCP / LiF / Al.

[0069] The thickness of the organic layer described herein may be 25 to 1200 Å, for example, 50 to 950 Å or even 100 to 700 Å.

[0070] In some embodiments, the bulk heterojunction may be prepared by, for example, vacuum thermal evaporation (VTE), rotational coating, or organic vapor phase deposition (OVPD). OVPD differs from vacuum thermal evaporation (VTE) in that OVPD uses a carrier gas to transport vapor into the deposition chamber. The spatial separation of the evaporation function and the transport function enables precise control of the deposition process and control of the organic surface morphology, for example, a flat layer with a smooth surface or a layer with protrusions.

[0071] In one embodiment, the bulk heterojunction is manufactured by spin coating. When manufacturing the bulk heterojunction via spin coating, the use of different solvent systems can affect the final efficiency of the photosensitive device upon completion. For example, the device may be manufactured using a solvent having a low boiling point temperature or a solvent having a high boiling point. Since low boiling point solvents evaporate rapidly, it may be preferable to use a high boiling point solvent to further control the morphology. In some embodiments, the use of a solvent such as 1,2-dichlorobenzene (DCB) in the initial manufacturing of the bulk heterojunction can ultimately result in a PV device exhibiting improved performance properties after solvent vapor annealing compared to a PV device manufactured with a low boiling point solvent.

[0072] In some embodiments, one or more first organic photoactive materials and one or more second organic photoactive materials are cast in a casting solvent having a boiling point of about 70°C or lower at 1 atm. Exemplary solvents may include chloroform. In another embodiment, one or more first organic photoactive materials and one or more second organic photoactive materials are cast in a casting solvent having a boiling point greater than about 130°C at 1 atm. In another embodiment, one or more first organic photoactive materials and one or more second organic photoactive materials are cast in a casting solvent having a boiling point greater than about 175°C at 1 atm. Exemplary solvents may include DCB.

[0073] To improve the characteristics of a bulk heterojunction PV cell, the film morphology of the deposited organic layer can be further optimized by exposing one or more organic photoactive materials to solvent vapor annealing. In some embodiments, optimal annealing can be achieved using one or more solvents. The exposure time may also affect the final form of the organic material.

[0074] An exemplary vaporization solvent is dichloromethane. In some embodiments, it may be preferable to expose the structure to the vaporized solvent within a sealed container. In some embodiments, the structure may be exposed to the vaporized solvent for a time of about 5 minutes to about 30 minutes or more, e.g., 6 minutes to about 15 minutes or even about 10 minutes to about 12 minutes.

[0075] In some embodiments, it may be desirable to further expose the heterojunction to thermal annealing. The thermal annealing step may help to further control the morphology, crystallinity, and / or improved performance of the manufactured device. For example, it may be desirable to thermally anneale the structure after exposing the bio-cast device to solvent vapor annealing. Thermal annealing may take place at a temperature sufficient to remove any remaining solvent from the vapor annealing step. For example, it may be desirable to thermally anneale the device by applying heat directly to the structure after exposing the structure to solvent vapor annealing with dichloromethane. This can be achieved by placing the structure on a hot plate heated to 50°C under an N2 atmosphere.

[0076] A method for improving the crystallinity of a bulk heterojunction comprising one or more first organic photoactive materials and one or more second organic photoactive materials in a photosensitive device is also described herein. In this embodiment, the method comprises the step of exposing at least a portion of the bulk heterojunction to a vaporized solvent, wherein the photosensitive device exhibits one or more of the following characteristics compared to a device not exposed to the vaporized solvent:

[0077] Increased charging rate (FF);

[0078] Increased external quantum efficiency (EQE); and

[0079] Increased current density versus voltage (JV).

[0080] In some embodiments, the method further comprises the step of thermally annealing the structure. In some embodiments, the thermal annealing step occurs after at least a portion of the structure has been exposed to the vaporized solvent.

[0081] Suitable methods and materials include, but are not limited to, the methods and materials discussed in detail below.

[0082] Examples

[0083] The present disclosure can be more easily understood by referring to the following detailed description of exemplary embodiments and examples. It is understood that other embodiments will become apparent to those skilled in the art in light of the description and examples disclosed herein.

