Significant Improvement of Optoelectronic and Photovoltaic Properties by Incorporating Thiophene

15 Pages·2015·2.51 MB·English

Article
Significant Improvement of Optoelectronic and
Photovoltaic Properties by Incorporating
Thiophene in a Solution-Processable D–A–D
Modular Chromophore
AaronM.Raynor1,AkhilGupta1,2,*,ChristopherM.Plummer1,SamL.Jackson1,AnteBilic3,
HemlataPatil1,PrashantSonar4,*andSheshanathV.Bhosale1,*
Received:6October2015;Accepted:25November2015;Published:4December2015
AcademicEditor:SergeiManzhos
1 SchoolofAppliedSciences,TheRoyalMelbourneInstituteofTechnology(RMIT)University,GPOBox2476,
MelbourneVictoria3001,Australia;[email protected](A.M.R.);
[email protected](C.M.P.);[email protected](S.L.J.);[email protected](H.P.)
2 MedicinalChemistry,MonashInstituteofPharmaceuticalSciences,MonashUniversity,
ParkvilleVictoria3052,Australia
3 VirtualNanoscienceLab,CommonwealthScientificandIndustrialResearchOrganization(CSIRO)
Manufacturing,ParkvilleVictoria3052,Australia;[email protected]
4 SchoolofChemistry,PhysicsandMechanicalEngineering,QueenslandUniversityofTechnology(QUT),
GPOBox2434,BrisbaneQLD4001,Australia
* Correspondence:[email protected](A.G.);[email protected](P.S.);
[email protected](S.V.B.);Tel./Fax:[phone](S.V.B.)
Abstract: Through the incorporation of a thiophene functionality, a novel solution-processable
small organic chromophore was designed, synthesized and characterized for application
in bulk-heterojunction solar cells. The new chromophore, (2Z,21Z)-2,21-(1,4-phenylene)bis(3-
(5-(4-(diphenylamino)phenyl)thiophen-2-yl)acrylonitrile)(codedasAS2), wasbasedonadonor–
acceptor–donor(D–A–D)modulewhereasimpletriphenylamineunitservedasanelectrondonor,
1,4-phenylenediacetonitrileasanelectronacceptor,andathiopheneringastheπ-bridgeembedded
betweenthedonorandacceptorfunctionalities.AS2wasisolatedasbrick-red,needle-shapedcrystals,
andwasfullycharacterizedby1H-and13C-NMR,IR,massspectrometryandsinglecrystalX-ray
diffraction. The optoelectronic and photovoltaic properties of AS2 were compared with those of
astructuralanalogue,(2Z,21Z)-2,21-(1,4-phenylene)bis(3-(4-(diphenylamino)phenyl)-acrylonitrile)
(AS1). Benefitingfromthecovalentthiophenebridges,comparedtoAS1thinsolidfilm,theAS2
filmshowed: (1)anenhancementoflight-harvestingabilityby20%;(2)anincreaseinwavelengthof
the longest wavelength absorption maximum (497 nm vs. 470 nm) and (3) a narrower optical
band-gap (1.93 eV vs. 2.17 eV). Studies on the photovoltaic properties revealed that the best
AS2-[6,6]-phenyl-C -butyric acid methyl ester (PC BM)-based device showed an impressive
61 61
enhanced power conversion efficiency of 4.10%, an approx. 3-fold increase with respect to the
efficiencyofthebestAS1-baseddevice(1.23%). Theseresultsclearlyindicatedthatembodimentof
thiophenefunctionalityextendedthemolecularconjugation,thusenhancingthelight-harvesting
ability and short-circuit current density, while further improving the bulk-heterojunction device
performance. Toourknowledge,AS2isthefirstexampleintheliteraturewhereathiopheneunithas
beenusedinconjunctionwitha1,4-phenylenediacetonitrileacceptingfunctionalitytoextendthe
π-conjugationinagivenD–A–Dmotifforbulk-heterojunctionsolarcellapplications.
Keywords: solution-processable; bulk-heterojunction devices; donor–acceptor–donor;
triphenylamine;thiophene;1,4-phenylenediacetonitrile
Molecules2015,20,21787–21801;doi:10.3390/molecules201219798 www.mdpi.com/journal/molecules
Molecules2015,20,21787–21801
1. Introduction
The development of renewable energy technologies is pivotal for accommodating the ever
increasingenergydemandsofthemodernsociety. Suchtechnologiesarealsoimportantforlowering
environmentalpollutionandgreenhousegasemissions. Towardsthisobjective,manyapproachesto
harvestsolarenergyhavebeeninvestigated. Thefabricationofbulk-heterojunction(BHJ)devicesis
onesuchpromisingstrategythathasattractedconsiderableattentionoverthepasttwodecadesdueto
theiradvantagesofbeinglightweight,lowcostandtheirflexibilityinlarge-areaapplications[1–7].
Suchdevicesarecomprisedofaninterpenetratingnetworkoforganicdonorandacceptordomains
that is formed during their fabrication via solution processing. Conventionally, semiconducting
donor polymers such as poly(3-hexylthiophene) (P3HT) and acceptors such as soluble fullerene
derivatives,PC BManditsC analogue(PC BM),havebeenusedtoobtainadeeperunderstanding
61 71 71
ofdevicedesignandmorphology[8–13]. ApartfromarchetypalP3HT,conjugatedpolymershavealso
beendevelopedandsignificantprogresshasbeenattainedwithpromisingBHJarchitecture. Power
conversionefficiency(PCE)valuesabove10%hasbeenreportedwithsuchpolymericdonors[14–17].
In the interim, solution-processed small molecular donor-based BHJ devices have also aroused
interest,mainlyduetotheiradvantagesofwell-definedchemicalstructure,convenientpurification
methods,suchassimplecolumnchromatography,andmonodispersemolecularweight[18–23]. These
advantagesallowandencourageresearcherstoexerteffortsforthedesignanddevelopmentofsmall
moleculardonors.Recently,immenseeffortshavebeendedicatedtodevelopingsmallmolecular-based
solution-processableorganicsolarcells[1,21]andsofar,thehighestPCEof9.95%wasachievedby
Kanetal.[24]whichisanalogoustothoseofthepolymer-basedsolution-processabledevices. Thus,in
viewofsuchreportsandthefactthatBHJdevicesincorporatingsmallmoleculardonorscancompete
withpolymer-baseddevices,thereisanoverwhelminginterestindevelopingsmallmoleculardonors.
Recent years have seen a dramatic surge not only in terms of device efficiency using small
molecular donors but also in their design and efficient synthetic development. A variety of small
molecule donor materials based on donor–acceptor (D–A) combinations such as D–A–D [25–27],
A–D–A[28,29],D–π–A[18,19,30]andstar-shapedarchitectures[31]havebeenreported. TheD–A–D
designinparticularisoneofthemostpromisingandsuccessfulmodulesbasedonwhichvariousdonor
andacceptorunitshavebeenexploredforhigh-performancesolution-processablephotovoltaicdevices.
Afinitenumberofcentralacceptingunits,suchasnaphthalenediimide[25],diketopyrrolopyrrole[27],
2-pyran-4-ylidenemalononitrile[32]andthiazolothiazole[33]havebeenreportedtosuittheD–A–D
module.Notonlythattheavailabilityandselectionofsuchacceptingblocksislimited,itisfurthermore
imperativethatthetargetchromophoremustpossessalowopticalbandgap,broadabsorptionprofile,
high mobility and appropriately tuned highest occupied molecular orbital (HOMO) and lowest
unoccupiedmolecularorbital(LUMO)energylevelsusingsuchblocks. Suchrequirementsdopossess
achallengeforanorganicchemistwhomustconsidersuchfactorswhiledesigninganewchromophore
basedontheD–A–Dmodule. Therefore,itisnotsurprisingthatthereexistsanenormousscopeforthe
designanddevelopmentofnewlight-harvestingmaterialsbasedonthechallengingD–A–Dmodule
andisanaspirationformostoftheresearchers.
Inourownstudiesofsmallmoleculechromophoresandchargetransportmaterialsbasedon
avarietyofD–Acombinations,wehavereportedexamplesofsuccessfulsolution-processableBHJ
photovoltaic devices [18,19,25,34–37]. Furthermore, we are highly interested to extend our efforts
on the design and development of new chromophores that are inspired by the D–A–D module.
In this study, we report the design, facile synthesis and characterization of the optoelectronic and
photovoltaic properties of two small organic chromophores, AS2 and AS1, (shown in Figure 1),
and their direct comparison. Both materials are based on a D–A–D structural motif where a
triphenyl-amine functionality has been chosen as a common donor at both ends of the central
acceptor unit, 1,4-phenylenediacetonitrile (PDA), so as to get symmetrical AS2 and AS1. AS2 is
astructuralanalogueofAS1whereathiopheneringhasbeenintroducedbetweenthedonorand
acceptor functionalities in order to vary the optoelectronic and photovoltaic properties (Figure 1).
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Whencomparedwiththecommonlyusedacceptinggroups,suchasdicyanovinylidene,aromatizable
cyanopyridone,indenedioneoroxoindenemalononitrile[38,39],PDAcanbeanacceptorofchoicefor
extendeMdolπec-ucleos n20j1u5,g 2a0,t pioagne–opavgee rthewholemolecularbackbone,mainlyduetoitsbidentatenature. Itis
notabletomentionthattheuseofthePDAunitforelectroluminescentconjugatedpolymershasbeen
the whole molecular backbone, mainly due to its bidentate nature. It is notable to mention that the
reportedusine othf ethlei tPeDraAtu urneit[ 4fo0r, 4e1le]catrsowluemllinaesscoennet -caonnjdugtwateod- pphoolytmonerssp heacst broeesnco rpepyosrtteudd iine sth[4e 2li–te4r6a]t.uHreo wever,
itssuita[b4i0l,i4t1y] aass awnelal cacse opnteo- rainnd stmwoa-lplhmotoolne csupelactrrocshcroopmy ostpuhdioerse [s4,2p–4a6r]t. iHcuolwarelvyerD, i–tsA s–uDitambiloitdyu alsa ar,nf orBHJ
applicataicocnepstiosr sinti sllmuanll kmnoolewcunla[r4 c,2h1ro].mTohphisorperso, pvairdtiecsulaanrlye nDc–oAu–rDa mgeomduelnart, afonrd BHsoJ mapeplsictraotinongs iins csteinll tivefor
unknown [4,21]. This provides an encouragement and some strong incentive for its investigation.
itsinvestigation. OwingtotheexplorationofPDAacceptorunitintheD–A–Dmodule,thisstudy
Owing to the exploration of PDA acceptor unit in the D–A–D module, this study continues our search
continuesoursearchforthegenerationofneworganicchromophoresforBHJapplications.
for the generation of new organic chromophores for BHJ applications.

