Composition

Abstract

A composition comprising an electron-donating material; a first non-fullerene electron accepting material; and a second non-fullerene electron-accepting material, wherein the second electron-accepting

Description

BACKGROUND Embodiments of the present disclosure relate to compositions of non-fullerene acceptors (NFAs) suitable for use in organic photodetectors and in particular for use in the near-5 infrared wavelength range. An organic photodetector may contain a photoactive layer of a blend of an electrondonating material and an electron-accepting material between an anode and a cathode. Known electron-accepting materials include fullerenes and NFAs. Detectivity of a photodetector at a given wavelength depends on both efficiency and dark 10 current. Dark current tends to increase as the peak absorption wavelength of the NFA increases, making high detectivity of near-infrared organic photodetectors particularly challenging. WO2020 / 109822 discloses a composition of first and second compounds of formula EAG-EDG-EAG in which EAG is a specific electron-accepting group and EDG is an electron-15 donating group. EAG of the first compound has more electron-withdrawing substituents than EAG of the second compound. WO2017 / 191466 discloses a blend of two or more organic electron acceptor compounds and an organic electron donor compound. CN113571639 discloses a mixture comprising an electron donor, a first electron acceptor 20 and a second electron acceptor. The first electron donor is a conjugated polymer. The energy gap of the first electron acceptor is less than 1.4 eV. At least one of molecular stackability, pi-pi* stackability and crystallinity of the second electron acceptor is smaller than that of the first electron acceptor, wherein the electron donor is used as a matrix and is used for blending the first electron acceptor and the second electron acceptor. 25 J Vollbrecht et al, "Design of narrow bandgap non-fullerene acceptors for photovoltaic applications and investigation of non-geminate recombination dynamics", J. Mater. Chern. C, 2020,8, 15175-15182 discloses solar cells containing donor polymer PTB7-Th or PBDBT and acceptor CETIC-4F (illustrated below) or COTIC-4F: SUMMARY The present disclosure provides a composition comprising an electron-donating material; a first non-fullerene electron-accepting material; and a second non-fullerene electron-5 accepting material, wherein the second electron-accepting material has a peak absorption wavelength greater than 1000 nm; the second electron-accepting material has a longer peak absorption wavelength than the first electron-accepting material; and the weight of the first electron-accepting material in the composition is greater than the weight of the second electron-accepting material in the composition. 10 Optionally, the first and second electron-accepting materials are each a compound of formula (I): A1 - (61)%1 - (D)y - (B2)x2 - A2 (I) 15 wherein: A1 and A2 independently in each occurrence is a monovalent electron-accepting group; D independently in each occurrence is an electron-donating group; B1 and B2 independently in each occurrence is a bridging group; x1 and x2 are each independently 0, 1, 2 or 3; and 20 y is at least 1. Optionally, B1 and B2 are each independently selected from furylene; thienylene; thienothienylene; phenylene; and vinylene, of which are unsubstituted or substituted with one or more substituents. Optionally, (B^x1 and (B2)x2 of the first electron-accepting material are different from 25 (B^x1 and (B2)x2 of the second electron-accepting material. Optionally, the difference between (B^x1 and (B2)x2 of the first and second electronaccepting materials is the only difference between the first and second electron-accepting materials. Optionally, x1 and x2 of the first electron-accepting material are each 1 and x1 and x2 of 5 the second electron-accepting material are each 2. Optionally, (B^x1 and (B2)x2 of the second electron-accepting material are each selected from furylene-vinylene; thienylene-vinylene; thienothienylene-vinylene; and phenylenevinylene. Optionally, (B^x1 and (B2)x2 of the first electron-accepting material are each selected from io furylene; thienylene; thienothienylene; and phenylene. Optionally, (D)y of the first electron-accepting material and (D)y of the second electronaccepting material are the same. Optionally, D in each occurrence of at least one (D)y of the first electron-accepting material and (D)y of the second electron-accepting material is a group of Formula: wherein YA is 0, S, Se or NR6; R51 is independently H or a substituent; and XA is C or Si; and R53 in each occurrence is independently a substituent. Optionally, A1 and A2 of the first electron-accepting material are the same as A1 and A2 of 20 the second electron-accepting material. Optionally, at least one of A1 and A2 is a group of formula (IIa-2) or (IIa-3): (IIa-3) wherein: G is C=0, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 and R40 is H or a substituent; each X7-X10 is independently CR12 or N wherein R12 in each occurrence is H or a substituent 5 selected from C1-20 hydrocarbyl and an electron withdrawing group; R3 is H or a substituent; and each Z is independently CN, CF3 or COOR40 wherein R40 in each occurrence is H or a substituent. Optionally, the electron withdrawing group R12 is F, Cl or CN. 10 Optionally, the first electron-accepting material : second electron-accepting material weight ratio is in the range of 2:1 - 10:1. Optionally, the composition further comprises a fullerene electron-acceptor. The present disclosure provides an organic electronic device comprising an active layer comprising a composition as described herein. 15 Optionally, the organic electronic device is an organic photoresponsive device comprising a photoactive layer comprising the composition disposed between an anode and a cathode. Optionally, the organic photoresponsive device is an organic photodetector. The present disclosure provides a photosensor comprising a light source and an organic photodetector as described herein wherein the photosensor is configured to detect light 20 emitted from the light source. Optionally, the light source emits light having a peak wavelength of greater than 1000 nm. The present disclosure provides a formulation comprising a composition as described herein dissolved or dispersed in one or more solvents. 5 The present disclosure provides a method of forming an organic electronic device as described herein wherein formation of the active layer comprises deposition of a formulation as described herein onto a surface and evaporation of the one or more solvents. DESCRIPTION OF THE DRAWINGS 10 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 is the absorption spectra of non-fullerene acceptor Compound Example 1 and non-fullerene acceptor Compound Example 2; 15 Figure 3 shows external quantum efficiencies of organic photodetectors containing only Compound Example 1, only Compound Example 2 and both Compound Example 1 and Compound Example 2; and Figure 4 shows dark currents of organic photodetectors containing only Compound Example 1, only Compound Example 2 and both Compound Example 1 and Compound 20 Example 2. 