WO2012146672A2

WO2012146672A2 - Use of fluorinated subphthalocyanine fused dimers as electron acceptors for solar cells

Info

Publication number: WO2012146672A2
Application number: PCT/EP2012/057684
Authority: WO
Inventors: Tomas Torres Cebada; Christian CLAESSENS; Anais MEDINA MARTIN; Bregt VERREET; Tom Aernouts
Original assignee: Katholieke Universiteit Leuven; Interuniversitair Microelektronica Centrum vzw IMEC
Current assignee: Katholieke Universiteit Leuven; Interuniversitair Microelektronica Centrum vzw IMEC
Priority date: 2011-04-28
Filing date: 2012-04-26
Publication date: 2012-11-01
Anticipated expiration: 2013-10-28
Also published as: ES2391191A1; ES2391191B1; WO2012146672A3

Abstract

The present disclosure relates to the use of fluorinated subphthalocyanine dimers as photo- and electroactive compounds for the preparation of photovoltaic devices, in particular, of organic and hybrid solar cells, as well as to the devices and solar cells themselves which comprise said dimers.

Description

USE OF FLUORINATED SUBPHTHALOCYANINE FUSED DIMERS AS ELECTRON ACCEPTORS FOR SOLAR CELLS

Technical Field

The present disclosure relates to the use of fluorinated subphthalocyanine fused dimers as electron acceptors in the manufacture of organic or hybrid solar cells and/or as photoactive dyes for photovoltaic devices. Background art

Subphthalocyanines (SubPcs) are the lower homologues of phthalocyanines, well-known two-dimensional aromatic systems, whose 1 8 π- electrons and planar structure impart them with unusual electrical and optical properties [Chem. Rev. 2002, 102, 835; Angew. Chem. Int. Ed. 2006, 45, 2834; Chem. Commun., 2007, 2000]. Subphthalocyanines are composed of three diiminoisoindole rings bound through the nitrogen atoms to a boron core. The 14 π-electron delocalized in their cone-shaped structure, as determined by X- ray crystallography, make them attractive compounds due both to their chemical and physical properties.

Subphthalocyanines are having a profound impact in many technological fields such as optical data storage or nonlinear optics. Also are very interesting their photophysical and optoelectronic properties in order to employ them as new components in photovoltaic materials.

The development and optimization of new synthetic methodologies for SubPc preparation has led to the efficient synthesis of fused subphthalocyanine dimers and the separation of their syn and ani/^' topoisomers [Angew. Chem. Int. Ed. 2002, 41 , 2561 ].

The curved aromatic system presented by these macrocycles converts them into remarkable structures. Despite this, litte attention has been paid to these nonplanar aromatic systems. SubPc dimers were found to present very different features from those of their corresponding SubPc monomers in terms of optical properties. These fused dimers usually present characteristic absorption peaks between 550 and 700 nm with an absorption coefficient ranging from 5 to 1 0 x 10⁴ M^"1 cm^"1. These values may be modulated by introducing different peripheral substituents.

Recent photovoltaic conversion efficiency advancements [Prog. Photovolt: Res. Appl. 2010; 1 8, 346] have transformed organic solar cells (OPVCs) into promising candidates as low-cost, renewable energy generators. This progress is partly related to the improvement of architecture of these devices, with the introduction of donor/acceptor (D/A) interfaces, bulk or block heterojunctions, and tandem structures. These improvements, although preliminary, are due in turn, to the development of improved donor materials that absorb at a wide range of the solar irradiance spectrum with energy levels that enable higher open-circuit voltages ( V_∞). On the contrary, in spite of the wide variety of donor materials, acceptor materials preferably used belong to the family of fullerenes. Compared to many other organic molecules, fullerenes present, on the one hand, high electron mobility and, on the other hand, high exciton diffusion length. However, as fullerenes absorb only at wavelengths below 560 nm, their overall contribution to the photocurrent is limited. The contribution of other alternative acceptor materials such as perylenes, CdSe, ZnO, or TiO₂, is also limited. Metallophthalocyanines (MPcs) are well-known donor materials in the field of organic solar cells. Also, peripherally fluorinated metallophthalocyanines have shown the ability to act as acceptor molecules. The incorporation of fluorine atoms increases the ionization potential with minimal changes to the optical bandgap. Subphthalocyanines (SubPc), have also shown power conversion efficiencies higher than 3% when paired with C₆o as an acceptor material, due to the high of at least 0.9 V. Recently, we achieved comparable V_oc by pairing SubPc with their fluorinated homologue (FSubPc) [Adv. Funct. Mater. 2007, 17, 2653; Adv. Funct. Mater. 2009, 19, 3435]. However, the overlapping of the absorption bands in the absorption spectre of SubPc and FSubPc ultimately limits the short-circuit current density (Jsc) of this D/A pair.

