Patent Application: US-201113161827-A

Abstract:
1 , 4 fullerene deriatives useful for solar cells are provided , where their structures allow for straightforward functionalizations to tune their properties in terms of solubility and lumo energy levels .

Description:
we herein introduce a new class of fullerene derivatives based on the 1 , 4 addition chemistry . 6 the interest for the synthesis of 1 , 4 addends include : ( i ) lower symmetry with consequent increased optical absorption in the visible ( onset at ca . 500 nm and extinction coefficient of ca . 8000 mol − 1 cm − 1 ); ( ii ) new chemistry which allows for straightforward functionalization and ( iii ) possibility to tune solubility and energy of the lumo . the enhanced absorption can favorably affect the short circuit current ( j sc ) by increasing the number of photo - charges generated in the electron - transporting layer of the device . tuning the energy of the lumo is desirable to couple the fullerene with a specific donor polymer . data obtained from devices incorporating these addends is encouraging . to the best of our knowledge , only one 1 , 4 - fullerene addend was used in solution processed solar cells and it was based on a benzoporphyrin and not a polymer . 7 these derivatives can be tuned for their solubility by assessing whether they are soluble in solvents , such as but not limited to , chlorobenzene , 1 , 2 - dichlorobenzene or chloroform . wherein the fullerene can either be fullerene c60 , c70 , c84 or higher ; where r1 - r10 can each independently be selected from hydrogen , alkyl , aryl , amino , oxo , thio , alkyl , halogen , and silanes . in another embodiment , r1 - r10 can be long alkyl chains such as , but not limited to 2 - ethylhexyloxy , and valeric acid methyl ester . in yet another embodiment , r1 - r10 can be electron withdrawing groups to stabilize / lower the energy of the lumo of the derivative , such as but not limited to , halogens ( f , cl ), nitriles , carbonyls , and nitro groups . in another embodiment , r1 - r10 can be electron donating groups to destabilize / raise the energy of the lumo of the derivative , such as but not limited to , alkyl , alkyloxy , alcohol , amino , and silanes . in yet another embodiment , the following 1 . 4 fullerene derivative is provided : wherein the fullerene can either be fullerene c60 , c70 , c84 or higher ; where r1 can be hydrogen or alkyl group , and r2 - r11 can each independently be selected from hydrogen , alkyl , aryl , amino , oxo , thio , alkyl , halogen , and silanes . the synthesis of fullerenol was previously reported . 6 from fullerenol , we herein report on the syntheses of a set of derivatives by arylation as described in fig1 . in a typical reaction , fullerenol is reacted with a specific substrate ( a substituted aryl ) used as the solvent in the presence of p - toluene sulfonic acid ( tsoh ) as the catalyst . following this procedure we synthesized : pehob ( fig2 ) ( c 60 functionalized with a phenyl group on c1 and an ethylhexyloxybenzene group on c4 ), pcvm ( fig3 ) ( phenyl on c1 and phenylvaleric acid methyl ester on c4 ), pthob ( fig4 ) ( phenyl on c1 and trihexyloxyphenyl on c4 ), pfoh ( fig5 ) ( phenyl on c1 and hydroxyl on c4 ); pftfp ( fig6 ) ( p - trifluorophenyl on c1 and pentafluorophenyl on c4 ) and anp ( fig7 ) ( phenyl on c1 and aniline on c4 ). 