Energy level alignment at polymer/electrode interfaces in light-emitting devices studied by photoelectron spectroscopy

Grzegorz Greczynski; Thomas Kugler; William R. Salaneck

doi:10.1117/12.416882

2 February 2001 Energy level alignment at polymer/electrode interfaces in light-emitting devices studied by photoelectron spectroscopy

Grzegorz Greczynski, Thomas Kugler, William R. Salaneck

Author Affiliations +

Proceedings Volume 4105, Organic Light-Emitting Materials and Devices IV; (2001) https://doi.org/10.1117/12.416882
Event: International Symposium on Optical Science and Technology, 2000, San Diego, CA, United States

Abstract

The band alignment at the interface between electroluminescent polymers and the electrodes in polymer- LEDs was studied using photoelectron spectroscopy. Chemical factors like the formation of InCl₃ during conversion of precursor-PPV on ITO could be directly monitored with XPS. Films of electroluminescent polymers were studied on a range of ITO and metal electrodes with different work functions, as well as with an intermediate, electrically conducting polymer layer, using UPS. For the polymers spin-coated directly onto the substrates, the vacuum levels are aligned. In the case of conducting polymer films on ITO or metal substrates, the F¹ermi levels are aligned. With a conducting polymer layer sandwiched between the electroluminescent polymer and the ITO electrode, the polymer bands align to the vacuum level of the conducting polymer. Thus, the barrier to hole injection into the electroluminescent polymer is determined by the work function of the conducting polymer instead of the work function of the ITO electrode. Furthermore, the study of the band alignment at polymer electrode interfaces was extended to three-layer structures: The results are in agreement with the common assumption that the potential drop over the polymer layer in a polymer LED is equal to the difference between the electrode work functions.

Citation Download Citation

Grzegorz Greczynski, Thomas Kugler, and William R. Salaneck "Energy level alignment at polymer/electrode interfaces in light-emitting devices studied by photoelectron spectroscopy", Proc. SPIE 4105, Organic Light-Emitting Materials and Devices IV, (2 February 2001); https://doi.org/10.1117/12.416882

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