Synthesis of photovoltaic conjugated polymers

Abstract

A method of making a fluorothieno[3,4-b]thiophene derivatives and photovoltaic polymers containing same using 3-bromothiophene-2-carboxylic acid as a starting material. This synthetic route provides an easier synthesis as well as greater yield and a purer product, which produces superior results over the prior art less pure products. The resulting materials can be used in a variety of photovoltaic applications and devices, especially solar cells.

Claims

1. A method of making a conjugated polymer having the formulae (IV): ##STR00031## wherein R1 is proton, halogens, alkyls, substituted alkyls, amino, N-substituted amino groups, aryls or substituted aryls; Ar is selected from the group consisting of ethenylene, ethynylene, monocyclic, bicyclic and polycyclic arlyenes; and monocyclic, bicyclic and polycyclic heteroarylenes; or unit being comprised of two or more compounds choosing from ethenylene, ethynylene, or monocyclic, bicyclic and polycyclic arylene, or monocyclic, bicyclic and polycyclic heteroarylenes; wherein R2 is F; and wherein said conjugated polymer is made using a compound according to formulae (I), (II) or a protected derivative thereof: ##STR00032## as a starting material, wherein R is hydrogen, C1-C20 alkyl, C1-C20 haloalkyl, aryl, heteroaryl, C1-C20 haloalkoxy, aryloxy, —C1-C20 alkyl-O—C1-C10 alkyl, C1-C10 alkyl-O-aryl, nitro, halo, amino, or mono- or di alkyl amino.

2. The method of claim 1, wherein the conjugated polymer is of formulae (V): ##STR00033## wherein R1′ is selected from proton, alkyls, substituted alkyls, aryls or, substituted aryls; wherein R2 is F; and wherein R3, R4, R5 and R6 are selected independently from proton, alkyls, substituted alkyls, alkoxyls, substituted alkoxyls, halogens, aryls or, substituted aryls.

3. The method of claim 1, wherein the method comprises the following reactions: i) protection of carboxylic acid with a protection group, ii) chloromethylation with two chloromethyl groups, iii) a cyclization reaction at the two chloromethyl groups, iv) hydrolysis of the carboxylate protection group, v) exchange fluorine for bromine, and vi) optional esterification of the carboxylate.

4. The method of claim 1, wherein said conjugated polymer has less than about 1% of formula I.

5. The method of claim 1, wherein said conjugated polymer has less than about 5% of formula I.

6. The method of claim 1, wherein said conjugated polymer has less than about 10% of formula I.

7. The method of claim 1, wherein said conjugated polymer has less than about 15% of formula I.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a further understanding of the nature and objects of the present inventions, reference should be made to the following detailed disclosure, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein:

(2) FIG. 1 shows a bulk heterojunction;

(3) FIG. 2 shows the synthesis route of FTT-K according to an embodiment of the present invention;

(4) FIG. 3 shows the synthesis route of FTT-E according to an embodiment of the present invention;

(5) FIG. 4 shows the synthesis route of CS-9 according to an embodiment of the present invention;

(6) FIG. 5 shows the current density-voltage relationship of solar cells made of the polymers synthesized by the method of the present invention and by conventional method;

(7) FIG. 6 shows the conventional synthesis route of FTT;

(8) FIG. 7a shows the test photovoltaic device of Example 5A; and

(9) FIG. 7b shows the test photovoltaic device of Example 5B.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(10) The following detailed description of various embodiments of the present invention references the accompanying drawings, which illustrate specific embodiments in which the invention can be practiced. While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains. Therefore, the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

(11) The invention provides a novel method for synthesizing FTT derivatives with high yield and easy to purify product. Specifically, 3-bromothiophene-2-carboxylic acid is used as a starting material instead of thiophene-2-carboxylic acid, so as to have improved fluorination conversion rate.

EXAMPLE 1: SYNTHESIS OF FTT-K

(12) The synthesis route to prepare 1-(4,6-dibromo-3-fluorothieno[3,4-b]thiophen-2-yl)-2-ethylhexan-1-one (FTT-K) is outlined in FIG. 2. As a general matter, using 3-bromothiophene-2-carboxylic acid or a protected derivative thereof as the starting material is crucial to this synthetic route. This ensures the later bromo-to-fluoro conversion at a significant improved rate, from less than about 20% to about 60-80%.

