Print Email Facebook Twitter Compositional and electric field dependence of the dissociation of charge transfer excitons in alternating polyfluorene copolymer/fullerene blends Title Compositional and electric field dependence of the dissociation of charge transfer excitons in alternating polyfluorene copolymer/fullerene blends Author Veldman, D. Ipek, Ö. Meskers, S.C.J. Sweelssen, J. Koetse, M.M. Veenstra, S.C. Kroon, J.M. van Bavel, S.S. Loos, J. Janssen, R.A.J. TNO Industrie en Techniek Publication year 2008 Abstract The electro-optical properties of thin films of electron donor-acceptor blends of a fluorene copolymer (PF10TBT) and a fullerene derivative (PCBM) were studied. Transmission electron microscopy shows that in these films nanocrystalline PCBM clusters are formed at high PCBM content. For all concentrations, a charge transfer (CT) transition is observed with absorption spectroscopy, photoluminescence, and electroluminescence. The CT emission is used as a probe to investigate the dissociation of CT excited states at the donor-acceptor interface in photovoltaic devices, as a function of an applied external electric field and PCBM concentration. We find that the maximum of the CT emission shifts to lower energy and decreases in intensity with higher PCBM content. We explain the red shift of the emission and the lowering of the open-circuit voltage (VOC) of photovoltaic devices prepared from these blends with the higher relative permittivity of PCBM (εr = 4.0) compared to that of the polymer (εr = 3.4), stabilizing the energy (ECT) of CT states and of the free charge carriers in blends with higher PCBM concentration. We show that the CT state has a short decay time (τ = ca. 4 ns) that is reduced by the application of an external electric field or with increasing PCBM content. The field-induced quenching can be explained quantitatively with the Onsager-Braun model for the dissociation of the CT states when including a high electron mobility in nanocrystalline PCBM clusters. Furthermore, photoinduced absorption spectroscopy shows that increasing the PCBM concentration reduces the yield of neutral triplet excitons forming via electron-hole recombination, and increases the lifetime of radical cations. The presence of nanocrystalline domains with high local carrier mobility of at least one of the two components in an organic heterojunction may explain efficient dissociation of CT states into free charge carriers. © 2008 American Chemical Society. Subject MaterialsIndustrial InnovationAbsorptionAbsorption spectroscopyAstrophysicsCharge transferCharged particlesDissociationElectric field effectsElectric field measurementElectric fieldsElectric instrument transformersElectroacupunctureElectromagnetic field theoryElectromagnetic fieldsElectromagnetismElectron microscopesElectron microscopyElectron opticsElectronsEmission spectroscopyFullerenesImaging techniquesIon exchangeLight emissionLuminescenceMagnetismMass transferMicroscopic examinationOptical propertiesPolymersSemiconducting cadmium tellurideThick filmsThin filmsTransmission electron microscopy(ethylene vinyl alcohol) copolymersAlternating polyfluorene (APFO)Applied (CO)Charge transfer excitonsCharge-transfer (CT) transitionsConcentration (composition)Donor-acceptor interfacesElectric field dependencesElectro optical propertiesElectron donor acceptor (EDA)emission shiftsExternal electric fieldsFluorene (FI)fullerene derivativesLower energiesNano crystallineOpen-circuit voltage (OCV)photovoltaic devicesred shiftingElectric chargecationcopolymerfluorene derivativefullerene derivativenanocrystalorganic compoundarticlechemical compositionchemical modelchemical structureconcentration (parameters)devicedissociationelectric fieldelectric potentialelectricityelectronenergyfilmintensity modulated radiation therapyquantitative analysistransmission electron microscopy To reference this document use: http://resolver.tudelft.nl/uuid:96716a5b-ecd3-44eb-a646-4c98368025db TNO identifier 280041 ISSN 0002-7863 Source Journal of the American Chemical Society, 130 (24), 7721-7735 Document type article Files To receive the publication files, please send an e-mail request to TNO Library.