TW202415727A - Composition - Google Patents

Abstract

A composition comprising an electron-donating polymer and an electron acceptor wherein the electron-donating polymer comprises a benzo[1,2-b:4,5-b']dithiophene repeat unit and wherein a film of the electron-accepting material has a peak absorption wavelength greater than 1000 nm. The composition may be used as a photosensitive layer of an organic photodetector.

Description

Composition

Embodiments of the present disclosure relate to compositions suitable for use in organic photodetectors.

A range of organic electronic devices comprising organic semiconductor materials are known, including organic light emitting devices, organic field effect transistors, organic photovoltaic devices and organic photodetectors (OPDs).

WO 2018/065352 discloses an OPD having a photoactive layer, wherein the photoactive layer contains: a small molecule acceptor without a fullerene moiety and a co-polymer electron donor having donor and acceptor units.

WO 2018/065356 discloses an OPD having a photoactive layer, which contains: a small molecule acceptor without a phenotype and a co-polymer electron donor having randomly distributed donor and acceptor units.

Yao et al., "Design, Synthesis, and Photovoltaic Characterization of a Small Molecular Acceptor with an Ultra-Narrow Band Gap", Angew Chem Int Ed Engl. 2017 Mar 6;56(11):3045-3049. Revealed a non-polyhedral acceptor with a 1.24 eV band gap.

Li et al., "Fused Tris(thienothiophene)‐Based Electron Acceptor with Strong Near‐Infrared Absorption for High‐Performance As‐Cast Solar Cells", Advanced Materials, Vol. 30(10), 2018, disclose a fused octacyclic electron acceptor (FOIC) for solar cells.

Gao et al., "A New Non-fullerene Acceptor with Near Infrared Absorption for High Performance Ternary-Blend Organic Solar Cells with Efficiency over 13%" Advanced Science, Vol. 5(6), June 2018, disclose a solar cell containing an acceptor-donor-acceptor (A-D-A) type non-fullerene acceptor 3TT-FIC having three fused thieno[3,2-b]thiophenes as the central core and difluoro-substituted indanones as end groups.

Wang et al., "Fused Hexacyclic Nonfullerene Acceptor with Strong Near-Infrared Absorption for Semitransparent Organic Solar Cells with 9.77% Efficiency" disclose solar cells containing an acceptor IHIC based on an electron-donating dithiophenecyclopentathieno[3,2- b ]thiophene flanked by an electron-withdrawing group 1,1-dicyanomethylene-3-indanone.

The following is a summary of the scope of certain embodiments disclosed herein. It should be understood that these scopes are presented only to provide the reader with a brief overview of these certain embodiments, and it is not intended that these scopes limit the scope of the present disclosure. In fact, the present disclosure may cover a variety of scopes and/or scope combinations that may not be described.

Embodiments of the present disclosure provide compositions comprising an electron donating polymer and an electron accepting material, wherein the electron donating polymer comprises benzo[1,2-b:4,5-b']dithiophene repeating units and wherein a film of the electron accepting material has a peak absorption wavelength greater than 1000 nm.

The electron accepting material is preferably a non-porous acceptor.

In a preferred embodiment, the electron acceptor is a compound of formula (I): EAG - EDG - EAG (I) wherein each EAG is an electron accepting group; and EDG is an electron donating group of formula (II) or (III): (II) (III) each X is independently O or S; Ar ³ and Ar ⁴ are independently monocyclic or polycyclic aromatic or heteroaromatic groups at each occurrence; Ar ⁵ is selected from the group consisting of thiophene, furan and benzene which are unsubstituted or substituted with one or two substituents; R ¹ and R ² are independently substituents at each occurrence; R ⁴ and R ⁵ are independently H or a substituent; R ³ and R ⁶ are independently H, a substituent or a divalent group bound to EAG; Z ¹ is a direct bond or Z ¹ and substituent R ⁴ together form Ar ¹ , wherein Ar ¹ is a monocyclic or polycyclic aromatic or heteroaromatic group; Z ² is a direct bond or Z ² and substituent R ⁵ together form Ar ² , wherein Ar ² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 1, 2, or 3; q is 1, 2, or 3; and ---- is the connection point to EAG.

In some embodiments, a formulation is provided that includes a composition as described herein dissolved or dispersed in one or more solvents.

In some embodiments, an organic photodetector is provided, comprising: an anode; a cathode; and a photosensitive organic layer disposed between the anode and the cathode, wherein the photosensitive organic layer comprises a composition as described herein.

In some embodiments, a circuit is provided that includes an organic photodetector as described herein and at least one of: a voltage source for applying a reverse bias to the organic photodetector and a device configured to measure a photocurrent generated by the photodetector.

In some embodiments, a method of forming an organic photodetector as described herein is provided, comprising forming a photosensitive organic layer on one of an anode and a cathode and forming the other of the anode and the cathode on the photosensitive organic layer.

The inventors have further discovered that OPDs containing donor polymers comprising benzo[1,2-b:4,5-b']dithiophene repeating units can achieve a good balance between high external quantum efficiency and low dark current, especially at longer wavelengths.

Thus, in some embodiments, a photo sensor is provided that includes a light source and an organic photodetector as described herein, the organic photodetector being configured to detect light emitted by the light source.

In some embodiments, a method of determining the presence and/or concentration of a target material in a sample is provided, the method comprising: irradiating the sample and measuring the response of an organic photodetector as described herein, the organic photodetector being configured to receive light emitted by the sample after irradiation.

Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise," "comprising," and similar forms are to be interpreted in an inclusive sense and not in an exclusive or exhaustive sense; that is, in the sense of "including but not limited to." As used herein, the terms "connected," "coupled," or any variations thereof, mean any direct or indirect connection or coupling between two or more elements; the coupling or connection between elements may be physical, logical, electromagnetic, or a combination thereof. In addition, when used in this application, the words "herein," "above," "below," and words of similar meaning refer to this application as a whole and not to any particular portions of this application. Where the context permits, words used in the embodiments in the singular or plural may also include the plural or singular respectively. The word "or" when referring to a list of two or more items includes all of the following interpretations of the word: any one of the items in the list, all of the items in the list, and any combination of the items in the list.

The teachings of the technology provided herein can be applied to other systems, not necessarily the following systems. The elements and functions of the various examples described below can be combined to provide other implementations of the technology. Some alternative technical implementations may include not only the additional elements of the implementations mentioned below, but also fewer elements.

These and other variations may be made to the technology in light of the detailed description below. Although the specification describes certain examples of the technology and describes the best modes contemplated, no matter how detailed the description is presented, the technology can be implemented in a variety of ways. Specific implementations of system details may vary significantly while still being covered by the technology disclosed herein. As mentioned above, when describing certain features or scopes of the technology, the use of a particular term should not be understood to imply that the term is redefined herein as being limited to any specific feature, characteristic, or scope of the technology associated with that term. In general, unless such terms are expressly defined in the implementation section, the terms used in the following claims should not be interpreted as limiting the technology to the specific examples disclosed in the specification. Therefore, the actual scope of the technology covers not only the examples disclosed, but also all equivalent ways of implementing or performing the technology according to the scope of the claims.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim scope forms, but the applicants contemplate various aspects of the technology in any number of claim forms. For example, while some aspects of the technology may be described as computer-readable medium claims, other aspects may also be implemented as computer-readable medium claims or in other forms, such as means-plus-function claims.

In the following description, for the purpose of explanation, many specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosed technology. However, it will be apparent to those skilled in the art that the embodiments of the disclosed technology can be implemented without these specific details.

FIG1 shows an OPD according to some embodiments of the present disclosure. The OPD includes a cathode 103, an anode 107, and a bulk heterojunction layer 105 disposed between the anode and the cathode. The OPD may be supported on a substrate 101, which may be a glass or plastic substrate.