Figure 1. Molecular structures of the newly designed AS2 and reference AS1 materials investigated
Figure1.MolecularstructuresofthenewlydesignedAS2andreferenceAS1materialsinvestigatedin
in this study.
thisstudy.
2. Results and Discussion
2. ResultsandDiscussion
2.1. Design Strategy, Synthesis
2.1. DesignStrategy,Synthesis
The materials AS2 and AS1 were synthesized via the Knoevenagel condensation of appropriate
aldehydes with active methylene groups of the PDA acceptor unit and their chemical structures were
ThematerialsAS2andAS1weresynthesizedviatheKnoevenagelcondensationofappropriate
confirmed by 1H- and 13C-NMR, mass spectrometry, and, where possible (AS2 only), by single crystal
aldehydes with active methylene groups of the PDA acceptor unit and their chemical structures
X-ray diffraction (XRD). The synthetic methodology for synthesizing AS1 was similar to an old literature
wereconrefipromrt e[4d2]b, aylb1eHit -diasnsidmi1l3aCr b-aNseM anRd, msolavsesnts wpeercet ruosmede ttor dy,eaaln wdi,thw ah heormeopgoensseoibulse re(AacStio2no snolluyt)i,obn.y single
crystalXK-nroaeyvedniafgferla ccotniodnen(sXatRioDn )r.eaTchtieons yofn atnh ealtdicehmydeet hwoitdho alcotigvye mfoerthsyylennteh gersoiuzpin isg aAn Sef1ficwieanst wsiamy iolfa rtoan
oldlitergaetnuerreatrinegp ao rdtou[4b2le] ,baolnbde bitetdwiesesnim a πil-abrribdages eanadn adccseopltvore nfutnwctieornealuitsye. Tdhteo udsee oafl swucihth chaemhoismtryo igs eneous
a common strategy to generate organic sensitizers for dye-sensitized solar cells [47]. However, the use
reactionsolution. Knoevenagelcondensationreactionofanaldehydewithactivemethylenegroupis
of same strategy to develop small molecular chromophores for BHJ applications is still limited [4,21].
anefficientwayofgeneratingadoublebondbetweenaπ-bridgeandacceptorfunctionality. Theuseof
Herein, not only we are demonstrating the Knoevenagel condensation reaction of PDA acceptor unit
suchchemistryisacommonstrategytogenerateorganicsensitizersfordye-sensitizedsolarcells[47].
but also the fabrication of solution-processable BHJ devices incorporating a fullerene acceptor (PC61BM)
Howeveanr,dt ehiteheurs AeSo2f osr aAmS1e ass tar daotengory cotomdpoenveenlto (Fpigsumrea 1l)l. Tmo othlee cbueslta orf cohurr oknmoowplehdoger,e tshifso isr tBheH fiJrsat ptimplei cations
isstillliPmDiAte dha[s4 b,2ee1n] .uHseedr teoi ng,enneorattoe nDl–yAw–De maroedduleamr somnasllt rmaotilencgultahr echKronmooepvheonreasg feolr cBoHnJd aepnpsliacatitioonnsr. eaction
of PDAInaictciael psctorerenuinngit obf uthtea BlsHoJ dtheveicfeasb rreivceaatlieodn thoaft sgoreluatteiro PnC-pEr wocaes sascahbielveedB HforJ AdSe2v i(c4e.1s0%in fcoor rApSo2r ating a
compared with 1.23% for AS1), as confirmed by the increased short-circuit current density (8.01 mA·cm−2
fullereneacceptor(PC BM)andeitherAS2orAS1asadonorcomponent(Figure1). Tothebestof
61
for AS2 and 3.15 mA·cm−2 for AS1), under simulated AM 1.5 illumination (100 mW·cm−2).
ourknowledge,thisisthefirsttimePDAhasbeenusedtogenerateD–A–Dmodularsmallmolecular
Both materials were based on the D–A–D module and the central acceptor moiety was directly
chromolpinhkoerde tso ftoher tBerHmJinaapl dpolincoart fiuonncsti.onInaliittiiaesl isnc orerdeenri tnog croeaftteh ae coBnHjuJgadteedv isctreusctruerve.e Tahleed detvhealotpgmreenatt erPCE
wasachoief vtheedsef toarrgAetS m2a(t4e.r1ia0l%s infocorrApoSra2tecso tmhep uasree odf wtwioth id1e.n2t3ic%al fdoornAorS u1n)i,tsa (strciophnefinrymlaemdinbey) otnh eeaicnhc reased
short-cisricduei tofc uthrer ecnenttdrael ncsoirtey, r(e8s.u0l1tinmgA in¨ csmym´m2eftorircaAl Sch2roamndop3h.o1r5esm. IAns¨ecrmtio´n 2off oar pAlaSn1a)r,, uconndjuegrasteidm ulated
AM1.5fiullnucmtioinnaaltitiyo,n su(1c0h0 ams tWhio¨pchmen´e2 )i.n AS2, between the donor and acceptor components of a target
material can provide greater absorption over visible light spectrum when compared with otherwise
BothmaterialswerebasedontheD–A–Dmoduleandthecentralacceptormoietywasdirectly
structurally similar compounds [38,48]. Moreover, the selection of thiophene over highly aromatic,
linkedtotheterminaldonorfunctionalitiesinordertocreateaconjugatedstructure. Thedevelopment
conjugating functionalities, such as phenyl, was based on the earlier work reported by Würthner et al.
ofthesetargetmaterialsincorporatestheuseoftwoidenticaldonorunits(triphenylamine)oneach
3
side of the central core, resulting in symmetrical chromophores. Insertion of a planar, conjugated
functionality, such as thiophene in AS2, between the donor and acceptor components of a target
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Molecules2015,20,21787–21801
materialcanprovidegreaterabsorptionovervisiblelightspectrumwhencomparedwithotherwise
structurallysimilarcompounds[38,48]. Moreover,theselectionofthiopheneoverhighlyaromatic,
conjugating functionalities, such as phenyl, was based on the earlier work reported by Würthner
etal.[49]andGuptaetal.[50]whereithasbeendemonstratedthatreplacementofaphenylgroup
Molecules 2015, 20, page–page
withthiophenecanprovidesignificantspectralred-shiftsandisadvantageousforsuperiorcharge
delocali[z49a]t iaonnd. GAupstaa erte aslu. [l5t0,]A wSh2eries itd heaesm beeedn tdoemexohnisbtriattead ltahragt ererpeldacesmhiefntt ooff laa pmhebndyal gmroauxpi mwuithm when
comparethdiowphitehnet hceanr epferroevnidcee csiogmnifpicoaunnt dspAecStr1a.l Broedth-shoiffttsh eanmd aitse raidavlsanwtaegreeousys nftohr essuizpeedriopr ecrhtahreger eaction
delocalization. As a result, AS2 is deemed to exhibit a large red shift of lambda maximum when
showninScheme1andwerepurifiedbysimplecolumnchromatography. Brick-red,needle-shaped
compared with the reference compound AS1. Both of the materials were synthesized per the reaction
crystals,suitableforsinglecrystalXRD,werepreparedbydiffusingmethanolintoadichloromethane
shown in Scheme 1 and were purified by simple column chromatography. Brick-red, needle-shaped
solutioncroyfstAalSs, 2s,uoitavbelre faopr psirnogxleim craystetally XtRhDre, weedrae ypsre.pHaroewd beyv derif,fnusoincgr ymsettahlagnorol iwnttoh a wdiachsloorbosmeervtheadnef orAS1.
Bothmasotelurtiiaolns owf AerSe2,s oyvnetrh aepspirzoexdiminatemlyo tdhreerea dteaytso. Hhoigwhevyeire, lndos c(rAysSta2l g=ro6w3%th wanasd oAbsSer1ve=d8 f6or% A)Sa1n. dwere
highlysBooltuhb mleatienriaalvs awreieret ysyonfthceosmizmedo inn morogdaenraictes tool vhiegnht sy,ieflodrs e(AxaSm2 =p 6le3%ch alnodro AbSe1n =z e8n6%e,) cahnldo rwoefroer m,and
highly soluble in a variety of common organic solvents, for example chlorobenzene, chloroform, and
toluene. Thesolubilityoforganicp-typematerialsisparamountforfabricatingsolution-processable
toluene. The solubility of organic p-type materials is paramount for fabricating solution-processable
BHJdevicesandboththematerialsfulfillthiscriterion. Infact,thesolubilityofAS2wasfoundtobe
BHJ devices and both the materials fulfill this criterion. In fact, the solubility of AS2 was found to be
higherby50%w/vwhencomparedwithAS1.
higher by 50% w/v when compared with AS1.

