On the electrical degradation and green band formation in α- and β-phase poly(9,9-dioctyfluorene) polymer light-emitting diodes

Arredondo, B.; Romero, B.; Gutiérrez–Llorente, Araceli; Martínez, A.I.; Álvarez, Antonio García; Quintana, Xabier; Otón, J. M.

doi:10.1016/j.sse.2011.02.004

Cited by 21 publications

(23 citation statements)

References 34 publications

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“…The EL spectrum can be used to infer long-range translational order within the polymer since the glassy phase exhibits emission for the 0-0 transition near wavelengths of 425 nm, while the β-phase has its maximal peak centered at 440 nm. This difference in 0-0 transition is a reliable indicator of the morphological phase of the layer [25]. Fig.…”

Section: Pacsmentioning

confidence: 90%

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

et al. 2016

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We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by conducting continuous wave (c.w.) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and 293 K using microwave frequencies between about 100 MHz and 20 GHz as well as pulsed EDMR at X-band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes (OLEDs) the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge carrier 2 injection conditions we conducted multi-frequency c.w. EDMR, electrically detected Rabi spinbeat experiments, Hahn-echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron spin-echo envelope modulation (ESEEM) due to the coupling of the carrier spins to nearby nuclei spins. Our results demonstrate that while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At 293 K and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy-phase, since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g-factors, appears to be somewhat more significant in the β-phase. PACS

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Section: Pacsmentioning

confidence: 90%

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

et al. 2016

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“…These peaks are attributed to the excitonic emission and its vibronic progression from noninteracting single chains [16]. The third peak is due to the formation of fluorenone defects (keto defects) which are incorporated as C=O in the PFO backbone [17][18][19]. The photooxidation, electrooxidation, and thermal oxidation are the major reasons for the generation of fluorenone ((C 6 H 4 ) 2 C=O) defect, which created lower energy emission at 525 nm.…”

Section: Electroluminescence Spectramentioning

confidence: 99%

Influence of TiO₂ Nanoparticles on Enhancement of Optoelectronic Properties of PFO‐Based Light Emitting Diode

Al‐Asbahi

Jumali

Yap

et al. 2013

Journal of Nanomaterials

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Improvement on optoelectronic properties of poly (9,9′-di-n-octylfluorenyl-2.7-diyl)- (PFO-) based light emitting diode upon incorporation of TiO2nanoparticles (NPs) is demonstrated. The PFO/TiO2nanocomposites with different weight ratios between 5 and 35 wt.% were prepared using solution blending method before they were spin coated onto Indium Tin Oxide substrate. Then a thin Al layer was deposited onto the nanocomposite layer to act as top electrode. The nanocomposites were tested as emissive layer in organic light emitting diodes (OLEDs). The TiO2NPs played the most crucial role in facilitating charge transport and electrical injection and thus improved device performance in terms of turn-on voltage, electroluminescence spectra (EL), luminance, and luminance efficiency. The best composition was OLED with 5 wt.% TiO2NPs content having moderate surface roughness and well distribution of NPs. The device performance was reduced at higher TiO2NPs content due to higher surface roughness and agglomeration of TiO2NPs. This work demonstrated the importance of optimum TiO2NPs content with uniform distribution and controlled surface roughness of the emissive layer for better device performance.

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“…The b-phase emission is very close in energy to that of the vibronic replica of the a-phase (473 nm), and as a result the glassy phase is hindered by the formation of the b-phase. 27 As shown in Fig. 4(a), the 452 nm peak gradually decreased for PFO concentrations up to 6 mg/ml, and the emission from the b-phase emerges instantaneously.…”

Section: Resultsmentioning

confidence: 77%

“…30 The fluorenone defects act as a low-energy trap, and we expect that there will be competition between the b-phase and the fluorenone defects for the excitons that were created within the PFO thin film. 27 The observed concentration dependent EL of the LEDs can also be explained by assuming that a ternary system exists, comprising a PFO a-phase, a b-phase and the fluorenone defects. In this case, the energy transfer can populate the double trap system to generate the EL emission spectra of the PFO/ZnO NR LEDs.…”

Section: Resultsmentioning

confidence: 99%

Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes

Zaman

Zainelabdin

Amin

et al. 2012

Journal of Applied Physics

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The effects of the polymer concentration on the performance of hybrid light emitting diodes (LEDs) based on zinc oxide nanorods (ZnO NRs) and poly(9,9-dioctylfluorene) (PFO) were investigated. Various characterization techniques were applied to study the performance of the PFO/ZnO NR hybrid LEDs fabricated with various PFO concentrations. The fabricated hybrid LEDs demonstrated stable rectifying diode behavior, and it was observed that the turn-on voltage of the LEDs is concentration dependent. The measured room temperature electroluminescence (EL) showed that the PFO concentration plays a critical role in the emission spectra of the hybrid LEDs. At lower PFO concentrations of 2-6 mg/ml, the EL spectra are dominated by blue emission. However, by increasing the concentration to more than 8 mg/ml, the blue emission was completely suppressed while the green emission was dominant. This EL behavior was explained by a double trap system of excitons that were trapped in the b-phase and/or in the fluorenone defects in the PFO side. The effects of current injection on the hybrid LEDs and on the EL emission were also investigated. Under a high injection current, a new blue peak was observed in the EL spectrum, which was correlated to the creation of a new chemical species on the PFO chain. The green emission peak was also enhanced with increasing injection current because of the fluorenone defects. These results indicate that the emission spectra of the hybrid LEDs can be tuned by using different polymer concentrations and by varying the current injected into the device.

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On the electrical degradation and green band formation in α- and β-phase poly(9,9-dioctyfluorene) polymer light-emitting diodes

Cited by 21 publications

References 34 publications

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

Influence of TiO₂ Nanoparticles on Enhancement of Optoelectronic Properties of PFO‐Based Light Emitting Diode

Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes

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On the electrical degradation and green band formation in α- and β-phase poly(9,9-dioctyfluorene) polymer light-emitting diodes

Cited by 21 publications

References 34 publications

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

Influence of TiO2 Nanoparticles on Enhancement of Optoelectronic Properties of PFO‐Based Light Emitting Diode

Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes

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Influence of TiO₂ Nanoparticles on Enhancement of Optoelectronic Properties of PFO‐Based Light Emitting Diode