Patent Publication Number: US-11639421-B2

Title: Unsymmetrical benzothtadiazole-based random copolymers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application which claims the benefit of and priority to U.S. patent application Ser. No. 15/644,208 filed Jul. 7, 2017, entitled “Unsymmetrical Benzothiadiazole-Based Random Copolymers,” which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     FIELD OF THE INVENTION 
     This invention relates to unsymmetrically substituted benzothiadiazole-based random copolymers. 
     BACKGROUND OF THE INVENTION 
     Solar energy using photovoltaic effect requires active semiconducting materials to convert light into electricity. Currently, solar cells based on silicon are the dominating technology due to their high conversion efficiency. Recently, solar cells based on organic materials showed interesting features, especially on the potential of low cost in materials and processing. Judging from the recent success in organic light emitting diodes based on a reverse effect of photovoltaic effect, organic solar cells are very promising. 
     Organic photovoltaic cells have many potential advantages when compared to traditional silicon-based devices. Organic photovoltaic cells are light weight, economical in the materials used, and can be deposited on low cost substrates, such as flexible plastic foils. However, organic photovoltaic devices typically have relatively low power conversion efficiency (the ratio of photons absorbed to energy generated. This is, in part, thought to be due to the morphology of the active layer. The charge carriers generated must migrate to their respective electrodes before recombination or quenching occurs. The diffusion length of an exciton is typically much less than the optical absorption length, requiring a tradeoff between using a thick, and therefore resistive, cell with multiple or highly folded interfaces, or a thin cell with a low optical absorption efficiency. 
     Conjugated polymers are polymers containing π-electron conjugated units along the main chain. They can be used as active layer materials for some types of photo-electric devices, such as polymer light emitting devices, polymer solar cells, polymer field effect transistors, etc. As polymer solar cell materials, conjugated polymers should possess some properties, such as high charge carrier mobility, good harvest of sunlight, good processability, and proper molecular energy levels. Some conjugated polymers have proven to be good solar cell materials. Conjugated polymers are made of alternating single and double covalent bonds. The conjugated polymers have a δ-bond backbone of intersecting sp 2  hybrid orbitals. The p z  orbitals on the carbon atoms overlap with neighboring p z  orbitals to provide π-bonds. The electrons that comprise the π-bonds are delocalized over the whole molecule. The semiconducting properties of the photovoltaic polymers are derived from their delocalized π bonds. The substituents of the polymers also largely influence the electronic properties. The optical bandgap, mobility and thin-film morphology are affected by both the type of functional group used as a substituent and the bulkiness and length of the side chain. Polymers which have only minor differences in the side chains will have large differences in the device performance. 
     There is a need in the art for polymer solar cells that exhibit increased power conversion efficiency and fill factor. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     A random copolymer comprising the monomer units A and B. In this random copolymer A comprises 
                         