Figure 1 shows an arrangement in which the cathode is disposed between the substrate and the anode. In other embodiments, the anode may be disposed between the cathode and the substrate.

The bulk heterojunction layer comprises a mixture of an electron acceptor and an electron donor. In some embodiments, the bulk heterojunction layer is composed of an electron acceptor and an electron donor. In some embodiments, the bulk heterojunction layer comprises another electron acceptor. Optionally, the other electron acceptor is .

Each of the anode and cathode may independently be a single conductive layer, or may include a plurality of layers.

The OPD may include layers other than the anode, cathode, and bulk, as shown in FIG1. In some embodiments, a hole transport layer is disposed between the anode and the bulk heterojunction layer. In some embodiments, an electron transport layer is disposed between the cathode and the bulk heterojunction layer. In some embodiments, a work function modification layer is disposed between the bulk heterojunction layer and the anode and/or between the bulk heterojunction layer and the cathode.

In use, a photodetector as described in the present 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 photodetector may be varied. In some embodiments, the photodetector may be continuously biased in use.

In some embodiments, a photodetector system includes a plurality of photodetectors as described herein, such as an image sensor of a camera.

In some embodiments, a sensor may include an OPD as described herein and a light source, wherein the OPD is configured to receive light emitted from the light source.

In some embodiments, the light from the light source may or may not be altered before reaching the OPD. For example, the light may be filtered, down-converted, or up-converted before it reaches the OPD.

In some embodiments, the light source has a peak wavelength greater than 750 nm, optionally less than 1500 nm.

The bulk heterojunction layer may contain an electron acceptor (n-type) compound of formula (I): EAG - EDG - EAG (I) wherein each EAG is an electron acceptor group; and EDG is an electron donating group. The electron donating group may be a group of formula (II) or (III): (II) (III) wherein: each X is independently O or S; Ar ³ and Ar ⁴ are independently monocyclic or polycyclic aromatic or heteroaromatic groups at each occurrence; Ar ⁵ is selected from the group consisting of thiophene, furan and benzene which are unsubstituted or substituted with one or two substituents; R ¹ and R ² are independently substituents at each occurrence; R ⁴ and R ⁵ are independently H or a substituent; R ³ and R ⁶ are independently H, a substituent or a divalent group bound to EAG; Z ¹ is a direct bond or Z ¹ and substituent R ⁴ together form Ar ¹ , wherein Ar ¹ is a monocyclic or polycyclic aromatic or heteroaromatic group; Z ² is a direct bond or Z ² and substituent R ⁵ together form Ar ² , wherein Ar ² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 1, 2, or 3; q is 1, 2, or 3; and ---- is the connection point to EAG.

The inventors have found that the compounds of formula (I) are capable of absorbing light of longer wavelengths, for example greater than 750 nm, preferably greater than 1000 nm, preferably less than 1500 nm, thereby allowing these compounds to be used in organic photodetectors, especially in light sensors containing such OPDs and near-infrared light sources.

As the case may be, R ¹ and R ² of formula (Ia) or (Ib) are independently selected at each occurrence from the group consisting of: a linear, branched or cyclic C _1-20 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, NR ¹² , CO or COO, wherein R ¹² is a C _1-12 alkyl group and one or more H atoms in the C _1-20 alkyl group may be replaced by F; and a group of formula (Ak)u-(Ar ⁶ )v, wherein Ak is a C _1-12 alkylene chain, wherein one or more C atoms may be replaced by O, S, CO or COO; u is 0 or 1; Ar ⁶ is independently at each occurrence an aromatic or heteroaromatic group which is unsubstituted or substituted with one or more substituents; and v is at least 1, and is 1, 2 or 3 as appropriate.

The C _1-12 alkyl group may be a C _1-12 alkyl group; an unsubstituted phenyl group; and a phenyl group substituted by one or more C _1-6 alkyl groups.

Ar ⁶ is preferably phenyl.

When present, a substituent of ^Ar6 may be a substituent ^R16 , wherein ^R16 at each occurrence is independently selected from _C1-20 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, ^NR12 , CO or COO and one or more H atoms in the _C1-20 alkyl may be replaced by F.

If v is 3 or more, -(Ar ⁶ )v can be a straight chain or a branched chain of an Ar ⁶ group. A straight chain of an Ar group as described herein has only one monovalent terminal Ar ⁶ group, while a branched chain of an Ar ⁶ group has at least two monovalent terminal Ar ⁶ groups.

Optionally, at least one of R ¹ and R ² at each occurrence is phenyl, which is unsubstituted or substituted with one or more substituents selected from R ¹⁶ as described above.

Optionally, each R ³ to R ⁶ is independently selected from: H; C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO; and an aromatic or heteroaromatic group Ar ⁶ which is unsubstituted or substituted by one or more substituents.

Ar ⁶ is preferably an aromatic group, more preferably a phenyl group.

When present, one or more substituents of ^Ar6 may be selected from _C1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO.

As used herein, a "non-terminal" C atom of an alkyl group means an alkyl C atom other than a methyl C atom of a straight chain (n-alkyl) or a methyl C atom of a branched alkyl chain.

Optionally, Ar ³ and Ar ⁴ are each independently selected from thiophene, furan, difuran and thienothiophene.

Ar ³ , Ar ⁴ and Ar ⁵ are each independently unsubstituted or substituted with one or more substituents. When present, preferred substituents for Ar ³ , Ar ⁴ and Ar ⁵ are selected from the above groups R ³ to R ⁶ except H, preferably C _1-20 alkyl, wherein one or more non-adjacent non-terminal C atoms are replaced by O, S, CO or COO.

As appropriate, EDG is selected from formula (IIa) and (IIIa): (IIa) (IIIa)

As appropriate, EDG is selected from formula (IIb) and (IIIb): (IIb) (IIIb) wherein R ⁷ at each occurrence is independently H or a substituent.

Optionally, R ⁷ is independently selected at each occurrence from: H; C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO; and an aromatic or heteroaromatic group Ar ⁶ , which is unsubstituted or substituted by one or more substituents.

In some embodiments, each of R ³ to R ⁶ and R ⁷ when present is H; C _1-20 alkyl; or C _1-20 alkoxy.

In some embodiments, at least one, optionally both, of ^R4 and ^R5 are not H, and each of ^R3 , ^R6 , and when present, ^R7 is H.

As the case may be, at least one of p and q is 2.

Optionally, ^Z1 is linked to ^R4 to form a monocyclic aromatic or heteroaromatic group and/or ^Z2 is linked to ^R5 to form a monocyclic aromatic or heteroaromatic group.

Optionally, ^Z1 is linked to ^R4 to form a thiophene ring or a furan ring and/or ^Z2 is linked to ^R5 to form a thiophene ring or a furan ring.

The LUMO level of each EAG is deeper (i.e., farther from the vacuum level) than that of EDG, preferably at least 1 eV deeper. The LUMO levels of EAG and EDG can be determined by modeling the LUMO level of EAG-H with the LUMO level of H-EDG-H, i.e., by replacing the bond between EAG and EDG with a hydrogen atom bond. Modeling can be performed using Gaussian09 software obtained from Gaussian, using Gaussian09 with B3LYP (functional) and LACVP* (basis function set).

Each EAG is a group of formula (IV) or (V), as appropriate: (IV) (V) wherein A is a 5- or 6-membered ring which is unsubstituted or substituted with one or more substituents; R ¹⁰ and R ¹¹ are independently a substituent at each occurrence; and Ar ⁷ is an aromatic or heteroaromatic group which is unsubstituted or substituted with one or more substituents.