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. 25 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 30 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, 5 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, 10 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 may be present. References to a layer "on" another layer when used in this application means that the layers are in direct contact. 15 References to an element of the Periodic Table include any isotope of that element 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. 20 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, 25 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 30 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 5 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. The present inventors have found that a mixture of first and second non-fullerene acceptors can provide high detectivity at wavelengths above about 1300 nm when: 10 - the second NFA has a longer peak absorption wavelength than the first NFA; - the second NFA has a peak absorption wavelength greater than 1000 nm; and the weight of the second NFA in the mixture is less than that of the first NFA. Preferably, the first NFA has a peak absorption wavelength which is at least 50 nm, optionally at least 80 nm less than that of the second NFA. Optionally, the first NFA has 15 a peak absorption wavelength which is no more than 200 nm, optionally no more than 150 nm or 100 nm, less than that of the second NFA. Preferably, the first NFA has a peak absorption wavelength in the range of 900-1000 nm. Optionally, the weight of the first NFA is at least 1.5 times the weight of the second NFA. Preferably, the weight of the first NFA is at least 2 times or at least 3 times the weight of so the second NFA. Optionally, the weight of the first NFA is up to 10 times or up to 5 times the weight of the second NFA Preferably, the first NFA has a LUMO that is deeper (further from vacuum level) than that of the second NFA. More preferably, the first NFA has a LUMO that is between 0.01-0.2 eV deeper that of the second NFA, optionally between 0.05-0.2 eV deeper that of the 25 second NFA. Preferably, both the first and second non-fullerene acceptors are compounds of Formula (I): A1 - (B1)x1 - (D)y - (B2)x2 - A2 (I) 30 wherein: A1 and A2 independently in each occurrence is a monovalent electron-accepting group; D independently in each occurrence is an electron-donating group; B1 and B2 independently in each occurrence is a bridging group; x1 and x2 are each independently 0, 1, 2 or 3, preferably 0, 1 or 2; and y is at least 1, preferably 1, 2 or 3, more preferably 1. 5 Each of the electron-accepting groups A1 and A2 has a lowest unoccupied molecular orbital (LUMO) level that is deeper (i.e., further from vacuum) than the LUMO of the electrondonating group or groups (D)y of the compound of formula (I), preferably at least 1 eV deeper. The LUMO levels of electron-accepting groups and electron-donating groups may be as determined by modelling the LUMO level of these groups, in which each bond to io adjacent group is replaced with a bond to a hydrogen atom. Modelling may be performed using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional) and LACVP* (Basis set). Electron-Accepting Groups A1 and A2 may each independently be selected from any such units known to the skilled 15 person. The A1 and A2 groups of the first compound of formula (I) may be the same or different, preferably the same. The A1 and A2 groups of the second compound of formula (I) may be the same or different, preferably the same. 20 The A1 and A2 groups of the first compound of formula (I) may be the same as or different from the A1 and A2 groups of the second compound of formula (I), preferably the same. Exemplary monovalent acceptor groups A1 and A2 include, without limitation, groups of formulae (Ila)-(IIp) (Hd) (Ilf) (Ilh) (Hj) (HI) U 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. G is C=O, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 wherein R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. 5 G is preferably C=O or SO2, more preferably C=O. The N atom of formula (Ilie) may be unsubstituted or substituted. R3 is H or a substituent, preferably H or a substituent selected from the group consisting of C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6 wherein R6 is H or a substituent, COO or CO and one or more H atoms of the alkyl may be 10 replaced with F; and an aromatic group, optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO. R6 is preferably H or a C1-20 hydrocarbyl group. A C1-20 hydrocarbyl group as described anywhere herein is preferably selected from C1-20 15 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-12 alkyl groups. Most preferably, R3 is H. J is 0 or S, preferably 0. R13 in each occurrence is a substituent, optionally C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F. R15 in each occurrence is independently H; F; C1-12alkyl wherein one or more non-adjacent 5 C atoms may be replaced with 0, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F; an aromatic group, optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO; or a group selected from: wherein Z40, Z41, Z42 and Z43 are each independently CR13 or N wherein R13 in each occurrence is H or a substituent, preferably a Ci 20 hydrocarbyl group; Y40 and Y41 are each independently 0, S, NX71 wherein X71 is CN or COOR40; or CX60X61 wherein X60 and X61 is independently CN, CF3 or COOR40; W40 and W41 are each independently 0, S, NX71 or 15 CX60X61 wherein X60and X61 is independently CN, CF3 or COOR40; and R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. R16 is H or a substituent, preferably a substituent selected from: -(Ar5)w wherein Ar5 in each occurrence is independently an unsubstituted or substituted aryl or heteroaryl group, preferably thiophene, and w is 1, 2 or 3; 20 and C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F. Ar6 is a 5-membered heteroaromatic group, preferably thiophene or furan, which is unsubstituted or substituted with one or more substituents. Substituents of Ar5 and Ar6, where present, are optionally selected from C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, COO or CO and one 5 or more H atoms of the alkyl may be replaced with F. T1, T2 and T3 each independently represent an aryl or a heteroaryl ring, optionally benzene, which may be fused to one or more further rings. Substituents of T1, T2 and T3, where present, are optionally selected from non-H groups of R15. In a preferred embodiment, T3 is benzothiadiazole. 