and B comprises
 
                         
Additionally, R1 R2, R3 and R4 are side chains independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2 are different and at least one is a Cl and the other is selected from the group consisting of: H, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which: 
         FIG.  1   , depicts the reaction of 4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole and tributyl(thiophen-2-yl)stannane to produce 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  2   , depicts the NMR of 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  3   , depicts the reaction of trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane and 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to produce 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  4   , depicts the NMR of 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  5   , depicts the reaction of 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole. 
         FIG.  6   , depicts the NMR of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole. 
         FIG.  7   , depicts the synthesis of 4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole. 
         FIG.  8   , depicts the NMR of 4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole. 
         FIG.  9   , depicts the synthesis of 4-bromo-7-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole. 
         FIG.  10   , depicts the synthesis of 5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  11   , depicts the NMR of 5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
         FIG.  12   , depicts the synthesis of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole. 
         FIG.  13   , depicts the NMR of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole. 
         FIG.  14   , depicts the reaction of Example 1. 
         FIG.  15   , depicts the reaction of Example 2. 
         FIG.  16   , depicts the reaction of Example 3. 
         FIG.  17   , depicts the reaction of Example 4. 
         FIG.  18   , depicts the reaction of Example 5 
         FIG.  19   , depicts a comparison of the UV-vis spectra of Examples 1-5. 
         FIG.  20   , depicts the reaction of Example 6 
         FIG.  21   , depicts the effect of the casting solution concentration on Example 6 on the open-circuit voltage of an organic photovoltaic device. 
         FIG.  22   , depicts the effect of the casting solution concentration on Example 6 on the short-circuit current density of an organic photovoltaic device. 
         FIG.  23   , depicts the effect of the casting solution concentration on Example 6 on the fill factor of an organic photovoltaic device. 
         FIG.  24   , depicts the effect of the casting solution concentration on Example 6 on the power conversion efficiency of an organic photovoltaic device. 
         FIG.  25   , depicts the effect of the annealing temperature concentration on Example 6 of an organic photovoltaic device. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow. 
     “Alkyl,” as used herein, refers to an aliphatic hydrocarbon chains. In one embodiment the aliphatic hydrocarbon chains are of 1 to about 100 carbon atoms, preferably 1 to 30 carbon atoms, and includes straight and branched chained, single, double and triple bonded carbons such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl, isopentyl, neo-pentyl, n-hexyl, isohexyl, thenyl, propenyl, butenyl, pentenyl, hexenyl, butadienyl, pentadienyl, hexadienyl, ethynyl, propynyl, butynyl, pentynyl, hexynyl, 2-ethylhexyl, 2-butyloctyl, 2-hexyldecyl, 2-octyldedodecyl, 2-decyltetradecy and the like. In this application alkyl groups can include the possibility of substituted and unsubstituted alkyl groups. Substituted alkyl groups can include one or more halogen substituents. 
     “Alkoxy,” as used herein, refers to the group R—O— where R is an alkyl group of 1 to 100 carbon atoms. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy (e.g., n-propoxy and isopropoxy), t-butoxy, pentoxyl, hexoxyl groups, and the like. In this application alkoxy groups can include the possibility of substituted and unsubstituted alkoxy groups. 
     “Alkylthio” as used herein refers to a —S— alkyl group. Examples of alkylthio groups include, but are not limited to, methylthio, ethylthio, propylthio (e.g., n-propylthio and isopropylthio), t-butylthio, pentylthio, hexylthio groups, and the like. In this application alkylthio groups can include the possibility of substituted and unsubstituted alkylthio groups. 
     “Aryl” as used herein, refers to an optionally substituted, mono-, di-, tri-, or other multicyclic aromatic ring system having from about 3 to about 50 carbon atoms (and all combinations and subcombinations of ranges and specific numbers of carbon atoms therein), with from about 6 to about 20 carbons being preferred. Non-limiting examples include, for example, phenyl, naphthyl, anthracenyl, and phenanthrenyl. Aryl groups can be optionally substituted with one or with one or more Rx. In this application aryl groups can include the possibility of substituted aryl groups, bridged aryl groups and fused aryl groups. As used herein aryl groups also include heteroaryls, including structures with more than one heteroatom. Non-limiting examples of heteroatoms that can be heteroaryls include B, N, O, Al, Si, P, S, Ge, Bi, Te, Sn, and Se. Some non-limiting examples of aryl groups with heteroaryls include: thiophene, pyridine, pyrrole, furan, stibole, arsole selenophene, imidazole, pyrazole, oxathiole, isoxathiole, thiazole, triazole, thiadiazole, diazine, oxazine, indole, and thiazine. 
