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Synthetic
Metals
jou rn a l h o m e pa ge : w w w . e l s e v i e r . c o m / l o c a t e / s y n m e t
1-(3-Methoxycarbonyl)propyl-2-selenyl-[6,6]-methanofullerene
as
a
n-Type
Material
for
Organic
Solar
Cells
Shih-Ching
Chuang
a,∗,
Chih-Wei
Chiu
a,
Shang-Chieh
Chien
b,
Chih-Wei
Chu
c,
Fang-Chung
Chen
b,∗∗ aDepartmentofAppliedChemistry,NationalChiaoTungUniversity,Hsinchu30010,Taiwan,ROCbDepartmentofPhotonicsandInstituteofElectro-OpticalEngineering,NationalChiaoTungUniversity,Hsinchu30010,Taiwan,ROC cResearchCenterforAppliedSciences,AcademiaSinica128Sec.2,AcademiaRd.,Nankang,Taipei11529,Taiwan
a
r
t
i
c
l
e
i
n
f
o
Articlehistory: Received24March2011
Receivedinrevisedform18April2011 Accepted19April2011
Available online 20 May 2011 Keywords:
[60]Fullerene Photovoltaic Device Organicsolarcell P3HT
a
b
s
t
r
a
c
t
Demandforgreenandrenewableenergyisstimulatingresearchintofuturematerialsforenergy produc-tion.Thinfilmsofmaterialspossessingbothelectronacceptinganddonatingfunctionsplayauniquerole insolarenergytechnologybecauseoftheirlightweight,flexibility,andeconomical,low-temperature,and large-areafabrication.A[60]fullerenederivative,[6,6]-2-selenyl-C61-butyricacidmethylester(SeCBM),
hasbeensynthesizedinthreesteps,namelythroughFriedel–Craftsacylationofselenophene, hydra-zoneformationandBamford-Stevenreaction.OrganicphotovoltaicdeviceincorporatingSeCBMandthe conductingpolymerP3HTexhibitedanaveragepowerconversionefficiencyof3.26%andachampion efficiencyashighas3.81%underAM1.5Girradiation.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Demandforgreenandrenewableenergyisstimulatingresearch intofuturematerialsforenergyproduction.Solarenergy technol-ogyisarguablythecleanestapproachtowardpowergeneration. Thinfilms of materials possessing both electron accepting and donating functionsplay a unique role in solar energy technol-ogy because of their light weight, flexibility, and economical, low-temperature, and large-area fabrication. Because fullerene derivativesaregoodelectronacceptors[1,2],theyhavebecome usefulmaterialsinthinfilmorganicsolarcells[3–18].Inparticular, thecommercializedfullerenederivativePCBM([6,6]-phenyl-C61 -butyricacidmethylester;[6,6]-3a)isatpresentthemostoften usedn-typematerial instudiesof organicphotovoltaics(OPVs) [19].ImprovedpowerconversionefficiencygenerallyusedPCBM [20,21,8,22–24]ornon-methanofullerenes[25,26]asn-type mate-rials, or alternatively utilized other newly designed polymers [27–33].Severalstructurallysimilarfullerenesalsoexhibit remark-ablephotoconversionefficiencieswhenblendedwithconductive polymers poly(3-hexylthiophene) (P3HT); for example, ThCBM
([6,6]-2-thienyl-C61-butyricacidmethylester;[6,6]-3b)displays
∗ Correspondingauthor.Tel.:+88635731858;fax:+88635723764. ∗∗ Correspondingauthor.Tel.:+88635131484;fax:+88635735601.
