Fullerene derivative blends, and production methods and uses thereof

Abstract

To provide electron acceptor materials useful in electronic applications such as organic photovoltaic devices.SOLUTION: A composition comprises: a first fullerene derivative comprising a methanofullerene; and a second fullerene derivative comprising a Diels-Alder adduct comprising a single functional group; where the ratio of the first fullerene derivative to the second fullerene derivative is between 97:3 and 70:30.SELECTED DRAWING: None

Description

[Technical field]

[0001] This patent application claims the benefit of the earlier filing date of U.S. Patent Application No. 62 / 780,569, filed December 17, 2018, the contents of which are incorporated herein by reference in their entirety.

[0002] <Incorporated by reference> All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The patent documents and scientific literature referenced herein establish knowledge available to those skilled in the art. Issued patents, applications, and other publications cited herein are incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference. In case of conflict, the present disclosure will control.

[0003] This application relates generally to materials. More particularly, this application relates to fullerene blends and photovoltaic devices including fullerene blends. [Background technology]

[0004] Organic photovoltaic devices (OPVs) based on liquid-processed bulk heterojunctions have great potential for use in an ever-increasing number of applications that require low weight, flexibility, or the ability to generate electricity at limited illumination levels (e.g., for indoor energy harvesting). However, for widespread deployment, a sufficiently high power conversion efficiency (PCE) that remains largely stable throughout the device lifetime is preferred. Over the past few years, great progress has been made in the development of a new class of low band gap polymers that more efficiently absorb solar light, efficiently form excitons, and subsequently transport charges to the electrodes. Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the initial PCE in devices using such polymers as electron donor materials was often significantly increased, the stability, as assessed, for example, by light soaking experiments, was often disappointing. [Means for solving the problem]

[0006] In one embodiment of the present invention, a composition is provided, comprising a first fullerene derivative and a second fullerene derivative, wherein the first and second fullerene derivatives are of different types; and the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 60:40.

[0007] In some embodiments, the first fullerene derivative is a methanofullerene.

[0008] In some embodiments, the first fullerene is a Diels-Alder adduct.

[0009] In some embodiments, the second fullerene derivative is a Diels-Alder adduct.

[0010] In some embodiments, the second fullerene derivative is a methanofullerene.

[0011] In some embodiments, the first fullerene derivative is a Diels-Alder adduct and the second fullerene derivative is a methanofullerene.

[0012] In some embodiments, the first fullerene derivative is a methanofullerene and the second fullerene derivative is a Diels-Alder adduct.

[0013] In some embodiments, the first fullerene derivative is C 60 The second fullerene derivative is C 70 It is a fullerene derivative.

[0014] In some embodiments, the first fullerene derivative is C 70 The second fullerene derivative is C 60 It is a fullerene derivative.

[0015] In some embodiments, the first fullerene derivative and the second fullerene derivative are 60 It is a fullerene derivative.

[0016] In some embodiments, the first fullerene derivative and the second fullerene derivative are 70 It is a fullerene derivative.

[0017] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 70:30.

[0018] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is between about 95:5 and about 70:30.

[0019] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is between about 92:8 and about 70:30.

[0020] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 75:25.

[0021] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is about 95:5.

[0022] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is about 90:10.

[0023] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is about 85:15.

[0024] In some embodiments, the ratio of the first fullerene derivative to the second fullerene derivative is about 75:25.

[0025] In some embodiments, the composition further comprises a third fullerene derivative.

[0026] In some embodiments, the composition further comprises a non-fullerene material that functions as an electron acceptor.

[0027] In some embodiments, the non-fullerene material comprises quantum dots.

[0028] In some embodiments, the non-fullerene material emits a photon after absorbing light. The emitted photon can be absorbed in the active layer, for example by a donor material, to form an exciton, thereby generating further charge transport.

[0029] In some embodiments, the methanofullerene is a phenyl-C 61 -Butyric acid-methyl-ester (

[60] PCBM), thiophenyl-C 61 -Butyric acid-methyl-ester (

[60] ThCBM),

[70] PCBM, phenyl-C 61 -Butyric acid hexyl ester (

[60] PCBC6), phenyl-C 71 -Butyric acid hexyl ester (

[70] PCBC6) and other [6,6]-phenyl C 61 Butyric acid or [6,6]-phenyl C 71 butyric acid derivatives.

[0030] In some embodiments, the Diels-Alder adduct is selected from the group consisting of optionally substituted indenes, n-hexyl esters, α-substituted o-quinodimethanes, and esters of 3-(1-idynyl)propionic acid.

[0031] In some embodiments, the first fullerene derivative is

[60] PCBM or

[70] PCBM and the second fullerene derivative is a Diels-Alder indene adduct, an α-substituted o-quinodimethane adduct, or an ester of 3-(1-indenyl)propionic acid.

[0032] In some embodiments, the first fullerene derivative is

[60] PCBM and the second fullerene derivative is the following compound:

[0033] [ka]

[0034] In some embodiments, the composition further comprises a semiconducting polymer.

[0035] In some embodiments, the semiconducting polymer is selected from the group consisting of poly(3-hexylthiophene), (poly[2-3,7-dimethyloctyloxy)-5-methyloxy]-paraphenylenevinylene) (MDMO-PPV), carbazole-based copolymers, diketopyrrolopyrrole (DPP)-based copolymers, cyclopentadithiophene-based copolymers, and some liquid crystal containing small molecules (e.g., functionalized hexabenzone coronene), pentacene derivatives, oligothiophenes, triphenylamines, functionalized anthradithiophenes, and many conventional low molecular weight colorants, e.g., from the thiophene and indoline systems.

