Patent Application: US-201213526371-A

Abstract:
a method of regioselectively preparing a pyridine - containing compound is provided . in particular embodiments , the method includes reacting halogen - functionalized pyridalthiadiazole with organotin - functionalized cyclopentadithiophene or organotin - functionalized indacenodithiophene . also provided is a method of preparing a polymer . the method includes regioselectively preparing a monomer that includes a pyridalthiadiazole unit ; and reacting the monomer to produce a polymer that includes a regioregular conjugated backbone section , wherein the section includes a repeat unit containing the pyridalthiadiazole unit . a polymer that includes a regioregular conjugated backbone section , and electronic devices that include the polymer , are also provided .

Description:
in the method of preparing a regioregular polymer , a monomer is regioselectively prepared . in some embodiments , the monomer is prepared by reacting halogen - functionalized pt with organotin - functionalized cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene . the reaction can be carried out at a temperature in the range of about 50 ° c . to about 150 ° c ., and the regioselectivity of the reaction can be 95 % or greater . in other embodiments the monomer is prepared by reacting halogen - functionalized pt with organotin - functionalized indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene ( idt ), where the reaction can be carried out at a temperature in the range of about 50 ° c . to about 150 ° c . and the regioselectivity of the reaction can be 95 % or greater . in other embodiments the monomer is prepared by reacting halogen - functionalized pt with organoboron - functionalized cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene or organboron - functionalized indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene ( idt ), where the reaction can be carried out at a temperature in the range of about 50 ° c . to about 150 ° c . and the regioselectivity of the reaction can be 95 % or greater . in some embodiments the monomer is prepared by reacting halogen - functionalized pt with cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene or indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene ( idt ) by direct arylation polyerization , in which direct arylation allows the formation of carbon - carbon bonds between aromatic units having activated hydrogen atoms without the use of organometallic intermediates , where the reaction can be carried out at a temperature in the range of about 50 ° c . to about 150 ° c . and the regioselectivity of the reaction can be 95 % or greater . where x 1 and x 2 are each independently a halogen , and in particular embodiments can be i , br , cl , or cf 3 so 3 . where each r is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain , each r 2 is independently methyl or n - butyl , and x is c , si , ge , n or p . in some embodiments , the r groups can be the same and the r 2 groups can be the same . the term “ alkyl ” refers to a branched or unbranched saturated hydrocarbyl group such as methyl , ethyl , n - propyl , isopropyl , n - butyl , isobutyl , t - butyl , octyl , decyl and the like . the term “ aryl ” refers to an aromatic hydrocarbyl group containing a single aromatic ring or multiple aromatic rings that are fused together , linked covalently , or linked to a common group such as a methylene or ethylene moiety . the term “ alkoxy ” refers to an alkyl group bound through a single , terminal ether linkage . the term “ substituted ” refers to a hydrocarbyl group in which one or more bonds to a hydrogen atom contained within the group is replaced by a bond to a non - hydrogen atom of a substituent group . examples of non - hydrogen atoms include , but are not limited to , carbon , oxygen , nitrogen , phosphorus , and sulfur . examples of substituent groups include , but are not limited to , halo , hydroxy , amino , alkoxy , aryloxy , nitro , ester , amide , silane , siloxy , and hydrocarbyl groups . the substituent can be a functional group such as hydroxyl , alkoxy , thio , phosphino , amino , or halo . in particular embodiments of the cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene or indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene : the substituted or non - substituted alkyl , aryl or alkoxy chain can be a c 6 - c 30 substituted or non - substituted alkyl or alkoxy chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ); and / or x can be si . in some embodiments , the halogen - functionalized pt and / or the organotin - functionalized cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene are compounds of scheme 1 or 2 . in other embodiments , the halogen - functionalized pt and / or the organotin - functionalized indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene are compounds of scheme 4 . where each r is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain , each r 2 is independently methyl or n - butyl , x is c , si , ge , n or p , and x 2 is a halogen . in particular embodiments , x 2 can be i , br , cl , or cf 3 so 3 . in some embodiments , the monomer has the following structure : in these embodiments , each r or r 1 is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain , and each r 2 is independently methyl or n - butyl . in some embodiments , the substituted or non - substituted alkyl , aryl or alkoxy chain can be a c 6 - c 30 substituted or non - substituted alkyl or alkoxy chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), or —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ); and / or x can be si . in some embodiments , the r groups can be the same , the r 1 groups can be the same , and the r 2 groups can be the same . in the method , the monomer is regioselectively prepared , then the monomer is reacted or polymerized to form a regioregular polymer having a regioregular conjugated main chain section . to form the regioregular polymer when the monomer is a cdt - pt monomer , the monomer can be reacted to itself , or reacted to another monomer containing a cyclopenta [ 2 , 1 - b : 3 , 4 - b ] dithiophene unit . when the monomer is a pt - idt - pt monomer , the monomer can be reacted to another monomer containing an idt - pt unit . the polymerization reaction can take place at a temperature in the range of about 80 ° c . to about 200 ° c . when the monomer is a cdt - pt monomer , and can take place at a temperature in the range of about 80 ° c . to about 200 ° c . when the monomer is a pt - idt - pt monomer . the regioregular conjugated main chain section can comprise 5 - 100 , or more , contiguous repeat units . in some embodiments , the number of repeat units is in the range of 10 - 40 repeats . the regioregularity of the conjugated main chain section can be 95 % or greater . the regioregular polymer in some embodiments has a main chain section that includes a repeat unit containing a pyridine of the structure or a combination thereof , where each ar is independently nothing or a substituted or non - substituted aromatic functional group , each r is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain , and x is c , si , ge , n or p . when ar is nothing , the valence of the respective pyridine or thiophene ring is completed with hydrogen . in some embodiments , the r groups can be the same . the substituted or non - substituted aromatic functional group can include one or more alkyl or aryl chains , each of which independently can be a c 6 - c 30 substituted or non - substituted alkyl or aryl chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ). the substituted or non - substituted alkyl , aryl or alkoxy chain can be a c 6 - c 30 substituted or non - substituted alkyl or alkoxy chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ). in embodiments of the regioregular polymer , the repeat unit of the regioregular conjugated main chain section can contain a pyridine unit of table 1 , where each r is independently a substituted or non - substituted alkyl chain , which can be a c 6 - c 30 substituted or non - substituted alkyl chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ); in some embodiments , the r groups can be the same . in embodiments of the regioregular polymer , the repeat unit of the regioregular conjugated main chain section can contain a dithiophene unit of table 2 , where each r is independently a substituted or non - substituted alkyl , aryl or alkoxy chain , which can be a c 6 - c 30 substituted or non - substituted alkyl or alkoxy chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ); in some embodiments , the r groups can be the same , and in some embodiments , a repeat unit may contain any combination of a pyridine unit of table 1 and dithiophene unit of table 2 . where each r is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain , and x is c , si , ge , n or p . in particular embodiments , the repeat unit has the following structure : where each r 1 is independently hydrogen or a substituted or non - substituted alkyl , aryl or alkoxy chain . in some embodiments , the r groups can be the same , and the r 1 groups can be the same . in some embodiments , each r or r 1 can be a c 6 - c 30 substituted or non - substituted alkyl , aryl or alkoxy chain , —( ch 2 ch 2 o ) n ( n = 2 ˜ 20 ), c 6 h 5 , — c n f ( 2n + 1 ) ( n = 2 ˜ 20 ), —( ch 2 ) n n ( ch 3 ) 3 br ( n = 2 ˜ 20 ), or —( ch 2 ) n n ( c 2 h 5 ) 2 ( n = 2 ˜ 20 ), 2 - ethylhexyl , phc m h 2m + 1 ( m = 1 - 20 ), —( ch 2 ) n si ( c m h 2m + 1 ) 3 ( m , n = 1 to 20 ), or —( ch 2 ) n si ( osi ( c m h 2m + 1 ) 3 ) x ( c p h 2p + 1 ) y ( m , n , p = 1 to 20 , x + y = 3 ); and / or x can be si . in some embodiments , the polymer is prepared by any of the methods described herein , or shown in scheme 1 , 2 , or 4 . the charge carrier mobility of the regioregular polymer can be greater than the charge carrier mobility of a regiorandom polymer of similar composition . embodiments of the polymer may be incorporated in electronic devices . examples of electronic devices include , but are not limited to , field effect transistors , organic