E-mailaddresses:[email protected],[email protected]
(S.-C.Chuang),[email protected](F.-C.Chen).
avalueofpowerconversionefficiency(PCE)comparabletothat of[6,6]-3a (ca.4.0%)[34–36].We thoughtthatincorporationof selenyl moiety in thedevicemay improvephotovoltaic perfor-mance.TheLUMOenergylevelsofthefullerenescanbeslightly adjustedthroughhomo-conjugationinthemethanofullerenes[37]. Althoughsyntheticmethodshavebeenavailableforpreparationof
PCBMandThCBM,transferoftheapproachestothesynthesisof
SeCBMislimitedbythepoorreactivityofselenophenefor
function-alization.Inthispaper,wepresentourstudiesindevelopingnovel derivativeofSeCBM([6,6]-2-selenyl-C61-butyricacidmethylester; [6,6]-3c)possessingselenylmoietyandexploringits electrochem-icalpropertiesandphotovoltaicperformanceincorporatedintoan organicsolarcelldevice.
2. Experimental
2.1. Materialandmethods 2.1.1. BF3-mediatedsynthesisof
5-oxo-5-selenophen-2-yl-pentanoicacidmethylester(1c)
Toasealedtubecontainingselenophene(150mg,1.14mmol), methyl5-chloro-5-oxovalerate(224mg,1.36mmol)and1.2equiv of BF3 etherate inanhydrous 1,2-dichloroethane washeatedat 84◦Cfor5hunderargon.Thereactionmixtureswerecooledand pouredontosat.NaHCO3(aq)andextractedwithdichloromethane. TheextractwasdriedwithNa2SO4,andsubjectedtoSiO2 chro-matography to give72% of 1c (251mg) after dryness. Rf: 0.33
0379-6779/$–seefrontmatter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.04.021
Table1
Friedel–Craftsacylationsofselenopheneandthiophenewithmethyl 5-chloro-5-oxovalerate.
Entry Reactanta Reagenta Solvent Temp(◦C) t(h) Yield(%)
1 Selenophene AlCl3 DCM rt 5 48
2 Selenophene BF3 DCM rt 18 60
3 Selenophene BF3 DCE 84 6 72
4 Thiophene AlCl3 DCE rt 5 45
5 Thiophene BF3 DCM rt 5 Trace
6 Thiophene BF3 DCE 84 6 53 a1equivwithrespectivetothatofmethyl5-chloro-5-oxovalerate.
(CH2Cl2). 1H NMR (300MHz, CDCl3): ␦ 2.08 (m, 2H), 2.45 (t, J=7.2Hz,2H),3.00(t,J=7.2Hz,2H),3.68(s,3H),7.37–7.41(m,1H), 7.94(d,J=3.1Hz, 1H),8.37(d,J=5.1Hz,1H).13C NMR(75MHz, CDCl3):␦19.6,32.8,37.2,51.3,130.6,134.1,139.7,150.8,173.3, 193.2.EI-Msm/z:calcdforC10H12O3Se(M+):260.0;found:260.0 (M+),158.9(100%),156.9(48%).HRMS(FAB):calcdforC
10H12O3Se (M+):259.9952;found:259.9954.FT-IR(cm−1)713,1149,1175, 1211,1425,1529,1656,1734,2951,3097. 2.1.2. Synthesisof 5-Selenophen-2-yl-5-(toluene-4-sulfonylimino)-pentanoicacid methylester(2c)
A mixture of 1c (146mg, 0.560mmol), p-toluenesulfonyl hydrazide(127mg,0.680mmol),andMeOH(1mL)wasrefluxed for3.5hunderargon.Tothismixturewasaddedp-toluenesulfonyl hydrazide (127mg, 0.680mmol) again. After 24h, the mixture was cooled to room temperature and added water. The prod-uct was collected by filtration, washed with water, and dried indichloromethane bysodiumsulfate toyield 191mg (79%) of tosylhydrazone2casyellowpowders.m.p.121–122◦C.Rf:0.17 (EA:Hexanes=1:1).1HNMR(600MHz,CDCl 3):␦1.73(m,2H),2.32 (t,J=3.0Hz,2H),2.41(s,3H),2.61(t,J=4.0Hz,2H),3.77(s,3H),7.21 (m,1H),7.29(m,2H),7.34(m,1H),7.89(m,2H),7.93(m,1H),9.12 (s,1H).13CNMR(150MHz,CDCl 3):␦21.1,21.5,26.1,32.0,52.3, 128.0,128.5,129.4,129.7,133.0,135.5,143.8,148.4,151.7,174.7. EI-Msm/z:calcdforC17H20N2O4SSe(M+):428.0;found:428.1(M+), 171.0(100%),91.1(72%).HRMS(EI):calcdforC17H20N2O4SSe(M+): 428.0309;found:428.0303.FT-IR(cm−1)563, 668,707,1168, 1227,1335,1350,1438,1715,1734,2925,2954,3202.