[0084] Example 1

[0085] SQ:PC spin-coated at a speed of 6,000 RPM (revolutions per minute) on an indium tin oxide (ITO) substrate pre-coated with 80 Å MoO3 70 X-ray diffraction (XRD) patterns of BM (1:6 wt concentration) thin films, 40 kV Cu K α It was obtained with a θ-2θ geometric structure using a Rigaku diffractometer utilizing a radiation source. When measured using a Woolam VASE ellipsometer, SQ:PC formed from a 20 mg / mL solution in chloroform 70 The thickness of the BM(1:6) blend was 680 Å.

[0086] Atomic force microscope (AFM) images were collected in tapping mode on a Noanoscope III AFM. For solvent annealed samples, SQ:PC 70 The BM (1:6) bulk membrane was subsequently annealed for a duration of 6 to 30 minutes in a sealed glass vial filled with 1 mL of dichloromethane (DCM). For thermal annealing samples, SQ:PC70 The BM (1:6) film was annealed for 10 minutes on a hot plate inside an N2 glove box at 50°C, 70°C, 110°C, and 130°C.

[0087] Next, the raw casting SQ:PC (from chloroform solvent) 70 DCM solvent annealing of BM (1:6) films was performed on solar cells having the following structure: ITO / MoO3 (80 Å) / SQ:PC 70 BM(1:6 680 Å) / LiF(8 Å) / Al(1000 Å). Next, the device is ITO / MoO3(80 Å) / SQ:PC 70 BM(1:6 680 Å) / C 60 Thermally evaporated C having a structure composed of (40 Å) / BCP(10 Å) / LiF(8 Å) / Al(1000 Å) 60 It was capped in layers. Then, 10 -7 MoO3 was thermally evaporated onto the ITO surface in a vacuum system using a base pressure of Torr. An 8 Å LiF and a 1000 Å thick Al cathode were thermally evaporated through a shadow mask to produce 7.9 x 10⁻⁶ -3 The device fabrication was completed by generating a device area of ​​cm². The current density-voltage (JV) characteristics and η of the device were obtained using Oriel 150 W solar simulator irradiation from a Xe arc lamp equipped with an AM1.5G filter and an NREL-corrected standard Si detector. ρ EQE was measured. Measurement and solar spectral correction were performed using standard methods. EQE was measured using monochromatic light from a Xe lamp that is briefly blocked at 400 Hz and focused into the device active region.

[0088] As shown in Fig. 1a, SQ:PC thermally annealed at 50°C, 70°C, 110°C, and 130°C for 10 minutes 70No arbitrary XRD peaks appeared to be present for the BM(1:6) bulk solar cell, which implies amorphous characteristics. In contrast, after performing DCM solvent annealing for longer than 12 minutes, two XRD peaks of SQ appeared to be present, which can be well indexed by peaks (001) and (002). Although we do not wish to be bound by any specific theory, SQ:PC after solvent annealing 70 Since the SQ peak appears relatively weak in the BM(1:6) mixture, SQ forms aligned / crystalline domains, and SQ and PC exist between these domains. 70 It is thought that amorphous sections of the BM exist. The average roughness of the AFM images for the raw casting (Fig. 1b) and four thermally annealed samples was approximately 0.58 ± 0.12 nm, and the SQ phase and PC 70 There was no clear phase separation contrast on the BM, which appeared to be consistent with the XRD measurement results. PC 70 BM can break the aggregation of SQ molecules and bio-cast SQ:PC 70 It is thought that it impairs the crystallinity of the BM membrane (Fig. 1a). In contrast, SQ:PC after solvent annealing 70 The roughness of the BM film appeared to increase in single-order increments from approximately 0.58 ± 0.12 nm (natural cast) to approximately 5.6 ± 1.2 nm (DCM annealing for 8 minutes - Fig. 1c). A longer DCM annealing time of 12 minutes was SQ:PC 70 It appeared to double the roughness of the BM(1:6) blend (Fig. 1d), which implies stronger phase separation occurring when more SQ clusters begin to grow polycrystalline. Therefore, amorphous bio-cast SQ:PC 70 It is thought that DCM annealing of the BM (1:6) film provided a nanocrystalline form of the SQ phase.