Optionally, each EAG is a group of formula (VI): (VI) wherein: R ¹⁰ is H or a substituent at each occurrence; ---- represents the attachment position to EDG; and each X ¹ to X ⁴ is independently CR ¹³ or N, wherein R ¹³ is H or a substituent at each occurrence.

Optionally, each R ¹³ is independently selected from H; C _1-12 alkyl; and an electron-withdrawing group. Optionally, the electron-withdrawing group is F or CN.

R ¹⁰ is preferably H.

The substituent R ¹⁰ is preferably selected from the group consisting of: C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl may be replaced by F; and an aromatic group Ar ⁹ , optionally phenyl, which is unsubstituted or substituted by one or more substituents selected from F and C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO.

Optionally, R ³ and/or R ⁶ is B(R ¹⁴ ) ₂ , wherein R ¹⁴ is a substituent at each occurrence, optionally a C _1-20 alkyl group, and one or both EAG groups are unsubstituted or substituted with a heteroaromatic group of formula (VII): (VII) wherein Ar ⁸ is a monocyclic or fused heteroaromatic group which is unsubstituted or substituted with one or more substituents; → is a bond to the boron atom of R ³ or R ⁶ ; and --- is a bond to EDG.

The or each substituent for Ar ⁸ (when present) may be selected from the substituents described for R ⁷ .

Optionally, R ¹⁴ is a C _1-20 alkyl group, R ¹⁴ is selected from C _1-12 alkyl; unsubstituted phenyl; and phenyl substituted by one or more C _1-12 alkyl groups.

Optionally, the group of formula (VII) is selected from formula (VIIa), (VIIb) and (VIIc): wherein R ¹⁵ is independently at each occurrence H or a substituent, optionally H or a substituent as described for R ^7. EDG, EAG and the B(R ¹⁴ ) ₂ substituents of EDG may be linked together to form a 5- or 6-membered ring.

As appropriate, EAG is selected from formula (XIV) to (XXV): (IXVa) (IXVb) (XVa) (XVb) (XVIa) (XVIb) (XVIc) (XVII) (XVIII) (XIX) (XX) (XXI) (XXII) (XXIV) (XXV)

J is O or S.

A is a 5- or 6-membered ring, which is unsubstituted or substituted with one or more substituents and may be fused to one or more other rings.

R ²³ is a substituent at each occurrence, optionally a C _1-12 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO, and one or more H atoms of the alkyl group may be replaced by F.

R ²⁵ is independently at each occurrence H; F; C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl may be replaced by F; or an aromatic group Ar ² , optionally phenyl, which is unsubstituted or substituted by one or more substituents selected from F and C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO.

R ²⁶ is a substituent, preferably a substituent selected from the following: -(Ar ¹³ ) _w , wherein Ar ¹³ is independently unsubstituted or substituted aryl or heteroaryl at each occurrence, preferably thiophene, and w is 1, 2 or 3; ; ; and C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl may be replaced by F.

Ar ¹⁴ is a 5-membered heteroaromatic group, preferably thiophene or furan, which is unsubstituted or substituted with one or more substituents.

When present, substituents for Ar ¹³ and Ar ¹⁴ are optionally selected from C _1-12 alkyl groups, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl group may be replaced by F.

Z ¹ is N or P

T ¹ , T ² and T ³ each independently represent an aryl or heteroaryl ring which may be fused to one or more other rings. When present, substituents for T ¹ , T ² and T ³ are optionally selected from non-H groups of R ¹⁵ .

Exemplary compounds of formula (XIVa) or (XIVb) include: ` wherein Ak is a C _1-12 alkylene chain, one or more C atoms of which may be replaced by O, S, CO or COO; An is an anion, optionally -SO ₃ ^- ; and each benzene ring is independently unsubstituted or substituted by one or more substituents selected from the substituents described for R ¹⁰ .

Exemplary EAGs of formula (XXI) are:

Exemplary EAG groups of formula (XXII) are:

Exemplary compounds of formula (I) are:

Wherein EH is ethylhexyl.

The inventors have found that ADA'DA type electron acceptors can provide high efficiency and/or low dark current when used in combination with electron donating polymers comprising benzo[1,2-b:4,5-b']dithiophene repeating units. The ADA'DA type electron acceptor can be a compound of formula (IX): (IX) wherein: ^D1 and ^D2 are independently electron donating groups at each occurrence; ^A1 is a divalent electron accepting group; ^A2 and ^A3 are independently monovalent electron accepting groups; ^B1 and ^B2 are independently bridging groups at each occurrence; x1 and x2 are independently 0, 1, 2 or 3; y1 and y2 are independently at least 1; and z1 and z2 are independently 0, 1, 2 or 3.

^A1 can be selected from the groups described herein as electron accepting repeating units, such as groups of formula (XVIIIa) to (XLI).

^A2 and ^A3 can be selected from the electron accepting groups EAG as described herein, preferably the groups of formula (V) or (VI). ^A2 and ^A3 can be the same or different, preferably the same.

D ¹ and D ² are preferably fused heteroaromatic groups containing 3 or more rings. Particularly preferred electron-donating groups D ¹ and D ² include fused thiophene or furan rings, optionally fused rings containing a thiophene or furan ring and one or more rings selected from the following: benzene, cyclopentadiene, tetrahydropyran, tetrahydrothiopyran and piperidine ring, each of which is unsubstituted or substituted with one or more substituents. Substituents may be selected from non-H groups R ²⁵ as described herein.

Exemplary groups ^D1 and ^D2 include, but are not limited to:

wherein R ²⁵ is as described above.

The bridging units ^B1 and ^B2 are preferably monocyclic or fused bicyclic aryl or heteroaryl, more preferably monocyclic or fused bicyclic heteroaryl, most preferably thiophene or thienothiophene. ^B1 and ^B2 may be unsubstituted or substituted with one or more substituents, optionally substituted with one or more non-H groups ^R25 .

Non-receptors can be used in combination with receptors.

The weight ratio of non-receptor:receptor may be in the range of about 1:0.1-1:1, preferably about 1:0.1-1:0.5.

The isocyanate may be _C60 , _C70 , _C76 , _C78 or _C84 isocyanate or a derivative thereof, including but not limited to PCBM-type isocyanate derivatives (including phenyl-C61-butyric acid methyl ester ( _C60 PCBM) and phenyl-C71-butyric acid methyl ester ( _C70 PCBM)), TCBM-type isocyanate derivatives (e.g. tolyl-C61-butyric acid methyl ester ( _C60 TCBM)) and ThCBM-type isocyanate derivatives (e.g. thienyl-C61-butyric acid methyl ester ( _C60 ThCBM)).

When present, the receptor may have the formula (VIII): wherein A and the CC group of R together form a monocyclic or condensed ring group which may be unsubstituted or substituted by one or more substituents.

Exemplary fluorine derivatives include formula (IIIa), (IIIb) and (IIIc): wherein R ³⁰ to R ⁴² are each independently H or a substituent.

The substituents R ³⁰ to R ⁴² are optionally and independently selected at each occurrence from the group consisting of: aryl or heteroaryl, optionally phenyl, which may be unsubstituted or substituted with one or more substituents; and C _1-20 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, CO or COO and one or more H atoms may be replaced by F.

When present, substituents of the aryl or heteroaryl R ³⁰ to R ⁴² are optionally selected from C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, CO or COO and one or more H atoms may be replaced by F.

The donor (p-type) compound is not particularly limited and can be appropriately selected from electron donating materials known to those skilled in the art, including organic polymers and non-polymeric organic molecules. The HOMO of the p-type compound is deeper (farther from the vacuum energy level) than the LUMO of the electron acceptor. Optionally, the gap between the HOMO energy level of the p-type donor and the LUMO energy level of the n-type acceptor compound is less than 1.4 eV.