[0036] In a second aspect of the present invention, there is provided an organic photovoltaic device comprising a composition comprising a first fullerene derivative and a second fullerene derivative, wherein the first and second fullerene derivatives are of different types; and the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 60:40.

[0037] In some embodiments, the device has improved stability compared to an OPV device that does not contain two fullerene derivatives, In some embodiments, the device has improved stability compared to an OPV device that does not contain two fullerene derivatives of different types.

[0038] In some embodiments, the devices exhibit improved thermal stability when heated up to 120° C. under air compared to an OPV device that does not contain the two fullerene derivatives.

[0039] In some embodiments, the devices have improved stability when exposed to 1 sun intensity irradiation as compared to an OPV device that does not contain the two fullerene derivatives. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is an exemplary schematic diagram of the device structure for a device using PV2001 as the donor material and

[60] PCBM, Blend I or Blend II as the acceptor material in the active layer.

[0041] [Diagram 2] FIG. 2 is an exemplary schematic diagram of the device structure for a device using PCE-11 as the donor material and

[60] PCBM, Blend I, or Blend II as the acceptor material in the active layer.

[0042] [Figure 3A] FIG. 3A is a graph of the power conversion efficiency (PCE, %) of ITO / ZnO / PV2001:acceptor / PEDOT:PSS / silver nanowire (AgNW) devices as a function of annealing time (120 °C in air) using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0043] [Figure 3B]FIG. 3B is a graph of the fill factor (FF, %) as a function of annealing time (in air at 120° C.) for ITO / ZnO / PV2001:acceptor / PEDOT:PSS / silver nanowire (AgNW) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0044] [Figure 3C] FIG. 3C is a graph of the short-circuit current (Jsc, mA / cm2) as a function of annealing time (120 °C in air) for ITO / ZnO / PV2001:acceptor / PEDOT:PSS / silver nanowire (AgNW) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0045] [Figure 3D] FIG. 3D is a graph of the open circuit voltage (V, V) as a function of annealing time (120° C. in air) for ITO / ZnO / PV2001:acceptor / PEDOT:PSS / silver nanowire (AgNW) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0046] [Figure 3E] FIG. 3E is a graph of light injection at 1.2 V (mA / cm2) as a function of annealing time (120 °C in air) for ITO / ZnO / PV2001:acceptor / PEDOT:PSS / silver nanowire (AgNW) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0047] [Figure 4A] FIG. 4A is a graph of the power conversion efficiency (PCE, %) of ITO / ZnO / PCE-11:acceptor / vapor-deposited MoOx / vapor-deposited silver (Ag) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material as a function of annealing time (120° C. in air).

[0048] [Figure 4B] FIG. 4B is a graph of the fill factor (FF, %) as a function of annealing time (120° C. in air) for ITO / ZnO / PCE-11:acceptor / vapor-deposited MoOx / vapor-deposited silver (Ag) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0049] [Figure 4C] FIG. 4C is a graph of the short-circuit current (Jsc, mA / cm2) as a function of annealing time (120 °C in air) for ITO / ZnO / PCE-11:acceptor / vapor-deposited MoOx / vapor-deposited silver (Ag) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0050] [Figure 4D] FIG. 4D is a graph of the open circuit voltage (Voc, V) as a function of annealing time (120 °C in air) for ITO / ZnO / PCE-11:acceptor / vapor-deposited MoOx / vapor-deposited silver (Ag) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0051] [Figure 4E] FIG. 4E is a graph of light injection at 1.2 V (mA / cm2) as a function of annealing time (120 °C in air) for ITO / ZnO / PCE-11:acceptor / evaporated MoOx / evaporated silver (Ag) devices using

[60] PCBM, Blend I, or Blend II as the acceptor material.

[0052] [Diagram 5] FIG. 5 is a graph of the normalized power conversion efficiency (PCE) over time of PCE-11 with three acceptor materials,

[60] PCBM, Blend I, and Blend II, under constant illumination with one sun LED light at 65° C. short circuit conditions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The initial PCE of devices using low band gap polymers as electron donor materials has been increased; however, their stability, as assessed, for example, by photoirradiation experiments, has often been disappointing. A strategy to eliminate, or at least minimize, the decrease in PCE over time (usually driven by the decrease in short circuit current, Jsc) is to use C 70 However, in the industrial stage, 70 The use of derivatives is 60 Approximately 10 times higher than the derivatives, C 70 Considering the price of the derivatives, it is not economically feasible, at least at this stage. Moreover, some blends of electron acceptor materials have been reported that have a significant decrease in performance due to the presence of electron traps (Lenes et al., Adv. Funt. Mater. 2009, 19, 3002-3007; Cowan et al., Adv. Funt. Mater. 2011, 21, 3083-3092; each of which is incorporated herein by reference in its entirety). Differences in the functionalization of the blended acceptors can lead to different electronic structures, especially LUMO levels, producing electron traps and overall poor performance. Differences in functionalization can lead to undesirable morphologies that can reduce device stability. Differences in functionalization can maintain disappointing device stability without improving undesirable morphologies. High performance devices with improved stability using blends are not expected.