[0089] SQ:PC from chloroform solvent 70 BM(1:6) bulk battery raw casting, and SQ:PC thermally annealed at a temperature of 50°C to 130°C 70 The charge rate of the BM(1:6) bulk cell is shown in Fig. 2a. The thermal annealing process did not appear to improve the charge rate, which was consistent with the XRD data in Fig. 1a and suggested that thermal annealing produces a recognizable increase in crystallinity. SQ:PC cast from chloroform solvent after the DCM solvent annealing process. 70 The results for the BM(1:6) device are shown in Fig. 2b. As shown, it appears that there is an improvement in the filling rate when a DCM annealing time of 6 minutes is used at 1 solar illuminance. SQ:PC cast from DCB solvent 70 In the BM (1:6) device (Fig. 2c), the fill rate appears to decrease rapidly. In contrast, when a time of 10 minutes is used, the fill rate of the DCM annealed device appears to gradually increase at 1 solar irradiance. As shown in Fig. 1a, a longer duration of the DCM solvent annealing time increases the crystallinity of the SQ phase in the blend, and SQ:PC 70 Extended DCM annealing time in the BM (1:6) blend appears to improve the filling rate, which is thought to be at least partially due to the increased agglomerative / crystalline content of the SQ.

[0090] In Fig. 3a, the raw casting cast from DCB solvent and the solvent-annealed SQ:PC 70 The external quantum efficiency (EQE) of the BM(1:6) bulk cell implies a broad and excellent spectral response from 300 nm to 750 nm. The EQE peak at approximately λ=690 nm is thought to be due to SQ absorption, where the peaks concentrated at approximately λ=350 nm and 500 nm are PC 70It appears to have originated from BM absorption. When a DCM solvent annealing time of 10 minutes was used, the generated EQE peak increased, and the curve fluctuations suggest more balanced exciton dissociation and charge collection after the subsequent DCM solvent annealing process.

[0091] 1 SQ:PC cast from DCM solvent, illuminated at solar irradiance 70 The JV characteristics of the BM(1:6) bulk cell are shown in Fig. 3b. Subsequent DCM solvent annealing appears to increase the short-circuit current density and change the shape of the JV curve, implying that the device exhibits higher conductivity. When using 10 minutes of DCM annealing, SQ:PC 70 The FF of the BM(1:6) bulk device appears to exhibit relatively higher values ​​at higher power intensities compared to the bio-cast device, which implies superior carrier charge transport within the bulk film. Additionally, Fig. 3c shows that the DCM solvent-annealed device η P It shows that there is a significant improvement in high power intensity. These results appear to be consistent with the behavior of the thermally annealed and solvent-annealed devices shown in Figures 2a and 2b.

[0092] Example 2

[0093] SQ:PC spin-coated at a low speed of 1000 RPM (revolutions per minute) for 30 seconds on an indium tin oxide (ITO) coated glass substrate pre-coated with 80 Å MoO3 70 X-ray diffraction (XRD) patterns of BM (relative weight concentration of 1:6) thin films, 40 kV Cu K αIt was obtained with a θ-2θ geometric structure using a Rigaku diffractometer utilizing a radiation source. When measured using a Ulam VASE ellipsometer, SQ:PC formed from a 42 mg / mL solution of 1,2-dichlorobenzene (DCM) heated on a hot plate for 12 hours was obtained. 70 The thickness of the BM(1:6) blend was 780 Å.

[0094] Atomic force microscope (AFM) images were acquired in tapping mode on a Nanoscope III AFM. SQ:PC 70 Solvent annealing of the BM(1:6) deposited film was performed for a duration of 6 to 30 minutes in a sealed glass vial filled with 1 mL of dichloromethane (DCM). For transmission electron microscopy (TEM) studies, SQ:PC on an ITO substrate coated with 80 Å MoO3 70 The BM(1:6) membrane was immersed in deionized (DI) water for 1 hour. Then, MoO3 was dissolved in water, and the organic layer was suspended on the surface of the DI water. Subsequently, the raw casting and solvent-annealed SQ:PC 70 A BM (1:6) film was transferred onto a Cu lattice coated with a holy carbon film. TEM images were taken using a 200 kV JEOL 2010F analytical electron microscope.

