Processing additives for fabricating organic photovoltaic cells

1. A method, comprising:

processing a solution to form a photoactive layer, the solution comprising an electron donor material, an electron acceptor material, a compound, and a solvent, the compound being different from the solvent and being selected from a group consisting of an alkane substituted with halo, CN, or COOR, R being H or C 1 -C 10 alkyl; a cyclopentadithiophene optionally substituted with C 1 -C 10 alkyl; a fluorene optionally substituted with C 1 -C 10 alkyl; a thiophene optionally substituted with C 1 -C 10 alkyl; a benzothiadiazole optionally substituted with C 1 -C 10 alkyl; a naphthalene optionally substituted with C 1 -C 10 alkyl; and a 1,2,3,4-tetrahydronaphthalene optionally substituted with C 1 -C 10 alkyl.

2. The method of claim 1 , wherein the compound is an alkane substituted with Cl, Br, I, CN, or COOCH 3 .

3. The method of claim 1 , wherein the alkane is a C 6 -C 12 alkane.

4. The method of claim 1 , wherein the alkane is an octane.

5. The method of claim 1 , wherein the compound is 1,8-diiodooctane, 1,8-dibromooctane, 1,8-dicyanooctane, or 1,8-di(methoxycarbonyl)octane.

6. The method of claim 1 , wherein the compound is of the following formula:

R 1 —(CH 2 ) n —R 2 ,

in which n is 1-20; and each of R 1 and R 2 , independently, is halo, CN, or COOR, R being H or C 1 -C 10 alkyl.

7. The method of claim 6 , wherein n is 6-12.

8. The method of claim 6 , wherein n is 8.

9. The method of claim 6 , wherein each of R 1 and R 2 , independently, is Cl, Br, I, CN, or COOCH 3 .

10. The method of claim 1 , wherein the solution comprises at least about 1 vol % of the compound.

11. The method of claim 1 , wherein the solution comprises at most about 10 vol % of the compound.

12. The method of claim 1 , wherein the electron donor material is selected from the group consisting of polythiophenes, polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes, polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s, polythiadiazoloquinoxaline, polybenzoisothiazole, polybenzothiazole, polythienothiophene, poly(thienothiophene oxide), polydithienothiophene, poly(dithienothiophene oxide)s, polyfluorenes, polytetrahydroisoindoles, and copolymers thereof.

13. The method of claim 12 , wherein the electron donor material comprises polythiophenes, polycyclopentadithiophenes, or copolymers thereof.

14. The method of claim 13 , wherein the electron donor material comprises poly(3-hexylthiophene) or poly(cyclopentadithiophene-co-benzothiadiazole).

15. The method of claim 1 , wherein the electron acceptor material comprises a material selected from the group consisting of fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquid crystals, carbon nanorods, inorganic nanorods, polymers containing CN groups, polymers containing CF 3 groups, and combinations thereof.

16. The method of claim 15 , wherein the electron acceptor material comprises a substituted fullerene.

17. The method of claim 16 , wherein the substituted fullerene comprises[6,6]-phenyl C61-butyric acid methyl ester or [6,6]-phenyl C71-butyric acid methyl ester.

18. The method of claim 1 , wherein the solvent comprises chlorobenzene, o-dichlorobenzene, trichlorobenzene, o-xylene, m-xylene, p-xylene, toluene, mesitylene, ethylbenzene, isobutylbenzene, t-butylbenzene, α-methylnaphthalene, tetralin, N-methylpyrrolidone, methyl ethyl ketone, or acetone.

19. The method of claim 1 , wherein the processing step comprises applying the solution on a surface.

20. The method of claim 19 , wherein the processing step further comprises drying the solution after the applying step to form the photoactive layer.

21. The method of claim 1 , further comprising disposing the photoactive layer between first and second electrodes to form a photovoltaic cell.

22. A method, comprising:

processing a solution comprising a compound to form a photoactive layer, the compound being selected from a group consisting of a substituted alkane of the following formula: R 1 —(CH 2 ) n —R 2 , in which n is 2-20; and each of R 1 and R 2 , independently, is halo, CN, or COOR, R being H or C 1 -C 10 alkyl; a cyclopentadithiophene optionally substituted with C 1 -C 10 alkyl; a fluorene optionally substituted with C 1 -C 10 alkyl; a thiophene optionally substituted with C 1 -C 10 alkyl; and a benzothiadiazole optionally substituted with C 1 -C 10 alkyl.

23. The method of claim 22 , wherein n is 6-12.

24. The method of claim 22 , wherein n is 8.

25. The method of claim 22 , wherein each of R 1 and R 2 , independently, is Cl, Br, I, CN, or COOCH 3 .

26. The method of claim 22 , wherein the solution comprises at least about 1 vol % of the compound.

27. The method of claim 22 , wherein the solution comprises at most about 10 vol % of the compound.

28. The method of claim 22 , wherein the solution further comprises an electron donor material.

29. The method of claim 28 , wherein the electron donor material is selected from the group consisting of polythiophenes, polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes, polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s, polythiadiazoloquinoxaline, polybenzoisothiazole, polybenzothiazole, polythienothiophene, poly(thienothiophene oxide), polydithienothiophene, poly(dithienothiophene oxide)s, polyfluorenes, polytetrahydroisoindoles, and copolymers thereof.

30. The method of claim 29 , wherein the electron donor material comprises polythiophenes, polycyclopentadithiophenes, or copolymers thereof.

31. The method of claim 30 , wherein the electron donor material comprises poly(3-hexylthiophene) or poly(cyclopentadithiophene-co-benzothiadiazole).

32. The method of claim 22 , wherein the solution further comprises an electron acceptor material.

33. The method of claim 32 , wherein the electron acceptor material comprises a material selected from the group consisting of fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquid crystals, carbon nanorods, inorganic nanorods, polymers containing CN groups, polymers containing CF 3 groups, and combinations thereof.

34. The method of claim 33 , wherein the electron acceptor material comprises a substituted fullerene.

35. The method of claim 34 , wherein the substituted fullerene comprises [6,6]-phenyl C61-butyric acid methyl ester or [6,6]-phenyl C71-butyric acid methyl ester.

36. The method of claim 22 , wherein the solution further comprises a solvent.

37. The method of claim 36 , wherein the solvent comprises chlorobenzene, o-dichlorobenzene, trichlorobenzene, o-xylene, m-xylene, p-xylene, toluene, mesitylene, ethylbenzene, isobutylbenzene, t-butylbenzene, α-methylnaphthalene, tetralin, N-methylpyrrolidone, methyl ethyl ketone, or acetone.

38. The method of claim 22 , wherein the processing step comprises applying the solution on a surface.

39. The method of claim 38 , wherein the processing step further comprises drying the solution after the applying step to form the photoactive layer.

40. The method of claim 22 , further comprising disposing the photoactive layer between first and second electrodes to form a photovoltaic cell.