Patent Application
20240049588
The present invention relates to the field of organic electronics, specifically organic photoresponsive devices. Further, the invention is directed to devices for sensitive detection of infrared light using an active layer adapted for reducing device noise current. The active layer includes a light sensitive material and an insulative component that modifies the output signal of the device.
The last two decades have witnessed the rise of soft condensed matter systems in the form of solution-processed organic semiconductors (OSCs) based on molecules and polymers. These materials have enabled a new generation of optoelectronic technologies owing to their synthetic modularity, distinct manufacturing paradigms, rich variety of optical and transport phenomena, and opportunities for modification of device structures that were not possible with inorganic materials.1-14 OSCs that effectively produce and harvest visible and near-IR light find utility in a variety of commercially relevant optoelectronic technologies such as the production of organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs).
The progression of organic materials into the infrared spectrum has encountered high dark current and noise due to increased thermally generated carriers.15 Noise is further amplified under the application of an external reverse bias, the normal operating mode of an organic photodetector or organic photodiodes (OPD). These issues remain challenging for enabling OPDs with high detectivity and low noise.
Photodetectors operating across the near infrared-shortwave infrared (NIR-SWIR, ═=0.9-1.8) are essential elements in modern scientific, industrial, energy, medical, semiconductor, and defense applications. Emerging technologies for NIR-SWIR photodetection are having a global societal impact in renewable energy, healthcare, information science, building and machine automation. However, these technologies are subject to stringent cooling requirements, high-costs, and are largely incompatible with silicon-based technologies, attributes that are prohibitive for many applications and emerging technologies.16-19 Despite widespread efforts in scientific and engineering disciplines, photodetection beyond the cut-off wavelength of silicon (λc˜1.1/1.0 μm) remains dependent on archetypal crystalline inorganic semiconductors such as germanium (Ge) or alloys of indium gallium arsenide (InGaAs).
These present-day photodetection devices rely primarily on semiconductors that, depending on their bandgap, are able to transduce photons of different energies into electrical signals for subsequent processing, image reconstruction and storage. Historically, this has been enabled by the use of photodiodes and phototransistors made from crystalline inorganic semiconductors such as silicon or Group III-V compounds—materials heavily used in modern electronics and optoelectronics. Infrared photon detection/sensing is currently dominated by indium antimonide (InSb), which covers the shortwave infrared (SWIR, λ=1-3 μm) and midwave infrared (MWIR, λ=3-5 μm) regions, and alloys of mercury-cadmium-telluride (MCT HgCdTe) for the longwave infrared (LWIR, λ=18-14 μm) region. These materials are fabricated from single crystals/epitaxial growth and suffer from limited modularity, intrinsic fragility, high-power consumption, requiring cryogenic cooling/low temperature operation, and are largely incompatible with integrated circuit technologies. They are very expensive and cannot be fabricated into large formats. Emerging technologies require significant cost reductions, form-factors, and mechanical properties that can provide pathways to embodiments and performance attributes that are not available from epitaxy-based/single-crystal technologies. For example, the cost of sensitive and fast image sensors is prohibitive for emerging applications.
A constraining feature of these narrow bandgap material systems is the high noise current density under an applied bias, resulting in specific detectivities (D*) under practical operating conditions that are too low for practical utilization. In contrast, organic photodiodes (OPDs) comprised of π-conjugated organic semiconductors (OSCs) overcome critical manufacturing and operating drawbacks of these inorganic semiconductors. Bulk-heterojunction (BHJ) active layers blend n-type and p-type materials, which provide significant advantages including low-costs, no cooling requirement, diverse production processes which are resource-friendly and energy-efficient, scalability, seamless complementary metal-oxide-semiconductor (CMOS) integration, tolerance toward structural defects and disorder and form factors (e.g., shapes and sizes) that are not realizable using crystalline photodiodes. These attributes, combined with flexibility in materials and device design, provide opportunities not available with inorganics, and contrast with the extreme levels of order, high temperatures, and strict growth requirements of conventional IR semiconductors.
State-of-the-art polymer photodetectors/OPDs largely operate in the visible to near-infrared (λ=0.4-1 μm, VIS-NIR) region. Current efforts in materials design and synthesis have developed OSCs with narrow bandgaps capable of optical to electrical transduction of longer-wavelength light. A property that allows a comparison of performance between different detector technologies is the specific detectivity (D*). Values for D* of 1012 Jones (cm·Hz1/2 W−1) or larger have been reported for OPDs operating in the visible region, similar to their Si-based counterparts. In contrast, D* is several orders of magnitude lower for NIR-SWIR OPDs. Furthermore, while D* values ranging from ˜1011-1012 Jones have been reported at 0 V within a spectral range of 0.6 μm-1.4 μm, these measurements do not always account for all contributions to the noise. Furthermore, OPDs usually operate in reverse bias, where the measured reverse dark current (Jdark) rises significantly from the value at 0 V. This results in a higher noise current density, resulting in D* values under practical operating conditions of about 108 Jones, far too low for practical utilization, meaning that inorganic semiconductor devices are the only viable technology for sensitively detecting faint NIR-SWIR light.