photovoltaic devices , polymer light emitting diodes , organic light emitting diodes , organic photodetectors and biosensors . the electronic devices can be solution coated , where the solution coating process can be , but is not limited to , the following : spin coating , ink jet printing , blade coating , dip coating , spraying coating , slot coating , gravure coating or bar coating . the present invention may be better understood by referring to the accompanying examples , which are intended for illustration purposes only and should not in any sense be construed as limiting the scope of the invention . to develop a region regular structure , the functionalized donor - acceptor ( da ) monomer 2 was targeted as a polymerization precursor . the more stable tributyltin was used as the functional group in the cdt unit because trimethyltin is not very stable during the purification procedure . an optimized stille cross - coupling procedure ( scheme 1 ) was conducted in comparatively mild reaction condition as low as 70 ° c ., which would allow for the regioselectively more preferred reaction at the c4 - position of br / pt to form da monomers 2a and 2b since more forcing conditions were needed for the c7 - position . it was found that higher temperatures result in relatively complex mixtures that require tedious separation procedures . the isolation of 2a and 2b followed by microwave assisted stille self - polymerization with ph ( pph 3 ) 4 as catalyst in xylenes afforded regioregular p1a and p1b with precisely controlled pt regularity along polymer backbone . it was found that p1b with longer alkyl side chain yielded a higher molecular weight of 28 . 1 kda than p1a with shorter alkyl side chains ( 15 . 4 kda ), a likely result of increased solubility during the polymerization reaction . alternatively , the coupling of 1a and 1b with 2 equivalents of ptbr 2 and regioselective reaction of ptbr 2 in c4 - position can lead to the symmetric acceptor - donor - acceptor ( ada ) 3a and 3b ( scheme 2 ) in high yield , respectively . two single sharp resonances at 8 . 57 ppm ( h in pt unit ) and 8 . 57 ppm ( h in cdt unit ) in the 1 h nmr spectra of both 3a and 3b match very well with their symmetric structures . microwave assisted stille polymerization of 3a and 3b with distannylated cdt monomer 4a and 4b yielded regiosymmetric polymers with high molecular weights of 27 . 1 kda and 55 . 9 kda for p2a and p2b , respectively . for comparison , the regiorandom copolymers p3a and p3b ( scheme 3 ), in which the pyridal - n atom in the pt unit is randomly aligned along the polymer backbone , were synthesized via a one - pot polymerization of ptbr 2 with distannyl cdt 4a or 4b . the obtained p3a and p3b have molecular weights of 20 . 0 kda and 40 . 2 kda , respectively . to gain insight into the regioregularity of the polymer structures , high temperature 1 h nmr spectroscopy was utilized ( fig1 ). the experiments where performed in deuterated tetrachloroethane ( d - tce ) at 110 ° c . for all the three polymers p1b , p2b and p3b , the resonance at approximately δ 8 . 99 ppm could be assigned to the proton in pt unit , and the signal at 8 . 67 ppm could be assigned to the proton on the cdt moiety closest to the n atom of pt unit . the peaks from the proton in cdt unit situated away from the pt unit show slightly different chemical shifts for p1b ( 8 . 14 ppm ), p2b ( 8 . 16 ppm ) and p3b ( 8 . 15 ppm ). in comparison to the narrow peaks for well - ordered p1b and p2b , the random p3b exhibits much broader peaks which might be generated from the complicated environment of the proton in cdt unit . the influence of the regioregular structure on the effective n - conjugated properties could also be recognized in the uv - vis - near ir absorption of the three classes of polymers ( fig2 ). in o - dichlorobenze solution and as thin films , the maximum absorption ( λ max ) exhibits a gradual bathochromic shift from 825 nm for random p3a to 915 nm of regular p1a , and that of p2a lies in - between . comparing the solution and film spectra , an approximate 50 nm bathochromic shift is observed when transitioning from solution to film , which could be attributed to the polymer interchain self - aggregation . p1b , p2b and p3b with c16 side chains displayed 20 - 30 nm shift ( fig4 ) to low energy wavelength , such shift could be attributed to the higher molecular weight and longer conjugation along polymer backbones . the optical band - gaps determined from the onset of film absorption were in range of 1 . 09 - 1 . 17 ev for all polymers ( table 3 ). heating the o - dcb solutions to 110 ° c . did not distinctly change the absorption profile of the ordered p1a and p2a . however , the random p3a exhibited a 30 nm blue - shift with respect to the 25 ° c . solution ( fig4 ), possibly indicating the breakup of the aggregates at this temperature . moreover , the absorption profiles after thermal annealing the films at 110 ° c . for 15 min . are very similar to the as casted films for all resulted polymers , with no distinct phase transition up to 300 ° c . by differential scanning calorimetry ( dsc ) measurement for all polymers ( fig5 ), which might indicate the weak interchain π - π stacking in films . the electrochemical properties of all polymers were investigated to gain insight into the affect of polymeric structure on the frontier molecular orbitals . full details on the cyclic voltammetry ( cv ) measurements can be found in the supporting information in example 2 ( fig6 and table 9 ). from the data presented in table 4 , it is clear the regioregularity of polymer backbone has minimal affect on the lowest unoccupied molecular orbital ( lumo ) level , while the highest occupied molecular orbital ( homo ) level energy is decreased with decreasing backbone order . the increase of the electrochemical band - gap of the random p3a and p3b compared to p2 and p1 , again implies less effective charge localization along the polymer backbone . the larger electrochemical band - gap in comparison to the optical band gap could be attributed to the interfacial barrier for charge injection during the cv measurements . next , the impact of the backbone structure on the charge carrier mobility was investigated . considering that the low - lying lumo energy level of polymer will improve electron injection and allow for effective electron transport , ambipolar ofets based on these polymers were investigated as shown in fig3 . bottom gate , top contact fets with structure of si / sio 2 / passivation layer / polymer ( p1a , p2a or p3a )/ ag were fabricated by spin - coating from polymer solution on a highly n - doped silicon wafer with 200 nm of thermally - grown sio 2 gate dielectrics passivated by ppcb or ots - 8 . ( fig7 and 8 ). distinct ambipolar characteristics were found at various thermal annealing temperatures . it is noticeable that both p1a and p2a exhibit higher charge mobility than that of the random copolymer p3a ( table 5 ). the strongly dependent of mobility of p1a on the annealing temperature was found . the best efficiency was obtained after thermal annealing of the device at 130 ° c ., and the hole and electron mobility passivated by ppcb amounts to 2 . 2 × 10 − 2 and 1 . 2 × 10 − 1 cm 2 v − 1 s − 1 , respectively , which is much higher than that from as - cast films ( table 6 ). moreover , for fet based on p2a with ots - 8 passivation layer , the device also shows evident ambipolar behavior , exhibiting a hole and electron mobility of 9 . 4 × 10 − 2 and 3 . 1 × 10 − 3 cm 2 v − 1 s − 1 upon ppcb passivation , which is also much higher than that of the random p3a ( table 7 ). the distinct improvement of charge carrier mobility might be attributed to a more uniform orientation of the polymer chains in the solid - state . the on / off ratio of the top contact device with silver electrode is approximately 500 . in order to achieve a higher on / off ratio , gold with a deeper work function was selected as electrode and moreover , bottom gate , and bottom contact fets were fabricated based on polymers with c16 side chain ( fig9 ). it was found that after thermal annealing at 110 ° c . for 10 min , the hole mobility reached 0 . 15 and 0 . 14 cm 2 v − 1 s − 1 for p1b and p2b , respectively , which are much higher than the 0 . 025 cm 2 v − 1 s − 1 obtained by random copolymer p3b . the current on / off ratios for all fets are improved to ˜ 10 4 for all devices ( table 8 ). in summary , cdt and pt based narrow band - gap polymers with well - ordered main chain were prepared by precisely controlled regioselective chemistry . the resulted copolymers with regioregular structures show much longer conjugation length and better charge localization along the polymer backbone . the low - lying lumo energy levels were realized for all polymers with the strong electron pt as acceptor , which resulted in the emergence of ambipolar properties for ofet devices . it was found that the regioregular polymers show much higher mobilities than the random copolymers under different ofet device configurations . nuclear magnetic resonance ( nmr ) spectra were obtained on bruker avance dmx500 mhz spectrometer . microwave assisted polymerizations were performed in a biotage initiator tm microwave reactor . gel permeation chromatography ( 135 ° c . in 1 , 2 , 4 - trichlorobenzene ) was performed on a polymer laboratories pl220 chromatograph . differential scanning calorimetry ( dsc ) was determined by a ta instruments dsc ( model q - 20 ) with about 5 mg polymers samples at a rate of 10 ° c ./ min in the temperature range of − 20 to 300 ° c . uv - vis absorption spectra were recorded on a shimadzu uv - 2401 pc dual beam spectrometer . cyclic voltammetry ( cvs ) measurements were conducted using a standard three - electrode configuration under an argon atmosphere . a three - electrode cell equipped with a glassy carbon working electrode , a ag wire reference electrode , and a pt wire counterelectrode was employed . the measurements were performed in absolute acetonitrile with tetrabutylammonium hexafluorophosphate ( 0 . 