From this and other related literature, and especially from the typical drawbacks in the application of subphthalocyanines in the preparation of photovoltaic cells, can be deduced the importance and interest of preparing analogues with more suitable properties. Summary of the disclosure

It is an aim of the present disclosure to propose acceptor molecules with improved optical properties and stability as well as improved processability, for use as active elements in photovoltaic devices, and more specifically in organic and hybrid solar cells. The inventors have found that subphthalocyanine fused dimers gather many of the desired features, such as optical and chemical stability, efficient solar light absorption, low aggregation and evaporation and anchoring to polymeric or inorganic substrates capabilities, which allow their application to the fabrication of these photovoltaic devices.

Thus, in a first aspect the present disclosure relates to the use of at least a fused subphthalocyanine dimer of structural formula I:

wherein

Ri and R₂, equal or different, represent an halogen atom selected from fluorine, chlorine, bromine and iodine; a cyano group; an azido group; a carboxylic group; an ester group; a COH group; a nitro group; an alkyl group, lineal or branched, from 1 to 1 6 carbon atoms; a OR₃ group; a SR₃ group or a N(R₃)₂ group, wherein R₃ is an alkyl group, lineal or branched, from 1 to 16 carbon atoms; a phenyl group, a phenoxy group, or a thiophenoxy group, optionally substituted in any one of their positions with one or two halogen atoms selected from fluorine, chlorine, bromine and iodine, one or two alkyl groups R₃, one or two OR₃ groups, one or two SR₃ groups, or one or two N(R₃)₂ groups, wherein R₃ has the same meaning indicated above, as a photo- and electroactive compound for the preparation of photovoltaic devices.

A second aspect of the present disclosure relates to a photovoltaic device comprising at least a fused subphthalocyanine dimer of formula I as has been previously defined.

Likewise, the disclosure relates to an organic or hybrid solar cell comprising at least a fused subphthalocyanine dimer of formula I as has been previously defined.

The present disclosure also relates to a method for preparing a photovoltaic device. This may be achieved by

• Providing a cathode,

• Providing an anode, and

• Providing a photoactive region including an electron donor material and an electron acceptor material, between said cathode and said anode, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in any embodiment of the first aspect.

The present disclosure also relates to a photoactive material including an electron donor material and an electron acceptor material, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in any embodiment of the first aspect.

Detailed description of preferred embodiments

The present disclosure will be described with respect to particular embodiments but the disclosure is not limited thereto but only by the claims.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the disclosure described herein can operate in other orientations than described or illustrated herein.

Furthermore, the various embodiments, although referred to as "preferred" are to be construed as exemplary manners in which the disclosure may be implemented rather than as limiting the scope of the disclosure.

The term "comprising", used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising A and B" should not be limited to devices consisting only of components A and B, rather with respect to the present disclosure, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components.

The compounds employed in the present disclosure correspond to fluorinated subphthalocyanine fused dimers. The stereochemistry of these dimers provides two types of topoisomers, syn topoisomer of formula la and anti topoisomer of formula lb:

la (syn topoisomer) lb (anti topoisomer)

As can be appreciated, syn topoisomer represents the structure in which the two substituents (Ri and R₂) of the boron atom in axial position are located pointing to the same side with respect to the aromatic skeleton of the molecule. In turn, anti topoisomer represents the structure in which the two substituents (Ri and R₂) of the boron atom in axial position are located pointing to opposite sides with respect to the aromatic skeleton of the molecule.

