Negative capacitance in organic semiconductor devices: bipolar injection and charge recombination mechanism

TL;DR

This paper investigates negative capacitance in organic semiconductor diodes, attributing it to recombination currents from electron-hole annihilation under bipolar injection, and models it with space charge limited current theory.

Contribution

It provides a quantitative explanation for negative capacitance in organic diodes by incorporating recombination currents into existing models, highlighting trap-mediated processes.

Findings

Negative capacitance appears only under bipolar injection.

Recombination current explains the negative capacitance phenomenon.

Recombination time depends on bias voltage, indicating trap mediation.

Abstract

We report negative capacitance at low frequencies in organic semiconductor based diodes and show that it appears only under bipolar injection conditions. We account quantitatively for this phenomenon by the recombination current due to electron-hole annihilation. Simple addition of the recombination current to the well established model of space charge limited current in the presence of traps, yields excellent fits to the experimentally measured admittance data. The dependence of the extracted characteristic recombination time on the bias voltage is indicative of a recombination process which is mediated by localized traps.