BACKGROUND

Embodiments of the present disclosure relate to photoactive compounds and more specifically, but not by way of limitation, to photoactive materials containing electron- donating units suitable for us as an electron-donating material or an electron-accepting material in a photoresponsive device.

Organic photoresponsive devices are known.

EP 3121211 discloses a polymer of formula:

W02012008556A1 discloses a photoelectric conversion element containing a polymer having a repeat unit represented by Formula (I): ( I >

WO201 1052712 discloses a photoelectric conversion element containing a polymeric compound having a structural unit represented by formula (1):

( 1 )

Liu et al, “Ternary Blend Strategy for Achieving High-Efficiency Organic Solar Cells with Nonfullerene Acceptors Involved” Adv. Func. Mat., 2018, 28 (29), 1-20, discloses non- fullerene acceptor COi8DFIC. He et al, “A-D-A small molecule acceptors with ladder-type arenes for solar cell” J. of Mat. Chem. A, 2018, 6, 8839-8854, discloses COi8DFIC with an ultranarrow bandgap of 1.26V.

Xu et al “The progress and prospects of non-fullerene acceptors in ternary blend organic solar cells” Mat. Horizons, 2018, 5, 206-221, discloses COi8DFIC.

Xiao et al, “26 mA cm 2 Jsc from organic solar cells with a low-bandgap nonfullerene acceptor” Sci. Bull., 2017, 62, 1494, discloses the A-D-A non-fullerene acceptor, COi8DFIC which has a narrow optical bandgap of 1.26eV.

SUMMARY

According to some embodiments of the present disclosure, there is provided a composition comprising an electron donor material and a first electron accepting material. The electron donor material is a polymer. The electron accepting material is a non-polymeric compound. The electron donor material and electron accepting material both comprise an electron donor group of formula (I): wherein:

X and Y are each independently selected from S, O or Se;

Z is O, S, NR ² or CR ³ ₂

Ar'-Ar ⁶ are each independently an unsubstituted or a substituted benzene, an unsubstituted or a substituted 5- or 6- membered heteroaromatic group or are absent;

A ¹ and A ² are each independently an unsubstituted or a substituted benzene, an unsubstituted or a substituted 5- or 6- membered heteroaromatic group, a non-aromatic 6-membered ring having ring atoms selected from C, N, S and O or are absent; n is 1, 2 or 3;

R ¹ independently in each occurrence is H or a substituent;

R ² is H or a substituent; and each R ³ is independently H or a substituent.

Optionally, the electron acceptor material is a compound of formula (II): wherein: m and o are each independently 0 or an integer of 1 or more;

L ¹ is a bridging group when m is 1 or more or a direct bond when m is 0;

L ² is a bridging group when o is 1 or more or a direct bond when o is 0; and each EAG ¹ independently represents an electron accepting group.

Optionally, the compound of formula (II) has formula (Ila):

Optionally, each EAG1 is independently a group of formula (IVa): wherein:

R ¹⁰ in each occurrence is H or a substituent selected from the group consisting of: Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic group Ar ⁷ which is unsubstituted or substituted with one or more substituents selected from F and Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO;

— represents a linking position in the compound of formula (II); and each X '-X ⁴ is independently CR ¹⁷ or N wherein R ¹⁷ in each occurrence is H or a substituent selected from Ci- ₂ ohydrocarbyl and an electron withdrawing group.

Optionally, the electron- accepting material is CO18DFIC:

Optionally, the electron donor polymer comprises a repeating structure of formula (III): wherein EAG ² is an electron-accepting group.

Optionally, the repeating structure of formula (III) has formula (Ilia): wherein each R ⁴ is independently H or a substituent.

Optionally, the electron donating polymer comprises a repeating structure of formula:

Optionally, the composition further comprises a second electron accepting material.

Optionally, the second electron-accepting material is a fullerene or a derivative thereof.

According to some embodiments of the present disclosure, there is provided a formulation comprising one or more solvents and a composition as described herein dissolved or dispersed in the one or more solvents.

According to some embodiments of the present disclosure, there is provided a photoresponsive device comprising an anode, a cathode and a photosensitive layer disposed between the anode and the cathode, wherein the photosensitive layer comprises a composition as described herein.