Thus, despite the increasing availability of organic IR materials, a major challenge facing IR-OPDs is higher dark current and noise as a consequence of decreasing bandgaps, due to higher rates of charge carrier recombination, trap states, and thermal population of free carriers.5,6 Consequently, dark current suppression in OPDs has been the subject of several reports in the literature, with the most frequently utilized approaches encompassing injection blocking/charge selective layers, improved contact alignment, manipulation of blend morphology and device geometry, prevention of shunt paths via layer thickness increase, and charge transport layer structuring.22, 23 In the context of molecular design, a decrease in noise can be realized from tuning the effective bandgap (energetic alignments) and the degree of electronic disorder in the BHJ devices through molecular design. However, this requires extensive control of molecular structure that is difficult to achieve in narrow bandgap material systems.
U.S. Pat. No. 9,236,574 B2 relates to dinaphthol [2,3-a:2′,3′-h]phenazine compounds, methods for their preparation and intermediates used therein, formulations comprising them, the use of these compounds and formulations useful as semiconductor materials in organic electronic (OE) devices, and OE devices comprising these compounds and formulations.
U.S. Publication No. 2018/0261768 relates to compositions comprising an organic semiconducting material, a solvent, and specifically selected polymer particles, which allow modification of the viscosity of such compositions. This publication also relates to the use of such compositions in the production of OE devices.
Shen et al., “Wettability Control of Interfaces for High-Performance Organic Thin-Film Transistors by Soluble Insulating Polymer Films”, ACS Publications,
https://pubs.acs.org/doi/10/1021/acsomega.0c00548, relates to the morphology, crystallization, and electrical properties of C8-BTBT/PMMA blend films when different, soluble insulating polymer films were employed.
Macdec et al., “Organic Field Effect Transistors From Ambient Solution Processed Poly(Triarylamine)-Insulator Blends”, RCS Publications,
https://pubs.rsc.org/en/content/articlelanding/2008/jm/b802801j, relates to two component blends of amorphous poly(triarylamines) with selected amorphous and semi-crystalline polymeric binders for use in a semiconducting layer in organic field effect transistors.
The following sentences may be used to describe the invention:
1. In a first aspect, the present invention relates to a photodetector configured for converting light to an electronic signal, comprising:
2. In a second aspect, the present invention relates to a photodetector configured for converting light to an electronic signal, comprising:
3. The photodetector of any one of sentences 1-2, wherein the photoactive polymer electron donor may include a polymer according to Formula I or Formula II:
wherein FG and FG′ are each independently selected from the group consisting of hydrogen, an optionally substituted hydrocarbyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an optionally substituted aryl group containing 6 to 20 carbon atoms, or from about 6 to 16 carbon atoms, an optionally substituted heteroaryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms, and an optionally substituted aryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms,
wherein πA is an electron-poor or electron-deficient aromatic moiety that provides a structural unit in the copolymer according to formulae (A)-(F):
wherein R1 and R2 are each individually selected from a hydrogen, a hydrocarbyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an alkoxyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an optionally substituted aryl group containing 6 to 20 carbon atoms, or from about 6 to 16 carbon atoms, and a heteroaryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms;
4. The photodetector of any one of sentences 1-3, wherein the hole transport component may include one or more conducting materials with a work function range between 4.5-5.5 eV.
5. The photodetector of any one of sentences 1-4, wherein the electron acceptor may include fullerenes, non-fullerene acceptors (NFAs), polymers or any material which can serve as an electron acceptor.
6. The photodetector of any one of sentences 1-5, wherein the electron acceptor may be selected from the group consisting of [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM), [60]PCBM, PCBM, C60, C70, fullerenes, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (BTP-4F), and combinations thereof.
7. The photodetector of any one of sentences 1-6, wherein the photodetector may be configured to detect radiation spanning the visible and infrared.
8. The photodetector of any one of sentences 1-7, wherein the one or more insulating materials may be integrated within the organic photoactive layer.
9. The photodetector of any one of sentences 1-8, wherein the one or more insulating materials may include an insulating polymer.
10. The photodetector of any one of sentences 1-8, wherein the one or more insulating materials may be selected from the group consisting of polyethylene, polystyrene, polysulfone, polymethyl(methacrylate), polycarbonate, polyisobutylene, polylactic acid, polyvinylchloride, polyvinylpyrrolidone, polypropylene, polyethylene terephthalate, acrylonitrile butadiene styrene, and any other polymer.
11. The photodetector of any one of sentences 2-10, wherein the one or more insulating materials may be located within the heterojunction or the one or more photoactive layers.
12. The photodetector of any one of sentences 1-11, wherein at least one electrode may include transparent conducting oxides, for example, indium tin oxide (ITO), tin oxide (TO), gallium indium tin oxide (GaITO), and zinc indium tin oxide (ZITO); thin metal layers having a thickness of 50-300 nm; transparent conducting polymers, for example, poly(3,4,-ethylenedioxythiophene), (PEDOT), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), polyaniline, and polypyrrole, or any other electrically conductive material.