[0095] The absorption spectra of the bio-cast and four DCM annealed films on a quartz substrate were measured using a Perkin-Elmer Lambda 1500 UV-NIR spectrometer. Photoluminescence (PL) was measured using an excitation wavelength of λ = 600 nm. The following solar cell structure was used: ITO / MoO3(80 Å) / SQ:PC 70 BM(1:6 780 Å) / C 60 (40 Å) / BCP(10 Å) / Al(1000 Å). Here, 10 -7MoO3 was thermally evaporated onto the ITO surface within a vacuum system using a base pressure of Torr. After rotational casting deposition and solvent annealing, an 8 Å LiF and a 1000 Å thick Al cathode were thermally evaporated through a shadow mask to form an 8x10 -3 The device fabrication was completed by generating a device area of ​​cm². The current density-voltage (JV) characteristics and power conversion efficiency (η) of the device were measured using Oriel 150 W artificial solar radiation from a Xe arc lamp equipped with an AM1.5G filter and an NREL-corrected standard Si detector. ρ ) was measured. Measurement and solar spectral correction were performed using standard methods. EQE was measured using monochromatic light from a Xe lamp that is briefly blocked at 200 Hz and focused into the device active region.

[0096] SQ:PC 70 Subsequent annealing of the BM(1:6) blend required exposing the film to DCM vapor for 6 to 30 minutes in a sealed glass vial enclosed in a glove box filled with ultra-high purity nitrogen at room temperature. As shown in Fig. 4, the deposited SQ:PC 70 The absence of X-ray diffraction (XRD) peaks for the BM film suggests an amorphous structure. In contrast, after annealing for 10 minutes, when the annealing time was extended to 30 minutes, a peak increasing in intensity appeared at approximately 2θ = 7.80 ± 0.08 o It appears in. This peak is the (001) reflection of SQ corresponding to an intermolecular spacing of approximately 11.26 ± 0.16 Å. After exposure to DCM for 30 minutes, a second peak corresponding to the (002) reflection appears, which suggests a continued increase in order. The average crystal sizes of SQ in the blends annealed for 12 and 30 minutes are estimated to be 2.0 ± 0.2 nm and 51 ± 4 nm, respectively, when inferred from XRD peak broadening using the Scherrer method.

[0097] The root mean square roughness obtained from the AFM image of the bio-cast film (Fig. 5a) is approximately 0.8 ± 0.1 nm. In contrast, after solvent annealing for 12 minutes, the roughness of the blend increases to approximately 8.4 ± 1.2 nm (Fig. 5b), which implies significant roughening due to the polycrystalline growth of SQ in the mixture. When a much longer annealing time of 30 minutes was used, SQ and PC, as implied by additional roughening to 12.0 ± 1.4 nm (Fig. 5c), 70 Phase separation of the BM continues. Roughening, which is thought to be partially attributed to phase separation, was also observed in the projection electron microscope (TEM) image (Fig. 5c) and the surface phase image measured by AFM (inset in Fig. 5c). As recognized from the XRD line broadening above, the average crystal domain size also appears to increase simultaneously with the roughening.

[0098] Bio-casts on quartz substrates and 4 DCM solvent-annealed SQ:PCs 70 The spectral analysis of the BM blend film in visible light is shown in Fig. 6a. Over the entire observed spectral range, the absorption coefficient of SQ increases with annealing time up to 8 min, but as time increases further, the change appears to saturate. Additionally, the crystalline blend film (DCM 12 min) appears to have a less pronounced absorption peak at λ=680 nm than the absorption peak of the amorphous film.