Optionally, the photoresponsive device is an organic photodetector.

According to some embodiments of the present disclosure, there is provided a photosensor comprising a light source and a photoresponsive device as described herein, wherein the photosensor is configured to detect light emitted from the light source.

Optionally, the light source emits light having a peak wavelength greater than 750 nm. Optionally, the photosensor is configured to receive a sample in a light path between the organic photodetector and the light source.

According to some embodiments of the present disclosure, there is provided a method of forming an organic photoresponsive device as described herein comprising formation of the photosensitive organic layer over one of the anode and cathode and formation of the other of the anode and cathode over the photosensitive organic layer.

Optionally, formation of the photosensitive organic layer comprises deposition of a formulation as described herein.

According to some embodiments of the present disclosure, there is provided a method of determining the presence and / or concentration of a target material in a sample, the method comprising illuminating the sample and measuring a response of an organic photodetector as described herein.

DESCRIPTION OF DRAWINGS

The disclosed technology and accompanying figures describe some implementations of the disclosed technology.

Figure 1 illustrates an organic photoresponsive device according to some embodiments;

Figure 2 shows external quantum efficiencies vs. wavelength for an organic photodetector according to some embodiments and a comparative organic photodetector containing a comparative non-fullerene electron acceptor IEICO-4F;

Figure 3 A shows external quantum efficiencies vs. wavelength for an organic photodetector according to some embodiments and a comparative organic photodetector containing a comparative non-fullerene electron acceptor IEICO-4CN;

Figure 3B shows current densities vs. voltage for the organic photodetectors of Figure 3 A which are not exposed to light; Figure 4A shows external quantum efficiencies vs. wavelength for an organic photodetector according to some embodiments and a comparative organic photodetector containing a comparative electron donor; and

Figure 4B shows current densities vs. voltage for the organic photodetectors of Figure 4A which are not exposed to light.

The drawings are not drawn to scale and have various viewpoints and perspectives. The drawings are some implementations and examples. Additionally, some components and/or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the disclosed technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular implementations described. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims.

DETAILED DESCRIPTION

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. References to a layer “over” another layer when used in this application means that the layers may be in direct contact or one or more intervening layers are may be present. References to a layer “on” another layer when used in this application means that the layers are in direct contact. References to a specific atom include any isotope of that atom unless specifically stated otherwise. The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms.

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

Figure 1 illustrates an organic photoresponsive device according to some embodiments of the present disclosure. The organic photoresponsive device comprises a cathode 103, an anode 107 and a bulk heterojunction layer 105 disposed between the anode and the cathode. The organic photoresponsive device may be supported on a substrate 101, optionally a glass or plastic substrate.

The bulk heterojunction layer comprises an electron donor material and a first electron acceptor material. The electron donor (p-type) material has a HOMO deeper (further from vacuum) than a LUMO of the first electron acceptor (n-type) material. Optionally, the gap between the HOMO level of the p-type donor material and the LUMO level of the n-type acceptor material is less than 1.4 eV. Unless stated otherwise, HOMO and LUMO levels of materials as described herein are as measured by square wave voltammetry.

The electron donor material and the first electron acceptor material both comprise an electron donor group of Formula (I): wherein:

X and Y are each independently selected from S, O or Se;

Z is O, S, NR ² or CR ³ ₂

Ar'-Ar ⁶ are each independently an unsubstituted or a substituted benzene, an unsubstituted or a substituted 5- or 6- membered heteroaromatic group or are absent;

A ¹ and A ² are each independently an unsubstituted or a substituted benzene, an unsubstituted or a substituted 5- or 6- membered heteroaromatic group, a non-aromatic 6-membered ring having ring atoms selected from C, N, Sand O or are absent; n is 1, 2 or 3;

R ¹ independently in each occurrence is H or a substituent;

R ² is H or a substituent; and each R ³ is independently H or a substituent.

In the case where n is 2 or 3, each of the n units may be linked in any orientation. For example, in the case where n = 2, formula (I) may be any of:

In some embodiments, each Z is the same. In some embodiments, one Z is one of O, S, NR ² or CR ³ 2 and another Z is another of O, S, NR ² or CR ³ 2.