1 m ) as the supporting electrolyte at a scan rate of 50 - 100 mv / s . polymer films were drop - cast onto the glassy carbon working electrode from a 2 mg / ml chloroform solution . the ferrocene / ferrocenium ( fc / fc + ) redox couple was used as an internal reference ( see fig6 and table 9 ). a dry three - neck round bottom flask was equipped with a schlenk adapter , dropping funnel , and rubber septum . under nitrogen , 4 , 4 - didodecyl - 4h - cyclopenta [ 1 , 2 - b : 5 , 4 - b ] dithiophene ( 0 . 51 g , 1 mmol ) was dissolved in dry thf ( 12 ml ) and cooled − 78 ° c . using a dry ice / acetone cold bath . under nitrogen , a solution of t - butyllithium ( 1 . 7 m in pentane , 1 . 25 ml , 2 . 1 mmol ) was added dropwise over 15 minutes to the reaction vessel . the reaction was stirred at − 78 ° c . under nitrogen for one hour and at 25 ° c . for 5 hours . then tributyltin chloride ( 0 . 81 g , 2 . 5 mmol ) was added dropwise over 5 minutes to the reaction vessel via syringe at − 78 ° c . the reaction was stirred at − 78 ° c . under nitrogen for 1 hour and subsequently warmed to room temperature and stirred overnight . the mixture was then poured into deionized water ( 3 × 100 ml ) and the organic phase was extracted with hexanes ( 3 × 100 ml ). the organic phases were collected and washed with deionized water ( 5 × 100 ml ), dried over sodium sulphate , filtered , and concentrated . the crude product was purified by flash column chromatography ( silica should be pretreated with 10 v / v % triethylamine / hexane solution ) and dried under high vacuum to give 1 . 04 g of final product as yellowish oil , yield 95 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 6 . 93 ( s , 2h ), 1 . 81 - 1 . 78 ( m , 4h ), 1 . 61 - 1 . 56 ( m , 12h ), 1 . 36 - 1 . 08 ( m , 60h ), 0 . 98 - 0 . 75 ( m , 28h ). a dry three - neck round bottom flask was equipped with a schlenk adapter , dropping funnel , and rubber septum . under nitrogen , 4 , 4 - didodecyl - 4h - cyclopenta [ 1 , 2 - b : 5 , 4 - b ] dithiophene ( 0 . 63 g , 1 mmol ) was dissolved in dry thf ( 12 ml ) and cooled − 78 ° c . using a dry ice / acetone cold bath . under nitrogen , a solution of t - butyllithium ( 1 . 7 m in pentane , 1 . 25 ml , 2 . 1 mmol ) was added dropwise over 15 minutes to the reaction vessel . the reaction was stirred at − 78 ° c . under nitrogen for one hour and at 25 ° c . for 5 hours . then tributyltin chloride ( 0 . 81 g , 2 . 5 mmol ) was added dropwise over 5 minutes to the reaction vessel via syringe at − 78 ° c . the reaction was stirred at − 78 ° c . under nitrogen for 1 hour and subsequently warmed to room temperature and stirred overnight . the mixture was then poured into deionized water ( 3 × 100 ml ) and the organic phase was extracted with hexanes ( 3 × 100 ml ). the organic phases were collected and washed with deionized water ( 5 × 100 ml ), dried over sodium sulphate , filtered , and concentrated . the crude product was purified by flash column chromatography ( silica should be pretreated with 10 v / v % triethylamine / hexane solution ) and dried under high vacuum to give 1 . 14 g of final product as yellowish oil , yield 95 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 6 . 98 ( s , 2h ), 1 . 86 ( m , 4h ), 1 . 78 - 1 . 52 ( m , 12h ), 1 . 46 - 1 . 12 ( m , 80h ), 1 . 01 - 0 . 88 ( m , 24h ). 13 c nmr ( 125 mhz , cdcl 3 ) ( ppm ): 158 . 34 , 140 . 37 , 133 . 89 , 127 . 78 , 50 . 13 , 35 . 90 , 32 . 76 , 30 . 02 , 29 . 68 , 28 . 20 , 27 . 80 , 27 . 75 , 27 . 55 , 27 . 46 , 27 . 18 , 27 . 09 , 27 . 00 , 25 . 94 , 25 . 52 , 25 . 33 , 25 . 30 , 25 . 07 , 24 . 94 , 23 . 37 , 22 . 76 . to a solution of 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 0 . 28 g , 0 . 95 mmol ) and 1a ( 1 . 04 g , 0 . 95 mmol ) in freshly distilled toluene ( 10 ml ) was added pd ( pph 3 ) 4 ( 109 . 8 mg , 0 . 095 mmol ) under nitrogen , and then capped with a rubber septum . the reaction mixture was stirred at 75 ° c . for 10 hours . the solvent was removed and purified by column chromatography ( silica was pretreated by 10 v / v % triethylamine / hexane solution ) with hexane as eluent . the column separation was repeated for 3 times to give 0 . 31 g of viscous purple oil , yield 30 %. 1 h nmr ( 500 mhz , cd 2 cl 2 ) δ ( ppm ): 8 . 55 ( s , 1h ), 8 . 53 ( s , 1h ), 7 . 01 ( s , 1h ), 1 . 95 - 1 . 91 ( m , 4h ), 1 . 63 - 1 . 56 ( m , 6h ), 1 . 37 - 1 . 31 ( m , 6h ), 1 . 26 - 1 . 12 ( m , 42h ), 1 . 08 - 0 . 97 ( m , 4h ), 0 . 91 - 0 . 82 ( m , 15h ); 13 c nmr ( cdcl 3 , 125 mhz ) δ ( ppm ): 163 . 11 , 160 . 01 , 156 . 33 , 148 . 10 , 147 . 92 , 145 . 92 , 143 . 99 , 142 . 26 , 141 . 81 , 140 . 27 , 129 . 80 , 127 . 62 , 106 . 17 , 37 . 85 , 31 . 88 , 29 . 96 , 29 . 61 , 29 . 52 , 29 . 34 , 29 . 31 , 28 . 98 , 27 . 21 , 24 . 57 , 22 . 66 , 13 . 85 , 13 . 44 , 10 . 95 . to a solution of 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 0 . 28 g , 0 . 95 mmol ) and 1b ( 1 . 14 g , 0 . 95 mmol ) in freshly distilled toluene ( 10 ml ) was added pd ( pph 3 ) 4 ( 109 . 8 mg , 0 . 095 mmol ) under nitrogen , and then capped with a rubber septum . the reaction mixture was stirred at 75 ° c . for 10 hours . the solvent was removed and purified by column chromatography ( silica was pretreated by 10 v / v % triethylamine / hexane solution ) with hexane as eluent . the column separation was run for 3 times to give 268 mg of viscous purple oil , with yield of 25 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 8 . 92 ( s , 1h ), 8 . 49 ( s , 1h ), 7 . 39 ( s , 1h ), 2 . 21 ( m , 4h ), 1 . 77 ( m , 6h ), 1 . 54 - 1 . 25 ( m , 68h ), 1 . 12 - 1 . 01 ( m , 15h ). 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 163 . 10 , 160 . 00 , 156 . 32 , 148 . 09 , 147 . 92 , 145 . 93 , 144 . 00 , 142 . 24 , 141 . 83 , 140 . 28 , 129 . 79 , 127 . 62 , 106 . 17 , 53 . 53 , 37 . 86 , 31 . 92 , 29 . 97 , 29 . 66 , 29 . 63 , 29 . 59 , 29 . 54 , 29 . 42 , 29 . 39 , 29 . 35 , 29 . 32 , 29 . 29 , 29 . 02 , 28 . 99 , 27 . 21 , 24 . 58 , 22 . 69 , 22 . 65 , 13 . 88 , 13 . 45 , 10 . 96 . to a solution of 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 0 . 22 g , 0 . 75 mmol ) and 1a ( 0 . 27 g , 0 . 25 mmol ) in freshly distilled toluene ( 10 ml ) was added pd ( pph 3 ) 4 ( 28 . 9 mg , 0 . 025 mmol ) under nitrogen . the reaction mixture was stirred at 75 ° c . for 48 hours . then the solvent was removed and the mixture was purified by column chromatography with chloroform / hexane ( from 0 to 60 v / v %). then the crude product was precipitated from dichloromethane and methanol to give 0 . 17 mg of purple oil , yield 72 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 8 . 63 ( s , 2h ), 8 . 57 ( s , 2h ), 2 . 06 - 2 . 03 ( m , 4h ), 1 . 26 - 1 . 13 ( m , 40h ), 1 . 09 ( t , j = 4 . 0 hz , 6h ); 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 162 . 05 , 156 . 40 , 147 . 88 , 147 . 69 , 146 . 03 , 143 . 60 , 143 . 09 , 126 . 80 , 107 . 39 , 54 . 63 , 37 . 83 , 31 . 87 , 29 . 96 , 29 . 63 , 29 . 59 , 29 . 56 , 29 . 52 , 29 . 34 , 29 . 31 , 24 . 66 , 22 . 66 , 14 . 10 . to a solution of 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 0 . 44 g , 1 . 5 mmol ) and 1b ( 0 . 60 g , 0 . 5 mmol ) in freshly distilled toluene ( 10 ml ) was added pd ( pph 3 ) 4 ( 57 . 8 mg , 0 . 05 mmol ) under nitrogen . the reaction mixture was stirred at 75 ° c . for 48 hours . then the solvent was removed and the mixture was purified by column chromatography with chloroform / hexane ( from 0 to 60 v / v %). then the crude product was precipitated from dichloromethane and methanol to give 280 mg of purple solid , yield 53 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 8 . 66 ( s , 2h ), 8 . 59 ( s , 2h ), 2 . 07 ( m , 4h ), 2 . 07 ( m , 4h ), 1 . 32 - 1 . 08 ( m , 56h ), 0 . 89 ( t , j = 6 . 70 hz , 6h ). 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 162 . 04 , 156 . 34 , 147 . 81 , 147 . 59 , 145 . 96 , 143 . 59 , 143 . 13 , 126 . 79 , 107 . 34 , 54 . 60 , 37 . 80 , 31 . 92 , 30 . 04 , 29 . 65 , 29 . 60 , 29 . 35 , 24 . 73 , 22 . 69 , 14 . 13 . a dry three - neck round bottom flask was equipped with a schlenk adapter , dropping funnel , and rubber septum . under nitrogen , 4 , 4 - didodecyl - 4h - cyclopenta [ 1 , 2 - b : 5 , 4 - b ′] dithiophene ( 0 . 51 g , 1 mmol ) was dissolved in dry thf ( 12 ml ) and cooled − 78 ° c . using a dry ice / acetone cold bath . under nitrogen , a solution of t - butyllithium ( 1 . 7 m in pentane , 2 . 35 ml , 4 mmol ) was added dropwise over 15 minutes to the reaction vessel . the reaction was stirred at − 78 ° c . under nitrogen for one hour and stirred at room temperature for 3 hours . under nitrogen , a solution of trimethyltin chloride ( 1 . 0 g , 5 mmol ) in dry pentane ( 2 ml ) was added dropwise over 5 minutes to the reaction vessel at − 78 ° c . the reaction was stirred at − 78 ° c . under nitrogen for 1 hour and subsequently warmed to room temperature and stirred overnight . the mixture was then poured into deionized water ( 3 × 100 ml ) and the organic phase extracted with hexanes ( 3 × 50 ml ). the organic phases were collected and washed with deionized water ( 3 × 50 ml ), dried over sodium sulphate , filtered , and concentrated . the product was dried under high vacuum with agitation for 48 hours to give 0 . 80 g of product as colorless oil , yield 95 %. 1 h nmr ( 500 mhz , cd 2 cl 2 ) δ ( ppm ): 6 . 94 ( s , 2h ), 1 . 79 - 1 . 76 ( m , 4h ), 1 . 29 - 1 . 15 ( m , 36h ), 1 . 08 - 1 . 02 ( m , 4h ), 0 . 88 ( t , j = 6 . 0 hz , 6h ), 0 . 39 ( s , 18h ). a dry three - neck round bottom flask was equipped with a schlenk adapter , dropping funnel , and rubber septum . under nitrogen , 4 , 4 - didodecyl - 4h - cyclopenta [ 1 , 2 - b : 5 , 4 - b ] dithiophene ( 0 . 63 g , 1 mmol ) was dissolved in dry thf ( 12 ml ) and cooled − 78 ° c . using a dry ice / acetone cold bath . under nitrogen , a solution of t - butyllithium ( 1 . 7 m in pentane , 2 . 35 ml , 4 mmol ) was added dropwise over 15 minutes to the reaction vessel . the reaction was stirred at − 78 ° c . under nitrogen for one hour and stirred at room temperature for 3 hours . under nitrogen , a solution of trimethyltin chloride ( 1 . 