In a preferred embodiment, the p-type donor compound is an organic conjugated polymer, which may be a homopolymer or copolymer including alternating, random or block copolymers. Preferred alternating copolymers contain electron donating repeating units and electron accepting repeating units. Preferably, it is a non-crystalline or semi-crystalline conjugated organic polymer. More preferably, the p-type organic semiconductor is a conjugated organic polymer with a low band gap, which is typically between 2.5 eV and 1.5 eV, preferably between 2.3 eV and 1.8 eV. As exemplary p-type donor polymers, there can be mentioned polymers selected from conjugated hydrocarbons or heterocyclic polymers, including polyphenylenes, polyanilines, polyazulenes, polybenzofurans, polyfluorenes, polyfurans, polyindenofluorenes, polyindoles, polyphenylenes, polypyrazolines, polypyrenes, polytantalums, polypyrrolidine ... , polypyridine, polytriarylamine, poly(phenylene vinylene), poly(3-substituted thiophene), poly(3,4-bissubstituted thiophene), polyselenophene, poly(3-substituted selenophene), poly(3,4-bissubstituted selenophene), poly(bisthiophene), poly(terthiophene), poly(bisselenophene), poly(triselenophene), polythieno[2,3-b]thiophene, polythieno[3,2-b]thiophene, polybenzothiophene, polybenzo[1,2-b:4,5-b']dithiophene, polyisobenzothiophene, poly(monosubstituted pyrrole), poly(3,4-bissubstituted pyrrole), poly-1,3,4- oxadiazole, polyisothiophene, its derivatives and copolymers. Preferred examples of p-type donors are copolymers of polyfluorene and polythiophene (each of which may be substituted), and polymers comprising benzothiadiazole-based and thiophene-based repeating units (each of which may be substituted). It should be understood that the p-type donor may also be composed of a mixture of a plurality of electron-donating materials.

Optionally, the donor polymer comprises repeating units of formula (XXX): (XXX) wherein R ⁵⁰ and R ⁵¹ at each occurrence are independently H or a substituent.

The substituents R ⁵⁰ and R ⁵¹ may be selected from the groups described with respect to R ⁷ except H.

Preferably, each R ⁵⁰ is a substituent. In a preferred embodiment, the R ⁵⁰ groups are linked to form a group of -Y ¹ -C(R ⁵² ) ₂ -, wherein Y ¹ is O, NR ⁵³ or C(R ⁵² ) ₂ ; R ⁵² is H or a substituent at each occurrence, preferably a substituent as described for R ¹ , most preferably a C _1-30 alkyl group; and R ⁵³ is a substituent, preferably a C _1-30 alkyl group.

Preferably, each R ⁵¹ is H.

Optionally, the polymer comprises electron donating benzo[1,2-b:4,5-b']dithiophene repeating units of formula (X): (X) wherein R ¹⁷ and R ¹⁸ are each independently selected from H; F; a C _1-20 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl group may be replaced by F; or an aromatic group or a heteroaromatic group Ar ¹⁰ which is unsubstituted or substituted by one or more substituents selected from F and a C _1-12 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO.

Ar ¹⁰ is preferably unsubstituted or substituted with thiophene.

Each R ¹⁷ is preferably selected from unsubstituted or substituted thiophene and C _1-11 alkoxy.

Optionally, the donor polymer comprises electron accepting repeating units selected from repeating units of the formula: (XVIIIa) (XIXa) (XXa) (XXIa) (XXIIa) (XXIVa) (XXVa) (XXXVIa) (XXXVIIa) (XXXVIIIa) XL XLI wherein R ²⁵ , Z ¹ , R ²³ and R ²⁵ are as described above and wherein R ²⁷ and R ²⁸ are each independently selected from H or a substituent, more preferably an electron withdrawing substituent. Exemplary electron withdrawing substituents are F; CN; NO ₂ ; and COOR ²⁹ , wherein R ²⁹ is C _1-20 alkyl, optionally C _1-12 alkyl or phenyl, optionally substituted with one or more C _1-12 alkyl groups.

In some embodiments, the donor is an alternating copolymer comprising alternating electron donating repeat units and electron accepting repeat units directly bonded to each other.

In some embodiments, the donor comprises alternating electron donating repeating units and electron accepting repeating units separated from each other by a bridging unit. Preferred bridging units are optionally substituted monocyclic aromatic or heteroaromatic units, more preferably 5-membered heteroaromatic units comprising ring atoms selected from C and one or more of S, O and N, most preferably thiophene. Substituents of the C atoms of the bridging unit may be selected from the non-H groups R ²⁵ as described above. Substituents of the N atoms of the bridging unit may be selected from the groups R ²³ as described above.

Exemplary donor materials are disclosed, for example, in WO2013/051676, the contents of which are incorporated herein by reference.

In some embodiments, the formation of the conjugated polymer donor comprises polymerization of a monomer of formula M-1 and a monomer of formula M-2: LG1-A-LG1 LG2-D-LG2 M-1 M-2 wherein: LG1 is a leaving group selected from one of the following: (a) a halogen or -OSO ₂ R ⁸ , wherein R ⁸ is an optionally substituted C1-12 alkyl or aryl group and (b) a boronic acid or ester. LG2 is the other of (a) and (b); A is a group for forming an electron accepting repeating unit; and

B is a group for forming an electron-donating repeating unit.

^R8 is preferably a _C1-12 alkyl group or a phenyl group which is optionally substituted by one or more F atoms.

In other embodiments, M-1 is replaced by a monomer of the formula M-1', or M-2 is replaced by a monomer of the formula M-2', wherein B is a bridge group as described herein: LG1-B-A-B-LG1                  LG2-B-D-B- LG2 M-1'                                        M-2'

Exemplary groups formed by reaction of monomers of formula M-1 include:

Optionally, the HOMO energy level of the p-type donor is no more than 5.5 eV away from the vacuum energy level. Optionally, the HOMO energy level of the p-type donor is at least 4.1 eV away from the vacuum energy level.

Unless otherwise stated, the HOMO and LUMO energy levels of compounds described herein were measured using square wave voltammetry with films of the compounds.

In some embodiments, the weight ratio of the donor compound to the acceptor compound is about 1:0.5 to about 1:2.

Preferably, the weight ratio of the donor compound to the acceptor compound is about 1:1 or about 1:1.5.

At least one of the first electrode and the second electrode is transparent so that light incident on the device can reach the bulk heterojunction layer. In some embodiments, both the first electrode and the second electrode are transparent.

Each transparent electrode preferably has a transmittance of at least 70%, and optionally at least 80%, for wavelengths in the range of 300 to 900 nm.

In some embodiments, one electrode is transparent and the other electrode is reflective.

Optionally, the transparent electrode comprises or consists of a transparent conductive oxide (preferably indium tin oxide or indium zinc oxide) layer. In a preferred embodiment, the electrode may comprise poly (3,4-ethylenedioxythiophene) (PEDOT). In other preferred embodiments, the electrode may comprise a mixture of PEDOT and polystyrene sulfonate (PSS). The electrode may consist of a PEDOT:PSS layer.

Optionally, the reflective electrode may include a reflective metal layer. The reflective material layer may be aluminum or silver or gold. In some embodiments, a double-layer electrode may be used. For example, the electrode may be an indium tin oxide (ITO)/silver double layer, an ITO/aluminum double layer, or an ITO/gold double layer.

The device may be formed by forming a bulk heterojunction layer on one of the anode and cathode supported by a substrate and depositing the other of the anode or cathode on the bulk heterojunction layer.