The following nomenclature will be used hereinafter to designate the compounds of general formula la:

Syn [R₁ ,R₂][hexadecafluoro]subphthalocyanine dimer

The following nomenclature will be used hereinafter to designate the compounds of general formula lb:

Anti [Ri ,R₂][hexadecafluoro]subphthalocyanine dimer

In a particular embodiment of the present disclosure, the compound of formula I is a combination of any two or more compounds with syn or anti stereochemistry, in any ratio among them.

Preferably, the compound of formula I is a combination of at least a syn topoisomer of formula la and at least an anti topoisomer of formula lb. More preferably, both topoisomers have the same chemical composition. An advantage of using an appropriate combination of syn/anti topoisomers is the possibility of improving in a very simple way the morphology of the active layers and as a consequence the efficiency of the device.

In a preferred embodiment, Ri and R₂, equal or different, represent an halogen atom selected from fluorine, chlorine, bromine and iodine. More preferably, Ri and R₂, equal or different, represent a fluorine or chlorine atom.

Still more preferably, the dimer is selected from:

- Syn-[CI,CI][hexadecafluoro]subphthalocyanine dimer

- Anti-[CI,CI][hexadecafluoro]subphthalocyanine dimer

- Syn-[F,F][hexadecafluoro]subphthalocyanine dimer

- Anti-[F,F][hexadecafluoro]subphthalocyanine dimer

and mixtures thereof.

In a preferred embodiment, the dimer of formula (I) is a combination of the syn-[CI,CI][hexadecafluoro]subphthalocyanine dimer and the anti- [CI,CI][hexadecafluoro]subphthalocyanine dimer in any ratio among them.

In another preferred embodiment, the dimer of formula (I) is a combination of the syn-[F,F][hexadecafluoro]subphthalocyanine dimer and the anti[F,F][hexadecafluoro]subphthalocyanine dimer in any ratio among them. The syn-[CI,CI][hexadecafluoro]subphthalocyanine and anti- [CI,CI][hexadecafluoro]subphthalocyanine dimers employed in the present disclosure can be obtained by chromatographic separation starting from a mixture of both of them, as is described in Angew. Chem. Int., Ed., 2002, 41 , 2561 .

The topoisomers of general formula la and lb can be obtained from syn- [CI,CI][hexadecafluoro]subphthalocyanine dimer or anti-

[F,F][hexadecafluoro]subphthalocyanine dimer respectively, or from a mixture of both of them, through a procedure of substitution in axial position well-known in the state of the art, reported in scientific literature both for subphthalocyanine dimers and for single subphthalocyanines [Chem. Rev. 2002, 1 02, 835; Angew. Chem. Int. Ed. 2002, 41 , 2561 ; Chem. Commun. 2005, 21 1 3; C. R. Chimie 2006, 9, 1094; Angew. Chem. Int. Ed. 201 1 , 50, 3506].

The derealization of π-electrons in the aromatic structure of these compounds, as well as the spatial disposition thereof, impart to these dimers photophysical and optoelectronic properties which make them very suitable for their incorporation in photovoltaic devices.

By "photovoltaic device" it should be understood a device capable of generating electricity from the light incident on it.

These photovoltaic devices usually incorporate, besides a cathode and an anode, a photoactive region disposed between both electrodes, which includes an electron donor material and an electron acceptor material. This photoactive region absorbs the electromagnetic radiation from the light causing the electron transfer from the donor to the acceptor, thus generating an electric current.

The dimer employed in the present disclosure can act as electron acceptor material and, therefore, this dimer can be used in combination with an electron donor material.

