16 February 2004 Fluorenone defects in polyfluorene-based light-emitting diodes: emission properties and device performance
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The spectral characteristics of polyfluorene (PF) based light-emitting diodes (LEDs) are discussed. First, conditions that facilitate photo-oxidation of PF are investigated. We show that dense chain packing and addition of hole-trapping moieties lead to increased defect formation. Second, devices containing either a defined low concentration of keto-defects or of the polymer poly(9,9-octylfluorene-co-benzothiadiazole) (F8BT) are presented. Both types of blend layers were tested in different device configurations with respect to the relative and absolute intensities of green and blue emission components. It is shown that either blending of hole-transporting molecules into the emission layer at low concentration or the incorporation of a suitable hole-transporting layer reduces the green emission in the PF:F8BT blend, similar to what is observed for the keto-containing PF layer. We conclude that photo-oxidation leads to the formation of keto-defects that mainly constitute weakly-emissive electron traps.
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Frank Jaiser, Frank Jaiser, Xiaohui Yang, Xiaohui Yang, Dieter Neher, Dieter Neher, Roland Guentner, Roland Guentner, P. Scanduicci de Freitas, P. Scanduicci de Freitas, M. Forster, M. Forster, Ullrich Scherf, Ullrich Scherf, "Fluorenone defects in polyfluorene-based light-emitting diodes: emission properties and device performance", Proc. SPIE 5214, Organic Light-Emitting Materials and Devices VII, (16 February 2004); doi: 10.1117/12.505209; https://doi.org/10.1117/12.505209

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