13. The photodetector of any one of sentences 1-12, wherein said optoelectronic device may be configured to generate an electrical current with reduced noise by at least an order of magnitude under bias up to ±5V in response to incident radiation relative to an optoelectronic device in the absence of the narrow bandgap electron donor.
14. In a third aspect, the present invention relates to a method for producing the photodetector of any one of sentences 1-13 comprising steps of:
15. The method of sentence 14, wherein the bulk heterojunction may be deposited via a method selected from the group consisting of spin coating, spray coating, blade coating, dip coating, screen printing, flexographic printing, slit coating, and ink-jet printing.
16. The method of any one of sentences 14-15, wherein the first electrode may be deposited onto the blended film via thermal evaporation in a vacuum chamber at a pressure of about 1×10 −6 torr.
17. The method of sentence 16, wherein in the photodetector a combination of the one or more photoactive polymeric electron donors and the electron acceptor may be present in the bulk heterojunction at a concentration of from about 5 mg/ml to about 10 mg/ml.
18. The method of sentence 16, wherein in the photodetector the one or more insulating materials may be present in the bulk heterojunction at a concentration of from about 7 mg/ml to about 30 mg/ml, or a concentration of from about 10 mg/ml to about 25 mg/ml.
19. In a fourth aspect, the present invention relates to a composition comprising an electron donor, an electron acceptor, and an insulating polymer,
wherein FG and FG′ are each independently selected from the group consisting of hydrogen, an optionally substituted hydrocarbyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an optionally substituted aryl group containing 6 to 20 carbon atoms, or from about 6 to 16 carbon atoms, an optionally substituted heteroaryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms, an optionally substituted aryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms,
The invention provides a method and process for preparing an IR sensitive device derived from a multi-component blend of π-conjugated polymers that function as electron donors, an electron acceptor, and an insulating polymer. Such devices demonstrate functionality spanning the visible to infrared spectral regions.
The following definitions of terms are provided in order to clarify the meaning of certain terms as used herein.
As used herein, the term “hydrocarbyl substituent” or “hydrocarbyl group” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having a predominantly hydrocarbon character. Each hydrocarbyl group is independently selected from hydrocarbon substituents, and substituted hydrocarbon substituents containing one or more of halo groups, hydroxyl groups, alkoxy groups, mercapto groups, nitro groups, nitroso groups, amino groups, pyridyl groups, furyl groups, imidazolyl groups, oxygen and nitrogen, and wherein no more than two non-hydrocarbon substituents are present for every ten carbon atoms in the hydrocarbyl group.
As used herein, the term “hydrocarbylene substituent” or “hydrocarbylene group” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group that is directly attached at two locations of the molecule to the remainder of the molecule by a carbon atom and having predominantly hydrocarbon character. Each hydrocarbylene group is independently selected from divalent hydrocarbon substituents, and substituted divalent hydrocarbon substituents containing halo groups, alkyl groups, aryl groups, alkylaryl groups, arylalkyl groups, hydroxyl groups, alkoxy groups, mercapto groups, nitro groups, nitroso groups, amino groups, pyridyl groups, furyl groups, imidazolyl groups, oxygen and nitrogen, and wherein no more than two non-hydrocarbon substituents is present for every ten carbon atoms in the hydrocarbylene group.
The term “alkyl” as employed herein refers to straight, branched, cyclic, and/or substituted saturated chain moieties of from about 1 to about 100 carbon atoms.
The term “alkenyl” as employed herein refers to straight, branched, cyclic, and/or substituted unsaturated chain moieties of from about 3 to about 10 carbon atoms.
The term “aryl” as employed herein refers to single and multi-ring aromatic compounds that may include alkyl, alkenyl, alkylaryl, amino, hydroxyl, alkoxy, halo substituents, and/or heteroatoms including, but not limited to, nitrogen, oxygen, and sulfur.
As used herein, the term “arylene” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a single and multi-ring aromatic compounds, such as defined in the term “aryl” that is directly attached at two locations of the molecule to the remainder of the molecule by a carbon atom and having a predominantly hydrocarbyl character. Each arylene group is independently selected from divalent single and multi-ring aromatic compounds, and substituted divalent hydrocarbon substituents containing alkyl, alkenyl, alkylaryl, amino, hydroxyl, alkoxy, halo substituents, and/or heteroatoms including, but not limited to, nitrogen, oxygen, and sulfur.
Additional details and advantages of the disclosure are set forth in part in the description which follows. The details and advantages of the disclosure may be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure and that the claims define the scope of the invention.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The drawings, which are incorporated in and form a portion of the specification, illustrate certain aspects of the invention and, together with the entire specification, are meant to explain preferred embodiments of the present invention to those skilled in the art. The drawings supplement the specification and are intended to illustrate further the invention and its advantages.
The present invention demonstrates that incorporating wide-bandgap insulating polymers within the BHJ suppresses noise current by dilution of the transport and trapping sites as determined using capacitance-frequency analysis. The resulting D* of NIR-SWIR OPDs operating from 600-1400 nm under an applied bias of −2 V was improved by two orders of magnitude from 108 Jones to 1010 Jones when the polymer PSU was incorporated within the blends. This strategy may be utilized to reduce noise in IR-OPDs using insulating polymers and allow the practical use of IR-OPDs under a reverse bias operation.