2.2. SynthesisofcompoundSeCBM([6,6]-3c)
Compound2c(43mg,0.10mmol)wasdissolvedin 1.5mLof anhydrouspyridine in a dried two-necked flaskprovided with argon inlet and a magnetic stirring bar. Then, NaOMe (11mg, 0.20mmol) wasadded,andthemixturewasstirredfor 30min.
A solution of 72mg (0.10mmol) of C60 in 8mL of anhydrous 1,2-dichlorobenzenewasadded,and thehomogeneousreaction mixturewasstirredat70◦C for23h. Next,tothis solutionwas added 1equivof NaOMeper hour until 5equivof NaOMe was added.ThecourseofthereactionwasfollowedbyHPLCandTLC (SiO2/toluene)analyses.Themixturewasaddedasmallamount ofhexanestoreducepolarityand thenthemixtures were sub-jectedtoflashchromatography.ThestartingmaterialC60(41mg, 57%)wasfirstrecoveredwithtolueneasinitialeluent.Next, com-pound[5,6]-3c/[6,6]-3c,withratioof13:87,wasisolatedasbrown solids(22mg,23%;53%basedonconvertedC60).Thewhole mix-turewastransformed to[6,6]-3c byirradiation witha halogen lamp.Rf:0.48(toluene).Thescaleofthisreactioncanbeconducted withagram-scaleofC60(1.008g)in110mLof1,2-dichlorobenzene andthisprovided287mgofSeCBM([6,6]-3c)in20%yield(50% basedonconvertedC60;with583mg(54%)recoveredC60). Spec-traldatafor[6,6]-3cfollow.1HNMR(700MHz,CDCl
3):␦2.26(m, 2H),2.59(t,J=7.0Hz,2H),2.96(m,2H),3.7(s,3H),7.36(dd,J=4.2, 6.2Hz,1H),7.66(d,J=4.2Hz,1H),8.17(d,J=6.2Hz,1H).13CNMR (175MHz,CDCl3):␦ 22.51,33.7,34.39,47.87,51.72,80.44,128.54, 132.15, 134.71, 138.14, 138.32, 140.77, 140.97,142.12, 142.15, 142.18, 142.93, 142.96, 143.03, 143.05, 143.07, 143.1, 143.12, 143.8, 143.83, 144.19, 144.51, 144.61, 144.67, 144.72, 144.74, 144.84, 145.08, 145.15, 145.21, 145.24, 145.26,145.69, 145.91, 147.49,148.28,173.49.UV–Vismax()(CHCl3,4.88×10−5M):229 (1.21×105),260(1.56×105), 327(4.68×104), 432(3.49×103), 493(2.26×103).FAB-MS m/z:calcd for C
70H12O2Se (M+):964; found:964.HRMS(FAB):calcdforC70H13O2Se(M++H+):965.0081; found:965.0083.FT-IR(cm−1)526,575,754,1172,1188,1213, 1250,1430,1456,1734,2946,3018.
2.4Thedevicefabricationprocedurewasidenticaltothatused previouslytoobtaindevicesbasedonP3HTand[6,6]-3a[38,39].