[0054] Described herein are organic photovoltaic devices, methods of making and using same. The devices include fullerene derivatives as electron acceptor materials.

[0055] In one embodiment of the present invention, a blend of electron acceptor materials is used in a bulk heterojunction (BHJ) based device, where at least two electron acceptors are fullerene derivatives of different types, i.e., not having the same appended groups. Using such a blend, in the appropriate ratio of the two components, not only results in a similar initial PCE as a BHJ with a similar low band gap electron donor polymer and pure

[60] PCBM or

[70] PCBM as the electron acceptor material. The blend also significantly improves the stability under light irradiation conditions, which is desirable for organic photovoltaic (OPV) devices.

[0056] Traditionally, pure fullerene or fullerene derivative compositions have been preferred for OPV applications. 60 and C 70 Fullerenes have different electronic structures, including different LUMO levels (Yang et al., J. Am. Chem. Soc. 1995, 117, 7801-7804; incorporated herein by reference in its entirety). Similarly, different types of fullerene derivatives have different electronic structures. Fullerene blends have been undesirable because these different electronic structures result in energy traps that trap electrons and contribute to the recombination of electron-hole pairs. The recombination of electron-hole pairs limits the short-circuit current. In addition, blends of fullerene derivatives increase the disorder of the polymer-acceptor blend, which can further reduce the electron mobility and energy conversion efficiency. Surprisingly, blends of different types of fullerene derivatives with appropriate ratios have initial PCEs similar to or greater than those of pure fullerene compositions, while also having improved stability.

[0057] <Fullerene derivatives> Fullerene derivatives include, for example, methanofullerenes, Prato fullerene derivatives, Bingel fullerene derivatives, diazoline fullerene derivatives, azafulleroids, ketolactams, and Diels-Alder fullerene derivatives. Fullerene derivatives can have one or more functional groups. In the case of multiple functionalization (usually 2 or 3), the functional groups can be the same or different. Fullerene derivatives are disclosed, for example, in International Patent Publication No. WO2015 / 192942, U.S. Patent Publication No. 2013 / 0306944, U.S. Patent Publication No. 2017 / 0294585, U.S. Patent No. 8,435,713, and U.S. Patent No. 9,527,797 (each of which is incorporated herein by reference in its entirety). Other fullerene derivatives include endohedral fullerene derivatives and open-ended fullerenes. Illustrative examples are described (but are not limited to) in Ross et al. (Nature Materials 2009, 8, 208-212, inclusive) and Chen et al. (Adv. Energy Mater. 2011, 1, 776-780, open-ended fullerenes), each of which is incorporated herein by reference in its entirety.

[0058] Methanofullerenes have the following general form:

[0059] [ka]

[0060] wherein A is a fullerene; X and Y are independently aryl, alkyl, or other groups attached via a diazoalkane addition; and n is an integer from 1 to 6. In some embodiments, X and Y are independently aryl or alkyl; and n is an integer from 1 to 4. In some embodiments, X and Y are independently aryl or alkyl; and n is 1 or 2. In some embodiments, X and Y are independently aryl or alkyl; and n is 1. Non-limiting examples of methanofullerenes include phenyl-C 61 -Butyric acid-methyl-ester (

[60] PCBM), thiophenyl-C 61-Butyric acid-methyl-ester (

[60] ThCBM),

[70] PCBM, phenyl-C 61 -Butyric acid hexyl ester (

[60] PCBC6), phenyl-C 71 -Butyric acid hexyl ester (

[70] PCBC6) and other [6,6]-phenyl C 61 Butyric acid or [6,6]-phenyl C 71 Butyric acid derivatives (C 60 -PCBX or C 70 -PCBX). Methanofullerenes can be prepared, for example, as described in U.S. Pat. No. 8,435,713 and U.S. Pat. Pub. No. 2005 / 0239717, each of which is incorporated herein by reference in its entirety. Methanofullerenes are often blended with polymers to function as electron acceptors in OPV devices. Blends of

[60] PCBM and

[70] PCBM may be prepared as described in U.S. Pat. Pub. No. 2017 / 0294585, each of which is incorporated herein by reference in its entirety. C 70 -PCBX may be prepared as described in U.S. Patent Publication No. 2017 / 0267628, which is incorporated herein by reference in its entirety.

[0061] In some embodiments, the methanofullerene is the following compound:

[0062] [ka]

[0063] In some embodiments, the methanofullerene is the following compound:

[0064] [ka]

[0065] In some embodiments, the methanofullerene is the following compound:

[0066] [ka]

[0067] The Prato derivatives have the following general form:

[0068] [ka]

[0069] wherein A is a fullerene; R1 is an optionally substituted aryl or aralkyl; and R2, R3, R4, and R5 are independently an optionally substituted alkyl, an optionally substituted cycloalkyl, an optionally substituted heteroalkyl, an optionally substituted heterocycloalkyl, an optionally substituted alkenyl, or an optionally substituted aralkyl. In some embodiments, R1 is an optionally substituted aryl or aralkyl; R2, R3, R4, and R5 are independently an optionally substituted alkyl, an optionally substituted cycloalkyl, an optionally substituted heteroalkyl, an optionally substituted heterocycloalkyl, or an optionally substituted aralkyl. In some embodiments, R1 is an aryl or aralkyl; R2, R3, R4, and R5 are independently an alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, or aralkyl. Prato derivatives include 2-aza-propane-(C n +2N). The Prato fullerene derivatives are C 60 Or C 70 It can be formed from either