In one aspect, the present invention relates to a photodetector configured for converting light to an electronic signal, including:
In a second aspect, the present invention relates to photodetector configured for converting light to an electronic signal, comprising:
One or more additional layers may be provided between the anode and the cathode. A hole-transporting layer and/or a hole-injecting layer may be provided between the anode and the bulk heterojunction layer. An electron-transporting layer and/or an electron injecting layer may be provided between the cathode and the bulk heterojunction layer.
Substrate 6, which supports the film is typically glass and can be other solid materials (rigid, semi-flexible, or flexible) including quartz, metal, plastic, silicon, silica, mineral, ceramic, semiconducting material, or any combination of these. The lower electrode is utilized as the anode 5 and the upper electrode 1 is utilized as the cathode. This electrode configuration and its polarity can also be presented in an inverted fashion. Suitable semiconducting materials are those that comprise a photoactive small molecule, oligomeric, or polymeric electron donor and an electron acceptor, preferably present in a weight ratio of from about 0.5 to about 1:3 or from 1:1 to 1:2.
The anode 5, for example, may be formed from indium-tin oxide (ITO), tin oxide (TO), gallium indium tin oxide (GaITO), zinc indium tin oxide (ZITO), indium zinc oxide (IZO), gold, palladium, silver, or platinum and is typically manufactured by sputtering, vapor deposition, and printing processes.
The hole transport layer 4, for example, may be comprised of transparent conductive polymers such as fused or unfused polythiophenes, optionally poly(ethylenedioxythiophene) (PEDOT) having a charge-balancing polyanion, optionally polystyrene sulfonate (PSS). Additional examples may include polyaniline and polypyrrole.
The photoactive layer 3, for example, may be comprised of an electron donor, an electron acceptor, and an insulating component. This insulating component may include but is not limited to polyethylene, polystyrene (PS), polysulfone (PSU), polymethyl(methacrylate) (PMMA), polycarbonate, polyisobutylene, polylactic acid, polyvinylchloride, polyvinylpyrrolidone, polypropylene, polyethylene terephthalate, acrylonitrile butadiene styrene, or any other suitable polymer.
The electron donors of the present disclosure may have a narrow bandgap of less than 1.4 eV, or from about 0 to about 1.4, or from about less than 1.4 to greater than 0.01 to less than 1 eV. For example, the electron donors of the present disclosure may comprise a polymer according to Formula I or Formula II:
wherein FG and FG′ are each independently selected from the group consisting of hydrogen, an optionally substituted hydrocarbyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an optionally substituted aryl group containing 6 to 20 carbon atoms, or from about 6 to 16 carbon atoms, an optionally substituted heteroaryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms, and an optionally substituted aryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms,
wherein R1 and R2 are each individually selected from a hydrogen, a hydrocarbyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an alkoxyl group containing 1 to 26 carbon atoms, or from about 5 to 26 carbon atoms, or from about 8 to about 16 carbon atoms, an optionally substituted aryl group containing 6 to 20 carbon atoms, or from about 6 to 16 carbon atoms, and a heteroaryl group containing 3 to 26 carbon atoms, or from about 3 to 20 carbon atoms, or from about 3 to about 10 carbon atoms,
Other suitable examples of electron donor polymers are disclosed in CN108365098, WO 2017/191466, US20190229269, and US2022/0102658, which electron donor polymers are hereby incorporated by reference herein. For example, the electron donor polymers may also include (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline), and a poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]] polymer (PBDB-T), having the following structure:
wherein n is an integer greater than 1.
The electron donors of the present invention may have in-chain donors and strong heterocyclic acceptor components. The πS and πA components of Formulae (I)-(II) hybridize with one another to collectively lower the highest occupied molecular orbital—lowest unoccupied molecular orbital (HOMO-LUMO) levels to provide bandgaps below 1.4 eV, or lower than 1.0 eV. This reduction in bandgap leads to reduced thermal noise generation.
The electron acceptors of the present invention may comprise fullerene and non-fullerene acceptors, for example molecules and polymers, having extended, rigid, π-conjugated electron-deficient frameworks that can facilitate exciton and charge delocalization. Suitable examples of non-fullerene acceptors may include substituted or unsubstituted 3,9-bis(2-methylene-(3-(1,1-5 dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC):
or a compound according to:
wherein R6 may be a halogen, for example Br, Cl, and F; a polyaromatic hydrocarbon, perylene diimide (PDI), or derivatives thereof, for example, ITIC-2F, alkylated ITIC, ITIC-Th, and IEICO-4F, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (BTP-4F), and combinations thereof.