3. Resultsanddiscussion
3.1. Synthesisandcharacterization
WepreparedSeCBMstartingwithFriedel–Craftsacylationof selenophene with methyl 5-chloro-5-oxovalerate, mediated by Lewisacids(Table1).Initially,weusedAlCl3tomediatethe acyla-tioninanhydrousCH2Cl2atroomtemperature,butobtainedonly 40–50%yieldsof1c(Table1,entry1)[40].Whenweswitchedto lessacidicBF3·OEt2astheLewisacid,weobtainedhigher acylat-ingyields:60%atroomtemperatureand72%at84◦C(entries2 and3,respectively);thelatterproviding1cinastraightforward mannerandlargequantityinasinglestep.Althoughthis acyla-tionapproachwasagoodalternativeforthelarge-scalesynthesis of1c,thecorrespondingacylationsofthiophenemediatedbyAlCl3
Fig.1. HPLCchromatogramsdisplayingtheratiosof[5,6]and[6,6]isomersobtained atreactiontimesof22hduringthesynthesesofPCBM([6,6]-3a),ThCBM
([6,6]-3b),andSeCBM([6,6]-3c)(Buckyprepcolumn;flowrate,1mLh−1;toluene;30◦C;
detectionwavelength=326nm).
orBF3providedonlymoderateyields(40–53%)of1b(entries4–6). Thenextreactionof1cwithp-tolylsulfonylhydrazinegave2cin goodyield(>90%).
Withprecursor2cavailableinabulkquantity,weperformed theBamford–StevenreactioninthedarktoprepareSeCBM
([6,6]-3c,Scheme1).Underconditionssimilartothoseusedtoprepare [6,6]-3aand[6,6]-3b,wefoundthattheadditionoflargeramounts ofbase(pyridineandNaOMe;>5equivaddedsequentially)was necessarytoachievecomparableyields(ca.40%).Inaverage,we achieved23%isolatedyieldsof[6,6]-3c(53%yieldsbasedon con-verted C60). This was attributed to the fact that precursor 2c incorporatingselenylfunctionalitywasrelativelylessreactiveas comparedtothoseforpreparing[6,6]-3aand[6,6]-3b.
Itwasinterestingtonotethatthe[5,6]-and[6,6]-isomericratios aredramaticallydifferentwhilepreparing[6,6]-3a,[6,6]-3band [6,6]-3b,respectively.FromHPLCanalyticaldataobtainedat22h ofthereactions,wefounda92:8mixtureof[5,6]-3aand[6,6]-3a,
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 800 700 600 500 400 300 200 Wavelength (nm) Absorption
Fig.2.UV–Visspectraof[6,6]-3a(—,5.1×10−5M),[6,6]-3b(---,5.1×10−5M),and
[6,6]-3c(–-–,4.9×10−5M)inCHCl3. -7 10 -2.5 -1.5 -0.5 Potential(V) Current( μ A) [6,6]-3a [6,6]-3b [6,6]-3c
Fig.3.CVtracesof[6,6]-3a(—,0.50mM),[6,6]-3b(---,0.45mM),and[6,6]-3c(– -–, 0.50mM)inanhydrouso-DCB.Scanningrate:50mVs−1.
anda63:37mixtureof[5,6]-3band[6,6]-3b;incontrast,anexcess ofthe[6,6]-3cproduct,witha[5,6]-3c/[6,6]-3cratioof13:87was observed(Fig.1).Whereastheisolatedmixturesof
[5,6]-3a/[6,6]-3aand[5,6]-3b/[6,6]-3bweretransformedtotheir[6,6]-3aand [6,6]-3b adducts,respectively, upon irradiationof theirtoluene solutionswithahalogenlampatadistanceof25cmfor3h,the
3c-[5,6]/3c-[6,6]mixturewasfullytransformedtothe[6,6]-3cisomer undermuchmilderconditions:bymereexposuretoambientlight orbyahalogenlampinfewminutes[41].Transformationofthe [5,6]-isomerto[6,6]-isomerisnecessarybecause[5,6]-isomerisa fully-conjugatedfulleroidthatexhibitslowerLUMOenergylevels andthusrendersittoformloweropen-circuitvoltage(Voc)with P3HTinthedevice.Forexamples,thefirstreductions(with ref-erencetoferrocene/ferrocenium)ofisomericmixturesconsisting of[5,6]-3a/[6,6]-3a(molarratio=92:8)isabout40mVmoreanodic shifttothatofpure[6,6]-3a.ItisnoteworthythatcommercialPCBM
comprisesonlythe[6,6]-isomer.