1h nmr , 13c nmr , 19f nmr and field desorption ( fd ) mass spectroscopy confirmed the identity of the products . the adducts were further characterized by cyclic voltammetry ( cv ) and uv - vis spectroscopy . all the fullerene derivatives displayed a nearly identical uv - vis profile with a broad signal at ca . 470 nm , typical for lower symmetrical derivative ( see fig8 ). the lower symmetry was also confirmed by 13c nmr , which showed at least 40 signals for the sp 2 fullerene carbons ; this is consistent with a c 1 symmetry . from the first reduction potential calculated by cv we determined the energy of the lumo . an estimated value of the homo was inferred from the onset of the uv - vis spectra . in order to modify the property of the derivatives , we appended ( i ) long alkyl chains to increase solubility and ( ii ) electron withdrawing or ( iii ) electron donating groups to stabilize or destabilize the energy of the lumo respectively . due to the spherical shape of c 60 , heteroatoms or functional groups appended on the fullerene can only affect the energy of the molecular orbitals by induction . therefore , an electron donating group directly bound to c 60 such a methoxy will stabilize the energy of the lumo because of the higher electronegativity of the oxygen . nevertheless , alkyloxy groups bound to a phenyl bound to c 60 , can exert their properties as electron donating groups either by resonance into the phenyl or through space . 8 we started from the synthesis of the simplest derivatives bearing 2 phenyl groups on c1 and c4 ( procedure described in the literature ) 6 . the energy of the lumo for this derivative was − 3 . 75 ev ( same as pcbm ). by changing the nature and the number of heteroatoms on the phenyl on c4 we lowered the lumo of ca . 200 mv and rose it of ca . 100 mv . these values are in agreement with previous reports . 8 , 9 table 1 ( see below ) summarizes the electrochemical data calculated for all the derivatives . the interest for tuning the lumo is to increase the number of possible combinations with novel low band - gap polymers . also , the difference in energy between the homo of the donor and the lumo of the acceptor is reported to determine the open circuit voltage ( v oc ) of the device . 10 thus , to increase the lumo can lead to an increased v oc . compared to the pcbm analogues described by hummelen 9 et al ., the 1 , 4 - fullerene addends with sub - stituents directly appended appear to affect their redox potentials to a greater degree . for instance , one pentafluoro - phenyl group on pcbm raises the redox potential from − 1 . 08 mv ( pcbm ) to − 1 . 042 mv ( net change 0 . 038 v ), whereas pftfp is increased from − 1 . 02 to − 0 . 910 mv ( net change 0 . 11 v ) device data of bulk heterojunction ( bhj ) solar cells fabricated with pehob / p3ht show that the efficiency is of the same order of magnitude of that one of pcbm . the solar cells fabricated with pehob and pthob derivatives displayed very high v oc , in particular pthob had a v oc higher than pc 70 bm ( fig9 ). in summary we have synthesized a set of 1 , 4 - fullerene addends and varied the properties of the materials by tuning the solubility and the energy of the lumo . by introduction of electron withdrawing groups we increased the electron accepting properties . by introducing electron donating groups , we decreased the electron acceptor properties with the possibility to increase the voc of the device . fig1 is a scheme showing arylation of fullerenol . r ═ h , — ch 3 , — och 3 , — fs , 2 - ethylhexyloxybenzene , phenylvaleric acid methyl ester , — nh . to a solution containing fullerenol ( 300 . 