Suitable examples of fullerene may include C60, C70, C78, and C84 fullerenes or a derivative thereof including, without limitation, PCBM-type fullerene derivatives (including phenyl-c61-butyric acid methyl ester (C60PCBM) and phenyl-C71-butyric acid methyl ester (C70PCBM), TCBM-type fullerene derivatives (e.g. tolyl-C61-butyric acid methyl ester (C6TCBM)), and ThCBM-type fullerene derivatives (e.g. thienyl-C61-butyric acid methyl ester (C60ThCBM)).
The photoactive organic layers may be applied over an area, for example, by spin coating, spray coating, blade coating, dip coating, screen printing, flexographic printing, slit coating, ink-jet printing, etc. These processes permit a large area to be coated, since no structuring of the semiconductor is required inside the active sensor area.
The cathode 1 may, for example, be formed from Ca, Al, Ag, Pd, Pt, Au, Au alloy, LiF, Mg, indium-tin oxide (ITO), tin oxide (TO), gallium indium tin oxide (GaITO), or zinc indium tin oxide (ZITO) and is typically applied by thermal evaporation or electron beam evaporation but can also be applied using various methods including printing. The work functions of the two electrodes forms an internal electrical field which separates the electron hole pairs caused by the absorption of light.
In use, the photodetectors as described in this disclosure may be connected to a voltage source for applying a reverse bias to the device and/or a device configured to measure photocurrent. The voltage applied to the photo detectors may be variable. In some embodiments, the photodetector may be continuously biased when in use.
The proposed methods and devices enable photoresponsive devices to be produced cost-effectively using solution-processing methods. These devices range from smaller single point devices to large area devices which span different technologies, and may be applied in the imaging, sensing, lighting, automotive, environmental, and space industries. By contrast with previously known photodetectors that are operated in the visible and infrared regions, the new photodetectors, which contain blends of conventional plastics, are not complex or expensive to produce and may be mounted on flexible substrates by simple printing processes. Furthermore, this method provides a simple approach to mitigate noise signals in organic photoresponsive devices under a reverse bias operation. This method also provides a means to modify the active layer, for example creating thick layers on CMOS components, and improving stability. This method can also provide an improved thermal stability relative to other methods.
Examples were carried out to demonstrate a versatile strategy to reduce the device noise, which relies on the incorporation of wide bandgap insulators within the BHJ. The incorporation of insulators has been previously demonstrated in organic photovoltaics (OPVs) and organic field-effect transistors (OFETs). It was reported to have retained the optical and electronic properties of the active material while improving their performance.24-29 However, there have been few reports in incorporating insulators for the optimization of OPDs.30, 31 Therefore, the present invention utilized a model system comprised of an IR sensitive donor-acceptor conjugated polymer (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline)) (CDT-TQ) and fullerene acceptor [6,6]-phenyl C71-buytic acid methyl ester (PC71BM) as the photoactive layer (
The specific detectivity (D*) is the main figure of merit that allows a comparison of performance between different detector technologies, and is the signal-to-noise ratio given by:
where q is the elementary charge, λ the wavelength, h the Planck constant, c the speed of light, A the device area in cm2, R the responsivity in A W−1, and Sn is the noise current spectral density (total noise of a photodiode) in A Hz−1/2. Applying a reverse bias of −2 V resulted in a concomitant increase in the EQE to 40% and an increase in R from 0.20 A W−1 to 0.37 A W−1 (
S
n(S1/f2+Sshot2+Sthermal2)1/2 (2)
where Sshot is the shot noise, Sthermal is the thermal noise, and S1/f is the flicker noise. The application of a reverse bias resulted in an increase in the total noise Sn at 400 Hz from 1.9×10−13 A Hz−1/2 at 0 V up to 1.4×10−10 A Hz−1/2 at −2 V (
These results demonstrated that achieving a high signal-to-noise ratio in the NIR-SWIR is often challenging due to the inherently large dark currents in narrow bandgap materials systems. In semicrystalline conjugated polymer:fullerene (i.e., D-A) BHJs, sub-bandgap trap states affect charge transport and carrier recombination, thereby increasing Sn.21, 32, 33 Unlike reverse bias conditions, common to OPD operation, the low level of dark current in the absence of a bias can be substantially affected by the existence/presence of carrier trapping within these sub-bandgap states. However, previous studies have demonstrated that carrier trapping can be suppressed by dilution of the transport and trapping sites of OSCs by blending with a wide-bandgap material or insulator (high bandgap polymer).34, 35
To address and understand these issues, ternary systems comprised of CPDT-TQ:PC71BM combination blended with insulating (high/wide bandgap) polymers including polystyrene (PS), poly(methyl methacrylate) (PMMA), and polysulfone (PSU) were tested. For consistency, devices were fabricated using the same architecture and maintaining a CDT-TQ:PC71BM constant ratio of 1:2, in an analogous manner to the control in
The active layer incorporated different weight ratios (17%, 29%, 45%) of each insulating polymer, which were prepared by first diluting the insulating polymer at a concentration of 5 mg/mL, 10 mg/mL, 20 mg/mL in chlorobenzene, then dissolving CPDT-TQ and PC71BM using this solution in lieu of neat solvent (i.e., control).