The present inventors have found that a bulk heteroj unction layer of an organic photodetector containing a donor material and an first acceptor material which both comprise a donor group of formula (I) may result in lower dark current, i.e. current when no electromagnetic radiation is incident on the device, as compared to a donor-acceptor system in which one of the donor and acceptor does not contain a donor group of formula (I).

The present inventors have found that an organic photodetector containing a donor material and an acceptor material which both comprise a donor group of formula (I) may be particularly suitable for detecting long wavelengths of light, e.g. greater than about 850 nm, optionally in the range of 850-1500 nm, optionally in the range of about 850-1000 nm.

The electron donor material and the first electron acceptor material may each contain an electron-donor group of formula (I) and an electron-accepting group (EAG).

For each electron donor material and electron acceptor material containing an electron donor group of formula (I) and an electron-accepting group the, or each, EAG has a LUMO level that is deeper (i.e. further from vacuum) than the group of formula (I), preferably at least 1 eV deeper. The LUMO levels of EAG and formula (I) may be as determined by modelling the LUMO level of EAG-H or H-EAG-H with that of H- [Formula (I)]-H, i.e. by replacing the bonds between EAG and Formula (I) with bonds to a hydrogen atom. Modelling may be performed using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional) and LACVP* (Basis set).

Preferably, the first electron acceptor has a molecular weight of less than 5,000 Daltons, optionally less than 3,000 Daltons. Preferably, the first electron acceptor contains no more than 3 groups of formula (I).

Preferably, the polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography of the electron donor polymer described herein is in the range of about 5xl0 ³ to lxlO ⁸ , and preferably lxlO ⁴ to 5xl0 ⁶ . The polystyrene-equivalent weight- average molecular weight (Mw) of the polymers described herein may be lxlO ³ to 1x10 ^s , and preferably lxlO ⁴ to lxlO ⁷ .

Preferably, the first electron acceptor is a non-polymeric compound. Preferably, the first electron acceptor contains only one group of formula (I).

The first electron acceptor material is more preferably a compound of formula (II): wherein: m and o are each independently 0 or an integer of 1 or more;

L ¹ is a bridging group when m is 1 or more or a direct bond when m is 0;

L ² is a bridging group when o is 1 or more or a direct bond when o is 0; and each EAG ¹ independently represents an electron accepting group. Preferably, m and o are 0, 1 or 2. Preferably, m and o are the same. Preferably, the compound of formula (II) has formula (Ila):

Preferably, n of formula (Ila) is 1. An exemplary compound of formula (Ila) is COi8DFIC:

Where the bridging groups L ¹ and L ² are present, L ¹ and L ² may each independently be a group of formula (XV) or formula (XVI): wherein:

X ¹ , X ² and X ³ are each independently S, O or Se; * represents a point of attachment to Formula (I);

** represents a point of attachment to EAG; and R ⁶ , R ⁷ , R ⁸ and R ⁹ are each independently H or a substituent, optionally a substituent selected from F; Ci- ₂₀ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and phenyl which is unsubstituted or substituted with one or more substituents, optionally one or more Ci- ₁₂ alkyl groups wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F.

By “non-terminal” C atom of an alkyl group as used herein is meant a C atom of the alkyl other than the methyl C atom of a linear (n-alkyl) chain or the methyl C atoms of a branched alkyl chain.

Preferably, F ¹ and F ² are each independently selected from the following formulae: wherein R is a C _{1 - 12} hydrocarbyl group, optionally Ci- ₁₂ alkyl.

Preferably, the electron donor material comprising a group of formula (I) is a polymer comprising a repeat unit of formula (I), more preferably a polymer comprising a repeating group of formula (III): wherein EAG ² is an electron-accepting group.

Preferably, the repeating structure of formula (III) has formula (Ilia): wherein X, Y, Z, R1 and EAG ² are as described above, and R ⁴ independently in each occurrence is H or a substituent. Preferably, each R ⁴ is independently selected from H or a substituent as described with respect to R ⁶ , R ⁷ , R ⁸ and R ⁹ . More preferably, each R ⁴ is H.