In a particular embodiment, the dimer employed in the disclosure is used in combination with one or more dyes or an organic or inorganic material. Combining the intrinsic properties of the dimers with specific properties of the dye or the organic or inorganic material is particularly advantageous, for example when these are electronically active materials. For example, combining the dimer with p-type or n-type materials can be particularly advantageous. As a dye or organic material, a chelating agent, a polymer, an oligomer or an organic copolymer can be employed. Using an appropriate chelating agent can be advantageous for improving the stability of the dimers. Incorporating the dimer as a blend with a polymer can improve the processability of the dimers.

In a preferred embodiment, the organic or inorganic material is an electronically active material. Preferably, the electronically active material is a p- type electron donor material selected from phthalocyanine, subphthalocyanine and pentacene. Also preferably, the electronically active material is an n-type electron donor material selected from fullerene, carbon nanotubes and graphene.

In a particular embodiment, the dimer employed in the disclosure is covalently bound to the backbone of a polymer, oligomer or copolymer. This is particularly advantageous as it improves the processability of the dimers while simultaneously combining the intrinsic properties of the dimers with the specific properties of the polymer, oligomer or copolymer. Furthermore, such covalent binding prevents phase separation between the dimer and the polymer, oligomer or copolymer, thereby improving the stability of the mixture. Preferably, said polymer is polyphenylenvinylene, polythiophene or derivatives thereof.

In a preferred embodiment, the photovoltaic device is an organic or hybrid solar cell. In a general manner, organic solar cell designates those in which the photo- and electroactive material consists only of materials of organic origin, and hybrid cell designates those in which materials of inorganic origin are also involved.

In particular, the dimers of the disclosure are useful in the manufacture of evaporated or solution-deposited small molecule solar cells, and in this type of devices they are usually in combination with other organic or inorganic compounds. Preferably, they are in combination with other organic compounds. More preferably, these organic compounds are p-type electron donor compounds, such as for example phthalocyanine, subphthalocyanine or pentacene. Nevertheless, they could also be in combination with n-type electron donor compounds, such as for example, fullerenes, carbon nanotubes and graphene.

In an additional aspect, the present disclosure relates to a photovoltaic device comprising at least a fused subphthalocyanine dimer as previously described.

Additionally, these photovoltaic devices can be used in combination with one or more photovoltaic devices, equal or different, in order to form tandem photovoltaic devices. Therefore, an additional aspect of the present disclosure consists of a tandem photovoltaic device comprising the combination of two or more photovoltaic devices as previously described.

Likewise, the disclosure relates to an organic or hybrid solar cell comprising at least a fused subphthalocyanine dimer as previously described.

In a particular embodiment, said solar cell is a small molecule solar cell obtainable by evaporation or solution deposition, in which said cell comprises at least a dimer as previously described in combination with a dye or an organic or inorganic material. This embodiment is advantageous because small molecules are available with improved purity when compared to polymers/

Preferably, the dimer is used in combination with an organic or inorganic electronically active material. More preferably, the electronically active material is a p-type material selected from phthalocyanine, subphthalocyanine and pentacene. Likewise, an n-type material selected from fullerene, carbon nanotubes and graphene can be employed.

In another preferred embodiment, the fused subphthalocyanine dimer is covalently bound to the backbone of a polymer, oligomer or copolymer. Said polymer can for instance be polyphenylenvinylene, polythiophene or derivatives thereof.

In another preferred embodiment, the fused subphthalocyanine dimer is adsorbed in a nanocrystalline semiconductor. This is advantageous as it permits the developing of new photosensitizers for dye sensitized solar cells with improved absorption in the visible and near infra-red (NI R).

As used herein and unless provided otherwise, a nanocrystalline semiconductor is a semiconducting nanomaterial with at least one dimension < ^"l OOnm and that is singlecrystalline. A further aspect of the present disclosure relates to a method for preparing a photovoltaic device, said method comprising:

• Providing a cathode,

• Providing an anode, and

· Providing a photoactive region including an electron donor material and an electron acceptor material, between said cathode and said anode, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in any embodiment of the first aspect of the present disclosure.