Increasing the insulator concentration decreased the peak EQE from 45% to ˜10% at 1100 nm under −2 V bias for PSU and as low as 2% for PS and PMMA, demonstrating that diluting the active components with an insulating polymer reduces the volumetric light harvesting efficiency of the blends.28, 35, 36 Table 1 summarizes the performance parameters of OPDs obtained from PS, PMMA, and PSU using various concentrations of insulating polymer. Examination of D* at −2 V for the control device at −2 V (D*=5.3×108 Jones) and devices using 20 mg mL−1 solutions demonstrated an improvement when employing PS and PMMA (D*=4.7×109 and 2.8×109 Jones, respectively), while the PSU device shows the highest specific detectivity of D*=6.6×1010 Jones.
2.4 × 1010
6.6 × 1010
The highest D* at −2 V bias was obtained using PSU, prompting a detailed investigation of this ternary blend. A decrease in J from 1.1×10−4 to 6.8×10−6 A cm−2 was observed as the PSU concentration was increased from 5 mg/mL to 20 mg/mL (17-45 wt %) (
In the case of BHJs, the addition of an inert component required that the donor and acceptor components be sufficiently mixed to enable efficient exciton dissociation and charge separation. Each functional species must also form a percolating structure in order to allow efficient charge transport for electrons and holes to their respective electrodes. Atomic force microscopy (AFM) images of BHJ films incorporating PSU films demonstrated that PSU was mixed throughout the bulk in the composite films, diluting the active semiconductor components, progressing from 5 mg/mL to 20 mg/mL (
Additional AFM-infrared spectroscopy (AFM-IR) was conducted to better understand the distribution of components within the blends. In the absence of PSU, a prototypical BHJ morphology was evident, with phase separated domains on the order of 120 nm (See
Trap states (i.e., defect states) with intra-gap energies were prevalent within BHJ OPDs on account of the disordered nature of OSCs, structural defects, varying morphological features, the presence of impurities, and other contributions. These traps act as recombination centers, capture charge carriers, and increase dark current. To further understand the trap distribution/density along with the addition of PSU, capacitance-frequency (C-f) measurements to characterize the density-of-states (DOS) distribution were utilized. In these measurements, an applied ac bias modulated the occupation of defect/trap states near the Fermi energy, enabling a determination of the fraction of trapped charges that are thermally excited to mobile transport states. The trap energy (Eω), corresponds to traps within the bandgap that can respond to ac modulation, and is expressed as a function of the measurement frequency by
where k is Boltzmann's constant, T is the temperature, and ω0 is the rate prefactor for thermal excitation from the trap and is around 1012 s−1 in typical OPDs. The trap/defect density of states (DOS) distribution connects the materials composition and electronic properties, specifically to estimate localized trap states and is extracted from the C-f measurement according to the following equation:37-39
where Vbi is the built-in potential, q is the elementary charge, A is the device active area, t is the film thickness, and C(ω) is the capacitance measured with an ac perturbation of angular frequency, ω. Here Vbi ranges from 0.17 V to 0.21 V for different PSU concentrations, and the temperature is ˜300 K. It is important to note that the capacitance measurement accounts for the sum of electron and hole traps rather than each component exclusively.
The C-f behavior in the dark at 0 V bias demonstrated a rapid change in slope dC(ω)/(dln(ω)), which reflects an increase of the trap DOS. As shown in the C-f plots in
where NG is the fitting yielded the density of deep states, σ is the disorder spread, and EG0 is the mean energy of the deep traps. The DOS for different PSU concentrations are depicted in
The Gaussian DOS distribution characterizes the localized, deep trap states in the band gap. Carriers trapped in these deep states are difficult to escape before recombination occurs. Excluding the range below 10 Hz, the decrease of the shallow trap density correlates with the reduction in the dark current at the expense of increasing deep traps which may have been the cause of the reduced EQE. This reduction was also concurrent with the microscopy images of the highest concentration of PSU which formed thick films with large insulator domains that could inhibit the percolation pathway of charge carriers. The decrease in shallow traps was attributed to the dilution of the charge carrier components with an insulator at the ternary blend interface which is consistent with the observation of Abbaszadeh et al.34
The following examples are illustrative, but not limiting, of the methods and compositions of the present disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which are obvious to those skilled in the art, are within the spirit and scope of the disclosure. All patents and publications cited herein are fully incorporated by reference herein in their entirety.
This example involved the detailed device fabrication procedure for the polymer-insulator blend using an architecture of ITO/PEDOT:PSS/BHJ (bulk heterojunction)/ZnO/Al. ITO substrates were ultrasonically cleaned in detergent, deionized water, acetone, and 2-propanol for 10 minutes each in sequential cleaning steps. The substrates were dried and treated with UV-ozone for 10 minutes. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was filtered through a 0.45 μm PTFE syringe filter before spin-coating it onto the dried ITO substrates at 3500 rpm. The coated ITO substrates were then annealed at 120° C. in ambient conditions before transferring them to an N2-filled glovebox. The photoactive polymer, (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) blended with [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) in a 1:2 weight ratio was dissolved in anhydrous chlorobenzene at a polymer concentration of 7 mg/mL. The insulating component, for example, polysulfone was dissolved in anhydrous chlorobenzene at a concentration of 20 mg/mL and this solution was used to further dissolve the active materials. The blend solutions were spin-coated onto the PEDOT:PSS/ITO substrates at 1000 rpm. After drying, a zinc oxide (ZnO) nanoparticle solution in methanol was spin-coated onto the dried device at 3000 rpm. To complete the fabrication of the device, 100 nm Al electrodes were deposited on top of the blend film by thermal evaporation in a vacuum chamber at a pressure of 1×10−6 torr. The effective areas of these photodetectors were 4 mm2.