     Fill Factor (FF) as used herein, is the ratio (given as a percentage) of the actual maximum obtainable power, (P m  or V mp *J mp ), to the theoretical (not actually obtainable) power, (J sc *V oc ). Accordingly, FF can be determined using the equation: FF=(V mp *J mp )/(J sc *V oc ) where J mp  and V mp  represent the current density and voltage at the maximum power point (P m ), respectively, this point being obtained by varying the resistance in the circuit until J*V is at its greatest value; and J sc  and V oc  represent the short circuit current and the open circuit voltage, respectively. Fill factor is a key parameter in evaluating the performance of solar cells. 
     Open-circuit voltage (V oc ) as used herein, is the difference in the electrical potentials between the anode and the cathode of a device when there is no external load connected. 
     Power conversion efficiency as used herein, of a solar cell is the percentage of power converted from absorbed light to electrical energy. The power conversion efficiency of a solar cell can be calculated by dividing the maximum power point (P m ) by the input light irradiance (E, in W/m 2 ) under standard test conditions and the surface area of the solar cell (A c  in m 2 ). standard test conditions typically refers to a temperature of 25° C. and an irradiance of 1000 W/m 2  with an air mass 1.5 (AM 1.5G) spectrum. 
     Random as used herein, refers to a chemical whose structural composition is a statistical mixture of different subunits or subunit orientations formed statistically during the chemical synthesis. The exact structural composition of each molecule resulting from the synthesis could be therefore distinct, but the composition of the product is most accurately described via a description that details the possible substitutions or orientations in a statistical mixture determined by the stoichiometry of the reactants. Random when used in conjunction with copolymers refers to polymers in which the monomer residues are located and/or oriented randomly within the chain of the polymer molecule, in which the probability of finding a given monomer residue at any given site depends only on the relative proportion of that comonomer in the reaction mixture. Non-limiting examples of random copolymers can include: 1) Linear polymers that are randomized only in relation to the orientation of asymmetric monomer residues along the polymer backbone, e.g. a statistical mixture of head-to-head, head-to-tail and tail-to-tail arrangement in the polymer backbone. Sometimes known as regiorandom polymers. 2) More than two different comonomers randomly located in the polymer structure. In one non-limiting example, a polymer formed from a reaction in which reactant A can react with either reactant B or C, but B cannot react with C, the resulting polymer structure is a statistical mixture of ABA and ACA repeat units. This concept could be extended to between 2 and 50 unique comonomers. Structures of this type are drawn as -(AB) x -(AC) y - where X and Y denote the relative molar percentage of reagent B and C used in the polymerization reaction and add to 100%. 3) More than two different comonomers randomly located in the polymer structure in which one or more of the comonomers is asymmetric. In one example, a polymer formed from the reaction which reactant A is asymmetric and can be oriented in either the A+ or A− orientation can react with either reactant B or C, but B cannot react with C, the resulting polymer structure is a statistical mixture of A+BA+, A−BA−, A+BA−, A−BA+, A+CA+, A−CA−, A+CA−, and A−CA+ repeat units. Structures of this type are drawn as -(AB) x -(AC) y - where X and Y denote the relative molar percentage of reagent B and C used in the polymerization reaction and add to 100%, the random orientation of the asymmetric subunits is implied by the structure but not always explicitly drawn out. 
     The present application relates to polymeric compounds that can be used as organic semiconductor materials. The present compounds can have good solubility in various common solvents and good stability in air. When incorporated into optical or optoelectronic devices including, but not limited to, photovoltaic or solar cells, light emitting diodes, and light emitting transistors, the present compounds can confer various desirable performance properties. For example, when the present compounds are used in a photoactive layer of a solar cell (e.g., bulk heterojunction devices), the solar cell can exhibit very high power conversion efficiency (e.g., about 7.0% or greater) and very high fill factor (e.g., about 68% or greater). 
     The present embodiment describes random copolymer comprising the monomer units A and B. In this random copolymer A comprises 
                         
and B comprises
 
                         
Additionally, R1 R2, R3 and R4 are side chains independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2 are independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups. In an alternate embodiment, X1 and X2 are identical and selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups. In yet another embodiment, X1 and X2 are different and at least one is a Cl and the other is selected from the group consisting of: H, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups.
 