Scheme 1. Reaction scheme for the synthesis of AS2 and AS1.
Scheme1.ReactionschemeforthesynthesisofAS2andAS1.
The precursor aldehyde 1 of AS2 was also crystallized by diffusion of methanol into chloroform
Thetop orbetcauinr syoerlloawld, enheeyddlee-s1hoapfeAdS c2rywstaalss.a Dlsioffrcarcytisotna lmliezaesdurbeymednitfsf uwseioren poefrfmoremtehda nato 2l0in0 tKo ocnh lao roform
to obtaiBnruykeelrl oAwpe,xn IeI eCdClDe- dsihffarpacetdomcertyers tuaslisn.g MDoif fKrαa crtaidoinatimone(λa s=u 0r.7e1m07e3n Åts) Twhee rsetrupceturfroe rwmereed soaltve2d0 0 K on
using dual space methods using the program SHELX-2014/7 [51] using the Olex2 1.2 GUI [52], with
a Bruker Apex II CCD diffractometer using Mo Kα radiation(λ = 0.71073 Å) The structure were
anisotropic thermal parameters for all non-hydrogen atoms. All non-hydrogen atoms were refined
solvedusingdualspacemethodsusingtheprogramSHELX-2014/7[51]usingtheOlex21.2GUI[52],
anisotropically by full-matric least-squares methods SHELX-2014/7. Molecular drawings were obtained
with anuissointgr oMpeirccuthrye r[5m3]a. lTphea ruatmiliteyt eorf s1 ffoorr daylle-nseonns-ithizyeddr sooglaern cealtlso mhass .beAenll rnepoonr-thedy d[5r4o],g heonwaetvoemr, s were
refinedaitns iussoet troo gpeincaerlalyteb symafull lml-moleacturliacr lceharsotm-soqpuhaorreess fmore BthHoJ dasppSlHicaEtLioXns- 2is0 s1e4l/do7m. M reoploercteudla [r4,d21r]a. wThiinsg swere
obtainesdtautes ionf gafMfaiersr ceunrcyou[r5a3g]e.s Tuhs eanudt iplirtoyviodfes1 af ostrrodnyge i-nsceennstiivtiez etod rseopolartr ictse lslysnhthaessibs eaennd rcerpysotarlt ed [54],
growth strategy.
however, its use to generate small molecular chromophores for BHJ applications is seldom
reported[4,2T1h]e. Tcohmispsotuantde o1 fwaafsfa cirryssetanllcizoeudr aing ethseu msoannodclpinrioc vsipdaeces agrsoturpo n(Pg 2in1/cc)e nwtiitvhe fotourr easpyomrtmietstrsicy nthesis
units in one cell. The thiophene group and the adjacent phenyl groups are planar with pendant
andcrystalgrowthstrategy.
phenyl groups displaced around nitrogen. The packing consist of a two-fold screw axis with centers
Thoefc ionvmerpsoiounn bdet1wweena ssuclrfyusr tmalolliezceudleisn ast hweelml aos nao gclildine ipclasnpea pceergpreonduipcu(lPar2 t1o/ thce) wthiiothphfeonuer palasnyem. metric
units inTohen epaccekliln.g Tish deomthinioaptehde bnye πg-πro fuacpe-aton-fdacteh setaackdijnagc ebnettwpehene nthyel tghiroopuhpensea arnedp plhaennayrl gwroituhpsp. endant
phenylTghroe uppensddainstp plhaecneydl agrroouupnsd arnei tsrtaobgielinze.dT bhye πp-aπc ekdigneg-tcoo-fnacsei ssttaocfkiangtw woit-hfo dlidstsacnrceesw ina xthies rwanitghe centers
2.771–3.283 Å as shown in Figure 2.
ofinversionbetweensulfurmoleculesaswellasaglideplaneperpendiculartothethiopheneplane.