In an embodiment, said photovoltaic device may be a small molecule solar cell and providing said photoactive region may comprise evaporating or depositing from solution said at least a fused subphthalocyanine dimer as defined in any embodiment of the first aspect, wherein the dimer is, optionally, deposited in combination with one or more organic or inorganic compounds.

A further aspect of the present disclosure relates to a photoactive material including an electron donor material and an electron acceptor material, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in any embodiment of the first aspect. Examples

Preparation of samples for molecular photovoltaic devices processed by evaporation

Thin films of [CI,CI][hexadecafluoro]subphthalocyanine dimer (mixture of syn and anti topoisomers) (thickness 1 1 nm) were deposited by thermal evaporation on Si/Si0₂ substrates. Atomic force microscopy (Pico LE from Agilent) measurements conducted in the tapping mode reveal these films to have a smooth surface with root-mean-square roughness of 6.1 A. Such a closeness of the layers eases the fabrication of multilayer devices, and prevents shunting between layers

Planar heterojunction devices with an area of 13.4 mm² were fabricated by vacuum thermal evaporation on an 85-nm-thick indium tin oxide (ITO) layer coated on glass substrates. As a reference device, we consider the device formed by molybdenum oxide (MoO_x, 1 0nm)/ axially chlorine-functionalized subphthalocyanine (16 nm)/C₆o (35 nm)/ bathocuproine (BCP, 10 nm)/Ag (150 nm). This device reaches an efficiency of 3.3%, where its most prominent feature is a high V_oc of 1090 mV (Table 1 a).

First, the C₆o was replaced with [CI,CI][hexadecafluoro] subphthalocyanine dimer (mixture of syn and anti topoisomers) in a similar device, MoOx (2 nm)/SubPc (13 nm)/ [CI,CI][hexadecafluoro]subphthalocyanine dimer (mixture of syn and anti topoisomers) (30 nm)/ C₆o (20 nm)/ BCP (10 nm)/Ag (150 nm). A similar current was observed and only slightly decreased V_oc of 960 mV was produced (Table 1 b). However, the fill factor (FF) dropped from 0.63 to 0.24. This lower FF is related to an s-shaped JV-curve with a high resistance, which in a planar heterojunction device can often be explained by bad charge extraction. To check how much the FF can be improved by using other cathodes, an inverted device with structure of spin-coated titanium oxide (TiO_x)/ [CI,CI][hexadecafluoro]subphthalocyanine dimer (mixture of syn and anti topoisomers) (20 nm)/ axially chlorine-substituted subphthalocyanine (20 nm)/ Μοθχ (5 nm) /Ag (150 nm), was fabricated (Table 1 c). Changing the electrodes had a clear impact on the s-shape, indicating that this s-shape is (at least partially) contact-related. With the improved contacting, a fill factor of 48% and an efficiency of 2.5% were obtained. We tried to improve the behavior of these devices by incorporating a C₆o layer acting as an electron transport layer (ETL) in between the [CI,CI][hexadecafluoro]subphthalocyanine dimer (mixture of syn and anti topoisomers) and BCP: MoOx (2nm)/ axially chlorine-functionalized subphthalocyanine (13 nm)/ [CI,CI][hexadecafluoro]subphthalocyanine dimer (mixture of syn and anti topoisomers) (30 nm)/ C₆o (20 nm)/ BCP (10 nm)/Ag (150 nm) (Table 1 d). This architecture improved the FF to 54%, while J_sc increased to 7.8 mA cm^"2. The resulting 4% efficiency outperformed the one obtained in the reference device which contained the axially chlorine- functionalized subphthalocyanine.