Preferably, formula (I) of the electron-donating polymer has formula:

Optionally, R ¹ of the group of formula (I) of the electron donor material or the electron acceptor material is, independently in each occurrence, selected from: H; F; Ci- ₂₀ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and phenyl which is unsubstituted or substituted with one or more substituents, optionally one or more Ci- ₁₂ alkyl groups wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F.

Optionally, R ² of the group of formula (I) of the electron donor material or the electron acceptor material is, independently in each occurrence, selected from H; Ci- ₃₀ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic group Ar ⁵ , optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and Ci- ₁₂ alkyl wherein one or more non- adjacent, non-terminal C atoms may be replaced with O, S, COO or CO. Preferably, R ² is selected from H; C i-30 alkyl; unsubstituted phenyl; or phenyl substituted with one or more substituents selected from C i-12 alkyl and C i-12 alkoxy.

Optionally, R ³ of the group of formula (I) of the electron donor material or the electron acceptor material is, independently in each occurrence, selected from H; F; Ci- ₂₀ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; Si(R ² ) ₃ ; and an aromatic group Ar ⁵ , optionally phenyl, which is unsubstituted or substituted with one or more substituents. Two R ² groups attached to the same carbon atom may be linked to form a ring, e.g. a cycloalkyl ring or an aromatic or heteroaromatic ring, e.g. fluorene.

Substituents of Ar ⁵ may be selected from selected from F; C i-30 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO; and COOH or a salt thereof.

Ar'-Ar ⁶ of the group of formula (I) of the electron donor material or the electron acceptor material are, independently in each occurrence, preferably benzene or thiophene, each of which is optionally and independently unsubstituted or substituted with one or more substituents.

Preferably, A ¹ and A ² of the group of formula (I) of the electron donor material or the electron acceptor material are, independently in each occurrence, cyclohexane, wherein optionally one or more carbon atoms are replaced with S, NR ² or O.

Preferably, A1 and A2 each independently have formula: wherein Z and R ¹ are as described above.

If A ¹ is present then preferably at least Ar ¹ and Ar ² of Ar'-Ar’ are present.

If A ² is present the preferably at least Ar ⁴ and Ar ⁵ of Ar ⁴ -Ar ⁶ are present. Ar ¹ , Ar ² , Ar ³ , Ar ⁴ , Ar ⁵ , Ar ⁶ A ¹ and A ² are each independently and optionally unsubstituted or substituted with one or more substituents, optionally one or more substituents selected from F; Ci- ₂₀ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and -B(R ¹⁴ ) ₂ wherein R ¹⁴ in each occurrence is a substituent, optionally a Ci- ₂ ohydrocarbyl group.

Z is preferably O or NR ² _.

X and Y are each preferably S .

The monovalent EAG ¹ groups of formula (II) may be the same or different, preferably the same. Optionally, each EAG of formula (II) is selected from formulae (IV)-(XIV):

- represents a bond to L ¹ , L ² or a position denoted by * of Formula (I)

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

R ¹⁰ is H or a substituent, preferably a substituent selected from the group consisting of Ci- ₁₂ alkyl wherein one or more non- adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic group Ar ⁷ , optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO. Preferably, R ¹⁰ is H.

J is O or S.

R ¹³ in each occurrence is a substituent, optionally Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F.

R ¹⁵ in each occurrence is independently H; F; Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; or an aromatic group Ar ⁷ , optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or

CO.

R ¹⁶ is a substituent, preferably a substituent selected from:

-(Ar ⁹ ) _w wherein Ar ⁹ in each occurrence is independently an unsubstituted or substituted aryl or heteroaryl group, preferably thiophene, and w is 1, 2 or 3;

Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F.

Ar ¹⁰ is a 5-membered heteroarylene group, preferably thiophene or furan, which is unsubstituted or substituted with one or more substituents.

Substituents of Ar ⁹ and Ar ¹⁰ , where present, are optionally selected from Ci- ₁₂ alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F.

Z ¹ is N or P

T ¹ , T ² and T ³ each independently represent an aryl or a heteroaryl ring which may be fused to one or more further rings. Substituents of T ¹ , T ² and T ³ , where present, are optionally selected from non-H groups of R ¹⁵ . Ar ⁸ is a fused heteroaromatic group which is unsubstituted or substituted with one or more non- El substituents R ¹⁰ .