0 mg , 0 . 37 mol ) in 6 ml of 2 - ethylhexyloxybenzene , tsoh ( 350 mg , 1 . 84 mol ) was added . the mixture was heated and stirred in an oil bath preset at 80 c . the reaction was monitored by tlc and stopped after 12 hours . after cooling , the mixture was poured in a centrifuge tube and the products precipitated with 15 ml of methanol . after removing the supernatant , the precipitate was chromatograph on silica gel ( 6 × 25 cm ) using cs 2 as eluent . the first fraction afforded ca . 5 mg of a brown compound that was not characterize . a second fraction was eluted ( ca . 1 mg ). the third fraction ( r f = 0 . 72 ) afforded pehob ( 35 mg , 10 %). the solution was concentrated to ca . 5 ml under reduced pressure and precipitated with 15 ml of methanol . after centrifuging and removing the supernatant , this procedure was repeated 3 more times . using cs 2 / toluene ( 2 / 1 , v / v ) we recovered 65 % of fullerenol . 1 h nmr ( 500 mhz , cs 2 / cdcl 3 ) δ ppm 1 . 6 - 0 . 9 ( m , 12h ), 1 . 78 ( m , 1h ), 3 . 9 ( d , 2h ), 7 . 01 ( d , 2h ), 7 . 47 ( m , 1h ), 7 . 55 ( m , 2h ), 7 . 97 ( d , 2h ), 8 . 13 ( d , 2h ). 13c nmr ( 500 mhz , cs 2 / dmso - d6 1 / 1 v / v ) δ ppm 11 . 40 , 14 . 39 , 23 . 46 , 24 . 19 , 29 . 26 , 29 . 91 , 30 . 68 , 61 . 50 ( sp 3 - c of c 60 ), 61 . 95 ( sp 3 - c of c 60 ), 70 . 14 ( och 2 ), 115 . 09 ( aryl c ), 127 . 31 ( aryl c ), 128 . 16 ( aryl c ), 128 . 34 ( aryl c ), 129 . 27 ( aryl c ), 131 . 62 ( aryl c ), 136 . 96 , 137 . 19 , 138 . 48 , 138 . 60 , 139 . 95 , 140 . 71 , 141 . 80 , 142 . 01 , 142 . 31 , 142 . 35 , 142 . 47 , 142 . 84 , 142 . 90 , 142 . 93 , 143 . 58 , 143 . 67 , 143 . 74 , 143 . 93 , 143 . 99 , 144 . 03 , 144 . 09 , 144 . 49 , 144 . 63 , 144 . 76 , 144 . 82 , 145 . 20 , 145 . 27 , 146 . 54 , 146 . 63 , 146 . 70 , 146 . 83 , 148 . 15 , 148 . 27 , 148 . 34 , 150 . 58 , 151 . 03 , 156 . 36 , 156 . 64 , 159 . 01 . fd + 1002 . 2 . uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . phenylvaleric acid ( 7 g ) was melted and heated at 80 c in a 25 ml round bottomed flask . fullerenol ( 225 mg , 0 . 28 mmol ) and tsoh ( 260 mg , 1 . 38 mmol ) were added and the solution was stirred for 12 hours . the solution was cooled down to room temperature and methanol ( 15 ml ) was added . after centrifugation , the supernatant was removed and this procedure repeated 2 more times . the crude was not characterized but was further reacted to produce the methyl ester according to the following procedure : 260 mg of crude was dissolved in 6 ml of 1 , 2 - dichlorobenzene and stirred . methanol ( 1 . 5 ml ) and concentrated hcl ( 0 . 2 ml ) were added and the mixture was stirred and heated at 45 c for 12 hours . the mixture was cooled to room temperature and poured into 15 ml of methanol , centrifuged and washed again with methanol for 3 times according to the general procedure described earlier . the crude was chromatographed on silica gel ( 6 × 20 cm ). using cs 2 as the eluent a first fraction , which was not characterized , was eluted . the second fraction ( r f = 0 . 62 ) was collected and afforded of a fullerene derivative bearing a phenyl on c1 and — och 3 group on c4 ( 45 mg ). using cs 2 / toluene 2 / 1 v / v we recovered fullerenol ( third fraction ) and pcvm ( 35 mg , fourth fraction ). 1 h nmr ( 500 mhz , cs 2 / cdcl 3 2 / 1 ) δ ppm 1 . 74 - 1 . 76 ( m , 4h ), 2 . 39 ( t , 2h ), 2 . 76 ( t , 2h ), 3 . 69 ( s , 3h ), 7 . 