10 Z1 is N or P. Preferred groups A1 and A2 are groups having a non-aromatic carbon-carbon bond which is bound directly to D or, if present, to B1. Preferably at least one of A1 and A2, preferably both A1 and A2, are a group of formula (IIa-1): >5 (IIa-1) wherein: G is as described above and is preferably C=0 or SO2, more preferably C=0; R3 is as described above; 20 Ar2 is an unsubstituted or substituted monocyclic or fused aromatic or heteroaromatic group, preferably benzene; a monocyclic 5- or 6-membered heteroaromatic group having C or N ring atoms only; or a bicyclic heteroaromatic group in which each ring of the bicyclic group is a 5- or 6-membered aromatic or heteroaromatic group having C or N ring atoms only; and each Z is independently CN, CF3 or COOR40 wherein R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. Preferably, each Z is the same. Preferably, each Z is CN. Ar2 may be unsubstituted or substituted with one or more substituents. Substituents of 5 Ar2 are preferably selected from H, F, Cl, CN, NO2, C116 alkyl or C116 alkoxy wherein one or more H atoms of the C116 alkyl or C116 alkoxy may be replaced with F. Optionally, the group of formula (IIa-1) has formula (IIa-2): (IIa-2) 10 wherein each X7-X10 is independently CR12 or N wherein R12 in each occurrence is H or a substituent selected from C1-20 hydrocarbyl and an electron withdrawing group. Preferably, the electron withdrawing group is F, Cl, Br or CN, more preferably F, Cl or CN; and most preferably CN. The Ci 20 hydrocarbyl group R12 may be selected from Ci 20 alkyl; unsubstituted phenyl; 15 and phenyl substituted with one or more C1-12 alkyl groups. In a particularly preferred embodiment, each of X7-X10 is CR12 and each R12 is independently selected from H or an electron-withdrawing group, preferably H, F or CN. According to his embodiment, R12 of X8 and X9 is an electron-withdrawing group, preferably F orCN. 20 Optionally, the group of formula (IIa-1) has formula (IIa-3): (IIa-3) wherein Ar3 is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic group. Preferably, Ar3 is benzene which is unsubstituted or substituted 5 with one or more substituents. Substituents of Ar3 may be selected from R11 as described above, more preferably R12 as described above. Exemplary groups of formula (IIa-3) include, without limitation: 10 Bridging units Bridging units B1 and B2 are preferably each selected from vinylene, arylene, and heteroarylene wherein the arylene and heteroarylene groups are monocyclic or bicyclic groups, each of which may be unsubstituted or substituted with one or more substituents. 5 The (B^x1 and (B2)x2 groups of the first compound of formula (I) may be the same or different, preferably the same. The (B^x1 and (B2)x2 groups of the second compound of formula (I) may be the same or different, preferably the same. The (B^x1 and (B2)x2 groups of the first compound of formula (I) may be the same as or 10 different from the (B1)x1 and (B2)x2 groups of the second compound of formula (I). The absorption wavelength of the first compound of formula (I) may be increased by increasing the value of x1 and I or x2. Accordingly, at least one of x1 and x2 of the second compound of formula (I) is greater than the corresponding x1 and x2 of the first compound of formula (I). Preferably x1 and x2 of the first compound are greater than the 15 corresponding values of x1 and x2 of the second compound. In some preferred embodiments, x1 and x2 of the first compound of formula (I) are each 1 and x1 and x2 of the second compound of formula (I) are each 2 or 3, more preferably 2. In the case where x1 is greater than 1, the groups B1 may be the same or different. 20 In the case where x2 is greater than 1, the groups B2 may be the same or different. Optionally, B1 and B2 are selected from vinylene and units of formulae (Illa) - (Ilin): R8 (Via) (VIb) (Vic) (Vid) (IHj) (HII) (IHn) wherein R6 is H or a substituent, preferably H or a Ci 12 hydrocarbyl group; R8 in each occurrence is independently H or a substituent, preferably H or a substituent selected from F; CN; NO2; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 5 O, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F; phenyl which is unsubstituted or substituted with one or more substituents. R8 is preferably H, C1-20 alkyl or C1-19 alkoxy. Vinylene units and units of formula (Vb) are particularly preferred. In some preferred embodiments, in the first compound of formula (I) x1 and x2 are both 1 10 and (B^x1 and (B2)x2 are each selected from formulae (Illa) - (Ilin), more preferably formula (Illb); and in the second compound of formula (I) x1 and x2 are both 2, one B1 and one B2 is a selected from formulae (Illa) - (Ilin), more preferably (Illb), and the other B1 and B2 are vinylene. Electron-Donating Groups Electron-donating groups D preferably are fused aromatic or heteroaromatic groups, more preferably fused heteroaromatic groups containing three or more rings. Particularly preferred electron-donating groups comprise fused thiophene or furan rings, optionally 5 fused rings containing thiophene or furan rings and one or more rings selected from benzene, cyclopentadiene, tetrahydropyran, tetrahydrothiopyran and piperidine rings, each of said rings being unsubstituted or substituted with one or more substituents. Exemplary electron-donating groups D include groups of formulae (IVa)-(IVq): (IVa) (IVb) (IVc) (IVd) (IVh) (IVn) (IVo) (IVq) wherein YA in each occurrence is independently O, S, Se or NR6; YA1 in each occurrence is independently 0, S or Se; XA is C or Si; ZA in each occurrence is 0, CO, S, NR6 or C(R54)2; R51, R52 R54 and R6 independently in each occurrence is H or a substituent; and R53 independently in each occurrence is a substituent. XA is preferably C or Si, more preferably C. YA in each occurrence is preferably O or S, more preferably S. Optionally, R51 and R52 independently in each occurrence are selected from H; F; Ci zoalkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO 5 and one or more H atoms of the alkyl may be replaced with F; and an aromatic or heteroaromatic group Ar3 which is unsubstituted or substituted with one or more substituents. In some embodiments, Ar3 may be an aromatic group, e.g., phenyl. The one or more substituents of Ar3, if present, may be selected from Ci 12 alkyl wherein 10 one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F. Preferably, each R54 is selected from the group consisting of: H; F; 15 linear, branched or cyclic C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced by 0, S, NR6, CO or COO wherein R17 is a C1-12 hydrocarbyl and one or more H atoms of the C1-20 alkyl may be replaced with F; and a group of formula -(Ak)u-(Ar7)v wherein Ak is a C1-20 alkylene chain in which one or more non-adjacent C atoms may be replaced with 0, S, NR6, CO or COO; u is 0 or 1; Ar7 in each 20 occurrence is independently an aromatic or heteroaromatic group which is unsubstituted or substituted with one or more substituents; and v is at least 1, optionally 1, 2 or 3. Substituents of Ar7, if present, are preferably selected from F; Cl; NO2; CN; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, CO or COO and one or more H atoms may be replaced with F. Preferably, Ar7 is phenyl. In a preferred 25 embodiment, u is 0 and v is 1. Preferably, each R51 is H. Optionally, R53 independently in each occurrence is selected from C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F; and a group of formula a group of 30 formula -(Ak)u-(Ar7)v, preferably phenyl, which is unsubstituted or substituted with one or more substituents, optionally one or more substituents selected from F; Cl; NO2; CN; and Ci-20alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, CO or COO and one or more H atoms may be replaced with F. Preferably, R6 as described anywhere herein is H or C1-20 hydrocarbyl group. 