The bandgaps,geometries,electronicstructures,polarizabilities,hyperpolarizabilities,dipole
moments, UV–visible,IR, 1H and 13C NMRofpoly(3,4-ethylenedioxythiophene)(PEDOT)andits
fluorine derivatives—Cn and [6,6] phenylCn butyric acidmethylesters(PCnBMs) bulk
heterojunction (BHJ)solarcellsareinvestigatedbyusingdensityfunctionaltheory(DFT)and
time-dependant densityfunctionaltheory(TD-DFT)calculations.Weaimtooptimizethe
performance ofthesesolarcellsbyalteringthefrontierorbitalenergygapsofpolymersand
fullerenes. Thiswasdonebyfunctionalizingthepolymersbackboneswithelectronwithdrawing
fluorines step-bystep,andbyaddingphenylbutyricacidmethylestertothebuckminsterC60
and C70 fullerenes. Thetheoreticaldatawerecomparedwiththeavailableexperimentaldata.
Based onthestrategyofreducingthebandgaps,thetrifluoroderivativeofPEDOT–buckminster
C70 fullerene blend(outof24blends)wasfoundtobethebestcandidateforpowerconversion
efficiency (PCE).Theadditionoffluorineatomstothepolymerbackboneiseffectivein
lowering bothHOMOsandLUMOs.Conformationalanalysisconfirmsthatthecoplanarproper-
tyof thiophenepolymersarenotdestroyedbytheincorporationoffluorineatoms.Whilestrong
localization ofHOMOsoccursonthePEDOTdonorsubunits,strongdelocaliztionofLUMOs
occurs onthebridgesbetweenthesubunits,provingtheflowoftheelectrondensityalongthe
polymer backbone.Thepolarizabilityterm bxxx and dipolemoment mx increase withincreasing
the powerconversionefficiency.Theabsorptionbandthatcorrespondstothemaximum
coefficient ofthePEDOTinvacuumismarginallyshiftedundertheeffectofincorporating
fluorines. VibrationalanalysisshowsthatfunctionalizingPEDOTleadstoamoreconjugated
polymer backboneandenhancesthechargetransfertoanacceptor.Thepowerconversion
efficiency ofthesolarcellincreaseswithincreasingthechemicalshiftsoftheconstituentC,H,
and Oatoms. |