Synthesis of methyl 3-bromothiophene-2-carboxylate (2)

(13) The starting material 3-bromothiophene-2-carboxylic acid is commercially available, e.g., from Sigma Aldrich, and can be purchased or made from simpler starting materials. It may also be possible to purchase protected derivatives of this chemical.

(14) The 3-bromothiophene-2-carboxylic acid was first protected at the carboxylic group. 3-bromothiophene-2-carboxylic acid was dissolved in methanol containing catalytic DCC. Mixture was reacted by refluxing overnight. After solvent was evaporated, the residues were applied on silica gel. Methyl 3-bromothiophene-2-carboxylate was obtained as a colorless liquid.

Synthesis of methyl 3-bromo-4,5-bis(chloromethyl)thiophene-2-carboxylate (3)

(15) 1.873 mmol of methyl 3-bromothiophene-2-carboxylate (i.e., compound (2)) and 9.36 mmol of chloromethyl methyl ether were mixed in a 100 ml flask cooled by an ice bath, and then 2.8 mmol of titanium tetrachloride was added drop-wise over about 30 minutes. After removal of the ice bath, the reactants were stirred at about ambient temperature for one hour, and subsequently heated to about 50-60° C. and stirred for about six hours. The resulting sticky reactant was then poured into 100 g ice water and extracted by diethyl ether. After the removal of volatile solvent, methyl 3-bromo-4,5-bis(chloromethyl)thiophene-2-carboxylate was obtained as a dark brown oily product, which was used without any purification.

Synthesis of methyl 3-bromo-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate (4)

(16) Compound (3) from the previous step was dissolved into 500 ml slightly boiling methanol, and a solution of sodium sulfide in 500 ml methanol was added drop-wise over about 1 hour at boiling temperature. The reactant was then kept at boiling temperature for about 1 hour. Methanol was removed by rotary evaporation and the sticky residue was absorbed by silica gel. The purification of product was performed by column chromatography using petroleum ether/ethyl acetate (30:1) as the eluent. Methyl 3-bromo-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate was obtained as colorless oil. The yield was about 75%.

Synthesis of 3-Bromo-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylic acid (5)

(17) Compound 4 from the previous step was dissolved in tetrahydrofuran (THF) and mixed with water containing LiOH. The reactants were stirred overnight. 3-Bromo-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylic acid was obtained as a white crystal. The yield was about 75%.

Synthesis of 3-Fluoro-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylic acid (6)

(18) 1.215 g of compound (5) (4.602 mmol) from the previous step was dissolved in THF. The mixture was cooled to about −78° C., and n-BuLi (2.5 M, 4.05 ml, 10.12 mmol) was added drop-wise to the mixture. The mixture was kept at about −78° C. for about 1 hour. N-fluoro-N-(phenylsulfonyl)benzenesulfonamide (2.17 g, 6.9 mmol) was then added. The resulting mixture was reacted at about −78° C. for about 2 hours, and then warmed up to about room temperature and reacted for about two hours. After reaction, the mixture was poured into water and extracted by ether. Compound 6 was obtained as a white solid. The yield was about 70%.

Synthesis of 3-fluoro-4,6-dihydrothieno[3,4-b]thiophene (7)

(19) 500 mg compound 6 from the previous step was mixed with 100 mg Cu powder and 20 ml quinolone. The mixture was heated at about 220° C. for about 2 hours. After cooling to about room temperature, the mixture was poured into 6 M HCl and extracted by ether 3 times. Compound 7 was dried by anhydrous Na.sub.2SO.sub.4. The yield was about 90%.

Synthesis of 2-ethyl-1-(3-fluoro-4,6-dihydrothieno[3,4-b]thiophen-2-yl)hexan-1-one (8)

(20) 2.31 mmol of AlCl.sub.3 was added to 20 ml DCM with 2.31 mmol 2-ethylhexanoyl chloride at about 0° C. Compound 7 from the previous step was added to the mixture. The mixture was reacted at about 0° C. for about 4 hours. After reacting, the reactant was poured into ice water. The organic phase was extracted by ether 3 times. Compound 8 was purified by silica gel. The yield was about 70%.