WecharacterizedSeCBM([6,6]-3c)usingspectroscopic meth-ods.Itsmolecularionappearedatm/z965.0083(HR-FAB+;calcd forC70H13O2Se,965.0081[M+H]+).The13C NMRspectrum sup-portedthestructureofa[6,6]isomericcompound,withthesignal for the C(61) carbon appearing at 47.9ppm and the only sp3 -hybridizedcarbonatomofthefullerene appearingat 80.4ppm. The IR spectrum of [6,6]-3c revealed the presence of an ester moiety at 1734cm−1. UV–Vis spectra of the three compounds [6,6]-3a–c revealed interesting features. Typical absorptions of fullerene mono-adducts appeared at 430nm for [6,6]-3b and [6,6]-3c,whereasthesignalappearedat424nmfor[6,6]-3a.The broadhumpsspanningfrom440to660nmwere hypsochromi-callyshiftedfor[6,6]-3band[6,6]-3c,relativetothatof[6,6]-3a. Thesmall,narrowerhumpsat660–720nmwereevenmore hyp-sochromically shifted for [6,6]-3b and [6,6]-3c. Notably, both
Table2
Half-wavereductionpotentials(V)aof[6,6]-3a–c.
Compound E1 E2 E3
C60b −1.13 −1.50 −1.95 [6,6]-3a −1.206 −1.581 −2.076 [6,6]-3b −1.194 −1.572 −2.066 [6,6]-3c −1.190 −1.569 −2.066
aVersusferrocene/ferrocenium.Conditions:ca.0.50mMC
60,[6,6]-3a,[6,6]-3b,
[6,6]-3cand0.050mMBu4NPF6inanhydrouso-DCB;referenceelectrode:Ag/0.01M
AgNO3and0.050mM(n-Bu)4NClO4inanhydrousMeCN;workingelectrode:glassy
carbon;auxiliaryelectrode:Pt;scanningrate:50mVs−1. bSeeRef.[42].
(a)
0 1 2 3 4 -2.2 -1.7 -1.2 -0.7 -0.2 Potential (V) Current ( μ A) [6,6]-3a [6,6]-3b [6,6]-3c(b)
0 7 -2.5 -1.5 -0.5 0.5 Potential (V) Current ( μ A) [6,6]-3a [6,6]-3b [6,6]-3cFig.4. (a)DPVand(b)OSWVtracesof[6,6]-3a(—),[6,6]-3b(---),and[6,6]-3c (–-–).Squareamplitude:25mV;frequency:15Hz;stepE:4mV.
[6,6]-3band[6,6]-3cexhibitedslightlylargermolarabsorptivities than[6,6]-3abetween420and550nm(Fig.2).
3.2. Redoxproperties
Next, we used cyclic voltammetry (CV), differential pulse voltammetry (DPV) and Osteryoung square wave voltamme-try(OSWV) toexamine theredox properties of [6,6]-3a–c and revealedanysubtlechangesintheirelectronicproperties.Table2 liststhehalf-wavereductionpotentials of[6,6]-3a–crelativeto ferrocene/ferrocenium. Fig.3 displayscyclic voltammograms of [6,6]-3a–cmeasuredatscanningrateof50mVs−1.Thefirst reduc-tivepotentialsof[6,6]-3aisca.12mVmorenegativethanthatof [6,6]-3b.Theselenylfullerene[6,6]-3cdisplayeditsfirsthalf-wave reductionpotentialat−1.190V;thisvalueisca.60mVmore
neg-Table3
Physicaldataofdevicesincorporating[6,6]-3a–candP3HT(1:1,w/w).
