Charge Transfer Absorption for π-Conjugated Polymers and Oligomers Mixed with Electron Acceptors

Panda, Priyadarshi; Veldman, Dirk; Sweelssen, J.; Bastiaansen, Jolanda J. A. M.; Langeveld-Voss, B.M.W.; Meskers, Stefan C. J.

doi:10.1021/jp070796p

Cited by 81 publications

(66 citation statements)

References 51 publications

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“…The CT state has a lower energy than the singlet excited state (S 1 ) of the polymer and PCBM in the blend. [5][6][7][8][9][10][11][12] When a forward bias is applied to the device, electrons will be injected from Al (cathode) into the LUMO of PCBM, and holes will be injected from ITO/PEDOT:PSS (anode) into the highest occupied molecular orbital (HOMO) of APFO-Green 5. Both holes and electrons will subsequently transfer to this intermediate low energy CT state, recombine there, and result in a long-wavelength emission.…”

Section: Electroluminescence Experimentsmentioning

confidence: 99%

Observation of a Charge Transfer State in Low‐Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

Zhou

Tvingstedt

Zhang

et al. 2009

Adv Funct Materials

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The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor–acceptor–donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1 eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated.

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Section: Electroluminescence Experimentsmentioning

confidence: 99%

Observation of a Charge Transfer State in Low‐Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

Zhou

Tvingstedt

Zhang

et al. 2009

Adv Funct Materials

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“…Also V oc is determined by the spectral properties of the CT excitons, again being morphology dependent. In general, the spectral position of the CT exciton correlates with the difference between the lowest unoccupied molecular orbital ͑LUMO͒ of the fullerene acceptor and the highest occupied molecular orbital ͑HOMO͒ of the donor polymer, 23 resulting in the widely observed correlation between V oc and this difference. 1,2,6,7 However, recently it has been argued that other CTC related parameters, such as the electronic coupling between donor and acceptor, also have an influence on V oc .…”

Section: Introductionmentioning

confidence: 99%

Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells

et al. 2010

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The open-circuit voltage ͑V oc ͒ of polymer:fullerene bulk heterojunction solar cells is determined by the interfacial charge-transfer ͑CT͒ states between polymer and fullerene. Fourier-transform photocurrent spectroscopy and electroluminescence spectra of several polymer:fullerene blends are used to extract the relevant interfacial molecular parameters. An analytical expression linking these properties to V oc is deduced and shown to be valid for photovoltaic devices comprising three commonly used conjugated polymers blended with the fullerene derivative ͓6,6͔-phenyl-C61-butyric acid methyl ester ͑PCBM͒. V oc is proportional to the energy of the CT states E CT . The energetic loss q⌬V between E CT and qV oc vanishes when approaching 0 K. It depends linearly on T and logarithmically on illumination intensity. Furthermore q⌬V can be reduced by decreasing the electronic coupling between polymer and fullerene or by reducing the nonradiative recombination rate. For the investigated devices we find a loss q⌬V of ϳ0.6 eV at room temperature and under solar illumination conditions, of which ϳ0.25 eV is due to radiative recombination via the CT state and ϳ0.35 eV is due to nonradiative recombination.

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“…[19] Using Photothermal Deflection Spectroscopy and photoluminescence spectroscopy, the formation of CTCs was also evidenced for solid-state blends of different types of polyfluorenes with PCBM. [20][21] 5…”

Section: Introductionmentioning

confidence: 99%

“…[17,19] For MDMO-PPV this difference has been determined from cyclic voltammetry measurements to be around 1.4 eV (table 1). This value is well below the bandgap of both MDMO-PPV (2.1 eV) and PCBM (1.7 eV), and is in the observed spectral range of the CT band (1.2 -1.6 eV) in the EQE spectrum.…”

Section: Introductionmentioning

confidence: 99%

The Relation Between Open‐Circuit Voltage and the Onset of Photocurrent Generation by Charge‐Transfer Absorption in Polymer : Fullerene Bulk Heterojunction Solar Cells

Vandewal

Gadisa

Oosterbaan

et al. 2008

Adv Funct Materials

533

535

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Photocurrent generation by charge-transfer (CT) absorption is detected in a range of conjugated polymer: [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) based solar cells. The low intensity CT absorption bands are observed using a highly sensitive measurement of the external quantum efficiency (EQE) spectrum by means of Fourier-transform photocurrent spectroscopy (FTPS). The presence of these CT bands implies the formation of weak groundstate charge-transfer complexes in the studied polymer:fullerene blends. The effective band gap (E g ) of the material blends used in these photovoltaic devices is determined from the energetic onset of the photocurrent generated by CT absorption. It is shown that for all

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Charge Transfer Absorption for π-Conjugated Polymers and Oligomers Mixed with Electron Acceptors

Cited by 81 publications

References 51 publications

Observation of a Charge Transfer State in Low‐Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

Observation of a Charge Transfer State in Low‐Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence Studies

Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells

The Relation Between Open‐Circuit Voltage and the Onset of Photocurrent Generation by Charge‐Transfer Absorption in Polymer : Fullerene Bulk Heterojunction Solar Cells

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