Tandem photovoltaic cells

1. An article, comprising:

first and second electrodes;

a recombination layer between the first and second electrodes, the recombination layer comprising a p-type semiconductor material and an n-type semiconductor material, and having a thickness of about 10 nm to about 200 nm;

a first photoactive layer between the first electrode and the recombination layer; and

a second photoactive layer between the second electrode and the recombination layer;

wherein:

the recombination layer is in direct contact with both the first photoactive layer and the second photoactive layer;

the first photoactive layer and the second photoactive layer comprise an electron donor material and an electron acceptor material;

the first photoactive layer and the second photoactive layer are single layers;

the p-type semiconductor material comprises a polymer selected from the group consisting of polythiophenes, polyanilines, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes, polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s, polythiadiazoloquinoxalines, polybenzoisothiazoles, polybenzothiazoles, polythienothiophenes, poly(thienothiophene oxide)s, polydithienothiophenes, poly(dithienothiophene oxide)s, polytetrahydroisoindoles, and copolymers thereof;

the n-type semiconductor material comprises a metal oxide;

the p-type and n-type semiconductor materials are blended in the recombination layer; and the article is configured as a photovoltaic system.

2. The article of claim 1 , wherein the metal oxide comprises an oxide selected from the group consisting of titanium oxides, zinc oxides, tungsten oxides, molybdenum oxides, and combinations thereof.

3. The article of claim 1 , wherein the electron donor material comprises a polymer selected from the group consisting of polythiophenes, polyanilines, 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, polytetrahydroisoindoles, and copolymers thereof.

4. The article of claim 3 , wherein the electron donor material comprises a polymer selected from the group consisting of polythiophenes, polycyclopentadithiophenes, and copolymers thereof.

5. The article of claim 4 , wherein the electron donor material comprises poly(3-hexylthiophene) or poly(cyclopentadithiophene-co-benzothiadiazole).

6. The article 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 CF3 groups, and combinations thereof.

7. The article of claim 6 , wherein the electron acceptor material comprises a substituted fullerene.

8. The article of claim 7 , wherein the substituted fullerene comprises PCBM.

9. The article of claim 1 , wherein the first photoactive layer has a first band gap and the second photoactive layer has a second band gap different from the first band gap.

10. The article of claim 1 , further comprising a hole carrier layer between the first photoactive layer and the first electrode.

11. The article of claim 10 , wherein the hole carrier layer comprises a polymer selected from the group consisting of polythiophenes, polyanilines, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, and copolymers thereof.

12. The article of claim 1 , further comprising a hole blocking layer between the second photoactive layer and the second electrode.

13. The article of claim 12 , wherein the hole blocking layer comprises a material selected from the group consisting of LiF, metal oxides, and combinations thereof.

14. The article of claim 1 , wherein the system comprises a tandem photovoltaic cell.

15. An article, comprising:

first and second electrodes;

first and second photoactive layers between the first and second electrodes, the first photoactive layer comprising a first semiconductor material and the second photoactive layer comprising a second semiconductor material;

the first photoactive layer and the second photoactive layer comprise an electron donor material and an electron acceptor material;

the first photoactive layer and the second photoactive layer are single layers; and

a recombination layer between and in direct contact with both the first and the second photoactive layers and having a thickness of about 10 nm to about 200 nm, the recombination layer comprising a p-type semiconductor material and an n-type semiconductor material, each of the p-type and n-type semiconductor materials is different from the first or second semiconductor material;

wherein:

the p-type semiconductor material comprises a polymer selected from the group consisting of polythiophenes, polyanilines, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes, polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s, polythiadiazoloquinoxalines, polybenzoisothiazoles, polybenzothiazoles, polythienothiophenes, poly(thienothiophene oxide)s, polydithienothiophenes, poly(dithienothiophene oxide)s, polytetrahydroisoindoles, and copolymers thereof;

the n-type semiconductor material comprises a metal oxide;

the p-type and n-type semiconductor materials are blended in the third layer;

the first photoactive layer comprises a first electron acceptor material and a first electron donor material;

the second photoactive layer comprises a second electron acceptor material and a second electron donor material; and the article is configured as a photovoltaic system.

16. The article of claim 15 , wherein the first electron donor material comprises a polymer selected from the group consisting of polythiophenes, polyanilines, 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, polytetrahydroisoindoles, and copolymers thereof.

17. The article of claim 15 , wherein the first electron donor material comprises a polymer selected from the group consisting of polythiophenes, polycyclopentadithiophenes, and copolymers thereof.

18. The article of claim 15 , wherein the first electron donor material comprises poly(3-hexylthiophene) or poly(cyclopentadithiophene-co-benzothiadiazole).

19. The article of claim 15 , wherein the first 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 CF3 groups, and combinations thereof.

20. The article of claim 15 , wherein the first electron acceptor material comprises a substituted fullerene.

21. The article of claim 15 , wherein the first electron acceptor material comprises PCBM.

22. The article of claim 15 , wherein the first electron acceptor material is the same as the second electron acceptor material, and the first electron donor material is the same as the second electron donor material.