[0099] The photoluminescence (PL) intensity of the film is quenched in the presence of charge transfer from photogenerated donor excitons to acceptor molecules (Fig. 6b). Therefore, SQ:PC 70 Efficient PL quenching in BM blends is the interfacial distance, i.e., L D It implies efficient exciton dissociation due to photogeneration within. As previously mentioned, the relevant length magnitude is 1.6 nm for SQ and PC70 In the case of BM, it is 20 nm to 40 nm. 10 minutes appears to produce maximum PL intensity extinction, and thereafter, as the annealing time is further increased, the extinction decreases. Although we do not intend to be bound by any specific theory, this is the inventors' L D and can be understood in terms of the average crystallite size δ value. PL quenching is L after approximately 10 to 12 minutes of annealing. D It appears to be strongest at ~δ~2 nm. Additional annealing is δ>>L D Since it appears to trigger the initiation of additional phase separation as a crystal at some point, excitons are no longer efficiently transported to the dissociation heterointerface.

[0100] In Fig. 6c, the EQE of the bio-cast and solvent-annealed solar cells is an absorption spectrogram spanning from wavelength λ=300 nm to λ=750 nm, suggesting a similarly broad spectral response. The EQE peak of SQ increases from approximately 26 ± 2% (bi-cast) to approximately 60 ± 1% (annealed for 10 minutes). After 12 minutes of annealing, the peak EQE decreases to less than 40% across the entire wavelength range. These results, similar to those obtained from absorption, suggest that the cell efficiency is L D Since it strongly depends on the microcrystal size having an optimal size comparable to that, SQ and PC 70 It further implies that it causes maximum exciton diffusion to the dissociation donor / acceptor interface between BMs.

[0101] 1. The JV characteristics of Fig. 6d measured under AM1.5G artificial solar radiation of solar illuminance are the short-circuit current density (J SCThis implies that ) improves from approximately 6.9 mA / cm² (raw casting) to approximately 12.0 mA / cm² (solvent annealing for 10 minutes), and then decreases to approximately 8.3 mA / cm² after exposure to DCM for 12 minutes. The FF results show a similar dependence on annealing time, suggesting that extended order reduces series resistance, as predicted for crystalline organic materials with improved molecular packing. The series resistivity R was determined by fitting the forward JV curve using the modified diode equation. SA ...was obtained. The bio-cast cell has an R of approximately 35.2 ± 1.0 Ω·cm². SA having, and then the above R SA The value gradually decreases to approximately 5.0 ± 0.5 Ω·cm² when the annealing time is 12 minutes. However, it is thought that further increases in the DCM annealing time may increase the density of pinholes between the active layer and the contact, thereby causing a shortened diode.

[0102] As shown in Fig. 7a, the optical and electrical changes due to annealing are η P It appears to increase. Here, the η of the bio-casting cell P appears to increase slightly with power intensity, then gradually decreases to approximately 2.4 ± 0.1% at 1 solar illuminance, while simultaneously FF decreases from approximately 0.40 ± 0.02 (0.002 solar illuminance) to approximately 0.36 ± 0.01 (1 solar illuminance) (see Fig. 7b). In contrast, for the cell annealed for 10 minutes, FF increases from approximately 0.42 ± 0.01 (0.002 solar illuminance) to approximately 0.50 ± 0.01 (1 solar illuminance), and during this increase, η P It appears to increase correspondingly from 1.5 ± 0.1% to 5.2 ± 0.3% (1 solar illuminance), at which point the peak measured value for cells within this group is 5.5% (J SC=2.0 mA / ㎠, FF=0.5 and V OC =0.92 V). Finally, the cell annealed for 12 minutes is η P It shows a decrease of about 3.2 ± 0.1% in, which can be attributed to reduced EQE and FF.

[0103] Example 3

[0104] To compare the double-layer structure with bulk solar cells, SQ / C 60 A planar cell was fabricated as a control cell. To investigate the effect of crystallinity on device performance, the bio-cast SQ thin film was annealed at temperatures ranging from 50°C to 130°C. As shown in Fig. 8a, the SQ films annealed at 110°C and 130°C exhibit (001) and (002) peaks, which suggest crystalline characteristics. The EQE of the planar cell (Fig. 8b) suggests that the photoresponse improves when annealing temperatures are increased up to 110°C. At an annealing temperature of 130°C, two peaks at approximately 650 nm and 750 nm, belonging to the SQ film, are present, suggesting that the monomeric SQ undergoes a dimerization process when annealing temperatures are increased. The cell annealed at 110°C exhibits FF=0.59, V at 1 solar irradiance. OC =0.76 V and J SC With an efficiency of approximately 4.6% (η) and =10.05 mA / cm² P It exhibits a peak indicating ), and FF rises to approximately 0.70 at lower intensity. When using an annealing temperature increased to approximately 130°C, η P is V OC Since it drops to 0.46 V, it appears to drop to 2.9% (see Figs. 9a and 9b). As shown in Fig. 8a, when an annealing temperature of 130°C is used, crystallinity is thought to increase and FF is thought to rise to 0.67 at higher power intensities.