     An alternate embodiment describes a random copolymer comprising the monomer unit C and two out of the three monomer units A, B, and D. In other embodiments, the monomer unit C contains only two out of the three monomer units A, B, and D. In the random copolymer A comprises 
                         
B comprises
 
                         
D comprises
 
                         
and C comprises an aryl group. Additionally, R1 R2, R3, R4, R3′, and R4′ are side chains independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups and wherein R3 and R3′ or R4 and R4′ are not equal.
 
     An alternate embodiment describes a random copolymer comprising the monomer units A, B and C. In this random copolymer A comprises 
                         
B comprises
 
                         
and C comprises an aryl group. Additionally, R1 R2, R3 and R4 are side chains independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2 are independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups.
 
     The polymers made from the random copolymer can be of any grouping such as ABC, ACB, BAC, BCA, CAB or CBA. These random copolymer can then be combined with another random copolymer to form random polymeric compounds. For example it is possible to form a polymer from a two copolymer system of ABC combined with either ABC, ACB, BAC, BCA, CAB or CBA. When the random copolymer contains four units the copolymer can contain subunits such as CBCD, CACB, CACDCD, CDCB, CBCA, CBCACD, CDCBCA. Additionally, the polymers made from the monomers can be randomized where two or more monomers can be combined in a randomized order. For example, monomers A, B, and C can be combined together to form AB and AC where the polymer can be completely randomized. In this example the polymer can be ABABABAC or even ACACACAB or any other randomized possibility. It is theorized that the randomness of the copolymer provides improved performance characteristics such as power conversion efficiency and fill factor. The length of the polymers formed from these random copolymer can range from as little as two copolymers to ten million copolymers. 
     The monomer C can be an aryl group selected from groups such as a benzodithiophenyl group, a silylene-bithiophenyl group, a carbazolyl group, and a dibenzosilole group, each of which can be optionally substituted as described herein. For example, the benzodithiophenyl group, the silylene-bithiophenyl group, the carbazolyl group, and the dibenzosilole group can be substituted with one, two, three or four solubilizing groups. Each solubilizing group can be a linear or branched aliphatic group (e.g., an alkyl group, an alkenyl group, an alkoxy group, or an alkylthio group) having 6-20 carbon atoms. In particular embodiments, each solubilizing group can be a branched C6-20 alkyl group or a branch C6-20 alkoxy group. Other examples of aryl groups such as polycyclic heteroaryl groups of C can include: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the above examples W can be C, Si or Se. R′, R″ can be independently selected from H, Cl, F, CN, an alkyl group, an alkoxy group, an aryl group, a C 6-20  alkyl group, a —O—C 6-20  alkyl group, a —O—C 6-20  alkenyl group, a —O—C 6-20  haloalkyl group, a —S—C 6-20  alkyl group, a —S—C 6-20  alkenyl group, a —S—C 6-20  haloalkyl group, a -thienyl-C 6-20  alkyl group, a -thienyl-C 6-20  alkenyl group, and a -thienyl-C 6-20  haloalkyl group 
     The formation of the random copolymer of coupling C can be performed by any conventionally known coupling reaction. Examples of different coupling reactions that can be used include, Wurtz reaction, Glaser coupling, Ullman reaction, Gomberg-Bachmann reaction, Cadiot-Chodkiewicz coupling, Pinacol coupling reaction, Castro-Stephens coupling, Gilman reagent coupling, Cassar reaction, Kumada coupling, Heck reaction, Sonogashira coupling, Negishi coupling, Stile coupling, Suzuki reaction, Hiyama coupling, Buchwald-Hartwig reaction, Fukuyama coupling, Liebeskind-Srogl coupling, Direct Heteroarylation and MacMillan coupling. 
     It is theorized that the random copolymer structure contributes to increased power conversion efficiency and increased fill factor. 
     The polymers or oligomers produced from the present disclosure can be used as part of a photovoltaic material or an active layer material in a photovoltaic device or an electronic device such as photodetector devices, solar cell devices, and the like. Photovoltaic devices, including solar cell devices, are generally comprised of laminates of a suitable photovoltaic material between a hole-collecting electrode layer and an electron-collecting layer. Additional layers, elements or a substrate may or may not be present. In one embodiment the electronic devices are field effect transistors, light emitting devices, and sensors, electrochromic devices and capacitors. 
     In one embodiment the molecular complex is used a polymer or oligomer for organic photovoltaic devices. In this embodiment the organic photovoltaic device comprises a cathode, disposed over an electron transport layer, disposed above a polymer or oligomer created from the molecular complex of the present teachings, disposed above an anode. In this embodiment the polymer the electron transport layer can comprise (AO x ) yy BO (1-y)  with an optional fullerene dopant. 
     The anode for the organic photovoltaic device can be any conventionally known anode capable of operating as an organic photovoltaic device. Examples of anodes that can be used include: indium tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum, silver, gold, carbon, carbon nanotubes, graphite, graphene, PEDOT:PSS, copper, metal nanowires or meshes, Zn 99 InO x , Zn 98 In 2 O x , Zn 97 In 3 O x , Zn 95 Mg 5 O x , Zn 90 Mg 10 O x , and Zn 85 Mg 15 O x . 
     The cathode for the organic photovoltaic device can be any conventionally known cathode capable of operating as an organic photovoltaic device. Examples of cathodes that can be used include: indium tin oxide, carbon, graphite, graphene, PEDOT:PSS, copper, silver, gold, aluminum, metal nanowires. 
     The electron transport layer of the organic photovoltaic device comprises (DO x ) y EO (1-y) . In this embodiment, (DO x ) y  and EO (1-y)  are metal oxides. A and B can be different metals selected to achieve ideal electron transport layers. 
     In one embodiment D can be aluminum, indium, zinc, tin, copper, nickel, cobalt, iron, ruthenium, rhodium, osmium, tungsten, magnesium, indium, vanadium, titanium and molybdenum. 
     In one embodiment E can be aluminum, indium, zinc, tin, copper, nickel, cobalt, iron, ruthenium, rhodium, osmium, tungsten, vanadium, titanium and molybdenum. 
     Examples of (DO x ) y EO (1-y)  include: (SnO x ) y ZnO (1-y) , (AlO x ) y ZnO (1-y) , (AlO x ) y InO z(1-y) , (AlO x ) y SnO z(1-y) , (AlO x ) y CuO z(1-y) , (AlO x ) y WO z(1-y) , (InO x ) y ZnO (1-y) , (InO x ) y SnO z(1-y) , (InO x ) y NiO z(1-y) , (ZnO x ) y CuO z(1-y) , (ZnO x ) y NiO z(1-y) , (ZnO x ) y FeO z(1-y) , (WO x ) y VO z(1-y) , (WO x ) y TiO z(1-y) , and (WO x ) y MoO z(1-y) . 
     In one embodiment, (DO x ) y EO (1-y)  contains from about 10% to about 25% atomic % of acetate as characterized with x-ray photoelectron spectroscopy. 
     In one embodiment, the production of (DO x ) y EO (1-y)  occurs from reacting an organic D precursor in the amounts of (1-y); an organic E precursor in the amounts of y; and a base in the amount of (1-y) to 1. 
     Examples of fullerene dopants that can be combined with the electron transport layer include 
                         