This example involved the detailed device fabrication procedure for the polymer-insulator blend using an architecture of ITO/ZnO/BHJ/MoOx/Ag. ITO substrates were ultrasonically cleaned in detergent, deionized water, acetone, and 2-propanol for 10 minutes each in sequential steps. The substrates were further dried and treated with UV-ozone for 10 minutes. Zinc oxide nanoparticles were spin coated onto the dried ITO substrates at 3000 rpm and annealed at 150° C. in ambient conditions before transferring them to an N2-filled glovebox. The photoactive polymer, (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) blended with [70]PCBM in a 1:2 weight ratio was dissolved in anhydrous chlorobenzene at a polymer concentration of 7 mg/mL. The insulating component, for example polysulfone, was dissolved in anhydrous chlorobenzene at a concentration of 20 mg/mL and was used to dissolve the active materials. The blend solutions were spin-coated on the ZnO/ITO substrates at 1000 rpm. To complete the fabrication of the device, 15 nm of MoOx, followed by 100 nm Ag, were deposited on top of the blend film by thermal evaporation in a vacuum chamber at a pressure of 1×10−6 torr. The effective areas of these photodetectors was 4 mm2.
This example involved the detailed device fabrication procedure for the polymer-insulator blend with the addition of non-fullerene electron acceptors using an architecture of ITO/ZnO/BHJ/MoOx/Ag. ITO substrates were ultrasonically cleaned in detergent, deionized water, acetone, and 2-propanol for 10 minutes each in sequential steps. The ITO substrates were further dried and treated with UV-ozone for 10 minutes. Zinc oxide nanoparticles were spin coated onto the dried ITO substrates at 3000 rpm and annealed at 150° C. in ambient conditions before transferring them to an N2-filled glovebox. The photoactive polymer, (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) and non-fullerene electron acceptor, 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6) were employed in a 1:1 weight ratio and dissolved in anhydrous chlorobenzene at a polymer concentration of 7 mg/mL. The insulating component, for example polysulfone, was dissolved in anhydrous chlorobenzene at a concentration of 10 mg/mL and was used to dissolve the active materials. The blend solutions were spin-coated on ZnO/ITO substrates at 2000 rpm. To complete the fabrication of the device, 15 nm of MoOx, followed by 100 nm Ag, were deposited on top of the blend film by thermal evaporation in a vacuum chamber at a pressure of 1×10−6 torr. The effective areas of these photodetectors was 4 mm2.
This example involved the detailed device fabrication procedure for the polymer-insulator blend using an architecture of ITO/ZnO/BHJ/MoOx/Ag. ITO substrates were ultrasonically cleaned in detergent, deionized water, acetone, and 2-propanol for 10 minutes each in sequential steps. The substrates were further dried and treated with UV-ozone for 10 minutes. A zinc oxide sol gel in 2-methoxyethanol was spin coated onto the dried ITO substrates at 3000 rpm and annealed at 200° C. in ambient conditions before transferring them to an N2-filled glovebox. The photoactive polymer, (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) blended with [70]PCBM in a 1:2 weight ratio was dissolved in anhydrous chlorobenzene at a polymer concentration of 7 mg mL−1. The insulating component such as poly methyl methacrylate was dissolved in anhydrous chlorobenzene at a concentration of 20 mg mL−1 and was used to dissolve the active materials. The blend solutions were spin-coated on the ZnO/ITO substrates at 1000 rpm. To complete the fabrication of the device, 15 nm of MoOx, followed by 100 nm Ag, were deposited on top of the blend film by thermal evaporation in a vacuum chamber at a pressure of 1×10−6 torr. The effective areas of these photodetectors was 4 mm2.
The donor polymer was (poly(4-(5-(4-(3,5-bis(dodecyloxy)benzylidene)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)thiophen-2-yl)-6,7-dioctyl-9-(thiophen-2-yl) [1,2,5]thiadiazolo[3,4-g]quinoxaline) and was synthesized as described previously.5, 25 The acceptor was [6,6]-Phenyl-C71-butyric acid methyl ester (PC71BM) which was purchased from Nano-C. Polysulfone (PSU) and the solvents were purchased from Sigma Aldrich and used as received.
All ternary blends investigated in this example comprised of a 1:2 ratio by weight of donor polymer CDT-TQ and PC71BM, to which varying concentrations of insulator (5 mg mL−1, 10 mg mL−1, 20 mg mL−1) was added by pre-dissolution, followed by removal of the solvent by drying under ambient conditions. The concentration of CDT-TQ was 8 mg mL−1. The % loading of insulator was 17%, 29%, and 45%.
