Admittance Spectroscopic Analysis of Polymer Light Emitting Diodes with the LiF Cathode Buffer Layer

Abstract

Admittance Spectroscopic analysis was applied to study the effect of LiF buffer layer and to model the equivalent circuit for poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymer light emitting diodes (PLEDs) with the LiF cathode buffer layer. The single layer device with ITO/MEH-PPV/Al structure can be modeled as a simple combination of two resistors and a capacitor. Insertion of a LiF layer at the Al/MEH-PPV interface shifts the lowest unoccupied molecular orbital (LUMO) level and the vacuum level of the MEH-PPV layer as a result of which the barrier height for electron injection at the Al/MEH-PPV interface is reduced. The admittance spectroscopic analysis of the devices with the LiF cathode buffer layer shows reduction in contact resistance (R_C), parallel resistance (R_P) and increment in parallel capacitance (C_P).

Keywords:

• admittance spectroscopy
• barrier height
• LiF buffer layer
• polymer light emitting diodes

Acknowledgments

This work was supported by the SRC program (Center for Nanotube and Nanostructured Composites) of MOST/KOSEF.