A preferred group of formula (IV) is formula (IV a).

Preferably at least one, more preferably each, EAG ¹ is a group of formula (IVa): wherein:

R ¹⁰ is as described above;

— represents a linking position to L ¹ , L ² or * of formula (I); and each X '-X ⁴ is independently CR ¹⁷ or N wherein R ¹⁷ in each occurrence is H or a substituent selected from Ci- ₂₀ hydrocarbyl and an electron withdrawing group. Optionally, the electron withdrawing group is F, Cl, Br or CN.

The C _1-20 hydrocarbyl group R ¹⁷ may be selected from Ci- ₂₀ alkyl; unsubstituted phenyl; and phenyl substituted with one or more Ci- ₁₂ alkyl groups.

Exemplary EAG ¹ groups of formula (Va) or (Vb) include:

wherein Ak is a Ci- ₁₂ alkylene chain in which one or more C atoms may be replaced with O, S, CO or COO; An is an anion, optionally -SO ₃ ; and each benzene ring is independently unsubstitued or substituted with one or more substituents selected from substituents described with reference to R ¹⁰ .

Exemplary EAG ¹ groups of formula (X) are:

An exemplary EAG ¹ group of formula (XII) is:

In the case where at least one EAG ¹ is a group of formula (XIV), the group of formula (I) is substituted with a group of formula -B(R ¹⁴ ) ₂ wherein R ¹⁴ in each occurrence is a substituent, optionally a Ci- ₂ ohydrocarbyl group; — is bound to a position denoted by * in Formula (I); and is a bond to the boron atom of -B(R ¹⁴ ) ₂ .

Optionally, R ¹⁴ is selected from Ci- ₁₂ alkyl; unsubstituted phenyl; and phenyl substituted with one or more Ci- ₁₂ alkyl groups.

The group of formula (I), the group of formula (XIV) and the B(R ¹⁴ ) ₂ substituent of formula (I) may be linked together to form a 5- or 6-membered ring.

In some embodiments, EAG of formula (XIV) is selected from formulae (XlVa) ,(XIVb) and (XIVc):

(XlVa) (XlVb) (XI Vc)

Divalent EAG ² groups of formula (III) are preferably selected from divalent analogues of formulae (IX)-(XI) wherein R ¹⁶ is a bond to * of formula (I); and divalent analogues (Xlla) and (XHIa) of formulae (XII) and (XIII), respectively:

(Xlla) (XHIa)

Preferred divalent EAG ² groups are: wherein X is S, Y is H or a substituent, e.g. a Ci- ₁₂ alkyl or F and R is R ¹³ . In some embodiments, the bulk heterojunction layer consists of the electron donor material and the first electron acceptor material. In some embodiments, the bulk heterojunction layer comprises or consists of the electron donor material, the first electron acceptor material and one or more further electron donor and / or electron acceptor materials. In some embodiments, the bulk heterojunction layer comprises or consists of the electron donor material, the first (non-fullerene) electron acceptor material and a second fullerene electron acceptor material.

[0001] Exemplary fullerene electron acceptor materials are C60, C70, C76, C78 and Cs4 fullerenes or a derivative thereof including, without limitation, PCBM-type fullerene derivatives (including phenyl-C61 -butyric acid methyl ester (CeoPCBM), TCBM-type fullerene derivatives (e.g. tolyl-C61 -butyric acid methyl ester (C60TCBM)), and ThCBM-type fullerene derivatives (e.g. thienyl-C 61 -butyric acid methyl ester (C60TI1CBM).

[0002] Fullerene derivatives may have formula (III):

[0003] wherein A, together with the C-C group of the fullerene, forms a monocyclic or fused ring group which may be unsubstituted or substituted with one or more substituents.

[0004] Exemplary fullerene derivatives include formulae (Ilia), (Mb) and (IIIc):

wherein R ²⁰ -R ³² are each independently H or a substituent.

[0005] Substituents R ²⁰ -R ³² are optionally and independently in each occurrence selected from the group consisting of aryl or heteroaryl, optionally phenyl, which may be unsubstituted or substituted with one or more substituents; and Ci-20 alkyl wherein one or more non-adjacent, non -terminal C atoms may be replaced with O, S, CO or COO and one or more H atoms may be replaced with F.