0 g , 5 mmol ) in dry pentane ( 2 ml ) was added dropwise over 5 minutes to the reaction vessel at − 78 ° c . the reaction was stirred at − 78 ° c . under nitrogen for 1 hour and subsequently warmed to room temperature and stirred overnight . the mixture was then poured into deionized water ( 3 × 100 ml ) and the organic phase extracted with hexanes ( 3 × 50 ml ). the organic phases were collected and washed with deionized water ( 3 × 50 ml ), dried over sodium sulphate , filtered , and concentrated . the product was dried under high vacuum with agitation for 48 hours to give 0 . 92 g of white solid , yield 97 %. 1 h nmr ( 500 mhz , cd 2 cl 2 ) δ ( ppm ): 7 . 03 ( s , 2h ), 1 . 85 ( m , 4h ), 1 . 46 - 1 . 18 ( m , 52h ), 1 . 04 ( m , 4h ), 0 . 92 ( t , j = 6 . 65 hz , 6h ), 0 . 42 ( t , 18h ). 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 160 . 57 , 142 . 11 , 137 . 21 , 129 . 58 , 52 . 21 , 37 . 62 , 34 . 63 , 34 . 57 , 31 . 97 , 31 . 94 , 31 . 59 , 30 . 03 , 29 . 69 , 29 . 63 , 29 . 59 , 29 . 36 , 25 . 24 , 24 . 63 , 22 . 66 , 20 . 42 , 13 . 88 . monomer 2a ( 0 . 16 g , 0 . 16 mmol ) was carefully weighed and added to a 2 - 5 ml microwave tube . the tube was transferred into a glovebox , and then pd ( pph 3 ) 4 ( 4 . 4 mg , 0 . 005 mmol ), and 3 . 2 ml of xylenes were added into the microwave tube . the tube was sealed , removed from the glovebox and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 120 ° c . for 2 min , 160 ° c . for 2 min and 200 ° c . for 40 min . the reaction was allowed to cool leaving a viscous liquid containing some solid material . after the polymerization , 2 - bromothiophene ( 1 . 9 μl 0 . 02 mmol ) and 2 ml of xylenes was added , the mixture was stirred at 110 ° c . for 2 hours . and then tributyl ( thiophen - 2 - yl ) stannane ( 0 . 01 ml , 0 . 04 mmol ) was added dropwise and stirred at 110 ° c . for 2 hours . then the mixture was dissolved in hot 1 , 2 - dichlorobenzene , then precipitated into methanol and collected via centrifugation . the residual solid was loaded into a cellulose extraction thimble and washed successively with methanol ( 3 hrs ), hexanes ( 16 hrs ), and acetone ( 3 hrs ). the remaining polymer was dried on a high vacuum line overnight . yield 92 mg ( 88 %). 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 9 . 00 ( s , 1h ), 8 . 67 ( s , 1h ), 8 . 14 ( s , 1h ), 2 . 30 - 0 . 76 ( m , 50h ). 13 c nmr ( solid - state , 75 mhz ), δ ( ppm ): 159 . 57 , 151 . 45 , 145 . 77 , 142 . 29 , 138 . 67 , 124 . 42 , 116 . 17 , 113 . 81 , 52 . 57 , 36 . 06 , 29 . 83 , 25 . 53 , 22 . 61 , 13 . 84 . monomer 2b ( 128 mg , 0 . 11 mmol ) and pd 2 ( dba ) 3 ( 5 . 2 mg , 0 . 0057 mmol ), p ( o - tol ) 3 ( 6 . 9 mg , 0 . 023 mmol ) and freshly distilled xylenes ( 4 ml ) was added to a 2 - 5 ml microwave tube under nitrogen . the mixture was heated to 95 ° c . on the oil bath and stirred for 12 hours . after that , tributyl ( thiophen - 2 - yl ) stannane ( 20 μl ) was added and the reaction was stirred at 95 ° c . for 6 hours , then 2 - bromothiophene ( 20 μl ) was added and the reaction was stirred for another 6 hours . the mixture was precipitated in methanol , the resulted dark green fibers were collected and was re - dissolved in hot 1 , 2 - dichlorobenzene . then re - precipitated in methanol and collected via centrifugation . the collected solid fibers were loaded into a cellulose extraction thimble and washed successively with methanol ( 6 hours ), acetone ( 6 hours ), hexanes ( 12 hours ) and chloroform ( 24 hours ). the solid residue in the thimble was collected and dried followed by re - dissolved in hot 1 , 2 - dichlorobenzene , filtrated and re - precipitated in methanol . then the resulted dark - green fibers were collected via centrifugation , dried over high vacuum line to give 61 mg of polymers , yield 80 %. 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 8 . 99 ( s , 11 - f ), 8 . 67 ( s , 1h ), 8 . 14 ( s , 1h ), 2 . 26 - 0 . 82 ( m , 66h ). the polymer was prepared following a previously reported microwave assisted polymerization technique . two monomers 3a ( 0 . 18 g , 0 . 19 mmol ) and 4a ( 0 . 17 g , 0 . 20 mmol ) were carefully weighed and added to a 2 - 5 ml microwave tube . the tube was transferred into a glovebox , and then pd ( pph 3 ) 4 ( 9 mg , 0 . 008 mmol ) and 3 ml of xylenes were added into the microwave tube . the tube was sealed , removed from the glovebox and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 120 ° c . for 2 min , 160 ° c . for 2 min and 200 ° c . for 40 min . the reaction was allowed to cool leaving a viscous liquid containing some solid material . after the polymerization , 2 - bromothiophene ( 1 . 9 μl , 0 . 02 mmol ) and 2 ml of xylenes was added , the mixture was stirred at 110 ° c . for 2 hours . and then tributyl ( thiophen - 2 - yl ) stannane ( 0 . 01 ml , 0 . 04 mmol ) was added dropwise and stirred at 110 ° c . for 2 hours . the mixture was dissolved in hot 1 , 2 - dichlorobenzene , then precipitated into methanol and collected via centrifugation . the residual solid was loaded into a cellulose extraction thimble and washed successively with methanol ( 4 hrs ), hexanes ( 16 hrs ), and acetone ( 3 hrs ). the remaining polymer was dried on a high vacuum line overnight . yield 225 mg ( 91 %). 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 8 . 99 ( s , 1h ), 8 . 67 ( s , 1h ), 8 . 16 ( s , 1h ), 2 . 30 - 0 . 72 ( m , 50h ). 13 c nmr ( solid - state , 75 mhz ) δ ( ppm ): 158 . 76 , 151 . 90 , 143 . 27 , 138 . 063 , 123 . 15 , 117 . 44 , 52 . 74 , 36 . 06 , 29 . 75 , 25 . 53 , 22 . 55 , 13 . 78 . monomers 3b ( 158 . 3 mg , 0 . 15 mmol ) and 4b ( 142 . 9 mg , 0 . 15 mmol ) were added to a 2 - 5 ml microwave tube , then pd ( pph 3 ) 4 ( 8 . 7 mg , 0 . 0075 mmol ) and freshly distilled xylenes ( 4 ml ) were added into the microwave tube . the tube was sealed and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 40 min . the reaction was allowed to cool to room temperature , then tributyl ( thiophen - 2 - yl ) stannane ( 20 μl ) was added and the reaction was subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 20 min . after the reaction was cooled to room temperature , 2 - bromothiophene ( 20 μl ) was added and the end - capping procedure was repeated once again . the mixture was precipitated in methanol , collected via centrifugation . the collected solid fibers were loaded into a cellulose extraction thimble and washed successively with methanol ( 6 hours ), acetone ( 6 hours ), hexanes ( 12 hours ), and the polymer comes out with chloroform ( within 2 hours ) from the thimble . chloroform was removed under reduced pressure and resulted dark - green solid was dried over high vacuum line to give 130 mg of polymer , yield 85 %. 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 8 . 99 ( s , 1h ), 8 . 67 ( s , 1h ), 8 . 16 ( s , 1h ), 2 . 30 - 0 . 81 ( m , 66h ). the polymerization was performed following the procedure for p2a in microwave reactor , just replacing monomer 3a by 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 44 . 2 mg , 0 . 15 mmole ). the resulted dark - green solid was dried over high vacuum line to give 91 mg of polymer , yield 80 %. 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 8 . 99 ( s , 1h ), 8 . 67 ( s , 1h ), 8 . 15 ( s , 1h ), 2 . 32 - 0 . 79 ( m , 50h ). 13 c nmr ( solid - state , 75 mhz ) δ ( ppm ): 159 . 04 , 152 . 06 , 142 . 95 , 138 . 39 , 124 . 16 , 117 . 54 , 52 . 87 , 36 . 01 , 29 . 72 , 25 . 67 , 22 . 53 , 13 . 76 . the polymerization was performed following the procedure for p2b in microwave reactor , just replacing monomer 3b by 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 44 . 2 mg , 0 . 15 mmole ). the resulted dark - green solid was dried over high vacuum line to give 101 mg of polymer , yield 86 %. 1 h nmr ( 500 mhz , c 2 d 2 cl 4 , 110 ° c .) δ ( ppm ): 8 . 99 ( s , 1h ), 8 . 67 ( s , 1h ), 8 . 15 ( s , 1h ), 2 . 35 - 0 . 84 ( m , 66h ). to apply the regioregular pt based copolymer in an opv device , we chose indacene - pt based copolymers due to ( 1 ) the broad narrow - bandgap absorption , ( 2 ) the two thiophene rings rigidified together with a central phenyl ring , which can provide strong intermolecular interactions for ordered packing to improve the charge carrier mobility , and ( 3 ) the low - lying homo level of the copolymer will provide high open - circuit voltage ( v oc ) ( see jen et al . [ 11 ]) as shown in scheme 4 , the copolymerization of dibromo monomer br - pt - idt - pt - br ( m2 ) with bis ( stannyl ) monomer me 3 sn - idt - snme 3 ( m1 ) was based on microwave assisted stille coupling reaction to generate the regioregular indacenothiophene - pt based copolymer ( pipt - rg ), which has the n - atom in the pt units selectively faced to the same indacene core . the reference polymer ( pipt - ra ) was synthesized based on microwave assisted step - growth stille copolymerization of m1 and 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( ptbr 2 ), thus providing the polymer with the n - atom in the pt units randomly distributed along the polymer main chain . both copolymers were purified by soxhlet extraction using methanol , acetone , hexane and finally collected by chloroform . the polymer structures are shown in scheme 5 . the number average molecular weight ( m n ) estimated by gel permeation chromatography ( gpc ) with chloroform as eluent and linear polystyrene as the reference at 35 ° c . is 68 kda ( pdi = 2 . 4 ) for pipt - rg and 59 kda ( pdi = 2 . 5 ) for pipt - ra ; the gpc profiles are shown in fig1 . in contrast , gpc in 1 , 2 , 4 - trichlorobenze ( 1 , 2 , 4 - tcb ) as eluent at 150 ° c . gave 46 kda and 42 kda for pipt - rg and pipt - ra , with a polydispersity of 2 . 3 and 2 . 