Synthesis of 2-ethyl-1-(3-fluorothieno[3,4-b]thiophen-2-yl)hexan-1-one (9)

(21) Compound 8 (233 mg, 0.812 mmol) from the previous step was dissolved into 20 ml chloroform and cooled down to about −40° C. by a liquid nitrogen/ethyl acetate bath, and then m-chloroperoxybenzoic acid (MCPBA) (140 mg, 0.812 mol) in chloroform (10 ml) was added drop-wise. After being stirred at about −40° C. for about 30 minutes, the reactant was warmed up to about ambient temperature and stirred for about 30 minutes. The chloroform was removed by rotary evaporation under vacuum, and 30 ml acetic acid anhydride was added to the reactant. The resulting mixture was refluxed for about 15 minutes. After removal of the volatile materials by rotary evaporation under vacuum, the oily residue was purified by column chromatography using petroleum ether/ethyl acetate (30:1) as eluent. Compound 9 (196.3 mg) was obtained. The yield was about 85%.

Synthesis of 1-(4,6-dibromo-3-fluorothieno[3,4-b]thiophen-2-yl)-2-ethylhexan-1-one (FTT-K) (10)

(22) Compound 9 (196.3 mg, 0.69 mmol) from the previous step was dissolved in 10 ml DMF. Under the protection of an inert atmosphere, NBS (368.5 mg, 2.07 mmol) was added in one portion. The reactant was stirred for about 4 hours and then poured into 50 ml of 5% sodium thiosulfate solution with ice. The mixture was extracted by diethyl ether. The purification was conducted by column chromatography using petroleum ether as eluent. Compound 10 (173.6 mg) was obtained as a pale yellow oil. The yield was about 60%.

EXAMPLE 2: SYNTHESIS OF FTT-E

(23) The synthetic route of FTT-E is illustrated in FIG. 3, wherein compound 6 from the previous example was used as the starting material.

Synthesis of 2-ethylhexyl 3-fluoro-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate (11)

(24) 500 mg of 3-fluoro-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylic acid (2.45 mmol) was dissolved in 10 ml of dry methylene chloride. This solution was cooled to about 0° C. 530 mg of dicyclohexylcarbondiimide (DCC) (2.57 mmol), 30 mg of N,N-dimethylamino pyridine and 1 ml of 2-ethylhexan-1-ol was added. This reaction mixture was stirred at about 0° C. for about 1 hour and then warmed up to about room temperature for about 3 hours. The DCC salt was filtered off and the solution was poured into 50 ml water, and extracted with methylene chloride three times. The organic layer was dried over Na.sub.2SO.sub.4. After removal of the solvent by rotary evaporation, the residue was purified by column chromatography to yield 481 mg of product. The yield was about 62.1%.

Synthesis of 2-ethylhexyl 3-fluorothieno[2,3-c]thiophene-2-carboxylate (12)

(25) 475 mg of 2-ethylhexyl 3-fluoro-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate (1.50 mmol) was dissolved in 10 ml of ethyl acetate, the solution was cooled to −78° C. 337 mg of 77% m-CPBA (1.50 mmol) in 3 ml ethyl acetate was added and the reaction mixture was allowed to warm up to room temperature overnight. The solvent was removed by rotary evaporation and the residue was re-dissolved in 10 ml acetic anhydride, and heated to reflux for about 30 min. The solvent was removed by rotary evaporation and the product was purified by column (silica gel, hexane:dichloromethane=4:1) to produce 361 mg of product. The yield was about 76.5% for the two steps.

Synthesis of 2-ethylhexyl 4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate (13)

(26) 350 mg of 2-ethylhexyl 3-fluorothieno[2,3-c]thiophene-2-carboxylate (1.11 mmol) was dissolved in 8 ml of dry DMF. This solution was cooled to about 0° C. 593 mg of NBS (3.33 mmol) in 3 ml DMF was added, and the reaction mixture was stirred at 0° C. for about 2 hours, then warmed up to about room temperature overnight. The reaction mixture was poured into 5% Na.sub.2S.sub.2O.sub.3 aqueous solution and extracted with diethyl ether 3 times. The organic layer was dried over Na.sub.2SO.sub.4. After removal of solvent, the residue was purified by column to produce 265 mg of product. The yield was about 50.4%.

