Compositionally graded bulk heterojunction devices and methods of manufacturing the same

1. A method of forming a graded bulk heterojunction (BHJ) structure, the method comprising:

providing a solution including a polymer donor material, an acceptor material, and an additive;

introducing a fluxing solvent to the solution; and

removing the fluxing solvent and the additive to form a graded BHJ structure, wherein the graded BHJ structure includes a graded composition of donor and acceptor materials with an increasing acceptor material percentage along a first direction.

2. The method of claim 1 , wherein the acceptor material comprises a fullerene-derivative.

3. The method of claim 2 , wherein the fullerene derivative is selected from the group consisting of [6,6]-phenyl-C61-butyric acid (PC 60 BM), [6,6]-(4-fluoro-phenyl)-C61-butyric acid methyl ester (FPCBM), [6,6]-phenyl-C71 butyric acid methyl ester (PC 70 BM), indene-C60 bisadduct (IC 60 BA), indene-C70 bisadduct (IC 70 BA), fullerene-C60, fullerene-C70, carbon nanotubes (CNT), a carbon onion, and combinations thereof.

4. The method of claim 1 , wherein the donor material includes a polymer donor selected from the group consisting of poly(3-hexylthiophene) (P3HT), poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-alt-[2-(2′-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl] (PBDTTT-CT), poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-enzothiadiazole)] (PCDTBT), Poly[6-fluoro-2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (FTQ), subphthalocyanine (SubPC), copper phthalocyanine (CuPc), Zinc phthalocyanine (ZnPc), poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene) (P3OT), poly(3-hexyloxythiophene) (P3DOT), poly(3-methylthiophene) (PMeT), poly(3-dodecylthiophene) (P3DDT), poly(3-dodecylthienylenevinylene) (PDDTV), poly(3,3 dialkylquarterthiophene) (PQT), poly-dioctyl-fluorene-co-bithiophene (F8T2), Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), poly-(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C12), poly[2,7-(9,9′-dihexylfluorene)-alt-2,3-dimethyl-5,7-dithien-2-yl-2,1,3-benzothiadiazole] (PFDDTBT), poly {[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisEH-PFDTBT), poly{[2,7-(9,9-bis-(3,7-dimethyl-octyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisDMO-PFDTBT), poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), poly[4,8-bis-substituted-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b]thio-phene-2,6-diyl] (PBDTTT-C-T), Poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione (PBDTTPD), poly((4,4-dioctyldithieno(3,2-b:2′,3′-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT), and combinations thereof.

5. The method of claim 1 , wherein the acceptor material comprises a fullerene, fullerene derivative, a perylene, a perylene derivative, a 2,7-dicyclohexyl benzo[lmn][3,8]phenanthroline derivative, a 1,4-diketo-3,6-dithienylpyrrolo[3,4-c:]pyrrole (DPP) derivative, a tetracyanoquinodimethane (TCNQ) derivative, a poly(p-pyridyl vinylene) (PPyV) derivative, a 9,9′-bifluorenylidene (99BF) derivative, a benzothiadiazole (BT) derivative, and combinations thereof.

6. The method of claim 1 , wherein the acceptor material comprises [70]PCBM and the donor comprises one of poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-alt-[2-(2′-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl] (PBDTTT-CT) or poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-enzothiadiazole)] (PCDTBT) or Poly[6-fluoro-2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (FTQ).

7. The method of claim 1 , wherein removing the fluxing solvent and the additive comprises:

spinning off the fluxing solvent, wherein during the spinning the additive fluxes away in a fluxing direction along with the fluxing solvent.

8. The method of claim 1 , wherein the additive comprises a material having a boiling point that is greater than a boiling point of a working solvent used to dissolve the polymer donor material and the acceptor material.

9. The method of claim 1 , wherein the additive comprises 1,8-diiodooctane (DIO) and wherein the working solvent comprises 1,2-Dichlorobenzene (DCB).

10. The method of claim 1 , wherein the additive is selected from the group consisting of 1,8-diiodooctane (DIO) chlorobenzene, 4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,9-nonanedithiol, class of 1,8-di(R)octanes with various functional groups, di(ethylene glycol)-diethyl ether, and n-methyl-2-pyrrolidinone, 1,6-diiodohexane, 1,4-diiodobutane.

11. The method of claim 1 , wherein providing a solution includes applying a layer of the solution on a substrate to form a solution layer on the substrate, and wherein introducing a fluxing solvent to the solution includes introducing the fluxing solvent to the solution layer.

12. The method of claim 11 , wherein applying a layer includes spin coating the solution onto the substrate.

13. The method of claim 11 , wherein the substrate includes indium tin oxide (ITO).

14. The method of claim 11 , further including forming an electrode layer on a first side of the graded BHJ structure opposite the substrate, wherein the acceptor material percentage is higher on the first side.

15. The method of claim 1 , wherein the fluxing solvent comprises an alcohol.

16. The method of claim 1 , wherein the fluxing solvent comprises one of methanol, ethanol or isopropanol.

17. A photoactive device, comprising:

a first electrode;

a second electrode; and

a graded bulk heterojunction (BHJ) structure between the first and second electrodes, wherein the graded BHJ structure is formed according to the method of claim 1 , and wherein the first direction is a direction from the first electrode to the second electrode.