8 , respectively . the slightly lower mn can be attributed to less aggregation in high temperature 1 , 2 , 4 - tcb solution . interestingly , both copolymers exhibited excellent solubility of higher than 15 mg / ml in xylenes , chloroform , chlorobenzene as well as 1 , 2 - dichlorobenzene , which provides the opportunity to fabricate thick films based solution process procedures . no noticeable phase transitions were observed by differential scanning calorimetry up to 300 ° c . in both cases ( fig1 ). uv - vis absorption profiles of pipt - rg and pipt - ra in thin films are shown in fig1 . the absorption profile shapes are essentially the same for both copolymers . the short wavelength absorption bas (˜ 417 nm ) is assigned to a delocalized excitonic π - π * transition and the long wavelength absorption band (˜ 715 nm ) is ascribed to intramolecular charge transfer ( ict ) interactions between the donor and acceptor moieties . however , the absorption intensity of pipt - rg is much stronger than that of pipt - ra , indicating a much higher molar absorption coefficient of pipt - rg . the optical band gaps ( e g ) calculated from the absorption onset are determined to be 1 . 60 ev for pipt - rg , which is slightly lower than that of 1 . 62 ev for pipt - ra . cyclic voltammetry ( cv ) and ultraviolet photoelectron spectroscopy ( ups ) were employed to evaluate the oxidation / reduction properties and electrical stability of the polymers . as can be seen in the cv curves in fig1 a , the onset of reduction ( e red ) of the two copolymers were nearly identical and was located at about − 1 . 20 v versus ag / ag + , while the onset of oxidation ( e ox ) were 0 . 45 v and 0 . 55 v for pipt - rg and pipt - ra , respectively . the slightly higher e ox of pipt - ra to that of pipt - rg might be attributed to the more disordered vector of the pt unit along the polymer main chain , which would disturb the π - conjugated electron distribution along the polymer backbone leading to a slightly raised e ox . the highest occupied molecular orbital energy level ( e homo ) and the lowest unoccupied molecular orbital energy level ( e lumo ) were calculated from the e ox and e red , on the basis of the assumption that e homo of ferrocene / ferrocenium ( fc / fc + ) is at 4 . 8 ev relative to vacuum . the calculated e homo are − 5 . 25 ev and − 5 . 35 ev for pipt - rg and pipt - ra , respectively , and the e lumo are both at − 3 . 60 ev . this is understandable since for such “ donor - acceptor ” based copolymers , the lumo is mainly located in the acceptor and the homo is well - delocalized along the conjugated backbone , thus the two copolymers exhibited nearly identical e lumo while slightly different e homo . further evaluation by ultraviolet photoelectron spectroscopy ( ups ) measurements ( fig1 b ) demonstrated that the e homo of the two copolymers are quite similar , located at − 5 . 31 ev and − 5 . 33 ev for pipt - rg and pipt - ra , respectively , nevertheless , the relatively low - lying e homo indicated that high v oc could be realized . the field - effect hole mobilities of pipt - rg and pipt - ra were extracted from the transfer characteristics ( fig1 ) of field - effect transistors ( fets ) fabricated with bottom contact , bottom gate geometry using au electrodes . it was noted that the calculated mobilities for pipt - rg at room temperature of 0 . 13 cm 2 / vs improved to 0 . 18 and 0 . 20 cm 2 / vs after thermal annealing at 100 ° c . and 150 ° c . for 10 min , respectively . these are higher than for devices prepared under the same conditions with a pipt - ra copolymer film of 0 . 04 cm 2 / vs at room temperature , and 0 . 09 and 0 . 04 cm 2 / vs attained after thermal annealing at 100 ° c . and 150 ° c . for 10 min , respectively . the higher carrier mobility achieved with regioregular pipt - rg than the regiorandom counterpart pipt - ra indicates that better charge transport in the active layer could be achieved . the detailed fet data were summarized in table 10 . the microstructures of two copolymer films were investigated by grazing incident x - ray diffraction ( xrd ). the samples were prepared on the top of ( n - decyl ) trichlorosilane ( dts ) treated silicon substrate according to the same procedure of fet devices . the films were thermally annealed at 100 ° c . for 10 min . as shown in fig1 , the scattering features with two distinct peaks centered at q values of 0 . 42 å − 1 ( spacing of 14 . 9 å ) and 1 . 42 å − 1 ( spacing of 4 . 4 å ) were realized for both copolymers . however , more fine structures could be realized for the random copolymer pipt - ra , which shows small bumpy scattering features with q values of 0 . 63 å − 1 ( spacing of 9 . 9 å ) and 1 . 21 å − 1 ( spacing of 5 . 2 å ). such relatively weak scattering features might be attributed to the combination of various structures in random copolymers . in considering that the copolymers were used as donor materials for bulk heterojunction solar cells , the contact of active layer with following deposited metal is of particular importance . the surface morphologies of copolymer : pc 71 bm ( 1 : 4 in wt : wt ) films were studies by tapping - mode atomic force microscopy ( afm ), and the films were spin - casted from copolymer : pc 71 bm solution on the top of ito / moox layer and followed the optimized conditions for solar cell devices . even though the solar cell devices based on pipt - rg : pc 71 bm as active layer showed much higher power conversion efficiency ( 5 . 1 %) than that of achieved by pipt - ra : pc 71 bm device ( 3 . 4 %), we noted that both films were quite smooth with root - mean - square ( rms ) value ˜ 0 . 3 nm ( fig1 ). to further understand the microstructure differences in both films , we used transmission electron microscopy ( tem ) to investigate the microstructure inside both films . it was realized that both pipt - rg : pc 71 bm ( fig1 a ) and pipt - ra : pc 71 bm ( fig1 b ) films exhibited relatively uniform images . it should be noted that the dark spots with size of 10 ˜ 20 nm in fig1 ( a ) might be attributed to the metallic residue . nuclear magnetic resonance ( nmr ) spectra were obtained on bruker avance dmx500 mhz spectrometer . gel permeation chromatography ( 150 ° c . in 1 , 2 , 4 - trichlorobenzene ) was performed on a polymer laboratories pl220 chromatograph . gpc with chloroform as eluent was performed in chloroform ( with 0 . 25 v / v % triethylamine ) on a waters system , and the molecular weight of polymers were estimated relative to linear ps standards . differential scanning calorimetry ( dsc ) was determined by a ta instruments dsc ( model q - 20 ) with about 5 mg polymers samples at a rate of 10 ° c ./ min in the temperature range of − 20 to 300 ° c . uv - vis absorption spectra were recorded on a shimadzu uv - 2401 pc dual beam spectrometer . cyclic voltammetry ( cv ) measurements were conducted using a standard three - electrode configuration under an argon atmosphere . a three - electrode cell equipped with a glassy carbon working electrode , a ag wire reference electrode , and a pt wire counterelectrode was employed . the measurements were performed in absolute acetonitrile with tetrabutylammonium hexafluorophosphate ( 0 . 1 m ) as the supporting electrolyte at a scan rate of 50 - 100 mv / s . polymer films for cv test were drop - casted onto the glassy carbon working electrode from a 2 mg / ml chloroform solution . the absolute energy level of ferrocene / ferrocenium ( fc / fc + ) to be 4 . 8 ev below vacuum . grazing incident x - ray diffraction was performed on rigaku smart instrument . atomic force microscopy ( afm ) was recorded on asylum mfp3d instrument . all the samples were prepared identical to optimized device structure and conditions prior to electrode deposition . transmission electron microscope ( tem ) was performed on fei tecnai g2 sphera microscope instrument . the samples were prepared by spin - casting on the top of glass substrate and floated in water , following by put on the top of copper grid . a dry three - neck round bottom flask was equipped with a schlenk adapter , dropping funnel , and rubber septum . under nitrogen , 2 , 7 - dibromo - 4 , 4 , 9 , 9 - tetrakis ( 4 - hexylphenyl )- 4 , 9 - dihydro - s - indaceno [ 1 , 2 - b : 5 , 6 - b ′] dithiophene ( 1 . 06 g , 1 mmol ) was dissolved in dry ti - if ( 20 ml ) and cooled − 78 ° c . using a dry ice / acetone cold bath . under nitrogen , a solution of n - butyllithium ( 1 . 6 m in hexane , 1 . 50 ml , 2 . 4 mmol ) was added dropwise over 15 minutes to the reaction vessel . the reaction was stirred at − 78 ° c . under nitrogen for one hour . then trimethyltin chloride ( 0 . 60 g , 3 . 0 mmol ) was added dropwise over 5 minutes to the reaction vessel via syringe at − 78 ° c . the reaction was stirred at − 78 ° c . under nitrogen for 1 hour and subsequently warmed to room temperature and stirred overnight . the mixture was then poured into deionized water ( 3 × 100 ml ) and the organic phase was extracted with hexanes ( 3 × 100 ml ). the organic phases were collected and washed with deionized water ( 5 × 100 ml ), dried over sodium sulphate , filtered , and concentrated . the crude product was recrystallized from hexane / ethanol ( 10 / 90 ) and dried under high vacuum to give 1 . 07 g of final product as white needles , yield 87 %. nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 7 . 48 ( s , 2h ), 7 . 21 ( d , 8h ), 7 . 13 ( d , 8h ), 2 . 63 ( t , j = 7 . 75 hz , 8h ), 1 . 66 - 1 . 57 ( m , 8h ), 1 . 42 - 1 . 30 ( m , 24h ), 0 . 89 ( m , 12h ), 0 . 41 ( s , 18h ). 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 157 . 64 , 153 . 75 , 147 . 14 , 142 . 31 , 141 . 90 , 141 . 54 , 134 . 71 , 130 . 44 , 128 . 35 , 128 . 28 , 127 . 81 , 127 . 75 , 117 . 65 , 62 . 19 , 35 . 48 , 31 . 76 , 31 . 66 , 29 . 16 , 22 . 64 , 13 . 89 , − 8 . 39 . hrms ( fd ) m / z , calcd for chemical formula : c 70 h 90 s 2 sn 2 ( m + ): 1232 . 45 . found : 1232 . 5 . to a 10 - 20 ml microwave tube was added m1 ( 0 . 616 g , 0 . 5 mmol ), 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 0 . 295 g , 1 mmol ), pd ( pph 3 ) 4 ( 57 . 8 mg , 0 . 05 mmol ) and freshly distilled toluene ( 10 ml ) under the protection of nitrogen , then the microwave tube was sealed . the microwave assisted stille coupling was performed in the following procedure : 120 ° c . for 10 min , 140 ° c . for 10 min , 160 ° c . for 10 min and 170 ° c . for 40 min . the reaction was cooled down to room temperature , extracted with chloroform ( 100 ml × 3 ), washed with deionized water ( 100 ml × 3 ) and dried over with anhydrous magnesium sulfate . after removing solvent under reduced pressure , the mixture was separated by silica column with hexane / chloroform ( form 100 / 0 to 0 / 100 in v / v ) to give 0 . 