5 D is preferably a group of formula (IVa) or (IVb). Exemplary groups of formula (IVa) include, without limitation: wherein He in each occurrence is independently a Ci 20 hydrocarbyl group, e.g.. Ci 20 alkyl, unsubstituted aryl, or aryl substituted with one or more C1-12alkyl groups. The aryl group is preferably phenyl. 10 Preferred groups of Formula (IVb) have formula: In some embodiments, y of formula (I) is 1. In some embodiments, y of formula (I) is greater than 1. In these embodiments, the chain of D groups may be linked in any orientation. For example, in the case where D is 15 a group of formula (IVa) and y is 2, -(D)y- may be selected from any of: Electron-donating material A bulk heterojunction layer as described herein comprises an electron-donating material and first and second non-fullerene acceptors as described herein. 5 Exemplary donor materials are disclosed in, for example, WO2013 / 051676, the contents of which are incorporated herein by reference. The electron-donating material may be a non-polymeric or polymeric material. In a preferred embodiment the electron-donating material is an organic conjugated polymer, which can be a homopolymer or copolymer including alternating, random or block 10 copolymers. The conjugated polymer is preferably a donor-acceptor polymer comprising alternating electron-donating repeat units and electron-accepting repeat units. Preferred are non-crystalline or semi- crystalline conjugated organic polymers. Further preferably the electron-donating polymer is a conjugated organic polymer with a low bandgap, typically between 2.5 eV and 1.5 eV, preferably between 2.3 eV and 1.8 eV. 15 Optionally, the electron-donating polymer has a HOMO level no more than 5.5 eV from vacuum level. Optionally, the electron-donating polymer has a HOMO level at least 4.1 eV from vacuum level. As exemplary electron-donating polymers, polymers selected from conjugated hydrocarbon or heterocyclic polymers including polyacene, polyaniline, polyazulene, polybenzofuran, polyfluorene, polyfuran, polyindenofluorene, polyindole, 20 polyphenylene, polypyrazoline, polypyrene, polypyridazine, polypyridine, polytriarylamine, poly(phenylene vinylene), poly(3-substituted thiophene), poly(3,4- bisubstituted thiophene), polyselenophene, poly(3-substituted selenophene), poly(3,4-bisubstituted selenophene), poly(bisthiophene), poly(terthiophene), poly(bisselenophene), poly(terselenophene), polythieno[2,3-b]thiophene, polythieno[3,2-b]th iophene, polybenzothiophene, polybenzo[l,2-b:4,5-b'] dithiophene, 5 polyisothianaphthene, poly(monosubstituted pyrrole), poly(3,4-bisubstituted pyrrole), poly-1,3,4-oxadiazoles, polyisothianaphthene, derivatives and co-polymers thereof may be mentioned. Preferred examples of donor polymers are copolymers of polyfluorenes and polythiophenes, each of which may be substituted, and polymers comprising 10 benzothiadiazole-based and thiophene-based repeating units, each of which may be substituted. Particularly preferred donor polymers are donor-acceptor (D-A) polymers comprising an electron-donating repeat unit and an electron-accepting repeat unit. A particularly preferred donor polymer comprises donor unit (IVa) provided as a repeat 15 unit of the polymer, most preferably with an electron-accepting repeat unit. Another particularly preferred donor polymer comprises repeat units of formula (V): wherein R18 and R19 are each independently selected from H; F; C1-12 alkyl wherein one or 20 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 or heteroaromatic group Ar6 which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with 0, S, COO or CO. 25 Acceptor repeat units of a donor-acceptor polymer include repeat units of formulae (Vla)-(Vij): (Via) (VIb) wherein Z1, R13, R15, T1, T2 and T3 are as described above. Electron-accepting repeat units of formulae (Via) and (VIb) are particularly preferred. Organic Electronic Device A composition comprising first and second non-fullerene acceptors as described herein 5 may be provided as an active layer of an organic electronic device. In a preferred embodiment, a bulk heterojunction layer of an organic photoresponsive device, more preferably an organic photodetector, comprises a composition as described herein. The bulk heterojunction layer comprises or consists of an electron-donating material and the first and second non-fullerene electron-accepting materials as described herein. 10 In some embodiments, the weight of the electron-donating material(s) to the electronaccepting materials is from about 1:0.5 to about 1:2. Preferably, the, or each, electron-donating material has a type II interface with each electron-accepting material, i.e. the electron-donating material has a shallower HOMO and LUMO that the corresponding HOMO and LUMO levels of the electron-accepting material. 15 Preferably, the first and second non-fullerene electron-accepting materials have a HOMO level that is at least 0.05 eV deeper, optionally at least 0.10 eV deeper, than the HOMO of the electron-donating material. Optionally, the gap between the HOMO level of the electron-donating material and the LUMO level of the first and second non-fullerene electron-accepting materials is less than 20 1.4 eV. Unless stated otherwise, HOMO and LUMO levels of materials as described herein are as measured by square wave voltammetry (SWV). Figure 1 illustrates an organic photoresponsive device according to some embodiments of the present disclosure. The organic photoresponsive device comprises a cathode 103, an 5 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. Each of the anode and cathode may independently be a single conductive layer or may comprise a plurality of layers. io 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. The transmittance of a transparent electrode may be selected according to an emission wavelength of a light source for use with the organic photodetector. 15 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 organic photoresponsive device may comprise layers other than the anode, cathode and bulk heterojunction layer shown in Figure 1. In some embodiments, a hole-20 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. 