The OPD area may be less than about 3 cm ² , less than about 2 cm ² , less than about 1 cm ² , less than about 0.75 cm ² , less than about 0.5 cm ² , or less than about 0.25 cm ² . The substrate may be, without limitation, a glass or plastic substrate. The substrate may be described as an inorganic semiconductor. In some embodiments, the substrate may be silicon. For example, the substrate may be a silicon wafer. In use, the substrate is transparent if incident light is transmitted through the substrate and the electrodes are supported by the substrate.

In use, the substrate supporting one of the anode and cathode may or may not be transparent if incident light is transmitted through the other of the anode and cathode.

The bulk heterojunction layer may be formed by any process including but not limited to thermal evaporation and solution deposition.

Preferably, the bulk heterojunction layer is formed by depositing a formulation comprising an acceptor material and an electron donor material dissolved or dispersed in a solvent or a mixture of two or more solvents. The formulation can be deposited by any coating or printing method including but not limited to spin coating, dip coating, roll coating, spray coating, doctor blade coating, wire bar coating, slit coating, inkjet printing, screen printing, gravure printing, and flexographic printing.

The one or more solvents in the formulation may optionally comprise or consist of benzene substituted with one or more substituents selected from chlorine, _C1-10 alkyl and _C1-10 alkoxy, wherein two or more substituents may be linked to form a ring which may be unsubstituted or substituted with one or more _C1-6 alkyl, optionally toluene, xylene, mesitylene, tetramethylbenzene, anisole, dihydroindene and alkyl-substituted derivatives thereof, and tetrahydronaphthalene and alkyl-substituted derivatives thereof.

The formulation may comprise a mixture of two or more solvents, preferably a mixture comprising at least one benzene substituted with one or more substituents as described above and one or more other solvents. The one or more other solvents may be selected from esters, optionally alkyl or aryl esters of alkyl or aryl carboxylic acids, optionally C _1-10 alkyl benzoates, benzyl benzoate or dimethoxybenzene. In a preferred embodiment, a mixture of trimethylbenzene and benzyl benzoate is used as a solvent. In other preferred embodiments, a mixture of trimethylbenzene and dimethoxybenzene is used as a solvent.

In addition to the electron acceptor, the electron donor and one or more solvents, the formulation may also contain other components. As examples of such components, there may be mentioned adhesives, defoamers, deaerators, viscosity enhancers, diluents, adjuvants, flow improvers, colorants, dyes or pigments, sensitizers, stabilizers, nanoparticles, surface-active compounds, lubricants, wetting agents, dispersants and inhibitors.

Organic photodetectors as described herein may be used in a wide range of applications, including, but not limited to, detecting the presence and/or brightness of ambient light; and in sensors comprising an organic photodetector and a light source. The photodetector may be configured such that light emitted from the light source is incident on the photodetector, and changes in the wavelength and/or brightness of the light may be detected, for example due to absorption and/or emission of light by a target material in a sample disposed in the light path between the light source and the organic photodetector. The sensor may be, but is not limited to, a gas sensor, a biosensor, an X-ray imaging device, an image sensor (such as a camera image sensor), a motion sensor (e.g., for use in security applications), a proximity sensor, or a fingerprint sensor. A 1D or 2D photosensor array may include a plurality of photodetectors as described herein in an imaging sensor. The photodetector may be configured to detect light emitted from a target analyte that emits light upon illumination by a light source, or to detect light emitted by a target analyte bound to a luminescent tag that emits light upon illumination by a light source. The photodetector may be configured to detect the wavelength of light emitted by the target analyte or a luminescent tag bound thereto. Example Synthesis

The compounds can be prepared according to the following reaction scheme:

Compound Example 1 was prepared according to the following reaction scheme: Phase 1

The aldehyde (3 g, 9.4 mmol) was dissolved in chloroform (30 mL) and pyridine (5 mL). The solution was degassed for 0.5 h and then cooled to 0 °C. Difluoromonomer (3.2 g, 15.5 mmol) was added and the reaction mixture was degassed for another 0.25 h and then warmed to room temperature for 3 h. Methanol was added and the solvent was removed to produce a red solid. The crude material was purified by column chromatography on silica eluted with petroleum ether:DCM 9:1. The fraction containing the product was concentrated to produce stage 1 material (3.5 g) with 98% purity. Stage 2

The fused thiophene material (which can be prepared as in the following references: Macromolecular Rapid Communications , 2011, 32, 1664 or Chem. Mater., 2017, 29, 8369) (1 g, 1.0 mmol) was dissolved in THF and cooled to -78 °C under nitrogen. n-Butyl lithium (1.65 mL, 4.1 mmol) was added dropwise and the solution was stirred at -78 °C for 1 hour, followed by the dropwise addition of THF (5 mL) containing tributyltin chloride (0.99 mg, 3.0 mmol). The reaction mixture was allowed to reach room temperature over 16 hours. Methanol was added to quench the reaction and the solvent was removed. The crude material was triturated several times with methanol to produce stage 2 material, which was used in the next step without further purification. Compound Example 1

Stage 1 material (1.3 g, 2.4 mmol) and Stage 2 material (1.5 g, 0.97 mmol) were dissolved in toluene and degassed. Tri(o-tolyl)phosphine (88 mg, 0.3 mmol) and dipalladium tris(benzylideneacetone) (71 mg, 0.08 mmol) were added and the reaction mixture was stirred at 80 °C for 5 hours. The reaction mixture was cooled and passed through a plug of celite and further dissolved with toluene. The filtrate was concentrated to give a black semisolid which was triturated with methanol to give the crude product as a solid. This product was purified by column chromatography on silica using DCM/hexanes. The product-containing fraction was concentrated to obtain a black solid product (530 mg) with a purity of 97.8%. Compound Example 2

Compound Example 2 was prepared according to the following reaction scheme: Intermediate 2:

n-Butyl lithium (97.4 ml, 1.6 M, 0.16 mol) was added to a solution of thieno[3,2-b]thiophene (1) (10 g, 0.07 mol) in THF (100 ml) at -78°C and the mixture was stirred at 25°C for one hour. After cooling to -78°C, THF (100 ml) containing trimethyltin chloride (35.5 g, 0.18 mol) was added and the mixture was stirred at 25°C for 16 hours. It was then quenched with water (200 ml) at 0°C, extracted with hexane (200 ml), the organic layer was washed with brine and dried over anhydrous sodium sulfate and concentrated. The crude solid was dissolved in chloroform (50 ml), methanol (250 ml) was added and the mixture was stirred at 0°C for 2 hours. The resulting slurry was filtered, washed with methanol (100 ml) and dried in vacuo to afford Intermediate 2 (20 g, 60% yield) as a white solid. HPLC: 98.45%. ¹ H-NMR (400 MHz, DMSO-d ₆ ): δ [ppm] 0.362 (s, 18H), 7.38 (s, 2H). Intermediate 4:

Intermediate 3 can be synthesized as described in the following reference: Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8, (10), 5163-5170, the contents of which are incorporated herein by reference.