and [6,6]-phenyl-C 60 -butyric-N-2-trimethylammonium ethyl ester iodide.
 
     In the embodiment of 
                         
R′ can be selected from either N, O, S, C, or B. In other embodiment R″ can be alkyl chains or substituted alkyl chains. Examples of substitutions for the substituted alkyl chains include halogens, N, Br, O, Si, or S. In one example R″ can be selected from
 
                         
Other examples of fullerene dopants that can be used include: [6,6]-phenyl-C 60 -butyric-N-(2-aminoethyl)acetamide, [6,6]-phenyl-C 60 -butyric-N-triethyleneglycol ester and [6,6]-phenyl-C 60 -butyric-N-2-dimethylaminoethyl ester.
 
     Representative Molecular Complex Synthesis. 
     The first step involves the synthesis of 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole (2.2 g, 0.007 mol), tributyl(thiophen-2-yl)stannane (2.5 g, 0.007 mol), and tetrakis(triphenylphosphine) palladium (0.387 g, 0.335 mmol) were combined in a 50 mL Schlenk flask. After the system was placed under vacuum and backfilled with argon three times, 50 mL of anhydrous toluene was injected. The reaction was heated at 105° C. for 3 days and then cooled to room temperature. The toluene solvent was removed by a rotary evaporator, and the resulting residue was purified on a silica gel column with hexane/dichloromethane (v/v, 1/1) as the eluent. Recrystallization from the mixture solvent of IPA/methanol produced a yellow crystal as product (1.4 g, 63.0%).  FIG.  1    depicts the reaction of 4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole and tributyl(thiophen-2-yl)stannane to produce 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.  FIG.  2    depicts the NMR of 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
     The next step involves the synthesis of 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. Trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane (2.449 g, 4.644 mmol), 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole 6 (1.4 g, 4.221 mmol), Pd 2 dba 3  (0.155 g, 0.169 mmol), and P(o-tol) 3  (0.206 g, 0.675 mmol) were combined in a 50 mL Schlenk flask. After the system was placed under vacuum and backfilled with argon three times, 15 mL of anhydrous toluene was injected. The reaction was heated at 105° C. for 2 days and cooled to room temperature. The toluene solvent was removed by a rotary evaporator, and the resulting residue was purified on a silica gel column with hexane/dichloromethane (v/v, 3/1) as the eluent. Recrystallization from the mixture solvent of IPA/methanol produced a red crystalline product (2.1 g, 80.8%).  FIG.  3    depicts the reaction of trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane and 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to produce 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.  FIG.  4    depicts the NMR of 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. 
     The next step involves the synthesis of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole. 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole 7 (2.09 g, 3.396 mmol) was added to a 100 mL Schlenk flask followed by 50 mL of anhydrous THF. The solution was cooled to 0° C. before N-bromosuccinimide (1.269 g, 7.132 mmol) was added in portions. The reaction was stirred overnight. The reaction was stopped by adding saturated potassium carbonate solution and then extracted with hexane. The combined organic layer was dried over anhydrous MgSO 4 . After the removal of solvent, the resulting mixture was subjected to column purification with hexane as the eluent. Red crystal (1.91 g, 72.7%) was obtained as product after recrystallization in isopropanol and drying in vacuo.  FIG.  5    depicts the reaction of 5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.  FIG.  6    depicts the NMR of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole. 
     Synthesis of 4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole depicted in  FIG.  7   : Trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane (1.759 g, 3.334 mmol), 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole (1 g, 3.031 mmol) and tetrakis(triphenylphosphine) palladium (0.175 g, 0.152 mmol) were combined in a 100 mL Schlenk flask. After the system was placed under vacuum and backfilled with argon three times, 30 mL of anhydrous toluene was injected. The reaction was heated at 105° C. for 48 h and cooled to room temperature. The toluene solvent was removed by a rotary evaporator, and the resulting residue was purified by using a silica gel column with hexane/chloroform mixture (v/v, 95/5) as the eluent. Removal of the solvent finally produced a yellow crystal as product (0.2 g, 10.8%). The NMR spectrum is shown in  FIG.  8   . 
     Synthesis of 4-bromo-7-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole depicted in  FIG.  9   : 4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole (2.14 g, 3.487 mmol) was added to a 100 mL Schlenk flask followed by 60 mL of anhydrous tetrahydrofuran (THF). The solution was cooled to −78° C. before N-bromosuccinimide (0.652 g, 3.661 mmol) was added in portions with the absence of light. The reaction was stirred overnight. The reaction was stopped by adding saturated potassium carbonate solution and then was extracted with hexane. The combined organic layer was dried over anhydrous MgSO 4 . After removal of the solvent, the resulting mixture was subjected to column purification with hexane as the eluent. A yellow crystal (0.83 g, 34.3%) was obtained as product after recrystallization in iso-propanol at −20° C. and being dried in vacuo at room temperature. 
     Synthesis of 5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole depicted in  FIG.  10   : 4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole (1.916 g, 0.003 mol), tributyl(thiophen-2-yl)stannane (1.282 g, 0.003 mol), and Pd 2 (dba) 3  (57.177 mg, 0.062 mmol) and P(o-tol) 3  (76.018 mg, 0.25 mmol) were combined in a 100 mL Schlenk flask. After the system was placed under vacuum and backfilled with argon three times, 20 mL of anhydrous toluene was injected. The reaction was heated at 105° C. for 2 days and cooled to room temperature. The toluene solvent was removed by a rotary evaporator, and the resulting residue was purified by using a silica gel column with hexane/dichloromethane mixture (v/v, 92/8) as the eluent. Recrystallization from the mixture solvent of iso-propanol (IPA)/hexane finally produced a yellow crystal as product (1.65 g, 85.9%). The NMR of 6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole is depicted in  FIG.  11   . 
     Synthesis of 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole, depicted in  FIG.  12   : 5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1.62 g, 2.626 mmol) was added to a 100 mL Schlenk flask followed by 50 mL of anhydrous tetrahydrofuran (THF). The solution was cooled to −78° C. before N-bromosuccinimide (0.486 g, 2.731 mmol) was added in portions in dark. The reaction was stirred overnight. The reaction was stopped by adding saturated potassium carbonate solution and then was extracted with hexane. The combined organic layer was dried over anhydrous MgSO 4 . After removal of the solvent, the resulting mixture was subjected to column purification with hexane as the eluent. A orange wax solid (1.36 g, 66.9%) was obtained as product after recrystallization in iso-propanol and being dried in vacuo at room temperature. The NMR is depicted in  FIG.  13   . 
     The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention. 