553 g of dark - red oil , yield of 83 %. 1 h nmr ( 500 mhz , cdcl 3 ) δ ( ppm ): 8 . 64 ( s , 2h ), 8 . 60 ( s , 2h ), 7 . 65 ( s , 2h ), 7 . 31 ( s , 8h ), 7 . 16 ( s , 8h ), 2 . 61 ( s , 8h ), 1 . 63 ( s , 8h ), 1 . 45 - 1 . 26 ( m , 24h ), 0 . 90 ( s , 121 - 1 ). 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ ( ppm ): 158 . 11 , 156 . 29 , 154 . 63 , 147 . 74 , 147 . 54 , 147 . 38 , 145 . 91 , 143 . 86 , 141 . 84 , 141 . 37 , 136 . 01 , 128 . 69 , 128 . 55 , 127 . 95 , 127 . 95 , 118 . 61 , 107 . 54 , 63 . 27 , 35 . 60 , 31 . 73 , 31 . 35 , 29 . 17 , 22 . 61 , 14 . 11 . hrms ( fd ) m / z , calcd for c 74 h 74 br 2 n 6 s 4 ( m + ): 1334 . 32 . found : 1334 . 3 . monomer m1 ( 123 . 3 mg , 0 . 1 mmol ), m2 ( 133 . 4 mg , 0 . 1 mmol ), pd ( pph 3 ) 4 ( 5 . 8 mg , 0 . 005 mmol ) and freshly distilled xylenes ( 3 ml ) was added to a 2 - 5 ml microwave tube under nitrogen . the tube was sealed and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 120 ° c . for 2 min , 160 ° c . for 2 min and 180 ° c . for 40 min . the reaction was allowed to cool to room temperature , then freshly distilled xylenes ( 2 ml ) and tributyl ( thiophen - 2 - yl ) stannane ( 20 μl ) was added and the reaction was subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 20 min . after the reaction was cooled to room temperature , 2 - bromothiophene ( 20 μl ) was added and the reaction was subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 20 min . the mixture was precipitated in methanol , collected via centrifugation , then re - dissolved in hot 1 , 2 - dichlorobenzene and re - precipitated in methanol and collected via centrifugation . the collected solid fibers were loaded into a cellulose extraction thimble and washed successively with methanol ( 12 hours ), acetone ( 12 hours ) and hexanes ( 12 hours ), and then chloroform ( 2 hours ) to collected the copolymer . the solid residue in the thimble was collected and dried followed by re - dissolved in hot 1 , 2 - dichlorobenzene , filtrated and re - precipitated in methanol . then the resulted dark - green fibers were collected via centrifugation , dried over high vacuum line to give 156 mg of polymers , yield 75 %. gpc with chloroform as eluent showed the mn = 68 kda ( pdi = 2 . 4 ). 1 h nmr ( 500 mhz , 1 , 2 - dichlorobenzene - d 4 , 110 ° c .) δ ( ppm ): 8 . 90 ( s , 1h ), 8 . 84 ( s , 1h ), 8 . 40 ( s , 1h ), 8 . 12 ( s , 1h ), 8 . 04 ( s , 1h ), 7 . 80 - 7 . 50 ( br s , 8h ), 7 . 30 - 7 . 15 ( br s , 8h ), 2 . 70 ( br s , 8h ), 1 . 71 ( s , 8h ), 1 . 55 - 1 . 32 ( m , 24h ), 0 . 98 ( s , 12h ). 13 c nmr ( 125 mhz , 1 , 2 - dichlorobenzene - d 4 , 110 ° c .) δ ( ppm ): 180 . 06 , 169 . 02 , 163 . 49 , 157 . 70 , 141 . 59 , 132 . 15 , 130 . 04 , 129 . 84 , 129 . 71 , 129 . 63 , 129 . 42 , 127 . 32 , 127 . 22 , 127 . 12 , 127 . 05 , 126 . 95 , 126 . 85 , 126 . 75 , 126 . 65 , 126 . 40 , 102 . 74 , 63 . 62 , 35 . 38 , 31 . 49 , 30 . 98 , 30 . 79 , 28 . 88 , 22 . 31 , 13 . 61 . the polymerization was performed following the procedure for pipt - rg in microwave reactor . the monomer m1 ( 246 . 6 mg , 0 . 2 mmol ), and replacing monomer m2 by 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 59 . 0 mg , 0 . 2 mmol ), pd ( pph 3 ) 4 ( 11 . 5 mg , 0 . 01 mmol ) and xylenes ( 3 ml ). the resulted dark - green solid was dried over high vacuum line to give 168 . 5 mg of polymer , yield 81 %. gpc with chloroform as eluent showed the mn = 59 kda ( pdi = 2 . 5 ). 1 h nmr ( 500 mhz , 1 , 2 - dichlorobenzene - d 4 , 110 ° c .) δ ( ppm ): 8 . 86 ( s , 1h ), 8 . 81 ( s , 1h ), 8 . 35 ( s , 1h ), 8 . 12 ( s , 1h ), 8 . 03 ( s , 1h ), 7 . 82 - 7 . 49 ( br s , 8h ), 7 . 36 - 7 . 18 ( br s , 8h ), 2 . 66 ( br s , 8h ), 1 . 70 ( s , 8h ), 1 . 52 - 1 . 38 ( m , 24h ), 0 . 92 ( s , 121 - 1 ). 13 c nmr ( 125 mhz , 1 , 2 - dichlorobenzene - d 4 , 110 ° c .) δ ( ppm ): 180 . 07 , 169 . 03 , 163 . 50 , 157 . 99 , 141 . 56 , 132 . 19 , 130 . 24 , 129 . 94 , 129 . 81 , 129 . 80 , 129 . 58 , 127 . 45 , 127 . 32 , 127 . 22 , 127 . 18 , 127 . 06 , 126 . 97 , 126 . 86 , 126 . 72 , 126 . 51 , 102 . 83 , 63 . 84 , 35 . 39 , 32 . 38 , 31 . 50 , 29 . 10 , 22 . 47 , 13 . 74 . an au film of 75 nm was deposited on a precleaned si substrate with a thin native oxide . a solution containing a mixture of pipt - ra ( or pipt - rg ): pc 71 bm ( 1 : 4 ) in odcb solvent with a concentration of 2 mg / ml was then spin - casted atop the au film . the total time of spin coating was kept at 60 s for the two samples . film fabrication was done in a n 2 - atmosphere glove box . to minimize possible influence by exposure to air , the films were then transferred from the n 2 - atmosphere dry box to the analysis chamber inside an air - free sample holder . subsequently , the samples were kept inside a high - vacuum chamber overnight , to remove solvent . the ups analysis chamber was equipped with a hemispherical electron - energy analyzer ( kratos ultra spectrometer ), and was maintained at 1 . 33 × 10 − 7 pa . the ups was measured using the he i ( hv = 21 . 1 ev ) source , and he electron energy analyzer was operated at constant pass energy of 10 ev . during the measurements , a sample bias of − 9 v was used in order to separate the sample and the secondary edge for the analyzer . in order to confirm reproducibility of ups spectra , we repeated these measurements twice on two sets of samples . semiconducting polymers , 0 . 5 wt % pipt - rg or pipt - ra dissolved in chlorobenzene . the copolymers were stirring under 110 ° c . before usage . heavily doped n - type silicon substrates with 200 nm thermally grown sio 2 were prepared as bottom gate electrode . after sio 2 dielectric was passivated by ots8 ( octyl ( trichlorosilane )), all three polymers were spun onto substrates by 2000 rpm / 1 min . 60 nm thick film was created . coated substrates were sequentially heated under 80 ° c . for 10 min . thermal evaporator was applied to deposit 100 nm metal contacts on polymer layer through a silicon shadow mask . defined channel was 20 μm long and 1 mm wide . devices were tested on a signatone probe station inside a nitrogen glovebox with atmosphere & lt ; 1 ppm oxygen concentration . data were all collected by a keithley 4200 system . mobility was extracted from saturation regime based on the following equation , i d = 1 2 ⁢ μ ⁢ ⁢ c ⁢ w l ⁢ ( v g - v t ) 2 where , w is the channel width ( 1 mm ), l is the channel length ( 20 μm ), μ is the carrier mobility , v g is the gate voltage , and v t is the threshold voltage . the capacitance , c , of the sio 2 is 14 nf / cm 2 . fabrication of pscs : polymer solar cells with conventional device architecture of ito / moo x / polymer : pcbm / al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . moo x film was deposited onto ito substrates by thermal evaporation in a vacuum of about 1 × 10 − 6 torr . the evaporation rate was 0 . 1 å / s . two solutions containing a mixture of pipt - ra : pc 71 bm ( 1 : 4 ) and pipt - rg : pc 71 bm ( 1 : 4 ) in o - dcb with a concentration of 10 mg / ml were spin - casted on top of moo x film , respectively . the thickness of blend films were controlled by the spin - casting speed and optimized at 80 nm . after that , the bhj films were annealing at 100 ° c . for 10 min . finally , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of device was 0 . 106 cm 2 . pscs characterization : the thickness of the multilayer was measured with a profilometer and atomic force microscope ( afm ), respectively . current density - voltage ( j - v ) characteristics were measured using a keithley 2602 source measure unit , under solar simulation conditions of 100 mw / cm 2 am 1 . 5 g using a 300 w xe arc lamp with an am 1 . 5 global filter . the illumination intensity of the solar simulator was measured using a standard silicon photovoltaic with a protective kg1 filter calibrated by the national renewable energy laboratory . devices data : fig1 ( a ) illustrates the characteristics of the optimized bhj solar cell using pipt - rg as donor materials . the optimized blend ratio of pipt and fullerene is 1 : 4 . detailed comparisons of different blend ratio are not shown here . using pipt - rg as donor materials shows a pce of 5 . 5 %. moreover , the ipce spectrum shown in fig1 18 ( b ) is in good agreement with the j - v values . preparation of moo x solution : the aqueous moo x solution was prepared by hydration method according to the procedure reported by liu et al ( fengmin liu , zhiyuan xie , et al . solar energy materials & amp ; solar cells . 2010 , 94 , 94842 - 845 , incorporated by reference herein ). ammonium molybdate (( nh 4 ) 6 mo 7 o 24 ) was dissolved in water to form 0 . 01 mol / l solution , marked as solution a . 2 mol / l hydrochloric acid ( hcl ) water solution was marked as solution b . solution b was dropped into solution a until the ph value of the mixed solution was adjusted between 1 . 5 and 2 . 0 . this mixed solution was marked as solution c , which is the aqueous moo x solution fabrication of pscs ( pre - thermal annealing ): polymer solar cells with conventional device architecture of ito / moo 3 / polymer : pcbm // al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . after treatment with uv / ozone for 20 min , moo x ( filtered at 0 . 45 μm ) was spin - coated from aqueous solution at 5000 rpm for 40 s to form a film of ˜ 8 nm thickness . the substrates were then baked at 160 ° c . for 25 min in air , and moved into a glovebox for spin - casting the active layer . two solutions containing a mixture of pipt - ra : pc 71 bm and pipt - rg : pc 71 bm with different blend ratios in o - dcb with a concentration of 10 mg / ml were spin - casted on top of moo x layer , respectively . the film thickness of ˜ 90 nm was optimized by controlling the spin - casting speed . after that , the bhj films were annealed at 100 ° c . for 10 min . finally , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of the devices was 0 . 