[0006] Substituents of aryl or heteroaryl, where present, are optionally selected from Ci-12 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, CO or COO and one or more H atoms may be replaced with F.

In some embodiments, the weight of the donor to the one or more acceptors is from about 1:0.5 to about 1:2.

Preferably, the weight ratio of the donor to the one or more acceptors is from about 1:1.1 to about 1:2.

Optionally, the weight of the first acceptor is greater than the weight of the donor.

At least one of the anode and cathode is transparent so that light incident on the device may reach the bulk heterojunction layer. In some embodiments, both of the anode and cathode are transparent. Each transparent electrode preferably has a transmittance of at least 70 %, optionally at least 80 %, to wavelengths in the range of 400-750 nm or 750-1000 nm. The transmittance may be selected according to an emission wavelength of a light source for use with the organic photodetector.

Figure 1 illustrates 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 area of the OPD 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 can be an inorganic semiconductor. In some embodiments, the substrate may be silicon. For example, the substrate can be a wafer of silicon. The substrate is transparent if, in use, incident light is to be transmitted through the substrate and the electrode supported by the substrate.

The bulk heterojunction layer may be formed by any process including, without limitation, thermal evaporation and solution deposition methods.

Preferably, the bulk heterojunction layer is formed by depositing a formulation comprising the electron donor material, the first electron acceptor material and any other components of the bulk heterojunction layer dissolved or dispersed in a solvent or a mixture of two or more solvents. The formulation may be deposited by any coating or printing method including, without limitation, spin-coating, dip-coating, roll-coating, spray coating, doctor blade coating, wire bar coating, slit coating, ink jet printing, screen printing, gravure printing and flexographic printing.

The one or more solvents of the formulation may optionally comprise or consist of benzene substituted with one or more substituents selected from chlorine, C _MO alkyl and Ci-io alkoxy wherein two or more substituents may be linked to form a ring which may be unsubstituted or substituted with one or more Ci- ₆ alkyl groups, optionally toluene, xylenes, trimethylbenzenes, tetramethylbenzenes, anisole, indane and its alkyl-substituted derivatives, and tetralin and its alkyl-substituted derivatives.

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 further solvents. The one or more further solvents may be selected from esters, optionally alkyl or aryl esters of alkyl or aryl carboxylic acids, optionally a C _HO alkyl benzoate, benzyl benzoate or dimethoxybenzene. In preferred embodiments, a mixture of trimethylbenzene and benzyl benzoate is used as the solvent. In other preferred embodiments, a mixture of trimethylbenzene and dimethoxybenzene is used as the solvent.

The formulation may comprise further components in addition to the electron acceptor, the electron donor and the one or more solvents. As examples of such components, adhesive agents, defoaming agents, deaerators, viscosity enhancers, diluents, auxiliaries, flow improvers colourants, dyes or pigments, sensitizers, stabilizers, nanoparticles, surface-active compounds, lubricating agents, wetting agents, dispersing agents and inhibitors may be mentioned.

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

The organic photoresponsive device may comprise layers other than the anode, cathode and bulk heterojunction layer shown in Figure 1. In some embodiments, a hole-transporting layer is disposed between the anode and the bulk heterojunction layer. In some embodiments, an electron-transporting 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.

A circuit may comprise the OPD 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 variable. In some embodiments, the photodetector may be continuously biased when in use.

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

In some embodiments, a sensor may comprise 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 changed before reaching the OPD. For example, the light may be reflected, filtered, down-converted or up- converted before it reaches the OPD.

The organic photoresponsive device as described herein may be an organic photovoltaic device or an organic photodetector. An organic photodetector as described herein may be used in a wide range of applications including, without limitation, detecting the presence and / or brightness of ambient light and in a sensor comprising the 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 wavelength and / or brightness of the light may be detected, e.g. due to absorption by, reflection by and / or emission of light from an object, e.g. a target material in a sample disposed in a light path between the light source and the organic photodetector. The sample may be a non-biological sample, e.g. a water sample, or a biological sample taken from a human or animal subject. The sensor may be, without limitation, a gas sensor, a biosensor, an X-ray imaging device, an image sensor such as a camera image sensor, a motion sensor (for example for use in security applications) a proximity sensor or a fingerprint sensor. A ID or 2D photosensor array may comprise a plurality of photodetectors as described herein in an image sensor.