[0105] SQ:PC 70A BM(1:6) bulk heterojunction was prepared in a manner similar to that described in Example 2. SQ:PC annealed at 50°C, 70°C, 110°C, and 130°C for 10 minutes. 70 There are no XRD peaks for the BM(1:6) bulk solar cell, which suggests amorphous characteristics. Although I do not wish to be bound by any specific theory, PC 70 BM is thought to disrupt the aggregation of SQ molecules and impair their crystallinity. The average roughness of the AFM images for the raw casting and four thermally annealed samples is approximately 0.579 ± 0.06 nm, and the SQ phase and PC 70 There is no clear phase separation contrast on the BM, which is consistent with the XRD measurement results. Additionally, SQ and PC through thermal annealing 70 The component reorganization of the BM is investigated by XPS (Fig. 10). PC 70 BM molecule (C 82 H 14 Since no N atom exists within O2), the N 1s peak with a binding energy of 402 eV is SQ:PC 70 SQ(C on the upper surface of the BM membrane 32 H 44 SQ and PC imply the presence of N2O6 aggregation. 70 Strong C 1s and O 1s peaks appearing to belong to the BM are present. SQ and PC on the surface for 5 samples 70 The composition of the BM is evaluated using the O / C atomic ratio obtained from XPS measurements (Fig. 10a). Since the N peak is too weak, the C / N or O / N atomic ratio is not applied for the verification of the composition. As shown in Fig. 10b, various SQ:PC 70The concentration obtained from the surface of the BM sample is consistent with AFM measurements, and there is no significant change in weight ratio after thermal annealing. Therefore, from XRD, AFM, and XPS measurements, it does not appear that there is a change in morphology or crystallinity in the rotary cast sample through thermal processing alone.

[0106] The device performance for the five devices is shown in Fig. 11. SQ:PC annealed at 70°C 70 The efficiency of the BM (1:6) bulk cell drops from about 5.3% (FF=0.48) at 0.02 solar (2 mW / cm²) AM1.5G illumination to about 4.0% (FF=0.37) at 1 solar illumination. The drop in FF suggests that these bulk solar cells maintain resistance and exhibit a lack of double-continuous charge transport pathways to each electrode (which can consequently suppress the extraction of free carriers).

[0107] SQ and PC in the bio-casting membrane 70 To further control the morphological changes and crystallinity of the BM, a combination of solvent annealing and thermal annealing was investigated. The solvent annealing time is controlled by holding the film inside a covered glass vial immediately after spin-coating in air. The vial is filled with 1 ml of dichloromethane (DCM). To prevent rapid evaporation of the solvent, the vial is covered with a lid. Then, to remove the remaining DCM solvent, the raw casting and four annealed films were placed on a hot plate inside an N2 glove box and annealed at 50°C. As shown in Fig. 12, SQ:PC 70The roughness of the BM membrane increases by a single-order magnitude from approximately 0.83 nm (Fig. 12a – raw casting without solvent or thermal annealing) to approximately 8.4 nm (Fig. 12c – thermal annealing at 50°C after solvent annealing with DCM for 30 minutes). The results for Figs. 12b and 12d represent the results for thermal annealing alone. XRD data (Fig. 12e – membrane thermally annealed at 50°C after exposure to various solvent annealing times) for the SQ:PC annealed for a longer period 70 This clearly demonstrates the presence of the (001) SQ peak for the BM film, which indicates that the DCM vapor phase utilizes SQ:PC through the solubility and volatility of the DCM annealing solvent. 70 This implies that it promotes nanoscale phase separation of BM mixtures. The results are SQ:PC 70 This implies that the morphology and molecular order of BM bulk solar cells can be controlled by the solubility and vapor pressure of the annealing solvent.