     Example 1 
     In a 25 mL Schlenk flask, 4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole (147.3 mg, 0.213 mmol), (3,3′-difluoro-[2,2′-bithiophene]-5,5′-diyl)bis(trimethylstannane) (35.088 mg, 0.066 mmol), [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane (111.1 mg, 0.155 mmol) and Pd 2 dba 3  (4.058 mg, 0.004 mmol) and P(o-tol) 3  (5.395 mg, 0.018 mmol) were combined. The mixture was placed under vacuum and backfilled with argon twice before 2.3 mL of anhydrous chlorobenzene was added. The solution was heated to 130° C. for 66 h. The reaction was stopped by being cooled to room temperature. The product was precipitated by adding into methanol and was further purified by Soxhlet extraction, using acetone (6 h), hexane (24 h), dichloromethane (24 h) and chloroform (16 h) as the solvents. The portion obtained from chloroform was the main product (169 mg, yield 90.2%) after precipitation from methanol and then drying overnight.  FIG.  14    depicts the reaction of this coupling. 
     Example 2 
     In a 10 mL Schlenk flask, 4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole (125.498 mg, 0.181 mmol), trimethyl({5-[5-(trimethyl stannyl)thiophen-2-yl]thiophen-2-yl}) stannane (46.42 mg, 0.094 mmol), [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane (67.6 mg, 0.094 mmol) and Pd 2 dba 3  (3.457 mg, 0.004 mmol) and P(o-tol) 3  (4.596 mg, 0.015 mmol) were combined. The mixture was placed under vacuum and backfilled with argon twice before 1.9 mL of anhydrous chlorobenzene was added. The solution was heated to 130° C. for 66 h. The reaction was stopped by being cooled to room temperature. The product was precipitated by adding into methanol and was further purified by Soxhlet extraction, using acetone (4 h), hexane (16 h), dichloromethane (4 h), chloroform (4 h) and chlorobenzene (5 h) as the solvents. The portion obtained from chlorobenzene was the main product (120 mg, yield 81.9%) after precipitation from methanol and then drying overnight.  FIG.  15    depicts the reaction of this coupling. 
     Example 3 
     In a 25 mL of Schlenk flask, (4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (120.7 mg, 118.707 μmol), 4-[5-bromo-4-(2-hexyldecyl)thiophen-2-yl]-7-(5-bromothiophen-2-yl)-5-chloro-2,1,3-benzothiadiazole (81.07 mg, 0.113 mmol), Pd 2 dba 3  (2.071 mg, 0.002 mmol), and P(o-tol) 3  (5.506 mg, 0.018 mmol) were combined. The mixture was placed under vacuum and backfilled with argon twice before 2.3 mL of anhydrous chlorobenzene was added. The solution was heated at 135° C. for 18 hours, and then the mixture was precipitated from methanol after being cooled to room temperature. The product was precipitated out in 40 mL methanol and purified by Soxhlet extraction, using acetone (4 hours), hexane (16 hours), and dichloromethane (4 hours) as solvents. The dichloromethane portion was the main product (99.4 mg, 67.1%) after precipitation from methanol and then drying overnight. 
     Example 4 
     In a 25 mL Schlenk flask, 4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole 4 (72.4 mg, 0.094 mmol), (4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (100.0 mg, 0.098 mmol), Pd 2 dba 3  (3.4 mg, 0.004 mmol), and P(o-tol)3 (4.6 mg, 0.015 mmol) were combined. The mixture was placed under vacuum and backfilled with argon twice before 1.6 mL of anhydrous chlorobenzene was added. The solution was heated at 130° C. for 18 hours, and then 20 mL of chloroform was added and the mixture was precipitated from methanol. The product was precipitated out in 40 mL methanol and purified by Soxhlet extraction, using methanol (4 hours), hexane (16 hours), and chloroform (3 hours) as solvents. The chloroform portion was the main product (113 mg, 88.1%) after precipitation from methanol and then drying overnight. The viscosity in chlorobenzene (10 mg/mL) was 1.105 mPa·s at 25.3° C.  FIG.  17    depicts the reaction mechanism of this coupling. 
     Example 5 
     In a 25 mL of Schlenk flask, (4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (34.482 mg, 0.038 mmol), (4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (58.139 mg, 0.057 mmol), 4,7-bis[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole 7 (106 mg, 0.1 mmol), Pd 2 dba 3  (3.68 mg, 0.004 mmol), and P(o-tol)3 (4.9 mg, 0.016 mmol) were combined. The mixture was placed under vacuum and backfilled with argon twice before 5.0 mL of anhydrous chlorobenzene was added. The solution was heated at 130° C. for 18 hours, and then the mixture was precipitated from methanol after being cooled to room temperature. The product was precipitated out in 40 mL methanol and purified by Soxhlet extraction, using acetone (4 hours), hexane (16 hours), and chloroform (2 hours) as solvents. The chloroform portion was the main product (87 mg, 73.0%) after precipitation from methanol and then drying overnight. The viscosity in chlorobenzene/dichlorobenzene (v/v, 1/1) (10 mg/mL) was 2.058 mPa·s at 25.0° C. 
     Photovoltaic devices for Examples 1-6 were created using the methodology of device fabrication below. 
     Device Fabrication 
     Zinc tin oxide (ZTO):phenyl-C 60 -butyric-N-(2-hydroxyethyl)acetamide (PCBNOH) sol-gel solutions were prepared by adding PCBNOH (1.7 mg, 2.4×10 −3  mmol), zinc acetate dihydrate (330 mg, 1.5 mmol), and tin (II) acetate (33 mg, 0.14 mmol) to 2-methoxyethanol (10.6 mL) and ethanolamine (92 μL, 1.5 mmol). Solutions were stirred in air for a minimum of 8 h before use. ITO-coated glass substrates were washed with detergent (2×15 min), DI water (2×15 min), acetone (2×15 min), and isopropanol (2×15 min) in an ultrasonication bath. The substrates were placed in an oven at 80° C. for 2+ hours and placed in a UV-ozone cleaner for 1 min. After filtration with a 0.2 μm PVDF syringe filter, ZTO:PCBNOH sol-gel was spin-coated onto the top of the ITO substrate at 4000 rpm for 40 s. The substrate was annealed at 210° C. in air for 15 min and taken into a glove box for deposition of the active layer. The photoactive layer solution was prepared by a 1:1.2 or 1:1.6 polymer:PCBM ratio at 14-27.5 mg/mL concentration with 1:1 ratio of chlorobenzene and 1,2-dichlorobenzene. See Table I for solution and casting conditions for each polymer. The solution was mixed in a glove box and heated at 80° C. for 12 hours. Afterward, 2.5 or 3 vol % of 1,8-diiodooctane was added. The photoactive layer solution and ZTO:PCBNOH coated ITO substrates were heated at 110° C. for 30 min. Spin coating was performed with the photoactive layer solution, and substrates were heated to 110° C. 80 μL was pipetted onto the hot substrate and spin coated at 600 rpm or 1000 rpm for 40 s, followed immediately by 1200 rpm for 2 s (only for P-27 and P-29). The substrates were placed in a closed glass Petri dish for 18 hours to allow for solvent annealing. After solvent annealing, the substrates were scratched at the edge to expose the ITO layer for cathode electrical connection. The substrates were then placed in the metal evaporator, and 3.5 nm of MoO x  and 120 nm of Ag were deposited. The deposition rate for the MoO x  was 1.5-2.3 Å/s and Ag was 1.7-2.5 Å/s. The devices were encapsulated by using UV-curable epoxy and a cover glass slide and exposed to a UV cure for 3 min. 
     A comparison of the UV-vis spectra of Examples 1-5 with PCBM is shown in  FIG.  19   . 
     The device performances of Examples 1-5 in a polymer are listed below in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Polymer 
                   