EXAMPLE 3: SYNTHESIS OF CS-9

(27) (4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (0.271 g) and 2-ethylhexyl-3-fluorothieno[2,3-c]thiophene-2-carboxylate (0.141 g) from previous example were dissolved in 10 ml toluene with 2 ml DMF. The mixture was purged with argon for about 10 minutes, and then Pd(PPh.sub.3).sub.4 (16 mg) was added. After being purged with argon for about 20 min, the reaction mixture was refluxed for about 16 hours under argon atmosphere. Then, the mixture was cooled to about room temperature, and the polymer was precipitated by addition of 100 ml methanol. The precipitated polymer was then re-dissolved in chloroform and again precipitated by hexane. The product was dried under vacuum to obtain 0.226 g of a dark blue solid. The yield was about 75%.

EXAMPLE 4: SYNTHESIS OF FTT-K BY CONVENTIONAL METHOD

(28) The fluorinated thieno[3,4-b]thiophene was synthesized via a modified route previously reported for ester substituted thieno[3,4-b]thiophene as shown in FIG. 6 and described in more detail in Liang, J Am. Chem. Soc. 131 (2009b) pp. 7792-7799. The fluorine was introduced to the fused ring unit from 4,6-dihydrothieno[3,4-b]thiophene-2-carboxylic acid after deprotonation by using BuLi and reacting with PhSO.sub.2NF. The fluorinated acid was first converted to an ester and then dibromo-substituted thieno[3,4-b]thiophene.

EXAMPLE 5A: FABRICATION OF REGULAR PHOTOVOLTAIC DEVICES

(29) The polymer from Example 3 was co-dissolved with PC.sub.61BM in a mixed solvent in the weight ratio of 1:1.6, respectively. The concentrations were 10 mg/ml, and the mixed solvent was dichlorobenzene/1,8-diiodooctane (97/3, v/v).

(30) Indium Tin Oxide (ITO)-coated glass substrates (15 Ω/sq) were cleaned stepwise in detergent, water, acetone and isopropyl alcohol under ultrasonication for about 15 minutes each and, subsequently, dried in an oven. A thin layer (˜30 nm) of PEDOT:PSS (Baytron P VP Al 4083) was spin-coated onto ITO surface, which was pre-treated by ultraviolet ozone for about 15 min. Low conductivity PEDOT:PSS was chosen to minimize measurement error from device area due to lateral conductivity of PEDOT:PSS.

(31) After being baked at about 150° C. for about 10 min, the substrates were transferred into a nitrogen filled glove box (<0.1 ppm O.sub.2 & H.sub.2O). A polymer/PC.sub.61BM composite layer (ca. 100 nm thick) was then spin-cast from the blend solutions at 1000 rpm on the ITO/PEDOT:PSS substrate without further special treatments. Then the film was transferred into the thermal evaporator, which is located in the same glove box. A Calcium layer (25 nm) and an Aluminum layer (80 nm) were deposited in sequence under the vacuum of 2×10.sup.−6-Torr. The effective area of film was measured to be 0.095 cm.sup.2. An exemplary diagram is provided as FIG. 7a.

EXAMPLE 5B: FABRICATION OF INVERTED PHOTOVOLTAIC DEVICES

(32) The polymer from Example 3 was co-dissolved with PC.sub.61BM in a mixed solvent in the weight ratio of 1:1.6, respectively. The concentrations were 10 mg/ml, and the mixed solvent was dichlorobenzene/1,8-diiodooctane (97/3, v/v).

(33) Indium Tin Oxide (ITO)-coated glass substrates (15 Ω/sq) were cleaned stepwise in detergent, water, acetone and isopropyl alcohol under ultrasonication for about 15 minutes each and, subsequently, dried in an oven. A thin layer (˜10 nm) of Zinc acetate dihydrate was spin-coated onto ITO surface, which was pre-treated by ultraviolet ozone for 15 min.