[0070] The bingel derivatives, a subclass of methanofullerenes, have the following general form:

[0071] [ka]

[0072] wherein A is a fullerene; X is an electron-withdrawing group; Y is hydrogen, aryl, substituted aryl, alkyl, substituted alkyl; and z is an integer from 1 to 6. Non-limiting examples of electron-withdrawing groups include esters, nitriles, nitro, cyano, ketones, dialkyl phosphates, substituted pyridines, trialkylsilylacetylenes, or trisubstituted silyl groups. In some embodiments, z is an integer from 1 to 4. In some embodiments, z is 1 or 2. Non-limiting examples of electron-withdrawing groups include esters, nitriles, nitro, cyano, ketones, dialkyl phosphates, substituted pyridines, trialkylsilylacetylenes, or trisubstituted silyl groups.

[0073] The diazoline derivatives have the following general form:

[0074] [ka]

[0075] wherein A is a fullerene; R6 and R7 are independently aryl.

[0076] The azafulleroid derivatives have the following general form:

[0077] [ka]

[0078] wherein A is a fulleroid; R8 is alkyl, aryl, substituted aryl, or SO2-R9, where R9 is alkyl, aryl, or substituted aryl.

[0079] Diels-Alder derivatives have the following general form:

[0080] [ka]

[0081] In the formula, A is a fullerene; R 10 and R 11 are independently H, alkyl, alkyloxy, -OC(O)R 12 , aryl, substituted alkyl, substituted aryl, heteroaryl, or substituted heteroaryl; R 12 are independently alkyl, alkyloxy, aryl, substituted alkyl, substituted aryl, heteroaryl, or substituted heteroaryl; X is O, alkyl, substituted alkyl, aryl, substituted aryl, heteroaryl, or substituted heteroaryl; Y is aryl, substituted aryl, heteroaryl, substituted heteroaryl, vinylene, or substituted vinylene; and n is an integer from 1 to 20. Non-limiting examples of Diels-Alder derivatives include the indene adduct, 2-methoxyindene-C 60 , other alkoxy-substituted indenes and o-quinodimethanes-C 60 and C 70 Adduct, α-substituted o-quinodimethane-adduct, C 60 Or C 70 Esters of 3-(1-indenyl)propionic acid adducts of bis-indene- and bis-o-quinodimethane-C 60 and C 70 Examples include adducts.

[0082] In some embodiments, the Diels-Alder derivative is the following compound:

[0083] [ka]

[0084] or the following ester of 3-(1-indenyl)propionic acid:

[0085] [ka]

[0086] In some embodiments, the Diels-Alder derivative is the following compound:

[0087] [ka]

[0088] In some embodiments, the Diels-Alder derivative is the following compound:

[0089] [ka]

[0090] In some embodiments, the Diels-Alder derivative is the following compound:

[0091] [ka]

[0092] <Fullerene blend> The blend of at least two fullerene derivatives is preferably a blend of two or more C 60 Derivatives, two or more C 70 Derivatives, or at least one C 60 Derivatives and at least one C 70 Derivatives may also be included.

[0093] A blend of at least two fullerene derivatives may contain two or more different types of fullerene derivatives, in some embodiments, each type of fullerene derivative contains a different type of fullerene derivative.

[0094] The blend of at least two fullerene derivatives may further include a non-fullerene acceptor material. Non-limiting examples of non-fullerene acceptors include an indacenodithiophene core flanked by benzothiadiazole and rhodanine groups (IDTBR), an indenofluorene analog of IDTBR (IDFBR), (5Z,50Z)-5,50-{(9,9-dioctyl-9H-fluorene-2,7-diyl)bis[2,1,3-benzothiadiazole-7,4-diyl(Z)methyl]-1,1,2,3-triphenylphosphine (PDP) ... iridine]}bis(3-ethyl-2-thioxo-1,3-thiazolidin-4-one) (FBR), n-octylidacaenodithiophene (O-IDTBR), 2-ethylhexylidacaenodithiophene (EH-IDTBR) or quantum dots (e.g., Liu et al., Adv. Mater. 2013, 25, 5772-5778; Holliday et al., Nature Communications vol. 7, Article number: 11585 (2016); Baran et al., Nature Materials, 2017, 16, 363-369; each of which is incorporated herein by reference in its entirety).

[0095] A blend of the two fullerene derivatives may have a ratio of about 97:3, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 60:40, or any ratio therebetween.

[0096] Blends of fullerene derivatives may be formed by adding each fullerene derivative in powder form to a solution using additives such as, but not limited to, toluene, o-xylene, o-dichlorobenzene, a blend of solvents, and 1,8-octanedithiol.

[0097] The blend may then be precipitated from the solution. To facilitate precipitation of the blend, the solution may be added to an antisolvent. The precipitated blend may be filtered and dried in an oven or vacuum, or a combination of oven and vacuum. Other methods will be apparent to those skilled in the art.

[0098] In some embodiments, the blend comprises a methanofullerene and a Diels-Alder derivative. The methanofullerene is C 60 Series or C 70 In some embodiments, the methanofullerene may be a PCBM. The Diels-Alder derivative may include an alpha-substituted indene adduct.