31 ( d , 2h ), 7 . 47 ( m , 1h ), 7 . 53 ( m , 2h ), 7 . 95 ( d , 2h ), 8 . 01 ( d , 2h ). 13c nmr ( 500 mhz , cs 2 / cdcl 3 2 / 1 v / v ) δ ppm 24 . 85 , 31 . 12 , 34 . 04 , 35 . 62 , 51 . 38 ( och 3 ), 61 . 64 ( sp 3 - c of c 60 ), 61 . 83 ( sp 3 - c of c 60 ), 70 . 14 ( och 2 ), 127 . 69 ( aryl c ), 127 . 72 ( aryl c ), 128 . 41 ( aryl c ), 129 . 52 ( aryl c ), 137 . 57 , 137 . 61 , 138 . 14 , 138 . 98 , 139 . 05 , 140 . 62 , 141 . 20 , 142 . 25 , 142 . 28 , 142 . 41 , 142 . 72 , 142 . 80 , 142 . 91 , 143 . 33 , 143 . 37 , 144 . 01 , 144 . 05 , 144 . 11 , 144 . 16 , 144 . 39 , 144 . 46 , 144 . 52 , 144 . 91 , 145 . 03 , 145 . 12 , 145 . 25 , 145 . 50 , 145 . 72 , 147 . 01 , 147 . 11 , 147 . 16 , 147 . 29 , 148 . 61 , 148 . 67 , 148 . 83 , 151 . 02 , 151 . 25 , 156 . 77 , 156 . 86 , 173 . 40 . uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . to a solution containing fullerenol ( 460 . 0 mg , 0 . 57 mol ) in 7 ml of trihexyloxybenzene ( synthesized according to literature procedure ), tsoh ( 537 mg , 2 . 28 mol ) was added . the mixture was heated and stirred in an oil bath preset at 80 c . the reaction was monitored by tlc and stopped after 12 hours . the mixture was poured in a centrifuge tube and the products precipitated with 15 ml of methanol . after removing the supernatant , the precipitate was chromatograph on silica gel ( 6 × 25 cm ) using cs 2 as eluent . the first fraction afforded ca . 10 mg of a brown compound that was not characterize . a second fraction was eluted ( ca . 1 mg ). the third fraction ( r f = 0 . 72 ) afforded pthob ( 120 mg , 19 %). the fraction was concentrated to ca . 5 ml under reduced pressure and precipitated with 15 ml of methanol . after centrifuging and removing the supernatant , this procedure was repeated 3 more times . using cs 2 / toluene 2 / 1 v / v we recovered 35 % of fullerenol . 1 h nmr ( 500 mhz , cdcl 3 ) δ ppm 0 . 94 ( m , 10h ), 1 . 39 ( m , 14h ), 1 . 70 ( m , 2h ), 1 . 8 ( s , 4h ), 4 . 08 ( m , 4h ), 4 . 25 ( m , 2h ), 6 . 78 ( d , 1h ), 7 . 43 ( m , 1h ), 7 . 47 ( m , 2h ), 7 . 81 ( d , 1h ), 8 . 09 ( d , 2h ). 13c nmr ( 600 mhz , cdcl3 ) δ ppm 14 . 03 , 14 . 10 , 22 . 58 , 22 . 58 , 22 . 67 , 22 . 71 , 25 . 60 , 25 . 88 , 29 . 39 , 29 . 91 , 31 . 67 , 31 . 72 , 31 . 85 , 59 . 61 , 61 . 72 , 68 . 90 , 73 . 80 ( sp 3 - c of c 60 ), 74 . 36 ( sp 3 - c of c 60 ), 108 . 21 , 124 . 20 , 126 . 52 , 127 . 70 , 128 . 03 , 129 . 26 , 137 . 96 , 137 . 99 , 138 . 80 , 138 . 96 , 140 . 89 , 141 . 82 , 142 . 20 , 142 . 30 , 142 . 45 , 142 . 67 , 142 . 82 , 142 . 86 , 143 . 06 , 143 . 21 , 143 . 26 , 143 . 28 , 143 . 43 , 143 . 63 , 143 . 84 , 143 . 92 , 144 . 03 , 144 . 10 , 144 . 24 , 144 . 39 , 144 . 42 , 144 . 46 , 144 . 49 , 144 . 56 , 144 . 65 , 144 . 67 , 144 . 91 , 145 . 02 , 145 . 05 , 145 . 22 , 145 . 26 , 145 . 57 , 145 . 61 , 145 . 67 , 145 . 90 , 146 . 87 , 146 . 92 , 147 . 14 , 147 . 20 , 147 . 48 , 147 . 62 , 148 . 20 , 148 . 73 , 148 . 89 , 150 . 79 , 151 . 57 , 152 . 53 , 153 . 91 , 156 . 33 , 156 . 98 , uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . fullerene c 60 ( 1 g , 1 . 39 mol ), p - trifluoromethylphenylhydrazine ( 490 mg , 2 . 78 mol ) and nano2 ( 192 g , 2 . 78 mol ) were sonicated in toluene ( 750 ml ) for 10 minutes . concentrated hcl ( 0 . 2 ml ) and water ( 30 ml ) were added and the mixture was stirred in an oil bath preset at 50 c for 6 hours . the solvent was removed under reduced pressure and the crude was chromatographed on silica gel ( 6 × 15 cm ). unreacted c 60 ( 50 %) was recovered using cs 2 as the eluent . trifluoromethylfullerenol ( pfoh ) was recovered using cs 2 / toluene 2 / 1 v / v ( 200 mg , 16 % yield ). 