Full characterization of electronic transport properties in working polymer light-emitting diodes via impedance spectroscopy

TL;DR

This paper uses impedance spectroscopy to comprehensively analyze the electronic transport properties of working polymer light-emitting diodes, including mobilities, tail states, and recombination, and also assesses aging effects.

Contribution

It provides a full characterization method for PLEDs' transport properties and demonstrates its application to degradation analysis.

Findings

Drift mobilities are thermally activated.

Localized tail state distributions are quantified.

Recombination constants are measured from impedance data.

Abstract

The electron and hole drift mobilities of organic semiconductor layers, localized tail state distributions, and bimolecular recombination constants in working polymer light-emitting diodes (PLEDs) are determined simultaneously using impedance spectroscopy (IS). The organic light-emitting layers of these PLEDs are composed of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). Electron and hole transit time effects are observed in the capacitance-frequency characteristics of the PLEDs and their drift mobilities are determined over wide temperature and electric field ranges. The drift mobilities exhibit thermally activated behavior and the localized tail state distributions from the conduction band and valence band mobility edges are then determined from analysis of the electric field dependences of the activation energies. The bimolecular recombination constants are determined from the inductive response of the impedance-frequency characteristics. The IS technique is also applicable to degradation analysis of the PLEDs; changes in the mobility balance, the localized tail state distributions, and the bimolecular recombination constant caused by aging are all shown.