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Issue 4, 2011
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ToF-SIMS imaging of the nanoscale phase separation in polymeric light emitting diodes: Effect of nanostructure on device efficiency

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Abstract

The nanostructure of the light emissive layer (EL) of polymer light emitting diodes (PLEDs) was investigated using force modulation microscopy (FMM) and scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) excited with focused Bi32+ primary beam. Three-dimensional nanostructures were reconstructed from high resolution ToF-SIMS images acquired with different C60+ sputtering times. The observed nanostructure is related to the efficiency of the PLED. In poly(9-vinyl-carbazole) (PVK) based EL, a high processing temperature (60 °C) yielded less nanoscale phase separation than a low processing temperature (30 °C). This nanostructure can be further suppressed by replacing the host polymer with poly[oxy(3-(9H-9-carbazol-9-ilmethyl-2-methyltrimethylene)] (SL74) and poly[3-(carbazol-9-ylmethyl)-3-methyloxetane] (RS12), which have similar chemical structures and energy levels as PVK. The device efficiency increases when the phase separation inside the EL is suppressed. While the spontaneous formation of a bicontinuous nanostructure inside the active layer is known to provide a path for charge carrier transportation and to be the key to highly efficient polymeric solar cells, these nanostructures are less efficient for trapping the carrier inside the EL and thus lower the power conversion efficiency of the PLED devices.

Graphical abstract: ToF-SIMS imaging of the nanoscale phase separation in polymeric light emitting diodes: Effect of nanostructure on device efficiency

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Publication details

The article was received on 20 May 2010, accepted on 13 Sep 2010 and first published on 11 Oct 2010


Article type: Paper
DOI: 10.1039/C0AN00335B
Citation: Analyst, 2011,136, 716-723
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    ToF-SIMS imaging of the nanoscale phase separation in polymeric light emitting diodes: Effect of nanostructure on device efficiency

    B. Yu, C. Kuo, W. Wang, G. Yen, S. Iida, S. Chen, W. Lin, S. Lee, W. Kao, C. Liu, H. Chang, Y. You, C. Chang, C. Liu, J. Jou and J. Shyue, Analyst, 2011, 136, 716
    DOI: 10.1039/C0AN00335B

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