The packing is dominated by π-π face-to-face stacking between the thiophene and phenyl groups.
Thependantphenylgroupsarestabilizedbyπ-πedge-to-facestackingwithdistancesintherange
2.771–3.283ÅasshowninFigure2. 4
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Molecules 2015, 20, page–page

Figure 2. Packing of 1 along the b axis.
Figure2.Packingof1alongthebaxis.
AS2 co-crystallizes with chloroform in the triclinic space group (P-1) with a center of symmetry
aroAuSn2d ctoh-ec rcyesnttarlalli zpehsewnyitlh gcrholuopr.o Tfohrem pianckthinegt risic dlionmicisnpaatecde gbyro fuapce(-Pto-1-f)awcei tπh-πa csetanctkeirnogf bseytmwmeeent ry
arocuenntdratlh pehceennytlrsa alnpdh tehniyoplhgeronuesp, .anTdh ebyp aecdkgien-tgo-ifsadceo mπ-iπn-astteadckbinyg fbaectew-teoe-nfa pceenπd-aπnts tpahcekninygl gbreotuwpese n
cenwtritahl tphhee dniystlasnacned 2.t7h7i2o pÅh aesn sehso,wannd inb Fyigeudrgee 3-t. oT-hfaec deeπta-iπls- sotfa pckaicnkginbge sttwruecetnurpe,e fnodrmanutlap,h cerynsytlalg sriozue ps
witohf 1th aenddi sAtaSn2 caere2 .d7e7s2crÅibaesd sihno Twabnlein 1.F igure3. Thedetailsofpackingstructure,formula,crystalsize
of1andAS2aredescribedinTable1.
Table 1. Details of crystal data and structure refinement parameters of 1 and AS2.
Table1.Detailsofcrystaldataandstructurerefinementparametersof1andAS2.
Identification Code CCDC:1420377(1) CCDC: 1420378 (AS2)
Empirical formula C23H17NOS C31H22OS
IdFeonrtmifiuclaat iwoneiCghotd e CCD3C5:51.4432 0377(1) CCDC4:4124.25053 78(AS2)
EmTepmirpicearlaftourrme/Kul a C2203H0(127)N OS C23010H(22)2 OS
FCorrymstualla swysetiegmht mon3o5c5li.n43ic mon4o4c2l.i5n5ic
TeSmpapceer agtruoruep/ K P2201/0c( 2) P20201 (2)
Crystaal/Åsy stem 1m9.o9n16o(c3li)n ic 5m.5o8n1o2(c7li)n ic
Spacbe/Ågr oup 6.66P8201(/9)c 47.12P02(16)
a/Å 19.916(3) 5.5812(7)
c/Å 13.4336(16) 9.2435(11)
b/Å 6.6680(9) 47.120(6)
α/° 90 90
c/Å 13.4336(16) 9.2435(11)
β/° 96.613(3) 103.343(3)
α/˝ 90 90
βγ//°˝ 969.06 13(3) 1039.03 43(3)
Voluγm/˝e/Å3 1772.910(4) 2365.930(5)
VolumZ e/Å3 1747 2.1(4) 23645 .3(5)
ρcalcgZ/cm3 1.3342 1.2443
ρcμal/cmg/mc−m1 3 0.119.343 2 0.11.5284 3
µ/Fm(00m0´) 1 7404..109 4 9208.1.05 8
CrystaFl( 0s0iz0e)/mm3 0.292 × 0.077464 .×0 0.063 0.667 × 0.912387. 0× 0.087
CrysRtaaldsiaizteio/nm m3 M0.o2K92α ˆ(λ0 =.0 07.671ˆ0703.0) 63 M0.o6K67αˆ (λ0 =.1 03.771ˆ0703.0) 87
2Θ range Rfoard diaattiao ncollection/ M4.o1K18α t(oλ 4=8.05.8781 073) M3o.4K5α8 t(oλ 6=7.08.4721 073)
2ΘrangIenfdoerxd raatnagceosl lection/ −22 ≤ h ≤ 234, .−171 8≤ tko ≤4 78,. 5−8185 ≤ l ≤ 15 −8 ≤ h ≤ 8, −733.4 ≤5 8k t≤o 7637, .−81442 ≤ l ≤ 12
Indexranges ´22ďhď23,´7ďkď7,´15ďlď15 ´8ďhď8,´73ďkď73,´14ďlď12
Reflections collected 15255 83,300
Reflectionscollected 15255 83,300
Independent reflections 2883 [Rint = 0.0707, Rsigma = 0.0447] 19,180 [Rint = 0.0616, Rsigma = 0.0596]
DIantad/erpesetnrdaienntts/rpeaflreacmtioentesrs 2883[Rint=2808.037/00/72,3R5s igma=0.0447] 19,180[Rint1=9108.006/11/65,9R5s igma=0.0596]
Data/restraints/parameters 2883/0/235 19180/1/595
GGooooddnneessss--ooff--fifitt oonn FF22 0.904.994 9 1.10.2082 8
FFiinnaall RR iinnddeexxeess [[II ě≥ 22σσ ((II))]] RR1 1= =0.004.01421, 2w,wR2R =2 0=.100.9150 95 RR1 1= =0.00.605695,9 w,wR2R =2 0=.105.13513 1
FFiinnaall RR iinnddeexxeess [[aallll ddaattaa]] RR1 1= =0.007.02702, 0w,wR2R =2 0=.102.7142 74 RR1 1= =0.00.907927,2 w,wR2R =2 0=.106.18648 4
LLaragrgesetstd dififf.fp. peaekak//hhoollee//ee ÅÅ−´3 3 00.1.177/−/0´.206. 26 00.2.299/−/0´.309.3 9