1 h nmr ( 500 mhz , cs 2 / cdcl 3 ) δ 4 . 06 ( s , 1h ), 7 . 93 ( d , 2h ), 7 . 53 ( d , 2h ). 19f nmr ( 500 mhz , cs 2 / cdcl 3 ) δ 62 . 13 ( s ). 13 - c nmr ( 500 mhz , cs 2 / cdcl 3 ) δ 61 . 03 ( sp 3 - c of c 60 ), 75 . 64 ( sp 3 - c of c 60 ), 126 . 70 , 126 . 73 , 137 . 83 , 138 . 80 , 139 . 09 , 139 . 76 , 141 . 34 , 141 . 50 , 141 . 60 , 142 . 25 , 142 . 48 , 142 . 55 , 142 . 70 , 142 . 80 , 143 . 14 , 143 . 21 , 143 . 37 , 143 . 40 , 143 . 49 , 143 . 53 , 143 . 63 , 143 . 73 , 143 . 86 , 143 . 97 , 144 . 02 , 144 . 15 , 144 . 20 , 144 . 24 , 144 . 32 , 144 . 39 , 144 . 60 , 144 . 76 , 144 . 6 , 145 . 37 , 145 . 79 , 145 . 83 , 145 . 97 , 146 . 75 , 146 . 90 , 147 . 11 , 147 . 17 , 147 . 21 , 147 . 27 , 147 . 34 , 147 . 98 , 148 . 72 , 149 . 14 , 150 . 43 , 151 . 27 , 152 . 71 , 152 . 97 . fd + 882 . 0 . uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . pfoh ( 50 . 0 mg , 0 . 06 mol ) was stirred in 7 ml of either hexafluorobenzene or pentafluorobenzene . tsoh ( 54 mg , 0 . 28 mol ) was added . the mixture was heated and stirred in an oil bath preset at 70 c . the reaction was monitored by tlc and stopped after 12 hours . the solvent was removed under reduced pressure . the residue was chromatograph on silica gel ( 6 × 10 cm ) using cs 2 as eluent . the first fraction afforded 25 mg of pftfp ( 40 % yield ). the product was not soluble enough to obtain a clear nmr spectrum . nevertheless mass spectroscopy confirmed the identity of the compound and 19f nmr revealed the presence of several fluorines . we speculate that some of the fluorines might undergo fluorodeprotonation and that the product might be a mixture of isomers with partially non - fluorinated phenyl . fd + k 1070 . 1 . uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . fullerenol ( 130 . 0 mg , 0 . 16 mol ) was stirred in 7 ml of aniline tsoh ( 175 mg , 0 . 92 mol ) was added . the mixture was heated and stirred in an oil bath preset at 80 c . the reaction was monitored by tlc and stopped after 12 hours . the mixture was poured in a centrifuge tube and the products precipitated with 15 ml of methanol . after removing the supernatant , the precipitate was chromatograph on silica gel ( 6 × 15 cm ) using cs 2 as eluent . the first fraction afforded 55 mg of anp ( 39 % yield ). 1 h nmr ( 500 mhz , cs 2 / cdcl 3 ) δ 5 . 34 ( s , 1h ), 7 . 02 ( m , 1h ), 7 . 32 ( m , 2h ), 7 . 52 ( m , 3h ), 7 . 65 ( m , 2h ), 8 . 37 ( d , 2h ). 13 - c nmr ( 500 mhz , cs 2 / cdcl 3 ) δ 61 . 87 ( sp 3 - c of c 60 ), 67 . 35 ( sp 3 - c of c 60 ), 120 . 69 ( aryl c ), 122 . 45 ( aryl c ), 127 . 86 ( aryl c ), 128 . 50 ( aryl c ), 129 . 53 ( aryl c ), 129 . 77 ( aryl c ), 138 . 07 , 138 . 12 , 139 . 38 , 139 . 61 , 140 . 61 , 141 . 05 , 141 . 48 , 142 . 17 , 142 . 46 , 142 . 63 , 142 . 71 , 142 . 75 , 143 . 03 , 143 . 10 , 143 . 28 , 143 . 39 , 143 . 46 , 143 . 57 , 143 . 72 , 143 . 79 , 143 . 97 , 144 . 24 , 144 . 28 , 144 . 33 , 144 . 38 , 144 . 61 , 144 . 68 , 144 . 83 , 144 . 95 , 145 . 24 , 145 . 57 , 145 . 57 , 145 . 75 , 145 . 89 , 146 . 61 , 146 . 80 , 146 . 95 , 147 . 14 , 147 . 20 , 147 . 29 , 147 . 32 , 147 . 72 , 147 . 89 , 148 . 68 , 148 . 83 , 148 . 98 , 149 . 79 , 152 . 60 , 152 . 70 , 155 . 03 . uv - vis ( 1 , 2 - dichlorobenzene ) λ max / nm 334 , 446 , 540 , 620 , 690 . 