EXAMPLES

Formulation Example 1

Semiconducting Polymer 1 (electron donor), CO18DFIC (non-fullerene electron acceptor) and PCBM (fullerene electron acceptor) were dissolved in 1,2,4-trimethylbenzene : 1,2- dimethoxybenzene (95 : 5 v / v) in a Polymer : CO18DFIC : PCBM weight ratio of 1 : 1.05 : 0.45.

Semiconducting Polymer Example 1

Phenyl-C61 -butyric acid methyl ester (PCBM)

Comparative Formulation 1A

For the purpose of comparison, a formulation was prepared as described for Formulation Example 1 except that CO18DFIC was replaced with the non-fullerene acceptor IEICO-4F:

Comparative Formulation IB

For the purpose of comparison, a formulation was prepared as described for Formulation Example 1 except that COi8DFIC was replaced with the non-fullerene acceptor IEICO-4CN:

Comparative Formulation 2

For the purpose of comparison, a formulation was prepared as described for Formulation Example 1 except that Semiconducting Polymer Example 1 was replaced with Comparative Polymer Example 1, PTB7-Th:

The HOMO, LUMO and band gap values of IEICO-4F, IEICO-4CN and COi8DFIC are provided in Table 1.

HOMO and LUMO measurement was carried out by square wave voltammetry using a CHI660D Electrochemical workstation with software (IJ Cambria Scientific Ltd), CHI 104 3mm Glassy Carbon Disk Working Electrode (IJ Cambria Scientific Ltd), a platinum wire auxiliary electrode and a reference Electrode (Ag/AgCl) (Havard Apparatus Ltd).

Acetonitrile (available as Hi-dry anhydrous grade-ROMIL) was used as the cell solution solvent. Ferrocene (available from FLUKA) may be used as the reference standard. Tetrabutylammoniumhexafluorophosphate (available from FLUKA) may be used as the cell solution salt. The HOMO and LUMO values are measured from a dilute solution (0.3w%) in toluene. The measurement cell contains the electrolyte, a glassy carbon working electrode, a platinum counter electrode, and a Ag/AgCl reference glass electrode. Ferrocene is added into the cell at the end of the experiment as reference material (LUMO (ferrocene) = -4.8eV).

Table 1

Device Example 1

A device having the following structure was prepared:

Cathode / Donor : Acceptor layer / Anode

A glass substrate coated with indium-tin oxide (ITO) was treated with polyethyleneimine (PEIE) to modify the work function of the ITO.

A ca. 600 nm thick bulk heterojunction layer of Formulation Example 1 was deposited over the modified ITO layer by bar coating. The resultant layer was dried under vacuum at 80°C.

An anode (Clevios HIL-E100) available from Heraeus was formed over the donor / acceptor mixture layer by spin-coating.

Comparative Devices 1A, IB and 2

Comparative Devices 1A, IB and 2 were prepared as described for Device Example 1 except that Comparative Formulations 1A, IB and 2, respectively, were used in place of Formulation Example 1.

IEICO-4F used in Comparative Device 1A has a smaller band gap than COi8DFIC used in Device Example 1, which would suggest that Comparative Device 1 would be more effective at absorbing light of long wavelengths. However, with reference to Figure 2, external quantum efficiency of Device Example 1 is surprisingly greater than that of Comparative Device 1 at wavelengths in the range of about 900-1000 nm.

In Comparative Device IB, the acceptor IEICO-4CN has an even smaller band gap than IEICO-4F. With reference to Figures 3 A and 3B, this device has higher external quantum efficiency at wavelengths above about 1000 nm as compared to Device Example 1, however Comparative Device IB has significantly higher dark current. With reference to Figure 4A, external quantum efficiency of Device Example 1 is greater than that of Comparative Device 2 at wavelengths greater than about 900 nm.

With reference to Figure 4B, Device Example 1 has lower dark current than Comparative Device 2.