5
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Molecules2015,20,21787–21801
Molecules 2015, 20, page–page

FFiigguurree 33.. PPaacckkiinngg ooff AASS22 aalloonngg tthhee cc aaxxiiss..
2.2. Optoelectronic Properties
2.2. OptoelectronicProperties
The optical properties of AS2 and AS1 were investigated by measuring their ultraviolet–visible
TheopticalpropertiesofAS2andAS1wereinvestigatedbymeasuringtheirultraviolet–visible
(UV–Vis) absorption spectra in chloroform solution and in pristine spin-cast films (Figure 4). The
(UV–Vis) absorption spectra in chloroform solution and in pristine spin-cast films (Figure 4). The
lloonnggeesstt wwaavveelleennggtthh aabbssoorrpptitoionn mmaxaixmimuumm (λ(mλax) e)xhexibhiitbeidte bdy bAySA2 Sin2 sinolusotilount iofonrmfo rwmasw aat s45a9t n45m9
max
wnmhicwh hwicahs rwedas-shreifdte-sdh bifyte 2d3 bnym2 w3hnemn cwomhepnarceodm wpiatrhe dthew siothlutthioen sλomluaxt ioofn AλS1. BootfhA thSe1 .abBsoortphtitohne
max
mabasxoirmputimon amndax eimxtuinmctiaonnd ceoxetfifnicciteionnt (cAoSef2fi c=i e5n9t,0(0A0S M2−=1·c5m9,0−10; 0AMS1´ 1=¨ c4m9,0´010; AMS−11·c=m4−91), 0i0n0crMea´s1e¨dc mw´it1h)
the insertion of thiophene functionality. With the insertion of thiophene ring we found enhancement
increasedwiththeinsertionofthiophenefunctionality. Withtheinsertionofthiopheneringwefound
to the peak molar absorptivity of >20% of AS2 compared with AS1. This enhanced profile allows a
enhancementtothepeakmolarabsorptivityof>20%ofAS2comparedwithAS1.Thisenhancedprofile
larger amount of the solar spectrum to be absorbed, thus exhibiting greater intramolecular charge
allowsalargeramountofthesolarspectrumtobeabsorbed,thusexhibitinggreaterintramolecular
transfer (ICT) transition. We observed a similar bathochromic absorption shift in the thin film spectrum
charge transfer (ICT) transition. We observed a similar bathochromic absorption shift in the thin
of AS2 compared with that of AS1 (Figure 4). The strong red-shift is attributed to the extended
filmspectrumofAS2comparedwiththatofAS1(Figure4). Thestrongred-shiftisattributedtothe
πex-cteonndjuegdaπti-ocnon wjuigthatiino nthwe itmhionletchuelmaro bleaccuklbaronbea cokfb oAnSe2o fthAaSt 2btehcaatmbee cpamosesipboles swibiltehw tihthe tihneseinrtsieornti oonf
thiophene functionality. This type of control over the absorption profile through the insertion of a
ofthiophenefunctionality. Thistypeofcontrolovertheabsorptionprofilethroughtheinsertionofa
strongly conjugated unit can help to fine tune optical energy levels, to enhance light harvesting and BHJ
stronglyconjugatedunitcanhelptofinetuneopticalenergylevels,toenhancelightharvestingand
device performance.
BHJdeviceperformance.
Density functional theory (DFT) calculations using the Gaussian 09 suite of programs [55] and
Density functional theory (DFT) calculations using the Gaussian 09 suite of programs [55]
the B3LYP/6-311 + G(d,p)//B3LYP/6-31G(d) level of theory indicated that the HOMO orbital densities
andtheB3LYP/6-311+G(d,p)//B3LYP/6-31G(d)leveloftheoryindicatedthattheHOMOorbital
of both AS2 and AS1 have a major distribution over the whole molecular backbone and the LUMO
densities of both AS2 and AS1 have a major distribution over the whole molecular backbone and
densities were delocalized through the central acceptor functionality and adjacent rings (Figure 5).
theLUMOdensitiesweredelocalizedthroughthecentralacceptorfunctionalityandadjacentrings
Inserted thiophene rings in case of AS2 can accommodate LUMO density with almost equal contribution
(Figure5). InsertedthiopheneringsincaseofAS2canaccommodateLUMOdensitywithalmostequal
as the central PDA, thus sparing the adjoining phenyl rings of the donor triphenylamine for an
contributionasthecentralPDA,thussparingtheadjoiningphenylringsofthedonortriphenylamine
efficient segregation of HOMO and LUMO densities. Such separation is ideal for the ICT transition
for an efficient segregation of HOMO and LUMO densities. Such separation is ideal for the ICT
and is attributed to the presence of a strong conjugated unit, of which thiophene is an example, in the
transition and is attributed to the presence of a strong conjugated unit, of which thiophene is an
given D–A–D system. Experimental estimation of the HOMO energies was carried out using photo
example,inthegivenD–A–Dsystem. ExperimentalestimationoftheHOMOenergieswascarriedout
electron spectroscopy in air (PESA) and the LUMO energies were calculated by adding the optical
usingphotoelectronspectroscopyinair(PESA)andtheLUMOenergieswerecalculatedbyadding
band gap (film spectra) to the HOMO values (see Figure 6 for energy level diagram and Figure S1
theopticalbandgap(filmspectra)totheHOMOvalues(seeFigure6forenergyleveldiagramand
[see Supplementary Material] for the PESA curve). Film spectra indicated that insertion of thiophene
FigureS1[seeSupplementaryMaterial]forthePESAcurve). Filmspectraindicatedthatinsertion
reduces the band gap of AS2 by 0.24 eV when compared with AS1. Furthermore, the estimation of
ofthiophenereducesthebandgapofAS2by0.24eVwhencomparedwithAS1. Furthermore,the
HOMO using PESA revealed that the HOMO energy level of AS2 was raised by 0.18 eV when
estimationofHOMOusingPESArevealedthattheHOMOenergylevelofAS2wasraisedby0.18
compared with the HOMO level of AS1. This is in agreement with the DFT calculations that the
eVwhencomparedwiththeHOMOlevelofAS1. ThisisinagreementwiththeDFTcalculations
presence of thiophene indeed plays a crucial role for: (1) density segregation; (2) tuning the optical
thatthepresenceofthiopheneindeedplaysacrucialrolefor: (1)densitysegregation;(2)tuningthe
energy levels; and (3) theoretical and experimental band gap reduction. These measurements and
opticalenergylevels;and(3)theoreticalandexperimentalbandgapreduction. Thesemeasurements
calculations provide a strong rational for our design strategy that the induction of a conjugated
functionality can indeed improve the optoelectronic properties of a given chromophore. The energy
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MMoolleeccuulleess 22001155,, 2200,, 2p1a7g8e7––p2a1g8e0 1
level diagram advised that the band gaps of these materials are all in the range required of donor
andcalculationsprovideastrongrationalforourdesignstrategythattheinductionofaconjugated
materials for BHJ devices. AS2 optical band gap is somewhat narrower in magnitude than 2.0 eV
functioMnoalelciutleys 2c0a15n, 2i0n, pdaegee–dpaigme provetheoptoelectronicpropertiesofagivenchromophore. Theenergy
measured for the conventional P3HT. The optical and electrochemical properties of both the materials
leveldiagramadvisedthatthebandgapsofthesematerialsareallintherangerequiredofdonor
in solution and film form are summarized in Supplementary Material Table S1.
level diagram advised that the band gaps of these materials are all in the range required of donor
materialsforBHJdevices. AS2opticalbandgapissomewhatnarrowerinmagnitudethan2.0eV
materials for BHJ devices. AS2 optical band gap is somewhat narrower in magnitude than 2.0 eV
measuredfortheconventionalP3HT.Theopticalandelectrochemicalpropertiesofboththematerials
measured for the conventional P3HT. The optical and electrochemical properties of both the materials
insoluitni osnoluatniodnfi alnmd ffiolmrm foarmre asrue msummamraizriezdedi ninS Suupppplleemmeenntataryry MMataertiearli TalabTlaeb Sl1e. S1.