(34) After being baked at about 170° C. for about 15 min, the substrates were transferred into a nitrogen filled glove box (<0.1 ppm O.sub.2 & H.sub.2O). A polymer/PC.sub.61BM composite layer (ca. 100 nm thick) was then spin-cast from the blend solutions at 1000 rpm on the ITO/PEDOT:PSS substrate without further special treatments. Then the film was transferred into the thermal evaporator, which is located in the same glove box. A MoO.sub.3 layer (10 nm) and a silver layer (100 nm) were deposited in sequence under the vacuum of 2×10.sup.−6-Torr. The effective area of film was measured to be 0.095 cm.sup.2. An exemplary diagram is provided as FIG. 7b.

EXAMPLE 6: CURRENT-VOLTAGE MEASUREMENT

(35) The fabricated device was encapsulated in a nitrogen filled glove box by UV epoxy (bought from Epoxy Technology) and cover glass. The current density-voltage (J-V) curves were measured using Keithley 2400 source-measure unit. The photocurrent was measured under AM 1.5G illumination at 100 mW/cm.sup.2 under Newport Thermal Oriel 91192 1000W solar simulator (4″×4″ beam size). The light intensity was determined by a mono-silicon detector (with KG-5 visible color filter) calibrated by National Renewable Energy Laboratory (NREL) to minimize spectral mismatch.

(36) External Quantum Efficiencies (EQEs) were measured using Model QEX7 purchased from PV Measurements, Inc. A calibrated mono silicon diode with known spectral response was used as a reference.

EXAMPLE 6: PHOTOVOLTAIC PROPERTIES COMPARISON

(37) The comparison of Current Density-Voltage relationship of the two devices, one made of the polymer synthesized by the method of the present invention and the other by conventional method, is shown in FIG. 5.

(38) As shown in FIG. 5, the device made with the polymer synthesized by the method of the present invention exhibits higher open circuit voltage than the polymer synthesized by conventional method. Specifically, the device fabricated by the polymer synthesized by the present invention has an open circuit voltage of 0.80 V, whereas the conventional synthesis route gives only 0.78 V. Additionally, as shown in the table below, the device fabricated by the polymer synthesized by the present invention also has higher short circuit current density (Jsc), Fill Factors (FF) and power conversion efficiency (PCE) comparing to the polymer synthesized by conventional method.

(39) TABLE-US-00001 Voc Jsc (mA/cm.sup.2) FF (%) PCE (%) Conventional 0.78 14.7 58.6 6.71 synthesis route New synthesis 0.80 15.8 66.7 8.41 route

(40) These results show that the synthetic method of the present invention not only achieves higher conversion rate in the synthesis, but also provides product of higher quality to be used in photovoltaic applications.

(41) The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and utilize the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims.

Definitions

(42) As used herein, the terms “a,” “an,” “the,” and “said” means one or more, unless the context dictates otherwise.

(43) As used herein, the term “about” means the stated value plus or minus a margin of error or plus or minus 10% if no method of measurement is indicated.

(44) As used herein, the term “or” means “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive.

(45) As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

(46) As used herein, the terms “containing,” “contains,” and “contain” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided above.

(47) As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided above.

(48) As used herein, the terms “including,” “includes,” and “include” have the same open-ended meaning as “comprising,” “comprises,” and “comprise,” provided above.

(49) As used herein, the phrase “consisting of” is a closed transition term used to transition from a subject recited before the term to one or more material elements recited after the term, where the material element or elements listed after the transition term are the only material elements that make up the subject. However, non-material elements that do not substantially change the nature of the invention, such as various buffers, differing salts, extra wash or precipitation steps, pH modifiers, and the like, may be included in the subject.

(50) As used herein, the phrase “protected derivative” means a chemical that is protected at reactive groups that are not to be reacted in the subsequent steps, such as the —COOH, e.g., by forming an ester at that group.

(51) As used herein, the term “simultaneously” means occurring at the same time or about the same time, including concurrently.