Structure JEQE ₂ Voc V FF % η %

mA cm^" mA cm

a) MoO_x/ axially chlorine-functionalized 4.9 4.7 1 .09 61 3.3 subphthalocyanine / C₆₀ / BCP

b) MoO_x/ axially chlorine-functionalized 5.1 4.5 0.96 24 1 .2 subphthalocyanine / [CI,CI][hexadecafluoro]subphthalocyanine

dimer / BCP

c) TiO_x/ 5.8 5.6 0.89 48 2.5

[CI,CI][hexadecafluoro]subphthalocyanine

dimer / axially chlorine-functionalized

subphthalocyanine / MoO_x

d) MoO_x/ axially chlorine-functionalized 7.8 7.3 0.95 54 4.0 subphthalocyanine /

[CI,CI][hexadecafluoro]subphthalocyanine

dimer / C₆₀/ BCP

Table 1. J_sc, V_oc, FF and efficiency η measurements for 100 mW cm^"2 AM1 .5G simulated solar illumination. J_EQE is the current density as calculated by integration of the EQE over the AM1 .5G solar spectrum.

Preparation of a polymer, oligomer or copolymer covalently bound to a fused subphthalocyanine dimer as defined in any aspect of the present disclosure.

A fused subphthalocyanine dimer is covalently bound to the backbone chain of an oligomer, polymer or copolymer, as a pendant group, by nucleophilic substitution of the fluorine or chlorine axial ligand of the corresponding dimer by an oligomer, polymer or copolymer containing nucleophilic groups in its structure. This is made via methods well known to the person skilled in the art. Preparation of a nanocrystalline semiconductor on which a fused subphthalocyanine dimer as defined in any aspect of the present disclosure is adsorbed.

A fused subphthalocyanine dimer is adsorbed onto a nanocrystalline semiconductor, like titanium oxide for example, by introducing first on the axial position of the dimer an appropriate anchoring group, for example a carboxyl substituent. This can be made easily by substituting the fluorine or chlorine axial ligand of the corresponding dimer by an appropriate nucleophile containing a carboxylic function, for example p-hydroxybenzoic acid. It is well known, that carboxylic groups are easily absorbed onto the surface of the nanocrystalline semiconductor.

Claims

1 . Use of at least a fused subphthalocyanine dimer of structural formula I:

I wherein

Ri and R₂, equal or different, represent an halogen atom selected from fluorine, chlorine, bromine and iodine; a cyano group; an azido group; a carboxylic group; an ester group; a COH group; a nitro group; an alkyl group, lineal or branched, from 1 to 1 6 carbon atoms; a OR₃ group, a SR₃ group or a N(R₃)₂ group, wherein R₃ is an alkyl group, lineal or branched, from 1 to 16 carbon atoms; a phenyl group, a phenoxy group, or a thiophenoxy group, optionally substituted in any one of their positions with one or two halogen atoms selected from fluorine, chlorine, bromine and iodine, one or two alkyl groups R₃, one or two OR₃ groups, one or two SR₃ groups, or one or two N(R₃)₂ groups, wherein R₃ has the same meaning indicated above,

as a photo- and electroactive compound for the preparation of photovoltaic devices.

2. Use according to claim 1 , wherein the dimer of formula (I) is a combination of any two or more compounds with syn stereochemistry of formula (la) or anti stereochemistry of formula (lb):

(la) (lb)

3. Use according to claim 2, comprising the employment of a combination of at least a syn topoisomer of formula (la) and at least an anf/^' topoisomer of formula

(lb).

4. Use according to anyone of claims 1 to 3, wherein F and R₂, equal or different, represent an halogen atom selected from fluorine, chlorine, bromine and iodine.

5. Use according to claim 4, wherein F and R₂, equal or different, represent a fluorine or chlorine atom.

6. Use according to anyone of claims 1 to 5, wherein the dimer is selected from:

- Syn-[CI,CI][hexadecafluoro]subphthalocyanine dimer

- Ani/^'-[CI,CI][hexadecafluoro]subphthalocyanine dimer

- Syn-[F,F][hexadecafluoro]subphthalocyanine dimer

- /4nf/^'-[F,F][hexadecafluoro]subphthalocyanine dimer

or mixtures thereof.

7. Use according to anyone of claims 1 to 6, comprising the employment of a combination of the syn-[CI,CI][hexadecafluoro]subphthalocyanine dimer and the anf/^'-[CI,CI][hexadecafluoro]subphthalocyanine dimer in any ratio among them.