                 Jsc 
                 Fill Factor 
                 Power Conversion 
                   
                 Rsh (Ω 
               
               
                 Example 
                 Voc (V) 
                 (mA/cm 2 ) 
                 % 
                 Efficiency % 
                 Rs (Ω cm 2 ) 
                 cm 2 ) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 0.779 
                 18.84 
                 72.6 
                 10.6 
                 3.5 
                 1390 
               
               
                 2 
                 0.718 
                 19.5 
                 72.3 
                 10.1 
                 3.1 
                 2620 
               
               
                 3 
                 0.810 
                 15.5 
                 74.0 
                 9.6 
                 6.8 
                 3000 
               
               
                 4 
                 0.829 
                 17.3 
                 74.3 
                 10.4 
                 3.1 
                 2300 
               
               
                 5 
                 0.814 
                 16.2 
                 74.7 
                 9.6 
                 3.2 
                 1900 
               
               
                   
               
            
           
         
       
     
     Example 6 
     A 500 mL dry Schlenk flask was purged with argon before 3-dodecylthiophene (9.79 g, 0.039 mol) and N,N,N′,N′-Tetramethylethylenediamine (TMEDA) (4.96 g, 0.043 mol) were added. Anhydrous THF (150 mL) was injected and the resulting solution was cooled to −78° C. n-Butyl lithium (2.5 M in hexane, 15.511 mL, 0.039 mol) was added dropwise by syringe. The reaction mixture was warmed to room temperature, and then heated to 60° C. for 1 hour. The reaction was again cooled to −78° C. and treated with a trimethyltin chloride solution (1.0 M in THF, 46.5 mL, 0.047 mol). The reaction was stirred overnight at room temperature. Water (100 mL) was poured into solution, the THF solvent was removed by rotary evaporator, and the aqueous layer was extracted with hexane (3×100 mL). The combined organic layers were washed with water (2×) and MeOH (1×) and then dried (Na2SO4), filtered, and concentrated to afford the product (12.8 g, 79.5%) as a colorless liquid. 
     (4-dodecylthiophen-2-yl)trimethylstannane (2.26 g, 5.4 mmol), 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1.64 g, 4.95 mmol), Pd2(dba)3 (0.18 g, 0.20 mmol), and P(o-tol)3 (0.24 g, 0.79 mmol) were combined in a 50 mL Schlenk flask. After the system was placed under vacuum and backfilled with argon three times, dry toluene (15 mL) was injected. The reaction was heated at 105° C. overnight, and then cooled to room temperature. The solvent was removed by a rotary evaporator, and the resulting residue was purified on a silica gel column with hexane/dichloromethane (v/v, 3/1) as the eluent. Recrystallization from a mixture of isopropanol and methanol produced an orange crystalline product (1.81 g, 72.7%). 
     5-chloro-4-(4-dodecylthiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1.81 g, 3.60 mmol) was added to a 100 mL Schlenk flask, followed by anhydrous THF (60 mL). The solution was cooled to −78° C. before N-bromosuccinimide (1.34 g, 7.55 mmol) was added in portions. The reaction was gradually warmed to room temperature and stirred overnight. The reaction was stopped by adding saturated potassium carbonate solution and then extracted with hexane. The combined organic layers were dried over anhydrous MgSO4. After the removal of solvent, the resulting mixture was subjected to column purification with hexane as the eluent. Red crystal (2.0 g, 81.7%) was obtained as product after recrystallization in isopropanol and drying in vacuo. 
     In a Schlenk flask, 4-(5-bromo-4-dodecylthiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole (72.9 mg, 0.11 mmol), 4,8-Bis[(2-hexyldecyl)oxy]-2,6-bis(1,1,1-trimethylstannanyl)benzo[1,2-b:4,5-b′]dithiophene (110 mg, 0.11 mmol), P(o-tol) 3  (5.4 mg, 0.018 mmol), and Pd 2 (dba) 3  (2.6 mg, 2.9 μmol) were combined and degassed for 30 min. After refilling with argon, dry chlorobenzene (1.8 mL) was added. Two freeze-pump-thaw cycles were performed, and the reaction was heated to 120° C. for 24 hours. After cooling to room temperature, the polymer was precipitated in MeOH, and the crude polymer was purified by Soxhlet extraction, washing sequentially with acetone, hexanes, and chloroform. The polymer, Example 6 (85 mg, 81%), was recovered in the chloroform fraction. The polymer is depicted in  FIG.  20   . 
     Device Fabrication 
     The photoactive layer consisted of the donor polymer and acceptor PCBM at a ratio of 1:1.2, respectively. The total solution concentration ranged from 36 to 14 mg/mL in 1:1 o-dichlorobenzene and chlorobenzene. The photoactive layer solution was stirred and heated at 80° C. overnight in a nitrogen filled glove box. The next day, 3 vol % of 1,8-diiodooctane (DIO) was added and the solution was heated on the hot plate at 80° C. for an hour. The solution was then filtered with a 2.7 μm glass fiber syringe filter. 
     Indium tin oxide (ITO) patterned glass substrates were cleaned by successive 15 min ultra-sonications in detergent, deionized water, acetone, and isopropanol. The freshly cleaned substrates were left to dry overnight at 80° C. Preceding fabrication, the substrates were further cleaned for 1 min in a UV-ozone chamber and the electron transport layer, zinc tin oxide:fullerene, was immediately spin coated on top. 
     Single component or mixed metal oxide solutions were filtered directly onto ITO with a 0.25 μm poly(tetrafluoroethylene) filter and spin cast at 4000 rpm for 40 seconds. Films were then annealed at 210° C. for 15 min, and directly transferred into a nitrogen filled glove box. 
     The photoactive layer was deposited from a 110° C. solution onto ITO/ZTO:PCBNOH substrates also at 110° C. The photoactive layer was spin cast at 600 rpm for 40 seconds and 1200 rpm for 2 seconds, and directly transferred into a glass petri dish to solvent anneal for 18+ h. Some devices were thermally annealed on a hot plate after drying for 18+ h. After solvent annealing, the substrates were loaded into the vacuum evaporator where MoO x  (hole transport layer) and Ag (anode) were sequentially deposited by thermal evaporation. Deposition occurred at a pressure of 1×10′ torr. MoO x  and Ag had thicknesses of 3.5 nm and 120 nm, respectively. The deposition rate for the MoO x  was 0.6-1 Å/s and Ag was 1.5-2 Å/s. Samples were then encapsulated with glass using an epoxy binder and treated with UV light for 3 min. 
     Device Testing 
     Devices with an active area of 0.08306 cm 2  were tested under AM 1.5G 100 mW/cm 2  conditions with a Newport Thermal Oriel 91192 1000 W solar simulator (4″×4″ illumination size). The current density-voltage curves were measured using a Keithley 2400 source meter. The light intensity was calibrated with a crystalline silicon reference photovoltaic (area=0.4957 cm 2 ) fitted with a KG-5 filter (calibrated by the Newport to minimize spectral mismatch. 
       FIG.  21    depicts the effect of the casting solution concentration on Example 6 on the open-circuit voltage of an organic photovoltaic device. 
       FIG.  22    depicts the effect of the casting solution concentration on Example 6 on the short-circuit current density of an organic photovoltaic device. 
       FIG.  23    depicts the effect of the casting solution concentration on Example 6 on the fill factor of an organic photovoltaic device. 
       FIG.  24    depicts the effect of the casting solution concentration on Example 6 on the power conversion efficiency of an organic photovoltaic device. 
       FIG.  25    depicts the effect of the annealing temperature concentration on Example 6 of an organic photovoltaic device. 
     The device parameters of Example 6 on different casting solution concentrations are listed below in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 Power 
               