Bis(triphenylphosphine)palladium(II) dichloride (144 mg, 0.2 mmol) was added to a mixture of intermediate 2 (4.8 g, 0.01 mol) and methyl 2-bromothiophene-3-carboxylate (3) (4.77 g, 0.02 mmol) in degassed toluene (100 ml) and the mixture was heated at 80°C for 16 hours. After cooling, the resulting slurry was filtered, washed with toluene (20 ml) and dried in vacuo to give intermediate 4 (4.5 g) as a yellow solid. HPLC: 95.7%. ¹ H-NMR (400 MHz, CDCl ₃ ):δ [ppm]1.57 (s, 4H), 3.88 (s, 6H), 7.28 (s, 2H), 7.54 (d, J = 5.40 Hz, 2H), 7.69 (s, 2H). Intermediate 6:

n-Butyl lithium (2.5 M in hexane, 17.1 ml, 0.04 mol) was added to a solution of 1-bromo-4-hexylbenzene (5) (12.0 g, 0.05 mol) in THF (60 ml) at -100°C and the mixture was stirred for 2.5 hours. Intermediate 4 (3 g, 0.01 mol) was added as a solid and the mixture was warmed to 25°C and stirred for 16 hours. After cooling to 0°C, it was quenched with _NH4Cl solution (20% aqueous solution, 30 ml), extracted with ethyl acetate (2 x 20 ml), washed with brine (30 ml), dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica column chromatography (2% EtOAc/hexane as solvent) to give intermediate 6 (4.5 g, 63% yield). LCMS: 96.5%. ¹ H-NMR (400 MHz, CDCl ₃ ): δ [ppm] 0.91 (t, J = 6.64 Hz, 12H), 1.33-1.37 (m, 24H), 1.59-1.64 (m, 8H), 2.62 (t, J = 7.88 Hz, 8H), 3.26 (bs, 2H), 6.47 (d, J = 5.36 Hz, 2H), 6.66 (s, 2H), 7.11-7.17 (m, 18H). Intermediate 7:

Boron trifluoride diethyl etherate (2.74 ml, 0.02 mol) was added dropwise to a solution of intermediate (6) (4.5 g, 0.004 mol) in anhydrous DCM (60 ml) at 0°C under nitrogen. After stirring at 26°C for 16 hours, the mixture was quenched with ice water (30 ml), diluted with dichloromethane (50 ml), the organic layer was washed with water (30 ml), dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica column chromatography (2 to 5% DCM/hexane as solvent) to give intermediate 7 (2 g, 46% yield) as an orange-red solid. HPLC: 98.1%. ¹ H-NMR (400 MHz, CDCl ₃ ): δ [ppm] 0.88 (t, J = 6.84 Hz, 12H), 1.29-1.37 (m, 24H), 1.55-1.63 (m, 8H), 2.56 (t, J = 7.92 Hz, 8H), 7.08-7.10 (m, 10H), 7.16-7.18 (m, 10H). Intermediate 8:

n-Butyl lithium (2.5 M in hexane, 16.5 ml, 0.04 mol) was added to a solution of intermediate 7 (10 g, 0.01 mol) in anhydrous THF (150 ml) at -78 °C. After 1 hour, tributyltin chloride (16.9 g, 0.05 mol) in THF (20 ml) was slowly added and the mixture was warmed to room temperature and stirred for 16 hours. The solvent was removed under reduced pressure and the crude residue was triturated with methanol and filtered to give intermediate 8 (4 g, about 75% desired product by LCMS) as a yellow solid. Intermediate 10:

Tri(o-tolyl)phosphine (147 mg, 0.48 mmol) and tris(dibenzylideneacetone)-dipalladium(0) (117 mg, 0.13 mmol) were added to a degassed solution of intermediate 8 (2.5 g, 1.61 mmol) and 5-bromo-4-[(2-ethylhexyl)oxy]thiophene-2-carbaldehyde (1.28 g, 4.02 mmol) in toluene (150 ml) and the mixture was heated to 80°C for 16 hours. The mixture was concentrated and the crude product was purified by silica column chromatography (0 to 50% DCM/hexane as solvent) to give intermediate 10 (1.1 g, LCMS purity 81%; and 0.3 g, LCMS purity 86%). Compound Example 2:

A degassed solution of intermediate 10 (550 mg, 0.38 mmol), intermediate 11 (461 mg, 1.89 mmol) and p-toluenesulfonic acid (540 mg, 2.84 mmol) in ethanol (25 ml) was stirred at 65° C. for 18 hours and the mixture was concentrated. Another 550 mg of intermediate 10 was also converted into compound example 1. The crude products were combined and purified twice by silica column chromatography (hexane: dichloromethane (1:1) as solvent). The fractions containing the desired product were combined and further triturated with ethanol and filtered to give compound example 2 (500 mg). HPLC: 93.79%. ¹ H-NMR (400 MHz, CDCl ₃ ): δ [ppm] 0.87-0.90 (m, 12H), 0.93-0.97 (m, 6H), 0.99-1.04 (m, 6H), 1.29-1.34 (m, 12H), 1.26-1.41 (m, 12H), 1.56-1.67 (m, 24H), 1.85-1.90 (m, 2H), 2.61 (t, J = 7.6 Hz, 8H), 4.17 (d, J = 4.8 Hz, 4H), 7.15-7.20 (m, 18H), 7.78 (s, 2H), 8.12 (s, 2H), 8.75 (br, s, 2H), 8.98 (s, 2H).

Intermediate 11 is formed according to the following reaction process: Intermediate 13

A mixture of 1,2-dibromo-4,5-dimethylbenzene (100 g, 0.38 mol), potassium hydroxide (105 g, 1.89 mol) and potassium permanganate (298 g, 1.89 mol) in water (2 L) was heated at 115 °C for 24 h. After cooling to room temperature, sodium bisulfite was added, the pH was adjusted to 8 using 10% potassium hydroxide solution, and the mixture was filtered through a diatomaceous earth pad and washed with water (2×50 ml). The aqueous layer was acidified to pH 1 with concentrated HCl to give a white precipitate, which was filtered, washed with water (2×250 ml) and triturated with methanol. The resulting solid was filtered and dried in vacuo to give intermediate 13 (46 g, 38% yield). ¹ H-NMR (400 MHz, DMSO-d6): δ [ppm] 8.18 (s, 2H). Intermediate 14:

Intermediate 13 (200 g, 618 mmol) in acetic anhydride (1 L) was heated at 130 °C for 4 h. After cooling to room temperature, the crude solid was filtered, washed with toluene (200 ml) and dried under vacuum to give intermediate 14 (200 g). Intermediate 15:

Tributyl acetoacetate (103 g, 654 mmol) was added to a mixture of intermediate 14 (200 g, 654 mmol), acetic anhydride (1 L) and triethylamine (600 ml) and the reaction mixture was stirred at 25°C for 16 hours. After quenching with a mixture of (10 M HCl, 1 L) and ice (1 kg) while maintaining the temperature below 50°C, the mixture was heated to 75°C for 2 hours and cooled to room temperature. The solid was filtered and dried to give intermediate 15 (132 g, 68% yield) as a brown solid. LCMS: 96.8%. ¹ H-NMR (400 MHz, DMSO-d6): δ [ppm] 3.28 (s, 2H), 8.25 (s, 2H). Intermediate 16:

A solution of intermediate 15 (120 g, 394 mmol), ethylene glycol (244 g, 3.9 mol) and p-toluenesulfonic acid (6.78 g, 39.4 mmol) in toluene (1.5 L) was heated at 125 °C for 40 hours. After cooling to room temperature, the reaction mixture was added to water (500 ml), the organic layer was separated and concentrated under vacuum. The crude residue was suspended in hexane (1 L), stirred for 30 minutes and filtered to give intermediate 16 (91 g, 59% yield). ¹ H-NMR (400 MHz, CDCl3): δ [ppm] 2.56 (s, 2H), 4.09 - 4.12 (m, 4H), 4.20 - 4.24 (m, 4H), 7.65 (s, 2H). Intermediate 17:

