Fullerene surfactants and their use in polymer solar cells

1. A fullerene compound, comprising:

(a) a fullerene group;

(b) one or more cationic nitrogen centers covalently coupled to the fullerene group;

(c) one or more hydrophilic groups covalently coupled to the fullerene group; and

(d) one or more counter ions associated with the cationic nitrogen center, wherein the compound has the structure:

wherein F is a fullerene group;

B is a N-containing ring having from 5-7 ring atoms;

R 1 and R 2 are independently selected from the group consisting of a polyalkylene oxide and a C1-C20 alkyl optionally substituted with an anionic center;

Ar is —C 6 H 5 -PEO, wherein —C 6 H 5 -PEO is selected from the group consisting of mono-, di-, tri-, and tetra-PEO substituted phenyl, and wherein PEO is a polyethylene oxide; and

A − is a counter ion associated with the cationic nitrogen center.

2. The compound of claim 1 , wherein the fullerene group is selected from the group consisting of C 60 , C 70 , C 76 , C 78 , C 82 , C 84 , and C 92 fullerene groups.

3. The compound of claim 1 , wherein the polyalkene oxide group is a polyethylene oxide group having the formula —(CH 2 CH 2 O) n —, where n is from 1 to about 20.

4. The compound of claim 1 further comprising an anionic center.

5. The compound of claim 4 , wherein the anionic center is selected from the group consisting of sulfonate (SO 3 2− ) and carboxylate (—CO 2 − ) groups.

6. The compound of claim 1 , wherein the compound is a bis-fulleropyrrolidium compound.

7. The compound of claim 1 having the structure:

8. A photovoltaic device, comprising an interfacial layer intermediate the cathode and active layer, the interfacial layer comprising a compound of claim 1 .

9. A photovoltaic device comprising:

(a) a first electrode;

(b) an active layer disposed on a surface of the first electrode;

(c) a layer comprising a compound of claim 1 disposed on a surface of the active layer opposite the first electrode; and

(d) a second electrode disposed on a surface of the layer comprising a compound of claim 1 opposite the active layer.

10. The device of claim 9 further comprising a charge transport layer intermediate the first electrode and the active layer.

11. The device of claim 9 , wherein the active layer comprises an active fullerene material.

12. The compound of claim 1 having the structure:

wherein

R is independently selected from the group consisting of C1-C20 straight chain and branched alkyl;

PEO is an alkylene oxide group independently selected from the group consisting of polyethylene oxide having the formula —(CH 2 CH 2 O) n —, where n is from 1 to about 20 or polypropylene oxide having the formula —(CH(CH 3 )CH 2 O) n —, where n is from 1 to about 20;

C 6 H 5 -PEO is selected from the group consisting of mono-, di-, tri-, and tetra-PEO substituted phenyl; and

A − is a counter ion selected from the group consisting of fluoride, chloride, bromide, iodide, trifluoromethyl sulfonyl (CF 3 SO 3 − ), tetrakis(imidazolyl)borate (BIm 4 − ), and tetrakis(3,5-bis(trifluoromethyl)phenyl]borate (TFPB − ).

13. The compound of claim 1 having the structure:

wherein

R is independently selected from the group consisting of C1-C20 straight chain and branched alkyl;

PEO is an alkylene oxide group independently selected from the group consisting of polyethylene oxide having the formula —(CH 2 CH 2 O) n —, where n is from 1 to about 20 or polypropylene oxide having the formula —(CH(CH 3 )CH 2 O) n —, where n is from 1 to about 20;

C 6 H 5 -PEO is selected from the group consisting of mono-, di-, tri-, and tetra-PEO substituted phenyl; and

A − is a counter ion selected from the group consisting of fluoride, chloride, bromide, iodide, trifluoromethyl sulfonyl (CF 3 SO 3 − ), tetrakis(imidazolyl)borate (BIm 4 − ), and tetrakis(3,5-bis(trifluoromethyl)phenyl]borate (TFPB − ).