[0099] In some embodiments, the blend comprises a ratio of methanofullerene:Diels-Alder derivatives between about 97:3 and 60:40. In some embodiments, the blend comprises a ratio of Diels-Alder:methanofullerene derivatives between about 97:3 and 60:40. In some embodiments, the blend comprises a ratio of methanofullerene:Diels-Alder derivatives between about 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, or 60:40. In some embodiments, the blend comprises a ratio of Diels-Alder:methanofullerene derivatives between about 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, or 60:40. In some embodiments, the blend comprises a ratio of Diels-Alder:methanofullerene derivatives between about 90:10, or 85:15. In some embodiments, the blend comprises a ratio of Diels-Alder:methanofullerene derivatives of about 90:10 or 85:15.

[0100] In some embodiments, the blend is a mixture of

[60] PCBM and C (containing an indene adduct with a functional group at the α-position or other positions). 60 In some embodiments, the blend comprises about 95%

[60] PCBM and about 5% C 60 In some embodiments, the blend comprises about 90%

[60] PCBM and about 10% C 60 In some embodiments, the blend comprises about 85%

[60] PCBM and about 15% C 60In some embodiments, the blend comprises about 5%

[60] PCBM and about 95% C 60 In some embodiments, the blend comprises about 10%

[60] PCBM and about 90% C 60 In some embodiments, the blend comprises about 15%

[60] PCBM and about 85% C 60 -indene adducts.

[0101] In some embodiments, the blend is a mixture of

[60] PCBM and C (containing an indene adduct with a functional group at the α-position or other positions). 70 In some embodiments, the blend comprises about 95%

[60] PCBM and about 5% C 70 In some embodiments, the blend comprises about 90%

[60] PCBM and about 10% C 70 In some embodiments, the blend comprises about 85%

[60] PCBM and about 15% C 70 In some embodiments, the blend comprises about 5%

[60] PCBM and about 95% C 70 In some embodiments, the blend comprises about 10%

[60] PCBM and about 90% C 70 In some embodiments, the blend comprises about 15%

[60] PCBM and about 85% C 70 -indene adducts.

[0102] In some embodiments, the blend comprises about 90%

[60] PCBM and about 10% of the following compounds:

[0103] [ka]

[0104] In some embodiments, the blend comprises about 10%

[60] PCBM and about 90% of the following compound:

[0105] [ka]

[0106] In some embodiments, the blend comprises about 15%

[60] PCBM and about 85% of the following compound:

[0107] [ka]

[0108] In some embodiments, the blend comprises about 85%

[60] PCBM and about 15% of the following compound:

[0109] [ka]

[0110] In some embodiments, the blend comprises about 90%

[60] PCBM and about 10% of the following compounds:

[0111] [ka]

[0112] In some embodiments, the blend comprises about 10%

[60] PCBM and about 90% of the following compound:

[0113] [ka]

[0114] In some embodiments, the blend comprises about 15%

[60] PCBM and about 85% of the following compound:

[0115] [ka]

[0116] In some embodiments, the blend comprises about 85%

[60] PCBM and about 15% of the following compound:

[0117] [ka]

[0118] <Performance measurement> Blends of two or more fullerene derivatives in an appropriate ratio may achieve power conversion efficiencies equal to or greater than current technology OPV devices. Power conversion efficiency is a measure of how efficiently a device converts photons into electricity.

[0119] The stability of the device is determined by illuminating the device and measuring performance over time under light illumination conditions. Performance may be quantified based on PCE. Stability may be measured under a variety of conditions, including temperature, humidity, and light intensity, depending on the conditions under which the device is operated. Stability may be determined by measuring performance continuously or before and after a period of use.

[0120] <Organic photovoltaic devices> Organic photovoltaic devices (OPVs), which use inexpensive, rapid, and large-scale roll-to-roll manufacturing methods, are likely to become a key technology for generating electricity.

[0121] OPV devices, also called polymer solar cells (PSCs) or polymer-fullerene composite solar cells, are lightweight, flexible, and offer the potential for a wide range of new applications, including large-area, flexible devices.

[0122] Without wishing to be bound by theory, in addition to tailoring the optical and electronic properties of materials used for light harvesting, carrier generation, transport, and collection, control of the nanoscale morphology of the active layer is another important factor in the direction of increasing power conversion efficiency (PCE) in the laboratory and especially for large area devices. In particular, nanoscale morphology can be a key factor in the optimization of OPVs.

[0123] Bulk heterojunction OPVs are a particular type of OPV device in which nanoscale morphology is formed between an electron donor material (most often, but not all, polymers) and an electron acceptor material. OPV devices contain an electron donor (e.g., poly(3-hexylthiophene) (P3HT)) blended with an electron acceptor, such as fullerene or its derivatives, in its active layer. When a blend of fullerene derivatives is combined with an electron donor polymer, the morphology of the fullerene-polymer blend depends on the ratio of the derivative of the fullerene derivative blend to the fullerene derivative blend. The use of blends of electron donor materials has also been reported (e.g., Lin et al., Synthetic Metals 2014,192,113-118; incorporated herein by reference in its entirety).

[0124] The device can be fabricated, for example, via liquid deposition of different layers such as electrodes, electron transport layers, etc. The active layer contains an electron acceptor and an electron donor.