25 The area of the OPD may be less than about 3 cm2, less than about 2 cm2, less than about 1 cm2, less than about 0.75 cm2, less than about 0.5 cm2 or less than about 0.25 cm2. Optionally, each OPD may be part of an OPD array wherein each OPD is a pixel of the array having an area as described herein, optionally an area of less than 1 mm2, optionally in the range of 0.5 micron2 - 900 micron2. 30 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 contains a compound of formula (I) or (II) as described herein and an electron-donating compound. The bulk heterojunction layer may consist of these materials or may comprise one or more further materials, for example one or more further electron-donating materials and / or one or more further electron-accepting 5 compounds. Fullerene In some embodiments, the first and second non-fullerene electron-accepting materials are the only electron-accepting material of a bulk heterojunction layer as described herein. 10 In some embodiments, a bulk heterojunction layer contains the first and second non-fullerene electron-accepting materials and one or more further electron-accepting materials. Preferred further electron-accepting materials are fullerenes. The first + second non-fullerene electron-accepting materials : fullerene acceptor weight 15 ratio may be in the range of about 1 : 0.1 - 1 : 1, preferably in the range of about 1 : 0.1 - 1 : 0.5.Fullerenes may be selected from, without limitation, Ceo, C70, C76, C78 and Cs4 fullerenes or a derivative thereof, including, without limitation, PCBM-type fullerene derivatives including phenyl-Csi-butyric acid methyl ester (CsoPCBM), TCBM-type fullerene derivatives (e.g. tolyl-Cei-butyric acid methyl ester (CeoTCBM)), and ThCBM-type fullerene 20 derivatives (e.g. thienyl-Cei-butyric acid methyl ester (CeoThCBM). Fullerene derivatives may have formula (VII): C—C I FULLERENE ] (VII) 25 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. Exemplary fullerene derivatives include formulae (Vila), (Vllb) and (Vile): (Vb) (Vc) wherein R20-R32 are each independently H or a substituent. Substituents R20-R32are optionally and independently in each occurrence selected from the 5 group consisting of aryl or heteroaryl, optionally phenyl, which may be unsubstituted or substituted with one or more substituents; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, CO or COO and one or more H atoms may be replaced with F. 10 Substituents of aryl or heteroaryl, where present, are optionally selected from Ci-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, CO or COO and one or more H atoms may be replaced with F. Formulations The bulk heterojunction layer may be formed by any process including, without limitation, 15 thermal evaporation and solution deposition methods. Preferably, the bulk heterojunction layer is formed by depositing a formulation comprising the electron-donating material(s), the electron-accepting materials 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 20 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 or naphthalene substituted with one or more substituents selected from fluorine, chlorine, Ci-ioalkyl and Ci-ioalkoxy 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 5 toluene, xylenes, trimethylbenzenes, tetramethylbenzenes, anisole, indane and its alkylsubstituted 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 10 from esters, optionally alkyl or aryl esters of alkyl or aryl carboxylic acids, optionally a Ci- 10 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. 15 The formulation may comprise further components in addition to the electron-accepting materials, the electron-donating material 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 20 agents and inhibitors may be mentioned. Applications 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 25 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 30 some embodiments, the light source has a peak wavelength of at least 900 nm or at least 1000 nm, optionally in the range of 900-1500 nm. 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 I or brightness of ambient light and in a sensor comprising the organic photodetector 5 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 10 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. 15 The photodetector may be configured to detect light emitted from a target analyte which emits light upon irradiation by the light source or which is bound to a luminescent tag which emits light upon irradiation by the light source. The photodetector may be configured to detect a wavelength of light emitted by the target analyte or a luminescent tag bound thereto. 20                              EXAMPLES Compound Example 1 Compound Example 1 was prepared according to the following reaction scheme: Toluene 110 °C Pd2dba3 P(o-tol)3 5 Qx-2CI Compound Example 1 Intermediate Qx-2CI used in synthesis of Compound Example 1 was prepared according to the following method: Step 1 Step 2 Step 3 Step 4 MeOH r.t., 16h dil. HCI 3h LiOH H2O 130°C 3h Ac2O Step 5 Step 6 1. Ac2O, NEt3 r.t., 16h 2. 1.5 M HCI 48h Malononitrile Pyridine r.t., 2h Qx-2CI Step 1: Qx-2CI Intermediate 1 (250g, 1.06 mol) was dissolved in 2.5 L of dichloroethane. N-Bromosuccinimide (754g, 4.24 mol), was added to reaction mixture portion wise and it 5 was heated at 75 °C for 16 hours. Solid impurities were filtered off and washed with heptane. Filtrate was concentrated under vacuum to get 255g of crude material. Product Qx-2CI Intermediate 2 was used in the next step without further purification. Step 2: Qx-2CI Intermediate 2 (99.9 g, 434 mmol) and Qx-2CI Intermediate 3 (55g, 310 mmol) io were dissolved in IL of ethanol, p-toluene sulfonic acid (4.69g, 24.7 mmol) was added to the reaction mixture and it was heated at 68 °C for 3 hours. Then, the reaction was concentrated under vacuum to give 105g of crude product which was purified by column chromatography with dichloromethane to give 80g of the desired product Qx-2CI Intermediate 4. 15 Step 3: Qx-2CI Intermediate 4 (50 g, 134 mmol) was dissolved in 500 mL of methanol. Lithium hydroxide monohydride (12.9 g, 308 mmol) was added to the reaction mixture, and it was stirred at room temperature for 16 hours. The reaction mixture was filtered and the obtained solid was stirred in diluted hydrochloric acid for 3 hours. The solid was filtered to 5 obtain 30g of the desired product Qx-2CI Intermediate 5. Step 4: Qx-2CI Intermediate 5 (30 g, 104 mmol) and acetic anhydride (600 mL) were combined in the flask. The reaction mixture was heated at 130 °C for 6 hours. After this time, it was cooled down and concentrated under reduced pressure to obtain 30g of crude product Qx-10 2CI Intermediate 6 which was used directly in the next step without further purification. Step 5 To stirred solution of Qx-2CI Intermediate 6 (30 g, lllmmol) in acetic anhydride (240 mL) was added triethylamine (11.2 g, 111 mmol). To this tert-butyl acetoacetate (18.3 g, 116 mmol) was added dropwise. The reaction mixture was stirred at room temperature 15 for 16 hours and then poured slowly into another flask containing 1.5 N