Potassium ferrocyanide (48.6 g, 132 mmol), 1-butylimidazole (42.9 g, 383 mmol) and cuprous (I) iodide (12.5 g, 65.6 mmol) were added in three portions to a solution of intermediate 16 (65 g, 165 mmol) in o-xylene (2.5 L). After heating at 140° C. for 44 hours, the reaction mixture was cooled to room temperature, filtered through a Florisil plug, and washed with toluene and then with ethyl acetate. The filtrate was concentrated to 1 L under reduced pressure and stirred at 25° C. for 16 hours. The obtained solid was filtered, washed with hexane and purified by silica column chromatography (hexane:ethyl acetate (2:8) as solvent). The fraction containing the desired product was concentrated under reduced pressure, hexane (1 L) was added to the residue, and the obtained solid was filtered and dried under vacuum to give intermediate 17 (30 g, 64% yield). HPLC: 98.9%. ¹ H-NMR (400 MHz, CDCl3): δ [ppm] 2.62 (s, 2H), 4.15 - 4.21 (m, 4H), 4.24 - 4.28 (m, 4H), 7.83 (s, 2H). Intermediate 18:

Diethyl ether (2 M, 500 ml, 1.0 mol) and water (5 ml) containing hydrogen chloride were added to a solution of intermediate 17 (90 g, 316 mmol) in tert-butyl methyl ether (1 L). After stirring at 25°C for 48 hours, the mixture was filtered, and the resulting solid was washed with diethyl ether (100 mL×3) and stirred with acetone (500 ml) 3 times for 1 hour and filtered. The resulting solid was dried under vacuum to give intermediate 18 (61 g, 80% yield). HPLC: 95%. 1H-NMR (400 MHz, CDCl3): δ [ppm] 3.07 (s, 2H), 4.20 - 4.36 (m, 4H), 8.11 (s, 1H), 8.16 (s, 1H). Intermediate 11

A solution of malononitrile (5.49 g, 83.2 mmol) in THF (200 ml) was added to a suspension of sodium hydride (3.31 g, 83.2 mmol) in THF (200 ml) at 25°C and stirred at 25°C for one hour. The resulting mixture was added to a suspension of intermediate 18 (20 g, 83.2 mmol) in THF (600 mL) at 0°C, and the reaction mixture was stirred at 25°C for 16 hours. The resulting mixture was concentrated under vacuum to give a dark purple crude solid. This procedure was repeated for another 40 g of intermediate 18. The crude materials were combined and purified by silica column chromatography (10 to 20% MeOH/DCM as solvent). The fractions containing the desired product were combined, concentrated under reduced pressure, and the residue was stirred in a mixture of dichloromethane and acetonitrile to give intermediate 11 (20.2 g, 33% yield). LCMS: 96.35% purity. ¹ H-NMR (400 MHz, CD3OD): δ [ppm] 3.61 (s, 2H), 5.55 (s, 1H), 7.73 (s, 1H), 8.29 (s, 1H). Compound Example 3

Compound Example 3 can be prepared according to Scheme 3: Process 3

Intermediate 20 can be synthesized as described in the following document: Adv. Sci. 2018, 5, 1800307, the contents of which are incorporated herein by reference. Modeling Data

Model the LUMO energy levels and HOMO-LUMO band gaps of the following compounds: Model compound example 3 Model compound example 4 Model compound example 5

The quantum chemical modeling can be performed using Gaussian09 software obtained from Gaussian using Gaussian09 with B3LYP (functional) and LACVP* (basis function set). Table 1 Compound HOMO (eV) LUMO (eV) Bandgap (eV) Model comparison compound 1 -5.028 -3.262 1.767 Model comparison compound 2 -5.129 -3.389 -1.740 Model compound example 1 -4.839 -3.267 1.572 Model compound example 2 -4.816 -3.235 1.580 Model comparison compound 3 -5.375 -3.419 1.956 Model compound example 3 -4.95 -3.41 1.54 Model compound example 4 -5.28 -3.85 1.44 Model compound example 5 -5.20 -3.80 1.40

Referring to Table 1, model compound examples 1 and 2 have shallower (i.e., closer to the vacuum level) HOMO and smaller band gap than model comparison compound 1 or 2. HOMO and LUMO measurements

The HOMO and LUMO values of Compound Example 1 were measured by square wave voltammetry.

In square wave voltammetry, the current at the working electrode is measured while the potential between the working electrode and the reference electrode is linearly scanned over time. The differential current between the forward pulse and the reverse pulse is plotted against the potential to produce a voltammogram. This can be measured using a CHI 660D potentiostat.

The equipment for measuring HOMO or LUMO energy levels by SWV may include: a cuvette containing 0.1 M tributylammonium hexafluorophosphate in acetonitrile; a 3 mm diameter glassy carbon working electrode; a platinum counter electrode and a leak-free Ag/AgCl reference electrode.

At the end of the experiment, ferrocene was added directly to the existing cuvette for calculation purposes, where the potential was determined by cyclic voltammetry (CV) for the oxidation and reduction of ferrocene relative to Ag/AgCl.

The samples were dissolved in toluene (3 mg/ml) and spun directly on a glassy carbon working electrode at 3000 rpm.

LUMO = 4.8 - E Ferrocene (peak to peak average) - E Sample reduced (peak maximum).

HOMO = 4.8-E ferrocene (peak-to-peak average) + E sample oxidation (peak maximum).

A typical SWV experiment was run at 15 Hz frequency; 25 mV amplitude and 0.004 V increment step. Results were calculated for three freshly centrifuged membrane samples based on the HOMO and LUMO data. Table 2 HOMO film (eV) LUMO film (eV) B _G film (eV) Compound Example 2 -5.26 -4.23 1.03 Compound Example 4 -5.28 -4.00 1.28 Compound Example 4

As shown in Table 2, Compound Example 2 has a significantly smaller band gap and a significantly deeper LUMO than Compound Example 4. Absorbance Measurement

Figure 2 shows the absorption spectra of films cast from 15 mg/ml solutions and Compound Example 2 in 15 mg/ml solutions.

The absorption spectra of the solution and the film were measured using a Cary 5000 UV-vis-IR spectrometer. As shown in FIG2 , Compound Example 2 showed absorption in the film at wavelengths up to about 1500 nm. Device Example 1

Prepare a device with the following structure: Cathode/donor:acceptor layer/anode

Glass substrates coated with indium tin oxide (ITO) were treated with polyethyleneimine (PEIE) to modify the work function of ITO.

A mixture of donor polymer 1 and compound Example 2 (acceptor) was deposited on the modified ITO layer by rod coating at a donor:acceptor mass ratio of 1:1.5 from a 15 mg/ml solution in a 1,2,4-trimethylbenzene:1,2-dimethoxybenzene 95:5 v/v solvent mixture. The film was dried at 80°C under vacuum to form a bulk heterojunction layer of about 500 nm thick.

On the bulk heterojunction, an anode stack of MoO ₃ (10 nm) and ITO (50 nm) was formed by thermal evaporation (MoO ₃ ) and sputtering (ITO). Donor polymer 1

The EQE and dark current of device example 7 are shown in Figures 3A and 3B, respectively. As shown in Figure 3A, an EQE of more than 10% is achieved at a wavelength between about 1000 and 1300 nm. Comparison devices 1 to 3

Comparative Devices 1 to 3 were prepared as described for Device Example 7, except that Comparative Donor Polymers 1 to 3 were used instead of Donor Polymer 1: Comparison with donor polymer 1 Comparison of donor polymer 2 Comparison of donor polymer 3

Referring to Table 3, despite being similar in HOMO shift and bandgap, the external quantum efficiency of the device containing donor polymer 1 at 1100 nm, 1300 nm, and 1400 nm is significantly higher than that of the comparative devices containing comparative donor polymers 1, 2, or 3. The exception is the EQE of comparative device 1 at 1400 nm, however this device suffers from a much higher dark current than device Example 7. Table 3 Device Donor material HOMO shift (eV) Eg (eV) Jd (mA/cm ² ) EQE (%) 1100 nm 1300 nm 1400 nm Comparison device 1 Comparison with donor polymer 1 0.21 0.82 0.79 11.56 6.69 2.31 Comparison device 2 Comparison of donor polymer 2 0.19 0.84 3.49 3.06 2.10 1.01 Comparison device 3 Comparison of donor polymer 3 0.42 0.61 0.11 0.36 0.58 0.51 Device Example 1 Donor polymer 1 0.2 0.83 0.03 20.42 11.23 1.86 Device Example 2

The device was prepared as described for Device Example 1, except that Acceptor 1 was used instead of Compound Example 2; the donor:acceptor ratio was 1:1; and a 10 mg/ml solution was deposited to form the bulk heterojunction layer:

The absorption spectrum of the film of receptor 1 is shown in Figure 4A.