106 cm 2 . fabrication of pscs ( post - thermal annealing ): polymer solar cells with conventional device architecture of ito / moo 3 / polymer : pcbm // al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . after treated with uv / ozone for 20 min , moo x ( filtered at 0 . 45 μm ) was spin - coated from aqueous solution at 5000 rpm for 40 to form a film of ˜ 8 nm thickness . the substrates were then barked at 160 ° c . for 25 min in air , and moved into a glovebox for spin - casting the active layer . two solutions containing a mixture of pipt - ra : pc 71 bm and pipt - rg : pc 71 bm with different blend ratio in o - dcb with a concentration of 10 mg / ml were spin - casted on top of moo x layer , respectively . the film thickness of ˜ 90 nm was optimized by controlling the spin - casting speed . after that , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . finally , the devices were annealing at 100 ° c . for 10 min . the active area of device was 0 . 106 cm 2 . fabrication of pscs ( additive ): polymer solar cells with conventional device architecture of ito / moo 3 / polymer : pcbm / al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . after treated with uv / ozone for 20 min , moo x ( filtered at 0 . 45 μm ) was spin - coated from aqueous solution at 5000 rpm for 40 s to form a film of ˜ 8 nm thickness . the substrates were then barked at 160 ° c . for 25 min in air , and moved into a glovebox for spin - casting the active layer . the solutions containing a mixture of pipt - rg : pc 71 bm ( 1 : 4 ) with different amount of additive in o - dcb with a concentration of 10 mg / ml were spin - casted on top of moo x layer , respectively . the film thickness of ˜ 90 nm was optimized by controlling the spin - casting speed . after that , the bhj films were annealing at 100 ° c . for 10 min . finally , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of device was 0 . 106 cm 2 . fabrication of pscs ( cpe ): polymer solar cells with conventional device architecture of ito / moo 3 / polymer : pcbm / al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . after treated with uv / ozone for 20 min , moo x ( filtered at 0 . 45 μm ) was spin - coated from aqueous solution at 5000 rpm for 40 s to form a film of ˜ 8 nm thickness . the substrates were then barked at 160 ° c . for 25 min in air , and moved into a glovebox for spin - casting the active layer . two solutions containing a mixture of pipt - ra : pc 71 bm and pipt - rg : pc 71 bm with different blend ratio in o - dcb with a concentration of 10 mg / ml were spin - casted on top of moo x layer , respectively . the film thickness of ˜ 90 nm was optimized by controlling the spin - casting speed . after that , the bhj films were annealing at 100 ° c . for 10 min . then , cpe was spin - casting on the active layer to form a very thin interfacial layer . finally , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of device was 0 . 106 cm 2 . pscs characterization : the thickness of the multilayer was measured with a profilometer and atomic force microscope ( afm ), respectively . current density - voltage ( j - v ) characteristics were measured using a keithley 2602 source measure unit , under solar simulation conditions of 100 mw / cm 2 am 1 . 5 g using a 300 w xe arc lamp with an am 1 . 5 global filter . the illumination intensity of the solar simulator was measured using a standard silicon photovoltaic with a protective kg1 filter calibrated by the national renewable energy laboratory . device data : fig1 ( a ) illustrates the j - v characteristics of the optimized bhj solar cell based on pipt - ra and pipt - rg as donor materials , respectively . detailed comparisons of different blend ratio are summarized in table 11 . it could be seen that the performance of pipt - rg devices is much better than that of pipt - ra devices , corresponding to pce increases of from 3 . 4 % to 5 . 1 %. from fig1 ( b ) we could see that the ipce spectrum of pipt - rg based devices is more broadened than that of pipt - ra based devices , which is in good agreement with the increased j sc . to achieve a better ff , more fabrication methods are used , such as post - thermal annealing ( annealing devices after evaporation cathode ), adding a different amount of additive ( dio ), and spin - casting cpe as interfacial layer between the active layer and cathode , et al . from a starting rough experiment value showed in fig2 , we find that post - thermal annealing is not as good as the pre - thermal annealing ( annealing active layer before al evaporation ), whereas adding a proper amount of dio to the fresh solution is a good way to get a better morphology of blend film . preparation of zno precursor : preparation of the zno precursor : the zno precursor was prepared by dissolving zinc acetate dihydrate ( zn ( ch 3 coo ) 2 . 2h 2 o , aldrich , 99 . 9 %, 1 g ) and ethanolamine ( nh 2 ch 2 ch 2 oh , aldrich , 99 . 5 %, 0 . 28 g in 2 - methoxyethanol ( ch 3 och 2 ch 2 oh , aldrich , 99 . 8 %, 10 ml ) under vigorous stirring for 12 h for the hydrolysis reaction in air . fabrication of inverted pscs : inverted solar cells were fabricated on ito - coated glass substrates . the ito - coated glass substrates were first cleaned with detergent , ultrasonicated in water , actone and isopropyl alcohol , and subsequently dried overnight in an oven . the zno precursor solution was spin - cast on top of the ito - glass substrate . the films were annealed at 150 ° c . for 1 h in air . the zno film thickness was approximately 30 nm , as determined by a profilometer . the zno - coated substrates were transferred into a glove box . a solution containing a mixture of pipt - rg : pc 71 bm ( 1 : 4 ) in o - dcb with a concentration of 10 mg / ml was spin - casted on top of a zno film with thickness of approximately 80 nm , respectively . the bhj film was heated at 100 ° c . for 10 min . then , a thin layer of moo x film (≈ 6 nm ) was evaporated on top of the bhj layer . finally , the anode ( ag , ≈ 60 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of device was 0 . 05 cm 2 . pscs characterization : the thickness of multilayers was measured with a profilometer and atomic force microscope ( afm ), respectively . current density - voltage ( j - v ) characteristics were measured using a keithley 2602 source measure unit , under solar simulation conditions of 100 mw / cm 2 am 1 . 5 g using a 300 w xe arc lamp with an am 1 . 5 global filter . the illumination intensity of the solar simulator was measured using a standard silicon photovoltaic with a protective kg1 filter calibrated by the national renewable energy laboratory . device data : fig2 ( a ) illustrates the j - v characteristics of the optimized bhj solar cell based on pipt - rg as donor material . the device shows a nice open circle voltage of 0 . 88 v and short circle current of 14 . 1 ma / cm 2 . although the ff is relatively low , the pce is up to 6 . 2 %, which is very comparable to our conventional devices . this consistent value indicated that even when using different device structures , region - regular pidtpt polymer can distinctly improved opv devices . the inventors recognize that achieving structurally more precise narrow band materials is relevant within the context of bulk heterojunction polymer solar cells , where improved charge carrier transport could potentially impart higher short circuit currency ( j sc ) and power conversion efficiencies ( pce ). copolymers based on cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene ( cdt ) as donor showed a relatively low open circuit voltage ( v oc ) of about 0 . 4 v . the inventors realize that replacement of the carbon bridge in cdt unit by a silicon bridge , with the new donor of silolo [ 3 , 2 - b : 4 , 5 - b ′] dithiophene ( sdt ), might decrease the highest occupied molecular orbital ( homo ) energy level , and that opvs incorporating sdt - pt - based conjugated copolymers might show higher voc values than that of cdt - pt copolymers . thus , using of sdt - pt - based regioregular copolymers as the active layer can achieve improved j sc and pce in opvs . monomers 4 , 4 - bis ( 2 - ethylhexyl )- 2 , 6 - bis ( trimethylstannyl )- 4h - silolo [ 3 , 2 - b : 4 , 5 - b ′] dithiophene ( 74 . 4 mg , 0 . 1 mmol ) and 4 , 4 ′-( 4 , 4 - bis ( 2 - ethylhexyl )- 4h - silolo [ 3 , 2 - b : 4 , 5 - b ′] dithiophene - 2 , 6 - diyl ) bis ( 7 - bromo -[ 1 , 2 , 5 ] thiadiazolo [ 3 , 4 - c ] pyridine ) ( 84 . 6 mg , 0 . 1 mmol ) were added to a 2 - 5 ml microwave tube , then pd ( pph 3 ) 4 ( 5 . 8 mg , 0 . 005 mmol ) and freshly distilled xylenes ( 3 ml ) were added into the microwave tube . the tube was sealed and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 40 min . the reaction was allowed to cool to room temperature , then tributyl ( thiophen - 2 - yl ) stannane ( 20 μl ) was added and the reaction was subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 20 min . after the reaction was cooled to room temperature , 2 - bromothiophene ( 20 μl ) was added and the end - capping procedure was repeated once again . the mixture was precipitated in methanol , collected via centrifugation . the collected solid fibers were loaded into a cellulose extraction thimble and washed successively with methanol ( 6 hours ), acetone ( 6 hours ), hexanes ( 12 hours ), and the polymer comes out with chloroform ( within 2 hours ) from the thimble . chloroform was removed under reduced pressure and resulted solid was dried over high vacuum line to final products with yield of 85 %. gpc with 1 , 2 , 4 - trichlorobenzene as eluent at 150 ° c . showed number average molecular weight ( mn ) of 22 kda with polydispersity ( pdi ) of 1 . 9 . monomers 4 , 4 - bis ( 2 - ethylhexyl )- 2 , 6 - bis ( trimethylstannyl )- 4h - silolo [ 3 , 2 - b : 4 , 5 - b ] dithiophene ( 74 . 4 mg , 0 . 1 mmol ) and 4 , 7 - dibromo - pyridal [ 2 , 1 , 3 ] thiadiazole ( 29 . 5 mg , 0 . 1 mmol ) were added to a 2 - 5 ml microwave tube , then pd ( pph 3 ) 4 ( 5 . 8 mg , 0 . 