FFiigguurreefF o44irg.. upNNrreioos 4rrtim.mn Neaa oalliriszmz-eceaaddlsi tzaaeebbdds s foaoilbrrmpspostti ri(opolnotniwo ssnepp rse)ep;c ce(ttfrcriatlarma oo sfof of cc fcoo oAmmmSppp2o ooauununndndd dAss sSAA A1S Sw2S2 ae2nra aedn ns dApdiSA nA1-S cSino11a C itineHnd CCC aHltH3 2sCCo0l0ll3u03 t ssirooopnllmuus tt(fiuioooprnn p1ss em (r(u)ui nappn ptpdoee rr)) aanndd
ffoorr pprriissttiinnee aass--ccaasstteedd fifillmmss ((lloowweerr));; ((fifillmmss ooff AASS22 aanndd AASS11 wweerree ssppiinn--ccooaatteedd aatt 22000000 rrppmm ffoorr 11 mmiinn ttoo
give a film thickness of ~70 nm).
ggiivvee aa fifillmm tthhiicckknneessss ooff ~~7700 nnmm))..

Figure 5. Orbital density distribution for the frontier molecular orbitals of AS2 and AS1. DFT
calculations were performed using the Gaussian 09 suite of programs and the B3LYP/6-311 +
G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical HOMO/LUMO energy levels and band-gaps
(vs. Vac scale) are also shown.
Figure 5. Orbital density distribution for the frontier molecular orbitals of AS2 and AS1. DFT
Fi gure 5. Orbital density distrib ution for the frontier molecular orbitals of AS2 and AS1. DFT
calculations were performed using the Gaussian 09 suite of programs and the B3LYP/6-311 +
calculations were performed using the Gaussian 09 suite of programs and the B3LYP/6-311 +
G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical HOMO/LUMO energy levels and band-gaps
G(d,p)//B3LYP/6-31G(d)leveloftheory.Theoretic7a lHOMO/LUMOenergylevelsandband-gaps(vs.
(vs. Vac scale) are also shown.
Vacscale)arealsoshown.

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Molecules 2015, 20, page–page