[0125] Further suitable electron donor materials include semiconducting polymers such as poly(3-hexylthiophene), (poly[2-3,7-dimethyloctyloxy)-5-methyloxy]-paraphenylenevinylene) (MDMO-PPV), carbazole-based copolymers, cyclopentadithiophene-based copolymers, diketopyrrolopyrrole (DPP)-based copolymers, and some liquid crystal containing small molecules (e.g., functionalized hexabenzone coronene), pentacene derivatives, oligothiophenes, triphenylamines, functionalized anthradithiophenes, and many conventional low molecular weight colorants derived from, for example, thiophene- and indoline systems.

[0126] <General Procedure for Preparation of Fullerenes> A fullerene derivative and, optionally, other compounds are added to the vessel in a specific ratio to produce the desired blend. A suitable type and amount of solvent is added to the component materials of the blend, preferably to completely dissolve them. In some embodiments, optionally and without limitation, solubility can be promoted by any combination of time, heat, sonication, stirring, rolling, agitation, and / or the use of excess solvent. In some embodiments, once the materials are dissolved, preferably completely dissolved, some solvent may be removed, if necessary, to achieve the desired concentration. In some embodiments, the solvated blend is then precipitated by some means, including but not limited to further concentration and / or addition of an antisolvent, or addition to an antisolvent. In some embodiments, it is desired that the precipitation is complete and uniform, so that the ratio of the component materials is approximately uniform and constant throughout the product. In some embodiments, the precipitated materials are then filtered, rinsed with an antisolvent, and dried in any number, order, or combination of steps using some combination of vacuum, heat, and / or time. In some embodiments, techniques including, but not limited to, sieving may be used to achieve the desired appearance and / or consistency of the product. Dryness of the material can be confirmed by thermogravimetric analysis (TGA). Once the material is dry, yield can be confirmed by mass. Various characterization methods including high performance liquid chromatography (HPLC) analysis can confirm component ratios, purity and degree of consistency throughout the solid. EXAMPLES

[0127] Particular embodiments are described in the following non-limiting examples.

[0128] <Preparation of Blend I> Blend I was prepared using the following compounds:

[0129] [ka]

[0130] A mass of

[60] PCBM equal to 9 / 10 of the total mass in the desired blend and a mass of Diels-Alder adduct equal to 1 / 10 of the total mass in the desired blend were added to a rotary evaporator flask large enough to reach 18 g / L of total fullerenes in the solvent. The flask was secured to the rotary evaporator. o-Xylene was added via the injection line and negative pressure to reach 18 g / L of solids in the solvent. The contents were stirred for 30-60 minutes in a water bath at ~200 Torr and 50 °C until the solids were completely dissolved. The pressure was reduced and the o-Xylene was evaporated until the concentration was 100 g / L, preferably not to exceed 100 g / L. The fullerene solution in o-Xylene was slowly poured into methanol to completely precipitate the fullerene adducts. The mixture was vacuum filtered through a 393 Sartorius grade filter paper (1-2 microns). The solid was rinsed with methanol and all the o-xylene was forced through the filtrate. The filtered solid was dried under vacuum, preferably at 70° C. for not less than 12 hours. The solid was removed from the oven, preferably below 50° C., the solid was sieved and the blend was continued to dry at 50° C. and high vacuum for not less than an additional hour. The solid was removed from the oven. The yield of the resulting solid was quantitative. Purity and component ratios based on HPLC analysis were recorded and the solid was analyzed by TGA to determine residual solvent content.

[0131] Preparation of Blend II Blend II was prepared using the following compounds:

[0132] [ka]

[0133] A mass of

[60] PCBM equal to 9 / 10 of the total mass in the desired blend and a mass of Diels-Alder adduct equal to 1 / 10 of the total mass in the desired blend were added to a rotary evaporator flask large enough to reach 18 g / L of total fullerenes in the solvent. The flask was secured to the rotary evaporator. o-Xylene was added via the injection line and negative pressure to reach 18 g / L of solids in the solvent. The contents were stirred for 30-60 minutes in a water bath at ~200 Torr and 50 °C until the solids were completely dissolved. The pressure was reduced and the o-Xylene was evaporated until the concentration was 100 g / L, preferably not to exceed 100 g / L. The fullerene solution in o-Xylene was slowly poured into methanol to completely precipitate the fullerene adducts. The mixture was vacuum filtered through a 393 Sartorius grade filter paper (1-2 microns). The solid was rinsed with methanol to push through all the o-xylene into the filtrate. The filtered solid was dried under vacuum, preferably at 70° C. for not less than 12 hours. The solid was removed from the oven, sieved, preferably below 50° C., and blending continued at 50° C. and high vacuum for not less than another 12 hours. The solid was removed from the oven. The yield of the resulting solid was quantitative. Purity and component ratios based on HPLC analysis were recorded, and the solid was analyzed by TGA to determine residual solvent content.