               
                 Concentration 
                   
                 Jsc 
                   
                 Conversion 
               
               
                 (mg/mL) 
                 Voc (V) 
                 (mA/cm 2 ) 
                 Fill Factor % 
                 Efficiency % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 14 
                 0.75 
                 11.3 
                 76 
                 6.2 
               
               
                 17 
                 0.741 
                 11.6 
                 76 
                 6.2 
               
               
                 20 
                 0.756 
                 14.7 
                 70 
                 7.6 
               
               
                 22 
                 0.754 
                 15.1 
                 67 
                 7.4 
               
               
                 24 
                 0.750 
                 15.2 
                 67 
                 7.2 
               
               
                 28 
                 0.737 
                 16 
                 54 
                 5.9 
               
               
                 32 
                 0.732 
                 14.0 
                 51.9 
                 5.3 
               
               
                 36 
                 0.727 
                 11.1 
                 49.5 
                 4.0 
               
               
                   
               
            
           
         
       
     
     The device parameters of Example 6 on different annealing temperatures are listed below in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Annealing 
                   
                   
                   
                   
               
               
                 Temperature 
                   
                 Jsc 
                   
                 Power Conversion 
               
               
                 (° C.) 
                 Voc (V) 
                 (mA/cm 2 ) 
                 Fill Factor % 
                 Efficiency % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 25 
                 0.741 
                 13.7 
                 71.9 
                 7.18 
               
               
                 40 
                 0.745 
                 14.8 
                 73 
                 7.15 
               
               
                 60 
                 0.944 
                 14.4 
                 70 
                 7.2 
               
               
                 80 
                 0.752 
                 13.0 
                 74 
                 6.9 
               
               
                 100 
                 0.759 
                 12.1 
                 74 
                 6.6 
               
               
                   
               
            
           
         
       
     
     ADDITIONAL EXAMPLES 
     In yet another embodiment additional examples are made: 
     
       
         
         
             
             
         
       
     
     In a non-limiting embodiment, polymer 6 can be created by combining 4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole, [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane, (3,3′-difluoro-[2,2′-bithiophene]-5,5′-diyl)bis(trimethylstannane), Pd 2 dba 3  and P(o-tol) 3 . The mixture was placed under vacuum and backfilled with argon twice and 2.3 mL of anhydrous chlorobenzene was added. The solution was heated then cooled to room temperature. The product was precipitated by pouring the solution into methanol. The solid was purified by Soxhlet extraction. The portion obtained from chloroform was the main product after precipitation from methanol and then drying overnight. 
     
       
         
         
             
             
         
       
     
     In a non-limiting embodiment, polymer 7 can be created by combining [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane, trimethyl({5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl})stannane, [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane, Pd 2 dba 3  and P(o-tol) 3 . The mixture was placed under vacuum and backfilled with argon twice before anhydrous chlorobenzene was added. The solution was heated to 130° C. and cooled to room temperature. The product was precipitated by adding into methanol and was further purified by Soxhlet extraction. The portion obtained from chlorobenzene was the main product after precipitation from methanol and then drying overnight. 
     
       
         
         
             
             
         
       
     
     In a non-limiting embodiment, polymer 8 can be created by combining 4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole, {2,8-bis[5-(2-butyloctyl)thiophen-2-yl]-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane), (3,3′-difluoro-[2,2′-bithiophene]-5,5′-diyl)bis(trimethylstannane), Pd2dba3, and P(o-tol)3. The mixture was degassed with argon before anhydrous chlorobenzene was added. The solution was heated then cooling to room temperature. The solid was filtered and purified by Soxhlet extraction. 
     The above examples can be made from the following monomers: 
                         
and aryl and hetero aryl groups. In these examples, R′, R″ can be independently selected from H, Cl, F, CN, an alkyl group, an alkoxy group, an aryl group, an heteroaryl group, a C 6-20  alkyl group, a —O—C 6-20  alkyl group, a —O—C 6-20  alkenyl group, a —O—C 6-20  haloalkyl group, a —S—C 6-20  alkyl group, a —S—C 6-20  alkenyl group, a —S—C 6-20  haloalkyl group, a -thienyl-C 6-20  alkyl group, a -thienyl-C 6-20  alkenyl group, and a -thienyl-C 6-20  haloalkyl group, which is unsubstituted, mono- or poly-substituted by F, Cl or CN, in which optionally one or more non-adjacent CH2 groups were replaced, in each case independently from one another by —O—, —S—, —NH—, NR′—, —SiR′R″—, —CO—, —COO—, —CH═CH— or aryl groups and heteroaryl groups.
 
     The device performances of Examples 6-8 in a polymer are listed below in Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Polymer 
                   
                 Jsc 
                 Fill Factor 
                 Power Conversion 
               
               
                 Example 
                 Voc (V) 
                 (mA/cm 2 ) 
                 % 
                 Efficiency % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 6 
                 0.72 
                 19.2 
                 71.9 
                 10.1 
               
               
                 7 
                 0.82 
                 20.3 
                 73.5 
                 12.1 
               
               
                 8 
                 0.84 
                 16.5 
                 59.1 
                 8.2 
               
               
                   
               
            
           
         
       
     
     In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention. 
     Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.