hydrochloric acid (400 mL) and 400 mL of ice water. This was then stirred for 48 hours at room temperature. The obtained solid was isolated by filtration to give 15 g of the desired product Qx-2CI Intermediate 7 as a black solid, which was used in the next step without further purification. so Step 6 Qx-2CI Intermediate 7 (5 g, 18.7 mmol) was dissolved in pyridine (90 ml). To this malononitrile (3.08 g, 46.7 mmol) was added and the mixture was stirred for 2 hours at room temperature. The reaction was concentrated under reduced pressure to give 9 g of crude material which was purified by neutral alumina column chromatography using 25 dichloromethane and 1% tri-ethylamine in methanol. The obtained product was triturated with hexane / dichloromethane and filtered off to give 2.013 g of pure Qx-2CI (98.81% by HPLC) as triethylamine salt. Compound Example 1, Intermediate 2 Intermediate 1 (3.05 g, 7.57 mmol) was dissolved in anhydrous THF (120 mL), then 30 cooled to -78 °C. The mixture was sparged with N2 for 15 minutes. n-Butyllithium (2.5 M in hexane, 6.32 mL, 15.8 mmol) was added dropwise to the mixture, ensuring that the internal temperature did not exceed -70 °C. The reaction was stirred at -78 °C for 90 minutes before being slowly warmed to 0 °C and left to stir at this temperature for a further 1 hour. The reaction was cooled back down to -78 °C before dropwise addition of neat tributyltin chloride (6.32 mL, 15.8 mmol), ensuring that the internal temperature did not exceed -70 °C. The reaction was stirred at -78°C for a further 1 hour, then allowed to warm to room temperature and stirred for a further 16 hours. The reaction was cooled to 5 0 °C and quenched by addition of water (75 mL). The organic layer was extracted with n- heptane (100 mL), then washed with water (3 x 75 mL) and then saturated brine solution (75 mL). The organic extracts were dried over MgSO4 and the solvent removed under reduced pressure to give Intermediate 2 as a pale yellow oil (8.38 g, 112% containing excess BusSnCI). The material was used directly in the next step without further io purification; HPLC purity = 34.58% - note that this is complex mixture of tin-containing species. LCMS m / z 981.5079 [M + H] + . Intermediate 4 Intermediate 2 (2.62 g, 2.67 mmol) and Intermediate 3 (3.03 g, 5.87 mmol) were 15 dissolved in anhydrous toluene (55 mL) and sparged with N2 for 15 minutes. Tris(dibenzylideneacetone) dipalladium(O) (195 mg, 214 pmol) and tris(o-tolyl)phosphine (243 mg, 801 pmol) were charged to the flask and the mixture sparged with N2 for a further 5 minutes. The mixture was heated to 110 °C and stirred under N2 for 1 hour. The cooled reaction mixture was passed through a silica plug, washing initially with n-heptane 20 (this filtrate was discarded), then with n-heptane / dichloromethane (1:1). The solvent was removed under reduced pressure to yield Intermediate 4 (6.17 g, 180%, containing excess intermediate 3 and tin-containing species) as a viscous red oil; HPLC purity = 52.54%. LCMS m / z 1275.9453 [M + H] + . Intermediate 5 25 Intermediate 4 (3.50 g, 2.74 mmol) was dissolved in THE (195 mL). Water (39 mL) was added before dropwise addition of trifluoroacetic acid (3.77 mL, 49.3 mmol). The reaction was warmed to 55 °C and stirred under N2 for 2.5 hours. The reaction was cooled to room temperature and then poured onto ice (200 g). A mixture of THF / n-heptane (4:1, 200 mL) was added before portion wise addition of saturated NaHCOs solution (~75 mL, until the 30 aqueous layer reached pH = 7). The organic layer was separated and washed with water (2 x 150 mL), then brine (150 mL). The combined organic extracts were dried over MgSO4 and the solvent removed under reduced pressure to yield a bright red oil. The crude material was purified by silica chromatography (heptane / dichloromethane, gradient elution from 0 to 100%) to yield Intermediate 5 (1.98 g, 66%) as a bright red viscous oil; HPLC purity = 93.95%. XH NMR (600 MHz, CDCI3): 6 [ppm] 9.77 (s, 2H), 7.49 (s, 2H), 7.36 (s, 2H), 4.11 (t, J = 5.2 Hz, 4H), 1.93 (dq, J = 10.4, 5.2 Hz, 6H), 1.65-1.58 (m, 4H), 1.55-1.48 (m, 4H), 5 1.45-1.25 (m, 50H), 1.06-0.97 (m, 11H), 0.97-0.87 (m, 23H), 0.73 (t, J = 6.1 Hz, 8H), 0.64 (t, J = 7.2 Hz, 6H). LCMS m / z 1103.7786 [M + H] + . Compound Example 1 Intermediate 5 (445 mg, 403 pmol), Qx-2CI (633 mg, 2.01 mmol) and p-toluenesulfonic 10 acid (520 mg, 3.02 mmol) were dissolved anhydrous toluene (40 mL) and anhydrous ethanol (15 mL). The mixture was sparged with N2 for 10 minutes, before warming to 65 °C and allowed to stir under N2 for 60 minutes. Once complete, the hot reaction mixture was filtered, then the remaining solid washed with hot MeOH (2 x 30 mL), hot EtOH (2 x 30 mL) and pentane (2 x 30 mL). The solid was dried on the filter paper under an N2 15 shower. The solid was dried in a vacuum oven for 18 hours (50 °C, 0.1 mbar) to yield Compound Example 1 (592 mg, 87%) as a deep blue solid; HPLC purity = 89.61%. XH NMR (600 MHz, toluene-d8): 6 [ppm] 8.81 (s, 2H), 8.17 (s, 2H), 8.00 (t, J = 5.3 Hz, 2H), 7.82 (t, J = 11.2 Hz), 7.45 (br s, 2H), 3.81 (s, 4H), 1.99 (dq, J = 11.5, 4.2 Hz, 4H), 1.86-1.77 (m, 2H), 1.68-1.60 (m, 4H), 1.77-1.52 (m, 4H), 1.49-1.36 (m, 39H), 1.21-1.10 20 (m, 10H), 1.10-1.01 (m, 12H), 0.99 (dt, J = 5.7, 1.2 Hz, 6H), 0.91 (dt, J = 6.9, 1.3 Hz, 6H), 0.89-0.84 (m, 2H), 0.78 (t, J = 7.4 Hz, 6H). LCMS m / z 1698.6919 [M + H] + . Compound Example 2 Compound Example 2 was prepared according to the following reaction scheme: Compound Example 1, Intermediate 5 1) NaH, THF 25 °C 2) HCI (1 M) 25 EC Intermediate 1 Tributyl (l,3-dioxolan-2-ylmethyl)phosphonium bromide (1.09 g, 2.97 mmol) was 5 charged to an oven-dried flask under N2. A solution of Compound Example 1, Intermediate 5 (1.50 mg, 1.35 mmol) in anhydrous THF (85 mL) was added. The mixture was sparged with N2 for 15 minutes, before addition of NaH (60 wt% in mineral oil, 176 mg, 4.45 mmol) in one portion. The reaction was stirred at r.t. for 20 h. The reaction was quenched by dropwise addition of 1 M HCI solution (16.8 mL, 16.8 mmol) and allowed to stir for a 10 further 2 h. Water (60 mL) was added, then the organic fraction extracted with n-heptane (2 x 40 mL). The combined organic extracts were washed with sat. brine solution (75 mL), dried over MgSCh and the solvent removed under reduced pressure to give Intermediate 1 (2.30 g, 130% containing residual Wittig reagent) as a deep red solid; HPLC purity = 90.39%. Note: the product shows possible instability on silica, so was used directly in the 15 next step without further purification. LCMS m / z 1155.7583 [M + H] + . Compound Example 2 Intermediate 1 (360 mg, 240 pmol), Qx-2CI (374 mg, 1.19 mmol) and p-toluenesulfonic acid (308 mg, 1.79 mmol) were dissolved anhydrous toluene (11 mL) and anhydrous 20 ethanol (24 mL). The mixture was sparged with N2 for 10 min, before warming to 65 °C and allowed to stir under N2 for 60 min. Once complete, the hot reaction mixture was filtered, then the remaining solid washed with hot MeOH (2 x 30 mL), hot EtOH (2 x 30 mL) and pentane (2 x 30 mL). The solid was dried on the filter paper under an N2 shower. The solid was dried in a vacuum oven for 18 h (50 °C, 0.1 mbar) to yield Compound Example 2 (592 mg, 87%) as a deep blue solid; HPLC purity = 88.76%. 