005 mmol ) and freshly distilled xylenes ( 3 ml ) were added into the microwave tube . the tube was sealed and subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 40 min . the reaction was allowed to cool to room temperature , then tributyl ( thiophen - 2 - yl ) stannane ( 20 μl ) was added and the reaction was subjected to the following reaction conditions in a microwave reactor : 80 ° c . for 2 min , 130 ° c . for 2 min , 170 ° c . for 2 min and 200 ° c . for 20 min . after the reaction was cooled to room temperature , 2 - bromothiophene ( 20 μl ) was added and the end - capping procedure was repeated once again . the mixture was precipitated in methanol , collected via centrifugation . the collected solid fibers were loaded into a cellulose extraction thimble and washed successively with methanol ( 6 hours ), acetone ( 6 hours ), hexanes ( 12 hours ), and the polymer comes out with chloroform ( within 2 hours ) from the thimble . chloroform was removed under reduced pressure and resulted solid was dried over high vacuum line to final products with yield of 80 %. gpc with 1 , 2 , 4 - trichlorobenzene as eluent at 150 ° c . showed number average molecular weight ( mn ) of 27 kda with polydispersity ( pdi ) of 2 . 1 . pc 7i bm ( 99 . 5 %) was purchased from nano - c . chlorobenzene ( cb , anhydrous , 99 %) was supplied by sigma - aldrich company . all materials were used as received . the structures of the regiorandom polymer psdtptr - eh and the regioregular polymer psdtpt2 - eh used in this study are shown in scheme 6 . fabrication of pscs : polymer solar cells with conventional device architecture of ito / pedot : pss / psdtpt : pcbm / al were fabricated according to the following procedure . the ito - coated glass substrates were firstly cleaned by ultrasonic treatment in detergent , deionized water , acetone and isopropyl alcohol for 30 minutes each , and subsequently dried in an oven overnight . after treated with uv / ozone for 20 min , pedot : pss ( baytron p vp ai 4083 , filtered at 0 . 45 μm ) was spin - coated from aqueous solution at 4000 rpm for 40 s to form a film of ˜ 40 nm thickness . the substrates were barked at 140 ° c . for 10 min in air , and then moved into a glovebox for spin - casting the active layer . two solution containing with psdtpt2 - eh : pc 71 bm ( 1 : 1 , w / w ) and psdtptr - eh : pc 71 bm ( 1 : 1 , w / w ) in cb with a concentration of 10 mg / ml were then spin - casted on top of pedot : pss layer , which were marked as device i and device ii , respectively . the film thickness of ˜ 80 nm was controlled by adjusting the spin - casting speed . in order to evaporate the solvent quickly , the bhj films were dried at 70 ° c . for 10 min . after that , the cathode ( al , ˜ 100 nm ) was deposited through a shadow mask by thermal evaporation in a vacuum of about 3 × 10 − 6 torr . the active area of device was 0 . 106 cm 2 . pscs characterization : the thickness of the active layer and pedot : pss was measured with a profilometer . current density - voltage ( j - v ) characteristics were measured using a keithley 2602 source measure unit , under solar simulation conditions of 100 mw / cm 2 am 1 . 5 g using a 300 w xe arc lamp with an am 1 . 5 global filter . the illumination intensity of the solar simulator was measured using a standard silicon photovoltaic with a protective kg1 filter calibrated by the national renewable energy laboratory . devices data : fig2 illustrates the characteristics of the two devices , and the detailed comparisons are summarized in table 12 . using the regioregular copolymers , the short circuit current density ( j sc ) of device ii increases as much as four times ( from 2 . 41 to 9 . 03 ma / cm 2 ) compared with that of device i using the regionrandom copolymers . as is known , the j sc is not only determined by the number of absorbed photons , but also heavily influenced by the component morphology in the active layer . therefore , a remarkable increase in j sc for the device ii implies that the morphology of the active layer has been substantially improved . moreover , the open circuit voltage ( v oc ) and fill factor ( ff ) increased slightly , and the power conversion efficiency ( pce ) of device ii is up to 1 . 96 %. high mobility lies in the heart of practical applications for organic electronics . high mobility enables low operating voltage and less energy consumption in organic thin film transistors ( otfts ). recently , narrow bandgap donor - acceptor ( da ) copolymers are attracting researchers &# 39 ; attention . the combination of da moieties on polymer chain can induce preferred charge transfer between da units with different electron affinities . therefore , delocalization , improved transport and higher mobility are expected . an outstanding class of polymers composed of cyclopenta [ 2 , 1 - b : 3 , 4 - b ′] dithiophene ( cdt ) and 2 , 1 , 3 - benzothiadiazole ( bt ) has been reported [ 14 - 18 ]. after replacing bt unit by pyridal [ 2 , 1 , 3 ] thiadiazole ( pt ) with larger electron affinity difference to cdt , higher mobility was demonstrated on regioregular - pcdtpt1 ( rr - p1 ) ( see fig2 ) and regioregular - pcdtpt2 ( rr - p2 ) but not in regiorandom - pcdtptr ( ra - p3 ). ra - p3 only gave μ = 5 × 10 − 3 cm 2 / vs while μ = 0 . 6 and 0 . 4 cm 2 / vs , respectively , were obtained by rr - p2 and rr - p1 [ 19 ]. molecular structures of the three polymers , device architecture , and work functions are shown in fig2 . in order to further increase the mobility , larger molecular weight and films with improved structural order are required . however , to precisely characterize the performance from the different mass distribution of the synthesized polymers , low polydispersity index ( pdi ) is important as well as molecular weight . using gel permeation chromatography ( gpc ), it is possible to fraction different partitions of molecular weight with low pdi from rr - p2 . by controlling collecting time of permeated polymer solution , high molecular weight 300 kda with pdi ≈ 1 . 6 was collected and high mobility , μ = 2 . 5 cm 2 / vs , was demonstrated after annealing . improved alky stacking with annealing temperature was confirmed by a growing peak in x - ray diffraction ( xrd ) spectra . obvious fiber structure was observed after the film was annealed over 300 ° c . thus , the high mobility , over 2 cm 2 / vs , after annealing could be correlated to the higher degree of structural order in films of high molecular weight rr - p2 . to push mobility even higher than 2 . 5 cm 2 / vs , inducing higher molecular weight and more ordering in polymer film are promising . however , to further increase the molecular weight by gpc is impractical because of the required collecting time and the quantity of the fractionated solution . the transfer and output characteristics of the otfts made of rr - p2 are shown in fig2 ( a ) and 24 ( b ) . the polymer film was drop cast on a prepatterned substrate with bottom contact ( bc ) architecture made of gold . the sio 2 gate dielectric was passivated by decyl ( trichloro ) silane ( dts ). fig2 ( a ) shows clear transistor behavior with linear and saturation regimes and on - off ration 6 × 10 6 . the positive shift of threshold voltage from negative v g to v g = 20 v elucidates the existence of hole traps on the interface of gold and polymer . table 13 is a mobility table showing drop casted films prepared from different concentration solutions after different annealing temperatures . the highest mobility value 2 . 5 cm 2 / vs , was achieved from the film prepared by 0 . 025 wt % solution and annealed at 350 ° c . even though the mobility values continuously increase with annealing temperature , the numbers saturate after 200 ° c ., mainly varying from 1 . 8 to 2 . 3 cm 2 / vs . height and phase images shown in fig2 ( a ) and 25 ( b ) were obtained by atomic force microscopy , showing fiber structure with length 100 to 200 nm after annealing at 350 ° c . xrd spectra with temperature dependence shown in fig2 ( a ) and 26 ( b ) confirms the ordered structure increasing with annealing temperature . the peak at 2θ = 3 . 3 ° can be correlated to 2 . 7 nm alkyl packing . as demonstrated in table 13 , because mobility values obviously increase with annealing temperature , the increasing mobility can be associated with the increasing ordered alkyl packing . to further optimize device performance , contact resistance ( r c ) was also studied . r c shown in fig2 demonstrates a largest r c = 21 . 5 kω at rt , decreases to 5 . 4 kω after 250 ° c . annealing , and increases to 14 . 7 kω after annealed at 350 ° c . r c was significantly reduced by factor 4 after annealed at 250 ° c . the increase of r c after 350 ° c . annealing could come from possible thermal decomposition of the polymer films that degrades the interface between polymer and metal contact . through comparing the temperature dependence among table 13 , afm images in fig2 , and xrd spectra in fig2 , we concluded the high mobility over 2 cm 2 / vs was from the ordered packing of the high molecular weight rr - p2 after annealing . in order to advance the performance of this polymer system , higher molecular weight and more ordering in polymer film are both important . pcdtpt2 ( p2 ) was originally synthesized with 55 kda and pdi & gt ; 4 . to collect high molecular weight p2 by gel permeated chromatography ( gpc ), 75 mg p2 was dissolved in chloroform ( 0 . 25 % triethylamine ) with 1 mg / ml concentration . permeated solution was collected within 6 sec and produced p2 with 300 kda and pdi = 1 . 6 . after drying , then , the high molecular weight p2 was dissolved in chlorobenzene with 0 . 1 , 0 . 075 , 0 . 05 , and 0 . 025 wt % for drop casting on bottom contact substrates passivated by decyl ( trichloro ) silane . the casted substrates were kept in a glovebox with oxygen level less than 2 ppm , drying for 6 hours . all devices were tested in a nitrogen environment and data were collected by keithley 4200 . the following publications are incorporated by reference herein in their entireties : 1 . 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