Figure 6. Energy level diagram depicting the band gaps of AS2 and AS1 in comparison with P3HT
Figure6.EnergyleveldiagramdepictingthebandgapsofAS2andAS1incomparisonwithP3HTand
and PC61BM. Experimental estimation of the HOMO energies was carried out using PESA and the
PC BM.ExperimentalestimationoftheHOMOenergieswascarriedoutusingPESAandtheLUMO
61
LUMO energies were calculated by adding the optical band gap (film spectra) to the HOMO values.
energieswerecalculatedbyaddingtheopticalbandgap(filmspectra)totheHOMOvalues.
Encouraging though the optoelectronic properties are, the compounds must display thermal
Encouraging though the optoelectronic properties are, the compounds must display thermal
stability given the rigorous conditions used in device fabrication such as annealing at temperature in
stabilitygiventherigorousconditionsusedindevicefabricationsuchasannealingattemperature
the excess of 100 °C. In line with this requirement and to determine the thermal stability of AS2 and
intheexcessof100˝C.InlinewiththisrequirementandtodeterminethethermalstabilityofAS2
AS1, thermogravimetric analysis (TGA) was conducted. TGA (Supplementary Material Figure S2)
andAS1,thermogravimetricanalysis(TGA)wasconducted. TGA(SupplementaryMaterialFigureS2)
indicated that both AS2 and AS1 are thermally stable and will not degrade during the annealing of
indicatedthatbothAS2andAS1arethermallystableandwillnotdegradeduringtheannealingof
BHJ devices.
BHJdevices.
After correlating the optoelectronic properties of AS2 and AS1 with those of the conventional
AftercorrelatingtheoptoelectronicpropertiesofAS2andAS1withthoseoftheconventional
PC61BM acceptor (see Figure 6), we screened their potency as donor materials (p-type) in solution-
PC BM acceptor (see Figure 6), we screened their potency as donor materials (p-type) in
pro6c1essable BHJ devices under simulated sunlight and monochromatic light illumination. The blend
solution-processableBHJdevicesundersimulatedsunlightandmonochromaticlightillumination.
solutions of both the materials and PC61BM were used to cast an active layer on top of the PEDOT:PSS
The blend solutions of both the materials and PC BM were used to cast an active layer on top of
surface. The BHJ device architecture used was ITO61/PEDOT:PSS (38 nm)/active layer/Ca (20 nm)/Al
(t1h0e0P nEmD)O wTh:PeSreS tshuer faaccteiv.eT lhayeeBr HwJads eav sioceluatirocnh iptercotcuerseseuds ebdlewnda sofI TeOith/ePrE ADSO2T o:Pr SASS(13 8anndm P)/Ca6c1BtiMve.
Flaoyre Ar/SC2a, a( 2p0ronmmi)s/inAgl P(1C0E0 nofm 4).1w0%he rweatsh aecahciteivveedl awyherenw tahsea fislomlu wtiaosn spprionc-ceosaseteddb flreonmd ao fcehiltohreorbAenSz2enoer
AS1andPC BM.ForAS2,apromisingPCEof4.10%wasachievedwhenthefilmwasspin-coated
solution as a6 11:1 blend with PC61BM. By contrast, the maximum PCE obtained for a device based on
AfroSm1 waacsh l1o.2ro3b%e,n wzehneen sfoalburtiicoanteads uan1d:1erb lseinmdilwari tchonPdCi6t1ioBnMs.. TBhyec oconmtrapsatr,athtievem cauxrirmenutm–vPoCltEagoeb ctuairnveeds
ffoorr tahde eovpitciembizaesedd bolenndAsS o1f wAaSs21 a.2n3d% A,Sw1h wenithfa PbCri6c1aBtMed auren dsherowsinm iinla Fricgounrde i7ti.o Hnisg.hT bhoeilcionmg psoalrvaetnivtes
current–voltagecurvesfortheoptimizedblendsofAS2andAS1withPC BMareshowninFigure7.
such as chlorobenzene are better not only from processing point of v6ie1w but also for achieving
sHmigohotbhoeirl ifnilgmsso wlviethnotsuts ucrcyhstaasllcizhalotiroonb oecnczuernreinagr eonb ethttee racntoivteo snulyrfafrcoems. Lpartotecre swsiansg pparotiincutloafrlvyi etrwueb uast
oalusro effofroratcsh tioe vcionngsstrmuocto BthHerJ fidlemviscewsi tuhsoinugt car yloswta-llbiozailtiinogn sooclcvuernrti,n sguochn tahse cahclotirvoefosrumrf,a aceffso.rLdaetdte eritwhaesr
puanretviceunl asrulyrftarcuees aosr omuirneoffro crrtasctkosc oonn stthrue catcBtiHveJ dsuevrfiacecessu. singalow-boilingsolvent,suchaschloroform,
affordTehde eoipthtiemriuzneedv denevsiucerfsa bceasseodr monin AorS2cr eaxckhsiboitnedth ae adcetcivreeassuedrf aocpeesn. circuit voltage (Voc) than the
devicTehs eboapsetdim oizne AdSd1e.v Ticheiss bina sfeadcto ins AcoSn2siesxtehnibt iwteidtha tdheec rmeaesaesduroepde HnOciMrcuOi tvvaolulteasg ew(hVeorce) ath hainghtheer
HdeOvMiceOs fboars AedS2o nwAouSl1d. pTrhedisicitn af alocwtiesr cVoonc.s Oisnte tnhtew otithhert hheanmde, athsue rsehdorHt OcirMcuOit vcaulrureenstw dhenerseitya (hJsicg) hfoerr
tHhOe dMeOvicfeosr fAabSr2icwatoeudl duspinregd AicSt2a wloaws herigVhoecr. tOhannt htheeo Jtsch eexrthraacntedd, tfhroemsh tohret dciervcuicietsc buarsreedn todne AnsSi1ty. T(Jhsics)
wfoarst hine adgerveeicmesenfat bwriitcha ttehde oubsisnegrvAedS 2bawthaoschhrigohmeirc tshhaifnt itnh ethJes caebxsotrrapcttieodn sfrpoemctrtuhme doef vAicSe2s cboamsepdaroedn
AwSit1h. ATSh1is. Twhaes pihnoatogvreoeltmaiecn ctewll iptahrathmeeotebrsse frovre AdSb2a-tbhaoscehdr odmeviiccessh iwfteirne t0h.8e8a Vb s[oorppetnio cnircspuietc vtroultmagoef,
AVoSc]2, 8c.o0m1 pmaAre·cdmw−2i t[hcuArrSe1n.t Tdheenspihtyo,t (oJvsc)o]l,t 0a.i5c8c e[flilllp faarcatmore, t(eFrFs)]f oarnAd S42.1-0b%as e[pdodweevri cceosnwveerrseio0n.8 e8ffVici[eonpceyn,
(cPirCcuEi)t].v oInltiatigael ,sVcorce]e,n8i.n0g1 mofA ¨thcme ´B2H[Jc udrerevnicteds enbsaisteyd, (Joscn) ],A0S.518:P[Cfil6l1BfaMct osrh,o(FwFe)d] amndod4e.1r0a%te [dpeovwiceer
pcoenrfvoerrmsiaonncee fwficitihen ac yh,ig(PhC VEo)c] .oIfn 0i.t9ia0l Vsc, rFeFe noifn g43o%f tJhsce oBf H3.J15d emvAic/ecsmb2a asnedd oann oAvSe1r:aPlCl P61CBEM osf h1o.2w3e%d.
Tmaokdeenr aatse ad ewvhicoelep, etrhfeo rimnsaenrtcieonw iotfh tahihoipghheVneoc foufn0c.t9io0nVa,lFitFy oinft4o3 %theJs cstoufd3i.e1d5 Dm–AA/–cDm s2taruncdtuarnaol vmeoratilfl
iPnCcoErpofor1a.2ti3n%g .PTDaAke anccaespatowr hfuonlec,titohneailnitsye rretisounltoedf tihni osipghneinfiecafnutn ecntihoannacleitmyeinntto oft hJesc satnudd iPeCdED v–aAlu–eDs
by factors >2 and >3, respectively, thus promoting the use of a smaller conjugated functionality, such
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Molecules2015,20,21787–21801
structural motif incorporating PDA acceptor functionality resulted in significant enhancement of
JscandMoPleCcuEles v20a1l5u, e20s, pbaygef–apcatgoe rs>2and>3,respectively,thuspromotingtheuseofasmallerconjugated
functionality,suchasthiophene,asaninterestingstructuralconceptforthedesignanddevelopment
Moalsec tuhleiso 2p0h15e, n2e0,, paasg ae–np aingete resting structural concept for the design and development of highly efficient
of highly efficient BHJ materials. Furthermore, it is notable to mention that AS2 showed optimal
BHJ materials. Furthermore, it is notable to mention that AS2 showed optimal performance with
perfaosri nmtheaxiopnpechneeswniveie,t haPsCi an61neB xMinpt eaenrnesdsi tvsiinemgPp sClter6 u1dBcetvMuircaeal n acrdocnhsciitemepcptt ulfeorerd , tethhveu idcs eepsariogrcvnhi dainitnedgc t dsueorvmee,elot hspturmosenpngtr ioonvfc iehdnigitnihvgley s teoof mfaipceipeslnyttr ong
inceBnHtivJ emtaotearpiaplsly. Fthuerthdeersmigonrec,o int cise pntorteapbloer tteod minentthioisn wthoartk AtoS2t hsehonwewedg oepnteimraatli opnesrfoofrmBHanJcme watietrhi als.
the design concept reported in this work to the new generations of BHJ materials.
inexpensive PC61BM and simple device architecture, thus providing some strong incentive to apply
the design concept reported in this work to the new generations of BHJ materials.