[0108] The performance of devices thermally annealed at 50°C after exposure to solvent annealing by DCM for various durations is presented in Fig. 13. For the sample annealed for 6 minutes at 0.02 solar AM1.5G illumination, the highest efficiency of approximately 5.3% (FF=0.47) is achieved, and this efficiency gradually decreases to approximately 4.4% (FF=0.39) at 1 solar illumination. When using DCM annealing for 6 minutes, SQ:PC 70The FF of BM bulk devices appears to have higher values ​​at higher power intensities compared to bio-cast devices, implying superior carrier charge transport within the bulk film. The crystallinity characteristics of SQ in the aforementioned mixture suggest that SQ molecules aggregate in an ordered manner capable of enhancing hole charge transport. DCM solvent annealing appears to reduce to some extent the charge imbalance that degrades device performance from thermal annealing alone. Since the FF of DCM-annealed devices remains lower than 0.50, SQ and PC 70 The well-controlled nanoscale phase separation of the BM mixture can be further investigated through various solvents and annealing times. Figure 14 shows the EQE response of the fabricated device described in Figure 13, exhibiting a spectroscopic response from about 300 nm to about 750 nm.

[0109] Except as in Examples or otherwise described, all numerical values ​​expressing amounts of ingredients, reaction conditions, analytical measurements, etc. used in this Specification and Claims should be understood in all cases as being modified by the term “about.” Accordingly, unless otherwise stated, numerical parameters described in this Specification and the appended Claims are approximations that may vary depending on the desired properties to be obtained with the present disclosure. Each numerical parameter should not be interpreted as an attempt to limit the application of the doctrine of equivalents to at least the claims, but should be interpreted with respect to significant numerical values ​​and ordinary rounding methods.

[0110] Although the numerical ranges and parameters describing the broad scope of this disclosure are approximations, the numerical values ​​described in the specific embodiments are reported as accurately as possible unless otherwise stated. However, any numerical value inherently contains some error resulting from the standard deviation found in their respective test measurements.

[0111] As used herein, singular terms mean "one or more" and should not be limited to "only one" unless explicitly stated otherwise. Accordingly, for example, "layer" should be interpreted to mean "one or more layers."

Claims

Claim 1 A method for manufacturing a photosensitive device comprising the following steps: providing a structure having one or more first electrodes and a bulk heterojunction, wherein the bulk heterojunction comprises one or more first organic photoactive materials and one or more second organic photoactive materials, wherein the first organic photoactive materials and the second organic photoactive materials are small molecule materials, and at least one of the first organic photoactive materials and the second organic photoactive materials is squaraine; providing a solvent, wherein the solvent is dichloromethane; vaporizing at least a portion of the solvent; and exposing at least a portion of the structure to the vaporized solvent for a time of 5 to 30 minutes, wherein the exposure to the vaporized solvent increases the crystallinity of one or more of the first organic photoactive materials and the second organic photoactive materials. Claim 2 A method according to claim 1, further comprising the step of thermally annealing the structure. Claim 3 A method according to paragraph 2 in which thermal annealing occurs after at least a portion of the structure is exposed to a vaporized solvent. Claim 4 A method according to paragraph 2 in which thermal annealing occurs at a temperature of 50°C or higher. Claim 5 A method according to claim 1, wherein the structure is manufactured by depositing one or more first organic photoactive materials and one or more second organic photoactive materials on one or more first electrodes. Claim 6 A method according to claim 5, wherein the deposition is performed by spin-casting. Claim 7 A method according to claim 1, further comprising the step of patterning one or more second electrodes on a bulk heterojunction. Claim 8 A method according to claim 5, further comprising the step of positioning an interface layer between one or more first electrodes and a bulk heterojunction. Claim 9 A method according to claim 7, further comprising the step of positioning one or more blocking layers between a bulk heterojunction and one or more second electrodes. Claim 10 A method according to claim 1, wherein the structure is exposed to a vaporized solvent within a sealed container.

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