The EQE and dark current of Device Example 8 are shown in FIGS. 4B and 4C , respectively.

Although the invention has been described with respect to specific exemplary embodiments, it should be understood that various modifications, variations and/or combinations of the features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

101: Substrate 103: Cathode 105: Body heterojunction layer 107: Anode

The disclosed technology and accompanying drawings describe some implementation schemes of the disclosed technology. FIG1 shows an organic photodetector according to an embodiment of the present disclosure; FIG2 shows the solution and film absorption spectra of an electron acceptor compound having a film peak absorption wavelength of more than 1000 nm; FIG3A is a graph of the external quantum efficiency (EQE) of an organic photodetector relative to wavelength, wherein the photoreaction layer contains a donor polymer 2 having a benzo[1,2-b:4,5-b']dithiophene repeating unit and compound example 2; FIG3B is a graph of the dark current density of the organic photodetector of FIG3A relative to voltage; FIG4A is a film absorption spectrum of acceptor 1; FIG4B is a graph of the external quantum efficiency (EQE) of an organic photodetector relative to wavelength, wherein the photoreaction layer contains a donor polymer 2 and an acceptor 1; and FIG. 4C is a graph of dark current density versus voltage for the organic photodetector of FIG. 4B . The accompanying figures are not drawn to scale and have various viewpoints and angles. The accompanying figures are some embodiments and examples. In addition, for the purpose of discussing some embodiments of the disclosed technology, some components and/or operations may be divided into different blocks or combined into a single block. In addition, although the technology is suitable for various modifications and alternative forms, specific embodiments have been illustrated in the accompanying figures and described in detail below. However, it is not desired to limit the technology to the specific embodiments described. Instead, it is desired that the technology cover all modifications, equivalents and alternatives that fall within the scope of the technology as defined in the attached patent application scope.

Claims (20)

A composition comprising an electron donating polymer and an electron accepting material, wherein the electron donating polymer comprises benzo[1,2-b:4,5-b']dithiophene repeating units and wherein a film of the electron accepting material has a peak absorption wavelength greater than 1000 nm. The composition of claim 1, wherein the electron accepting material is a non-electron acceptor. The composition of claim 2, wherein the electron acceptor is a compound of formula (I): EAG - EDG - EAG (I) wherein each EAG is an electron accepting group; and EDG is an electron donating group of formula (II) or (III): (II) (III) wherein: each X is independently O or S; Ar ³ and Ar ⁴ are independently monocyclic or polycyclic aromatic or heteroaromatic groups at each occurrence; Ar ⁵ is selected from the group consisting of thiophene, furan and benzene which are unsubstituted or substituted with one or two substituents; R ¹ and R ² are independently substituents at each occurrence; R ⁴ and R ⁵ are independently H or a substituent; R ³ and R ⁶ are independently H, a substituent or a divalent group bound to EAG; Z ¹ is a direct bond or Z ¹ and substituent R ⁴ together form Ar ¹ , wherein Ar ¹ is a monocyclic or polycyclic aromatic or heteroaromatic group; Z ² is a direct bond or Z ² and substituent R ⁵ together form Ar ² , wherein Ar ² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 1, 2 or 3; q is 1, 2 or 3; and ---- is the connection point to EAG. The composition of claim 3, wherein Ar ³ and Ar ⁴ are each independently selected from thiophene, furan, furanofuran and thienothiophene. The composition of claim 3 or 4, wherein EAG is selected from formula (IIa) and (IIIa): (IIa) (IIIa). The composition of claim 3 or 4, wherein EAG is selected from formula (IIb) and (IIIb): (IIb) (IIIb) wherein R ⁷ at each occurrence is independently H or a substituent. The composition of claim 3, wherein at least one of p and q is 2. The composition of claim 3, wherein Z ¹ is linked to R ⁴ to form a monocyclic aromatic or heteroaromatic group and/or Z ² is linked to R ⁵ to form a monocyclic aromatic or heteroaromatic group. The composition of claim 8, wherein Z ¹ is connected to R ⁴ to form a thiophene ring or thienothiophene and/or Z ² is connected to R ⁵ to form a thiophene ring or thienothiophene. The composition of claim 3, wherein each EAG is a group of formula (V): (V) wherein: R ¹⁰ is H or a substituent at each occurrence; ---- represents the attachment position to EDG; and each X ¹ to X ⁴ is independently CR ¹³ or N, wherein R ¹³ is H or a substituent at each occurrence. The composition of claim 10, wherein each R ¹³ is independently selected from H; C _1-12 alkyl; and an electron withdrawing group. The composition of claim 11, wherein the electron-withdrawing group is F or CN. A composition as claimed in claim 3, wherein R ¹ and R ² are selected from the group consisting of: a linear, branched or cyclic C _1-20 alkyl group, wherein one or more non-adjacent non-terminal C atoms can be replaced by O, S, NR ¹² , CO or COO, wherein R ¹² is a C _1-12 alkyl group and one or more H atoms in the C _1-20 alkyl group can be replaced by F; and a group of formula (Ak)u-(Ar ⁶ )v, wherein Ak is a C _1-12 alkyl chain, wherein one or more C atoms can be replaced by O, S, CO or COO; u is 0 or 1; Ar ⁶ is independently, at each occurrence, an aromatic or heteroaromatic group which is unsubstituted or substituted by one or more substituents; and v is at least 1. The composition of claim 3, wherein each R ³ to R ⁶ is independently selected from: H; C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO; and an aromatic or heteroaromatic group Ar ⁵ which is unsubstituted or substituted by one or more substituents. The composition of claim 6, wherein each R ⁷ is independently selected at each occurrence from: H; C _1-12 alkyl, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO; and an aromatic or heteroaromatic group Ar ⁵ which is unsubstituted or substituted by one or more substituents. The composition of claim 1, wherein the benzo[1,2-b:4,5-b']dithiophene repeating unit is a repeating unit of formula (X): (X) wherein R ¹⁷ and R ¹⁸ are each independently selected from H; F; a C _1-12 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO and one or more H atoms in the alkyl group may be replaced by F; or an aromatic group Ar ² which is unsubstituted or substituted with one or more substituents selected from F and a C _1-12 alkyl group, wherein one or more non-adjacent non-terminal C atoms may be replaced by O, S, COO or CO. A formulation comprising the composition of claim 1 dissolved or dispersed in one or more solvents. An organic photodetector comprises: an anode; a cathode; and a photosensitive organic layer disposed between the anode and the cathode, wherein the photosensitive organic layer comprises the composition of claim 1. A method of forming an organic photodetector as claimed in claim 18, comprising forming the photosensitive organic layer on one of the anode and the cathode and forming the other of the anode and the cathode on the photosensitive organic layer, wherein forming the photosensitive organic layer comprises depositing a formulation comprising an electron acceptor and an electron donating polymer dissolved or dispersed in one or more solvents. A photo sensor comprising a light source and an organic photodetector as claimed in claim 18, wherein the organic photodetector is configured to detect light emitted from the light source, wherein the light source emits light having a peak wavelength greater than 1000 nm.