Glass substrates with indium tin oxide (resistivity ≈20 Ωsq−1) (Ossila Ltd.) were sequentially cleaned via ultrasonication in detergent, deionized water, acetone, and isopropanol for 10 minutes. The substrates were further treated with UV-ozone for 15 minutes. A conventional architecture was adopted for the fabrication of the OPDs. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, or PEDOT:PSS (Heraeus 4083) was mixed with isopropanol in a 1:4 volume ratio and was spin-cast onto the clean substrates and annealed at 130° C. for 10 minutes under ambient prior to transfer into an N2 glovebox. The donor CDT-TQ and acceptor PC71BM were dissolved in chlorobenzene solutions of PSU and the ternary blend solutions were spun-cast to form BHJ films with thicknesses ≈180-580 nm, as measured by a stylus profilometer (Bruker Dektak XT). A ZnO nanoparticle solution was cast to form an ≈10 nm film for electron extraction. 100 nm of aluminum top electrodes were deposited through thermal evaporation under vacuum at 1×10−6 torr. The device's active area was 0.04 cm2.
Current density-voltage characteristics were recorded in a nitrogen atmosphere under the dark using a Keithley 2400 source measure unit. EQE measurements were performed using the Bentham PVE300, where the monochromatic light source was modulated at 400 Hz by an optical chopper, and the device photocurrent was amplified through a low-noise preamplifier (SRS 570) and measured with a lock-in amplifier (Bentham 496 DSP). Biased measurements were measured via the front end of the preamp. The noise spectral densities were obtained by measuring the device through a preamplifier connected to the signal analyzer (Keysight N9020B MXA).
Electrochemical impedance spectroscopy was performed with a Gamry Interface 1010E potentiostat in the dark and in the frequency range of 10 Hz to 2 MHz. A small AC voltage of 20 mV was used to maintain linearity of the response and high enough to minimize measurement noise. The DC bias was set at 0 V, −0.5 V, −1 V, and −2 V.
Table 3 shows the parameters obtained from the Gaussian distribution of trap DOS at −2 V. Parameters for the control device were unable to properly fit with equation 5.
The role of dark current noise was suppressed and achieved increased detectivity with the application of a reverse bias in the IR OPD' s of the present invention. A systematic change was observed in the photocurrent and dark noise as the concentration of insulating polymer was increased. These modifications provided improved results as the measured noise current from the device was suppressed under reverse bias. The insulating matrix caused a disruption of the charge carriers in the blends affecting the total photocurrent while suppressing noise. Although the overall noise was suppressed, some undesirable trade-offs involved lower shallow trap state density and slower charge carrier mobility as a result of increased film thickness due to a higher solution viscosity. Therefore, polymer insulated-modified devices based on narrow bandgap IR conjugated polymers exhibit increased detectivity despite a decrease in photocurrent signal. The present invention demonstrated that an insulating polymer can alleviate the long standing problems of current narrow band gap systems, which suffer from increased noise carriers.
Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. As used throughout the specification and claims, “a” and/or “an” and/or “the” may refer to one or more than one. Unless otherwise indicated, all numbers expressing quantities, proportions, percentages, or other numerical values are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
It is to be understood that each component, compound, substituent or parameter disclosed herein is to be interpreted as being disclosed for use alone or in combination with one or more of each and every other component, compound, substituent or parameter disclosed herein.
It is further understood that each range disclosed herein is to be interpreted as a disclosure of each specific value within the disclosed range that has the same number of significant digits. Thus, for example, a range from 1-4 is to be interpreted as an express disclosure of the values 1, 2, 3 and 4 as well as any range of such values.
It is further understood that each lower limit of each range disclosed herein is to be interpreted as disclosed in combination with each upper limit of each range and each specific value within each range disclosed herein for the same component, compounds, substituent or parameter. Thus, this disclosure to be interpreted as a disclosure of all ranges derived by combining each lower limit of each range with each upper limit of each range or with each specific value within each range, or by combining each upper limit of each range with each specific value within each range. That is, it is also further understood that any range between the endpoint values within the broad range is also discussed herein. Thus, a range from 1 to 4 also means a range from 1 to 3, 1 to 2, 2 to 4, 2 to 3, and so forth.
Furthermore, specific amounts/values of a component, compound, substituent or parameter disclosed in the description or an example is to be interpreted as a disclosure of either a lower or an upper limit of a range and thus can be combined with any other lower or upper limit of a range or specific amount/value for the same component, compound, substituent or parameter disclosed elsewhere in the application to form a range for that component, compound, substituent or parameter.
All references cited herein are hereby incorporated by reference in their entirety as if fully set forth herein.
This application claims the benefit of U.S. Provisional Application No. 63/370,013, filed on Aug. 1, 2022, the entire disclosure of which is hereby incorporated by reference as if set forth fully herein.
This invention was made with government support under grant/contract OIA—1757220 awarded by the National Science Foundation. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63370013 | Aug 2022 | US |