Compound Voc Jsc PCE FF [6,6]-3a 0.59 9.00 3.54 66% [6,6]-3b 0.58 9.18 3.02 57% [6,6]-3c 0.55 8.93 3.26 66% -10 -8 -6 -4 -2 0 0.15 0.35 0.55 -0.05 Voltage (V)
Current density (mA/cm
2) [6,6]-3a
[6,6]-3b [6,6]-3c
Fig.5. J–Vcurvesofsolarcellsincorporatingthefullerenederivatives[6,6]-3a, [6,6]-3aand[6,6]-3cwithP3HT.
ative(cathodicshift)thanthatofC60andonly4mVlessnegative
(anodicshift)thanthatof[6,6]-3b,respectively.Thesecond
reduc-tionof[6,6]-3coccurredat−1.569V,whichis12and3mVless
negativethanthoseof[6,6]-3aand[6,6]-3brespectively.
Sincethehalf-wavereductionpotentialdifferencesareminute,
weusedDPV(Fig.4a)andOSWV(Fig.4b)tracestoconfirmthe relativeordersofthesereductionpotentials of[6,6]-3a–c.Their firstreductionpotentialsare−1.196,−1.188and−1.196VbyDPV and−1.202,−1.194and−1.188VbyOSWV,respectively. Accord-ingtoCV,DPV and OSWVanalyses, [6,6]-3aremains tobethe onehaving thehighest LUMOenergylevel (referred toFc/Fc+). ButtheLUMOlevelsof[6,6]-3aand[6,6]-3baretooclosetobe distinguished;theirrelativesorderscouldnotbedetermined accu-rately.Theelectrochemicalstudysuggeststhat[6,6]-3apossesses thehighestLUMOenergylevelamongallthreeofthe[6,6]-isomers [6,6]-3a–c.Becauseoftheopencircuitvoltage(Voc)isdetermined bythedifferencebetweentheHOMOenergylevelofthepolymers andtheLUMOenergyleveloffullerenes.ThehigherLUMOlevels (withmorenegativereductionpotential)ofthefullerene deriva-tivescorrespondtohighervaluesofVocinthefabricateddevices [27,43,44].Thus,wewouldexpectthatdevicesincorporating
[6,6]-3aremainstoexhibitthelargestopen-circuitvoltage(Voc)among thestudiedcompounds.
300 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 IPCE (normalized) Wavelength (nm)
Fig.6.IPCEspectraofthinfilmconsistingof[6,6]-3b/P3HT()and[6,6]-3c/P3HT (䊉).
Fig.7.Atomicforcemicroscopy(AFM)imageofthinfilmwith[6,6]-3c/P3HTasanactivelayer.