Figure 7. Current–voltage curves for the optimized devices based on AS2 and AS1 in blends with
Figure 7. Current–voltage curves for the optimized devices based on AS2 and A S1 in blends
with PPCC61BBMM (1(:11 :w1/ww)/ uwn)deurn sdimerulsaitmedu sluantelidghst u(AnMlig 1h.5t, (1A00M0 W1.·5m,−21)0. D00evWice¨ mstr´u2ct)u.reD wevasic: IeTOst/rPuEcDtuOrTe-was:
FiPgSuSr6 e1( 378. nCmu)r/raecntitv–ev loalytaegr/eC cau (r2v0e ns mfo)/rA tlh (e1 0o0p ntimm)i zwehde rdee tvhiece asc tbivaese lday oenrs AwSe2re a tnhde bAleSn1d isn o bf leeinthdesr wASit2h
ITO/PEDOT-PSS(38nm)/activelayer/Ca(20nm)/Al(100nm)wheretheactivelayersweretheblends
PCo6r1 BAMS1 ( 1a:n1d w P/wC6)1 uBnMd sepr usinm ounl atotepd o sfu tnhlei gfhilmt (sA oMf P1E.5D, 1O0T0:0P WSS· mus−i2n).g D cehvloicreo bsternuzcetnuer es owlvaesn: ItT. O/PEDOT-
ofeitherAS2orAS1andPC BMspunontopofthefilmsofPEDOT:PSSusingchlorobenzenesolvent.
PSS (38 nm)/active layer/C6a1 (20 nm)/Al (100 nm) where the active layers were the blends of either AS2
The incident photon-to-current-conversion efficiency (IPCE) spectra of these BHJ devices are
or AS1 and PC61BM spun on top of the films of PEDOT:PSS using chlorobenzene solvent.
Tshheowinnc iind eFnigtuprhe o8t.o Tnh-teo I-PcuCrEr emnet-acsounrevmeersnito onf etfhfiecseie BnHcyJ (dIePvCicEes) swpaesc tbrraoaodf tshpeecsteruBmH, Jtydpeivcaiclleys are
showncovinTehriFeni ggin umcrioedset8n o.tf ptThhheo evtoiIsnPib-CtloeE- rcaumnrgreeean,s ftur-coromenm v3e5en0rs ttiooo n7f 5et0hf fneimcsiee. nABcSyH2 (JaIPnddCe EvA)iS cs1ep seexcwhtriabas itoebfd rt ohhaiegdshe spBplHaetcJe tadruuesvm aict, e~ts4y 0ap%riec ally
shaonwdn ~ 2i7n% F fiogru trhee 8b.e sTth BeH IJP dCeEv icmese aresuspreecmtievnetl yo. fT hthee IsPeC BEH spJ edctervuimce so fw AaSs2 ,b wrohaidch scpaerrciterdu ma t, htiyoppihceanlley
coveringmostofthevisiblerange,from350to750nm. AS2andAS1exhibitedhighplateausat~40%
cofvuenrcitniogn maloitsyt, owf aths er evdi-ssihbilfet erdan wghe,e fnr ocmom 3p5a0r etod 7w50it hn mA.S A1,S a2 f ainnddi nAgS t1h aetx ihsi bcoitnesdi shteignht wpliathte tahues r aets u~l4t0 o%f
and~27%forthebestBHJdevicesrespectively. TheIPCEspectrumofAS2,whichcarriedathiophene
anthdi ~n2 f7il%m f aobr stohrep btieosnt BspHeJc tdreuvmic. eTsh ree sspigencitfiivcealnyt.l yT hheig IhPeCr Ep esapke cItPrCuEm o off A ASS22 c, owmhpicahr ecda rtroi eAdS a1 t ihnidoipchateende
functionality,wasred-shiftedwhencomparedwithAS1,afindingthatisconsistentwiththeresultof
that the superior performance of AS2 can be rationalized in terms of enhanced light-harvesting and
functionality, was red-shifted when compared with AS1, a finding that is consistent with the result of
thinfialpmpraobpsroiarptetliyo ntusnpedec otrputimca.l Tenheergsyig lnevifieclsa, nthtleyrehbiyg hcoerrropbeoarkatIiPnCg Ethoe fdAesSig2nc porminpciaprleed. toAS1indicated
thin film absorption spectrum. The significantly higher peak IPCE of AS2 compared to AS1 indicated
thatthesuperiorperformanceofAS2canberationalizedintermsofenhancedlight-harvestingand
that the superior performance of AS2 can be rationalized in terms of enhanced light-harvesting and
appropriatelytunedopticalenergylevels,therebycorroboratingthedesignprinciple.
appropriately tuned optical energy levels, thereby corroborating the design principle.

Figure 8. IPCE spectra of AS2 and AS1 with PC61BMblends.

To examine the physical microstructure of the blend surface, we used atomic force microscopy
(AFM) in tapping mFoigdFueigr. ueTr8he.e 8I .aP IcCPtuCEaEsl p sspeuecrctfrtaraacoe o ffm AAoSSr22p haannoddlo AAgySS 11o wfw tihtihteh PbPClCe61nBdMB fbMillmebnlsde nso.df sA.S2/AS1:PC61BM (1:1
61
w/w) is shown in Figure 9. Physically, both the blends were found to be smooth and the root mean
To examine the physical microstructure of the blend surface, we used atomic force microscopy
9
(AFM) in tapping mode. The actual surface morphology of the blend films of AS2/AS1:PC61BM (1:1
w/w) is shown in Figure 9. Physically, both the blends were found to be smooth and the root mean
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Molecules2015,20,21787–21801
Toexaminethephysicalmicrostructureoftheblendsurface,weusedatomicforcemicroscopy
(AFM) in tapping mode. The actual surface morphology of the blend films of AS2/AS1:PC BM
Molecules 2015, 20, page–page 61
(1:1w/w)isshowninFigure9. Physically, boththeblendswerefoundtobesmoothandtheroot
smqeuaanres qrouuagrehnroesusg ohfn 0e.s4s1o nfm0. 4a1ndn m0.3a5n dnm0. 3w5ansm obwsearsveodb sfeorrv eAdS2fo arnAdS A2Sa1n dreAspSe1ctrievseplye.c tNivoe lcyr.acNkos
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61
chlorobenzene solution. Topographic (left) and phase images (right) are shown.
chlorobenzenesolution.Topographic(left)andphaseimages(right)areshown.
3. Experimental Section
3. ExperimentalSection
3.1. Materials and Instruments
3.1. MaterialsandInstruments
All reagents and chemicals used, unless otherwise specified, were purchased from Sigma-Aldrich
Allreagentsandchemicalsused,unlessotherwisespecified,werepurchasedfromSigma-Aldrich
(Sydney, Australia). The solvents used for reactions were obtained from Merck Speciality Chemicals
(Sydney,Australia). ThesolventsusedforreactionswereobtainedfromMerckSpecialityChemicals
((SSyyddnneeyy,, AAuussttrraalliiaa)) aanndd wweerree uusseedd aassr reecceeiivveedd.. UUnnlleessss ootthheerrwwiissee ssppeecciififieedd,,a allll1 1HH-- aanndd 1133CC--NNMMRR ssppeeccttrraa
were recorded using a Bruker AV300 spectrometer at 300 and 75 MHz or a Bruker AV400 spectrometer
at 400 and 100 MHz, respectively (Bruker Corporation, Billerica, MA, USA). Chemical shifts (δ) are
21796
reported in parts per million (ppm). Thin-layer chromatography (TLC) was performed using 0.25 mm
thick plates precoated with Kieselgel 60 F254 silica gel (Merck, Darmstadt, Germany) and visualized
using UV light (254 nm and 365 nm). Melting points were measured using a MPD350 digital melting
10