(52) As used herein, “starting material” means that the recited chemical is made or purchased for use as an early reactant in the synthetic pathway. However, if made, rather than purchased, there may be other ingredients that pre-date same.

Abbreviations

(53) The following abbreviations are used herein:

(54) TABLE-US-00002 Abb. Name Structure 3-bromothiophene-2- carboxylic acid 0 AC2O Acetic anhydride, or ethanoic anhydride BHJ Bulk heterojunctions BDT 4,8-dialkoxybenzo[1,2-b:4,5- b]dithiophene BDT-FTT benzo[1,2-b:4,5- b′]dithiophene- fluorothienothiophene CS-9 P-2-ethylhexyl-4-(4,8-bis(5- (2-ethylhexyl)thiophen-2- yl)benzo[1,2-b:4,5- b′]dithiophen-2-yl)-3- fluorothieno[3,4-b]thiophene- 2-carboxylate DCC N,N′- Dicyclohexylcarbodiimide DCM Dichloromethane or methylene chloride DMAP 4-Dimethylaminopyridine DMF Dimethylformamide FF Fill Factor FTT Fluorothieno[3,4-b]thiophene (usually a dibromo derivative herein) FTT-E 2-alkyl-4,6-dibromo-3- fluorothieno[3,4-b]thiophene- 2-carboxylate FTT-K 1-(4,6-dibromo-3- fluorothieno[3,4-b]thiophen- 2-yl)-4-alkyl-1-one 0 FTT-K, alkyl is ethylhexan 1-(4,6-dibromo-3- fluorothieno[3,4-b]thiophen- 2-yl)-2-ethylhexan-1-one HOMO Highest occupied molecular orbital Jsc Short Circuit Current Density LUMO Lowest unoccupied molecular orbital MCPBA m-chloroperoxybenzoic acid MeOH Methanol n-BuLi n-Butyllithium NBS N-Bromosuccinimide OPV organic photovoltaics OPVC organic photovoltaic cell PCE Power conversion efficiency PC.sub.61BM [6,6]-phenyl-C.sub.61-butyric acid methyl ester PC.sub.71BM [6,6]-phenyl-C.sub.71-butyric acid methyl ester Pd(PPh.sub.3).sub.4 Tetrakis(triphenylphosphine) palladium PEDOT Poly(3,4- ethylenedioxythiophene) PSS poly(styrene sulfonate) PVC photovoltaic cell, aka solar cell THF Tetrahydrofuran TT Thieno[3,4-b]thiophene (usually a dibromo derivative herein) TT-E 2-alkyl-4,6- dibromothieno[3,4-b]thio- phene-2-carboxylate TT-K 1-(4,6-dibromothieno[3,4- b]thiophen-2-yl)-4-alkyl-1-one 0 VOC Open Circuit Voltage

INCORPORATION BY REFERENCE

(55) All patents and patent applications, articles, reports, and other documents cited herein are fully incorporated by reference to the extent they are not inconsistent with this invention. In particular, the following are incorporated by reference herein in their entirety: WO03032072; US20110124822; WO2010008672; US20110008926; US20100276071; US20100326497; US20100018581; US2010078074; Hsiang-Yu Chen, et al., Polymer Solar Cells with Enhanced Open-Circuit Voltage and Efficiency, NATURE PHOTONICS 3 (2009) p. 649; Lijun Huo, et al., Replacing Alkoxy Groups with Alkylthienyl Groups: A Feasible Approach to Improve the Properties of Photovoltaic Polymers, ANGELA. CHEM. INT. ED. 50(41) (2011) pp. 9697-9702; Yongye Liang, et al., For the Bright Future—Bulk Heterojunction Polymer Solar Cells with Power Conversion Efficiency of 7.4%, ADV. ENERGY MATERIALS 22 (2010) pp. E135-E138; Yongye Liang, Development of New Semiconducting Polymers for High Performance Solar Cells, J. AM. CHEM. SOC. 131 (2009a) pp. 56-57; and Yongye Liang, Highly Efficient Solar Cell Polymers Developed via Fine-Tuning of Structural and Electronic Properties, J. AM. CHEM. SOC. 131 (2009b) pp. 7792-7799.