[0134] Fabrication of Devices Using Blend I or Blend II with Donor PV2001 in the Active Layer Devices were fabricated with PV2001 as the donor material and Blend I, Blend II, or

[60] PCBM as the acceptor material using an inverted structure as shown in Figure 1. A glass substrate (101) (25 mm × 25 mm, standard layout, 0.1 cm) was precoated with indium tin oxide (ITO) (102). 2The glass substrates (resulting in six solar cells on each substrate) were pre-cleaned by wiping with a soft tissue and toluene. The glass substrates were then further cleaned in an ultrasonic bath, first with acetone and then with IPA for 5 min each. A ZnO solution in IPA was deposited by doctor blading, followed by annealing at 120° C. for 4 min under air to form the ZnO oxide layer (103). The active layer (104) contained PV2001 as the donor and

[60] PCBM, Blend I or Blend II as the acceptor. In preparing the active layer ink, 13.5 mg of PV2001 (purchased from Raynergy Tek, Hsinchu, Taiwan) and 19.5 mg of

[60] PCBM, Blend I or Blend II were dissolved in 1 mL of o-xylene at 120° C. under nitrogen and stirring for at least 8 h. The optical density measured by a spectrophotometer at 670-675 nm before deposition on the ZnO oxide layer (103) by doctor blading at room temperature was 0.7-0.8. Subsequently, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS, HTL388) (105) was deposited as a hole transport layer again by doctor blading, followed by annealing at 140 °C for 4 min in a glove box. Finally, silver nanowires (106) were deposited from an aqueous solution as the top electrode.

[0135] Fabrication of Devices Using Blend I or Blend II with Donor PCE-11 in the Active Layer Devices were fabricated with PCE-11 as the donor material and Blend I, Blend II, or

[60] PCBM as the acceptor material using the inverted structure shown in Figure 2. A glass substrate (201) (25 mm × 25 mm, standard layout, 0.1 cm) was precoated with indium tin oxide (ITO) (202). 2The glass substrates (resulting in six solar cells on each substrate) were pre-cleaned by wiping with a soft tissue and toluene. The glass substrates were then further cleaned in an ultrasonic bath, first with acetone and then with IPA for 5 min each. A ZnO solution was deposited by doctor blading, followed by annealing at 120° C. for 4 min under air to form a ZnO oxide layer. The active layer (207) contains PCE-11 as the donor and

[60] PCBM, Blend I or Blend II as the acceptor. In preparing the active layer ink, 13.5 mg of PCE-11 (PffBT4T-2OD, purchased from 1-Material Inc., Dorval, Quebec, Canada) and 19.5 mg of

[60] PCBM, Blend I or Blend II were dissolved in 1 mL of o-xylene at 120° C. under nitrogen and stirring for at least 8 h. The optical density measured by spectrophotometer at 687 nm before deposition on the ZnO oxide layer (203) by doctor blading at room temperature was 0.7-0.8. Then 10 nm of MoOx (208) was deposited as a hole transport layer. Finally, 100 nm of Ag (209) was deposited as a top electrode by evaporation.

[0136] <Stability measurement> The thermal stability of both devices with PV2001 or PCE-11 in the active layer was evaluated by thermal oxidation in the dark at 120 °C in ambient air. For this purpose, the final cells were measured at 1 sun intensity in nitrogen. The cells were subsequently annealed in air at 120 °C in a dark atmosphere. The performance of the cells was regularly measured as a function of the annealing time. For this purpose, a solar simulator (LOT Quantum Design LSO 916) and a source measurement unit KEYSIGHT B2901A were used. After each measurement, the cells were placed back in the oven and the annealing procedure continued. Potentials of -1 to 1.5 V were applied to the devices while they were illuminated and the current was measured. From the obtained current-voltage (IV) curves, the power conversion efficiency, fill factor, short circuit current, open circuit voltage and light injection data were extracted. The power conversion efficiency (PCE, %), fill factor (FF, %), short circuit current (Jsc, mA / cm) and the power conversion efficiency (PCE, %) of the devices using PV2001 as donor material were measured. 2 ), open circuit voltage (Voc, V), and 1.2V (mA / cm 2 ) are shown in Figures 3A-3E, while corresponding data from a device using PCE-11 as the donor material are shown in Figures 4A-4E.

[0137] Enhanced thermal stability of Blends I and II compared to the use of

[60] PCBM was observed for both of the donor materials investigated, PV2001 and PCE-11. The degradation of performance over time observed for all material systems investigated here was less pronounced with the use of Blends I or II, and is primarily driven by the reduction in short circuit current (J), shown in Figures 3C and 4C. Such improved thermal stability is of commercial relevance, especially in applications where annealing steps of limited duration are required, e.g., in the context of device integration.

[0138] Furthermore, lifetime measurements were performed under inert gas and temperature controlled at 65 °C, and exposure to LED light near sunlight (no UV) at 1 sun intensity. The evolution of power conversion efficiency (PCE), normalized to the initial measurements, for

[60] PCBM, Blend I and Blend II using PCE-11 as donor material over a sustained period of 650 h is shown in Figure 5. Both Blend I and Blend II showed evidence of enhanced long-term stability compared to the acceptor material

[60] PCBM. Continuation of exposure is expected to show even more accentuated differences.

[0139] As will be apparent to one skilled in the art from reading this disclosure, further embodiments of the invention can be presented in forms other than those specifically disclosed above. The specific embodiments described above are therefore considered to be illustrative and not limiting. Those skilled in the art will recognize or be able to ascertain, without more than routine experimentation, numerous equivalents to the specific embodiments described herein. While the present invention has been described and illustrated in the foregoing exemplary embodiments, it will be understood that the disclosure has been made by way of example only, and that numerous changes in the details of the implementation of the invention are possible without departing from the spirit and scope of the invention, the scope of which is limited only by the following claims. The features of the disclosed embodiments can be combined and rearranged in various ways within the scope and spirit of the invention. The scope of the invention is not limited to the examples contained in the foregoing description, but is as set forth in the appended claims and their equivalents.