8. Use according to anyone of claims 1 to 6, comprising the employment of a combination of the syn-[F,F][hexadecafluoro]subphthalocyanine dimer and the anf/^'-[F,F][hexadecafluoro]subphthalocyanine dimer in any ratio among them.

9. Use according to anyone of claims 1 to 8, wherein the dimer of formula (I) is used in combination with one or more dyes or an organic or inorganic material.

10. Use according to claim 9, wherein the dye or the organic material is a chelating agent, a polymer, an oligomer or an organic copolymer.

1 1 . Use according to claim 9 or 10, wherein the organic or inorganic material is an electronically active material.

12. Use according to claim 1 1 , wherein the electronically active material is a p- type electron donor material selected from phthalocyanine, subphthalocyanine and pentacene.

13. Use according to claim 1 1 , wherein the electronically active material is an n- type electron donor material selected from fullerene, carbon nanotubes and graphene.

14. Use according to claim 9, wherein the fused subphthalocyanine dimer is covalently bound to the backbone of a polymer, oligomer or copolymer.

15. Use according to claim 14, wherein the polymer, oligomer or copolymer is polyphenylenvinylene, polythiophene or derivatives thereof.

16. Use according to anyone of claims 1 to 15, wherein the photovoltaic device is an organic or hybrid solar cell.

17. Use of at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8 in the manufacture of small molecule solar cells through evaporation or solution deposition, wherein the dimer is, optionally, in combination with one or more organic or inorganic compounds.

18. Use according to claim 1 7, wherein the organic compound is a p-type electron donor.

19. Use according to claim 1 8, wherein the p-type donor organic compound is selected from phthalocyanine, subphthalocyanine, pentacene and derivatives thereof.

20. Use according to claim 17, wherein the dimer is in combination with one or more n-type electron donor compounds.

21 . Use according to claim 20, wherein the n-type electron donor compounds are selected from fullerenes, carbon nanotubes and graphene.

22. Photovoltaic device comprising at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8.

23. Tandem photovoltaic device comprising the combination of two or more photovoltaic devices as defined in claim 22.

24. Organic or hybrid solar cell comprising at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8.

25. Organic solar cell according to claim 24, obtainable through evaporation or solution deposition, wherein said cell comprises at least a dimer as defined in anyone of claims 1 to 8 in combination with a dye or organic or inorganic material.

26. Hybrid solar cell according to claim 24, comprising the combination of a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8 with a dye or organic or inorganic material.

27. Solar cell according to claims 25 or 26, wherein the organic or inorganic material is an electronically active material.

28. Solar cell according to claim 27, wherein the electronically active material is a p-type electron donor material selected from phthalocyanine, subphthalocyanine and pentacene.

29. Solar cell according to claim 27, wherein the electronically active material is an n-type electron donor material selected from fullerene, carbon nanotubes and graphene.

30. Solar cell according to claim 24, wherein the fused subphthalocyanine dimer is covalently bound to the backbone of a polymer, oligomer or copolymer.

31 . Hybrid solar cell according to claim 24, wherein the fused subphthalocyanine dimer is adsorbed in a nanocrystalline semiconductor.

32. A method for preparing a photovoltaic device, said method comprising:

• Providing a cathode,

• Providing an anode, and

• Providing a photoactive region including an electron donor material and an electron acceptor material, between said cathode and said anode, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8.

33. A method according to claim 32 wherein said photovoltaic device is a small molecule solar cell and wherein providing said photoactive region comprises evaporating or depositing from folution said at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8, wherein the dimer is, optionally, deposited in combination with one or more organic or inorganic compounds.

34. A photoactive material including an electron donor material and an electron acceptor material, wherein said electron acceptor material comprises at least a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8.

35. A polymer, oligomer or copolymer covalently bound to a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8.

36. A nanocrystalline semiconductor on which a fused subphthalocyanine dimer as defined in anyone of claims 1 to 8 is adsorbed.