1H NMR (600 MHz, l,2-dichlorobenzene-d4): 6 [ppm] 8.80 (t, J = 13.0 Hz, 2H), 8.50 (q, 5 J = 9.5 Hz, 2H), 8.17 (s, 2H), 8.02 (s, 2H), 7.59 (s, 2H), 4.10 (q, J = 5.2 Hz, 4H), 2.11 (dq, J = 10.8, 5.0 Hz, 4H), 2.00-1.92 (m, 2H), 1.72-1.63 (m, 4H), 1.92-1.55 (m, 4H), 1.51-1.43 (m, 10H), 1.43-1.22 (m, 54H), 1.15-0.99 (m, 18H), 0.92 (dt, J = 5.8, 0.7 Hz, 7H), 0.88 (t, J = 6.3, 0.7 Hz, 8H), 0.81-0.76 (m, 6H), 0.76-0.72 (m, 6H). LCMS m / z 1750.7188 [M + H] + . 10 UV-vis (1,2,4-trimethylbenzene) / Uax (e): 1079 (131000), 955 (66600). SWV (solution, toluene): HOMO = -5.08 eV; LUMO = -4.12 eV; Eg = 0.96 eV. SWV (film, toluene): HOMO = -5.36 eV; LUMO = -4.19 eV; Eg = 1.17 eV. Measurements Unless stated otherwise, HOMO and LUMO levels of materials as described herein are as 15 measured by square wave voltammetry (SWV). In SWV, the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time. The difference current between a forward and reverse pulse is plotted as a function of potential to yield a voltammogram. Measurement may be with a CHI 660D Potentiostat. 20 The apparatus to measure HOMO or LUMO energy levels by SWV may comprise a cell containing 0.1 M tertiary butyl ammonium hexafluorophosphate in acetonitrile; a 3 mm diameter glassy carbon working electrode; a platinum counter electrode and a leak free Ag / AgCI reference electrode. Ferrocene is added directly to the existing cell at the end of the experiment for calculation 25 purposes where the potentials are determined for the oxidation and reduction of ferrocene versus Ag / AgCI using cyclic voltammetry (CV). Measurements are carried out in an acetonitrile / toluene solvent mixture (1:1 ratio) using 0.1 M solution of tertiary butyl ammonium hexafiuorophosphate as an electrolyte in a three-electrode system, with each solution being purged with argon prior to measurement. 30 For film measurement the working electrode with spin coated material is used. For solution measurements, 1 ml solution of the material with concentration 3mg / ml in toluene is added to the cell with electrolyte and CV experiment is run after the addition. LUMO = 4.8-E ferrocene (peak to peak average) - E reduction of sample (peak maximum). HOMO = 4.8-E ferrocene (peak to peak average) + E oxidation of sample (peak 5 maximum). A typical SWV experiment runs at 15 Hz frequency; 25 mV amplitude and 0.004 V increment steps. Results are calculated from 3 freshly spun film samples for both the HOMO and LUMO data. Unless stated otherwise, absorption spectra were measured using a Cary 5000 UV-VIS-10 NIR Spectrometer. Measurements were taken from 175 nm to 3300 nm using a PbSmart NIR detector for extended photometric range with variable slit widths (down to 0.01 nm) for optimum control over data resolution. Unless stated otherwise, absorption values are of a solution. Absorption data are obtained by measuring the intensity of transmitted radiation through a solution sample. Absorption 15 intensity is plotted vs. incident wavelength to generate an absorption spectrum. A method for measuring absorption may comprise measuring a 15 mg / ml solution in a quartz cuvette and comparing to a cuvette containing the solvent only. Unless stated otherwise, solution absorption data as provided herein is as measured in 1,2,4-trimethylbenzene solution. 20 Absorption spectra of Compound Examples 1 and 2 are shown in Figure 2 and SWV and peak absorption values are shown in Table 1. Table 1 Compound Solution HOMO (eV) Solution LUMO (eV) Film HOMO (eV) Film LUMO (eV) 7max (nm), extinction coefficient (dm3 mol 1 cm4) Compound Example 1 -5.27 -4.25 eV -5.48 eV -4.23 eV 983 (233000), 880 (92300), 785 (29400) Compound Example 2 -5.08 -4.12 -5.36 -4.19 1079 (131000), 944 (62700) General Device Method A glass substrate coated with a 150 nm thick layer of indium-tin oxide (ITO) was coated with a 0.2 % polyethyleneimine (PEIE) solution in water to form a less than 5 nm film 5 modifying the work function of the ITO. A ~250-400 nm thick bulk heterojunction layer of a mixture of Donor Polymer 1 (50 wt %) and electron acceptors (50 wt %) was deposited over the modified ITO layer by bar coating from a 10 mg / ml solution in a 1,2,4-trimethylbenzene I 1,2-dimethoxybenzene solvent mixture (95:5 v / v) followed by drying in a vacuum oven. An anode stack of MoOs (lOnm) and ITO (70nm) was formed over the 10 bulk heterojunction by thermal evaporation (MoOs) and sputtering (ITO). The completed device was encapsulated. Donor Polymer 1 Device Example 1 containing the fullerene C60PCBM and the non-fullerene acceptors Compound Example 1 and Compound Example 2 was formed by the general device 15 method. For comparison, Comparative Devices 1 and 2 were formed in the same way except that Compound Example 1 is the only non-fullerene acceptor in Comparative Device 1 and Compound Example 2 the only non-fullerene acceptor in Comparative Device 2. The ratios of the CeoPCBM and non-fullerene acceptor(s) are set out in Table 2. 5 Table 2 Device C60PCBM Compound Example 1 Compound Example 2 Device Example 1 0.3 0.55 0.15 Comparative Device 1 0.3 0.7 Comparative Device 2 0.3 0.7 With reference to Figure 3, Comparative Device 1 (containing Compound Example 1) has relatively high external quantum efficiency compared to Comparative Device 2 (containing Compound Example 2) but EQE of Comparative Device 1 at wavelengths below about 1400 io nm but its EQE tails off rapidly at above 1400 nm. Comparative Device 2 has higher external quantum efficiency than Comparative Device 1 at wavelengths above about 1400 nm, which is consistent with the narrower band gap of Compound Example 2 as compared to Compound Example 1. However, Comparative Device 2 has a generally low EQE (below about 10%), both below and above 1400 nm. 15 Device Example 1 (containing both Compound Example 1 and Compound Example 2) maintains a higher EQE than Comparative Device 2 up to wavelengths of about 1500 nm. With reference to Figure 4, Device Example 1 has a lower dark current than either Comparative Device 1 or Comparative Device 2. This is surprising given the known tradeoff between efficiency and dark current (see for example Giulio Simone et al, "Organic 20 Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current", Adv. Funct. Mater. 2020, 30, 1904205). As shown in Table 3, the combination of high efficiency and low dark current provides Device Example 1 with a detectivity (D*) at 1450 nm which is around 6 times greater than Comparative Device 1 and around 3 times greater than Comparative Device 2. Table 3 Device Jd (3V) / pA cm 2 EQE (1450 nm, 3V) / % D* (1450 nm, 3V) / Jones Comparative Device 1 327 3.5 3.5xl09 Comparative Device 1 421 6.9 7.0xl09 Device Example 1 138 11.5 2.0X1010