1 . the solar cell devices were fabricated on indium tin oxide ( ito )- coated glass substrates , which were previously cleaned by ultrasonication with detergent , deionized water , acetone , and isopropyl alcohol , sequentially . poly ( 3 , 4 - ethylenedioxythiophene ): poly ( styrenesulfonate ) ( pedot : pss ) ( baytron ph ) was spin - coated onto the ito - coated glass and then baked at 140 ° c . for 10 min in air . 2a . pcdtbt - based cells : after transferring to a n 2 - filled glove box , the blend solution ( 0 . 7 wt %) pcdtbt : acceptor ( 1 : 4 ratio by weight ), which was dissolved in cosolvent of 1 , 2 - dichlorobenzene ( dcb ) and chlorobenzene ( cb ) ( 3 : 1 ratio by volume ), was spin - cast ( 6000 rpm , 40 s ) onto the pedot : pss layer . the film was dried for 10 min at 70 ° c . in the glove box . 2b . p3ht - based cells : the p3ht : acceptor weight ratio was fixed at 1 : 0 . 8 . p3ht and acceptor ( 1 wt %) were dissolved in dcb in a n2 - filled glove box . the active layers of each device were formed by spin - coating ( 800 rpm , 60 s ), with the blend solutions passing through a 0 . 2 mm ptfe filter on the pedot : pss layer . for the devices fabricated by the solvent - annealing process , the growth rate of the blend films was controlled by keeping the spin - coated films in a small , capped glass jar to protect against fast solvent evaporation and penetration of outside n2 gas during 30 min . the film was annealed for 10 min at 110 ° c . in the glove box . 3 . the tiox precursor solution diluted 1 : 200 in methanol was spin - coated in air on top of the pcdtbt : pc70bm layer ( 5 , 000 rpm , 40 s ). the sample was heated at 80 ° c . for 10 min in air . to complete the device fabrication , an al electrode ( 100 nm ) was deposited on top of the photoactive layer by thermal evaporation under high vacuum (& lt ; 3 × 10 − 6 torr ). fig8 shows a uv - vis of pehob ( pink ) and pcbm ( blue ) in 1 , 2 - dichlorobenzene . derivative lumo ( ev ) e 1 red e 2 red e 3 red pcbm − 3 . 74 − 1 . 056 − 1 . 471 − 1 . 957 pehob − 3 . 74 − 1 . 062 − 1 . 496 − 1 . 963 pcvm − 3 . 76 − 1 . 021 − 1 . 484 − 1 . 959 pfoh − 3 . 86 − 0 . 940 − 1 . 460 − 1 . 894 pftfp − 3 . 91 − 0 . 911 − 1 . 375 pthob − 3 . 65 − 1 . 150 − 1 . 589 − 2 . 072 anp − 3 . 81 − 0 . 992 − 1 . 532 − 1 . 900 table 1 shows electrochemical data and energy of the lumo . experimental conditions : values in v vs fc / fc + ; 1 , 2 - dichlorobenzene , bu4nclo4 ( 0 . 1 m ) as supporting electrolyte . pt wire counter electrode ; 50 mv / s scan rate . fig9 shows i - v curves and opv parameters of some devices . although the present invention has been described in connection with the preferred embodiments , it is to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention , as those skilled in the art will readily understand . accordingly , such modifications may be practiced within the scope of the following claims . 1 . barry , c . t . ; jean , m . j . f ., polymer - fullerene composite solar cells . angew . chem . int . ed . 2008 , 47 , ( 1 ), 58 - 77 . 2 . hummelen , j . c . ; knight , b . w . ; lepeq , f . ; wudl , f . ; yao , j . ; wilkins , c . l ., preparation and characterization of fulleroid and methanofullerene derivatives . j . org . chem . 1995 , 60 , ( 3 ), 532 - 538 . 3 . lacramioara m . popescu ; patrick van &# 39 ; t hof ; alexander b . sieval ; harry t . jonkman ; hummelen , j . c ., thienyl analog of 1 -( 3 - 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