Claims

1. A first fullerene derivative; and A second fullerene derivative; A composition comprising: the first and second fullerene derivatives are of different types; and the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 60:40; composition.

2. The composition of claim 1 , wherein the first fullerene derivative is a methanofullerene.

3. The composition of claim 1 , wherein the first fullerene is a Diels-Alder adduct.

4. The composition according to claim 1 or 2, wherein the second fullerene derivative is a Diels-Alder adduct.

5. The composition of claim 1 or 3, wherein the second fullerene derivative is a methanofullerene.

6. 2. The composition of claim 1, wherein the first fullerene derivative is a Diels-Alder adduct and the second fullerene derivative is a methanofullerene.

7. 2. The composition of claim 1, wherein the first fullerene derivative is a methanofullerene and the second fullerene derivative is a Diels-Alder adduct.

8. The first fullerene derivative is C ６０ a C-type fullerene derivative, ７０ The composition according to claim 1 , which is a fullerene derivative.

9. The first fullerene derivative is C ７０ a C-type fullerene derivative, ６０ The composition according to claim 1 , which is a fullerene derivative.

10. The first fullerene derivative and the second fullerene derivative are ６０ The composition according to claim 1 , which is a fullerene derivative.

11. The first fullerene derivative and the second fullerene derivative are ７０ The composition according to claim 1 , which is a fullerene derivative.

12. The composition according to any one of claims 1 to 11, wherein the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 70:

30.

13. The composition according to any one of claims 1 to 12, wherein the ratio of the first fullerene derivative to the second fullerene derivative is between about 95:5 and about 70:

30.

14. The composition according to any one of claims 1 to 13, wherein the ratio of the first fullerene derivative to the second fullerene derivative is between about 92:8 and about 70:

30.

15. 12. The composition according to any one of claims 1 to 11, wherein the ratio of the first fullerene derivative to the second fullerene derivative is between about 97:3 and about 75:

25.

16. The composition according to any one of claims 1 to 12, wherein the ratio of the first fullerene derivative to the second fullerene derivative is about 95:

5.

17. The composition according to any one of claims 1 to 12, wherein the ratio of the first fullerene derivative to the second fullerene derivative is about 90:

10.

18. The composition according to any one of claims 1 to 12, wherein the ratio of the first fullerene derivative to the second fullerene derivative is about 85:

15.

19. The composition according to any one of claims 1 to 12, wherein the ratio of the first fullerene derivative to the second fullerene derivative is about 75:

25.

20. The composition according to any one of claims 1 to 19, further comprising a third fullerene derivative.

21. The composition of any one of claims 1 to 19, further comprising a non-fullerene acceptor.

22. The composition of any one of claims 1 to 19 and 21, further comprising quantum dots.

23. The methanofullerene is a phenyl-C ６１ -Butyric acid-methyl-ester ([60]PCBM), thiophenyl-C ６１ -butyric acid-methyl-ester ([60]ThCBM), [70]PCBM, phenyl-C ６１ -Butyric acid-hexyl-ester ([60]PCBC ６ ), phenyl-C ７１ -Butyric acid-hexyl-ester ([70]PCBC ６ ), and other [6,6]-phenyl C ６１ Butyric acid or [6,6]-phenyl C ７１ The composition according to any one of claims 1 to 22, which is selected from the group consisting of butyric acid derivatives.

24. 23. The composition of any one of claims 1 to 22, wherein the Diels-Alder adduct is selected from the group consisting of optionally substituted indenes, n-hexyl esters, α-substituted o-quinodimethanes, and esters of 3-(1-idinyl)propionic acid.

25. 2. The composition of claim 1, wherein the first fullerene derivative is [60]PCBM or [70]PCBM, and the second fullerene derivative is a Diels-Alder indene adduct, an α-substituted o-quinodimethane adduct, or an ester of 3-(1-indenyl)propionic acid.

26. A composition, wherein the first fullerene derivative is [60]PCBM and the second fullerene derivative is the following compound: 【Chemistry 1】

27. The composition of any one of claims 1 to 26, further comprising a semiconducting polymer.

28. 28. The composition of claim 27, wherein the conductive polymer is selected from the group consisting of poly(3-hexylthiophene), (poly[2-3,7-dimethyloctyloxy)-5-methyloxy]-paraphenylenevinylene) (MDMO-PPV), carbazole-based copolymers, diketopyrrolopyrrole (DPP)-based copolymers, cyclopentadithiophene-based copolymers, and some small molecule containing liquid crystals (e.g., functionalized hexabenzone coronene), pentacene derivatives, oligothiophenes, triphenylamines, functionalized anthradithiophenes, and many conventional low molecular weight colorants derived from, for example, thiophene- and indoline systems.

29. 29. An OPV device comprising the composition of any one of claims 1 to 28.

30. 30. The OPV device of claim 29, wherein the device has improved thermal stability compared to an OPV device that does not include the two fullerene derivatives.

31. 30. The OPV device of claim 29, wherein the device has improved thermal stability when heated to 120°C under air compared to an OPV device that does not contain the two fullerene derivatives.

32. 30. The OPV device of claim 29, wherein the device has improved stability when exposed to 1 sun intensity irradiation as compared to an OPV device that does not include the two fullerene derivatives.

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