Claims

1. A composition comprising an electron-donating material; a first non-fullerene electron-accepting material; and a second non-fullerene electron-accepting material, wherein the second electron-accepting material has a peak absorption wavelength greater than 1000 nm; the second electron-accepting material has a longer peak absorption wavelength than the first electron-accepting material; and the weight of the first electron-accepting material in the composition is greater than the weight of the second electron-accepting material in the composition.

2. A composition according to claim 1 wherein the first and second electron-accepting materials are each a compound of formula (I):A1 - (B1)x1 - (D)y - (B2)x2 - A2(I)wherein:A1 and A2 independently in each occurrence is a monovalent electron-accepting group;□ independently in each occurrence is an electron-donating group;B1 and B2 independently in each occurrence is a bridging group;x1 and x2 are each independently 0, 1, 2 or 3; and y is at least 1.

3. The composition according to claim 2 wherein B1 and B2 are each independently selected from furylene; thienylene; thienothienylene; phenylene; and vinylene, of which are unsubstituted or substituted with one or more substituents.

4. The composition according to claim 2 or 3 wherein (B1)x1 and (B2)x2 of the first electron-accepting material are different from (B^x1 and (B2)x2 of the second electron-accepting material.

5. The composition according to claim 4 wherein the difference between (B1)x1 and (B2)x2 of the first and second electron-accepting materials is the only difference between the first and second electron-accepting materials.

6. The composition according to claim 4 or 5 wherein x1 and x2 of the first electronaccepting material are each 1 and x1 and x2 of the second electron-accepting material are each 2.

7. The composition according to claim 6 wherein (B^x1 and (B2)x2 of the second electron-accepting material are each selected from furylene-vinylene; thienylene-vinylene; thienothienylene-vinylene; and phenylene-vinylene.

8. The composition according to claim 7 wherein (B^x1 and (B2)x2 of the first electronaccepting material are each selected from furylene; thienylene; thienothienylene; and phenylene.

9. The composition according to any one of claims 2-8 wherein (D)y of the first electronaccepting material and (D)y of the second electron-accepting material are the same.

10. The composition according to any one of claims 2-9 claim wherein D in each occurrence of at least one (D)y of the first electron-accepting material and (D)y of the second electron-accepting material is a group of Formula:wherein YA is O, S, Se or NR6; R51 is independently H or a substituent; and XA is C or Si; and R53 in each occurrence is independently a substituent.

11. The composition according to any one of claims 2-10 wherein A1 and A2 of the first electron-accepting material are the same as A1 and A2 of the second electronaccepting material.

12. The composition according to any one of claims 2-11 wherein at least one of A1 and A2 is a group of formula (IIa-2) or (IIa-3):(IIa-3)wherein:G is C=0, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 and R40 is H or a substituent;each X7-X10 is independently CR12 or N wherein R12 in each occurrence is H or a substituent selected from C1-20 hydrocarbyl and an electron withdrawing group;R3 is H ora substituent; andeach Z is independently CN, CF3 or COOR40 wherein R40 in each occurrence is H or a substituent.

13. The composition according to claim 12 wherein the electron withdrawing group R12 is F, Cl orCN.

14. The composition according to any one of the preceding claims wherein the first electron-accepting material : second electron-accepting material weight ratio is in the range of 2:1 - 10:1.

15. The composition according to any one of the preceding claims wherein the composition further comprises a fullerene electron-acceptor.

16. An organic electronic device comprising an active layer comprising a composition according to any one of the preceding claims.

17. The organic electronic device according to claim 16 wherein the organic electronic device is an organic photoresponsive device comprising a photoactive layer comprising the composition disposed between an anode and a cathode.

18. The organic electronic device according to claim 17 wherein the organic photoresponsive device is an organic photodetector.

19. A photosensor comprising a light source and an organic photodetector according to claim 18 wherein the photosensor is configured to detect light emitted from the light source.

20. The photosensor according to claim 19, wherein the light source emits light having a peak wavelength of greater than 1000 nm.

21. A formulation comprising a composition according to any one of claims 1-15 dissolved or dispersed in one or more solvents.

22. A method of forming an organic electronic device according to claim 16 wherein formation of the active layer comprises deposition of a formulation according to claim 21 onto a surface and evaporation of the one or more solvents.45

Images