3.3. Photovoltaicperformancestudies
Witha largeamountof SeCBMin hand,we fabricated pho-tovoltaicdevices incorporating [6,6]-3a–cand P3HT(1:1, w/w) respectively. We fabricated photovoltaic cells by spin-coating theblendsfromo-DCBsolution.TheOPVs,withlayered config-uration of glass/ITO/PEDOT:PSS/P3HT:fullerenes (15mg/mL 1:1, w/w)/Ca/Al,werefabricatedusingknownmethods[38,39].Table3 summarizesthedeviceperformancesofthesolarcells incorporat-ing[6,6]-3a–candP3HT(seeFig.5forJ–Vplots).Theaveragepower conversionefficiency(PCE)of3.54%forthe[6,6]-3a/P3HT-based deviceiscomparabletoreportedvalues[38];thePCEforthe
[6,6]-3b/P3HT-baseddevicewaslower(3.02%),presumablybecauseof
thepoorersolubilityof[6,6]-3b.However,thedeviceincorporating
SeCBM([6,6]-3c)exhibitedaslightlyhigherPCE(3.26%)thanthat
ofthedevicecontaining[6,6]-3b,featuringVoc,JscandFFof0.55, 8.93,and66%respectively.ThebestPCEwasrecordedat3.81%for [6,6]-3candP3HT(1:1,w/w)!Itisnoteworthythatdevice incorpo-rating[6,6]-3c/P3HTdisplaysslightlyhigheraveragePCE(3.26%) ascomparedtothatincorporating[6,6]-3b/P3HT(3.02%)despite theLUMOenergylevelof[6,6]-3b isslightlyhigher,whichwas likelyattributedtothepoorersolubilityof[6,6]-3b.Thisdifference canalsobeinterpretedfromtheirnormalized incident photon-to-currentconversionefficiency(IPCE)asshowninFig.6.Inthis measurement,thehigherPCEfor[6,6]-3c/P3HTfilmisconfirmed bytheintegrationfrom300to800nm–theoverallintegrationfor [6,6]-3c/P3HTisslightlyhigherthanthatof[6,6]-3b/P3HT.Inthe morphologystudy,thesurfaceofthephotoactivefilmconsistingof [6,6]-3c/P3HTpossesseshomogeneousmorphologieswithslightly higherroughness(rmsroughness=11.1nm),whichisverifiedby atomicforcemicroscopy(Fig.7).Itisinterestingtoobservethat themorphologyisquitesimilartothatdisplayedby[6,6]-3b/P3HT film.[36]
Thedeviceperformanceof[6,6]-3c/P3HTupto3.81%indicates that[6,6]-3ccouldbeservedasanothern-typecandidatematerials forapplicationinOPVs.Onemayarguesthatthestarting mate-rials–selenophene–usedforsynthesisof[6,6]-3ciscostlyand environmentalunfriendlyandthis studywillnotbehelpfulfor greenenergypursuit.However,selenophenecanbepreparedfrom dialkylselenidesorseleniumpowderwithacetyleneinpractical syntheses;thus,itssourceisnotanissue.SeCBM,incorporatinga seleniumatominthemolecule,isnottoxicmaterialbecauseitis nonvolatilewithdecompositiontemperaturegreaterthan360◦C undervacuum.[45,46]
4. Conclusions
Theselenyl-fullerene[6,6]-3ccanbeobtainedinbulkquantities throughsequentialBF3·OEt2-mediatedacylationofselenophene,
hydrazone formation, and Bamford–Steven reaction. A device incorporating[6,6]-3candP3HTexhibitedanaveragePCEof3.26% andchampionefficiencyat3.81%,comparablewiththoseof cor-respondingdevicesbasedonPCBMandThCBM.Ourresultsshow thantheaveragedeviceperformanceincorporatingSeCBM super-sedesthatmadewithThCBMintheactivelayer.
Acknowledgements
We thank the National Science Council for supporting this researchfinancially(NSC962113M009028MY2).
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![Fig. 2. UV–Vis spectra of [6,6]-3a (—, 5.1 × 10 −5 M), [6,6]-3b (- - -, 5.1 × 10 −5 M), and](https://thumb-ap.123doks.com/thumbv2/9libinfo/7490515.115009/3.918.104.387.81.493/fig-uv-vis-spectra-of-m-m-and.webp)
![Fig. 4. (a) DPV and (b) OSWV traces of [6,6]-3a (—), [6,6]-3b (- - -), and [6,6]-3c (– - –)](https://thumb-ap.123doks.com/thumbv2/9libinfo/7490515.115009/4.918.97.425.82.707/fig-dpv-b-oswv-traces-a-b-c.webp)
![Fig. 7. Atomic force microscopy (AFM) image of thin film with [6,6]-3c/P3HT as an active layer.](https://thumb-ap.123doks.com/thumbv2/9libinfo/7490515.115009/5.918.161.752.87.300/fig-atomic-force-microscopy-image-film-active-layer.webp)
