Comment on "Validity of Einstein Relation in Disordered Organic Semiconductors"

TL;DR

This paper discusses the validity of the Einstein relation in disordered organic semiconductors, analyzing recent experimental findings that confirm its validity in certain conditions and contrasting them with previous theories and experiments.

Contribution

It critically examines recent experimental results supporting Einstein relation validity and discusses limitations of single-carrier diode experiments for this purpose.

Findings

Recent experiments show Einstein relation holds in thermal equilibrium.

Discrepancies with previous theories are analyzed and explained.

Single-carrier diode experiments may not be suitable for verifying Einstein relation.

Abstract

Wetzelaer, Koster, and Blom [PRL 107, 066605] recently observed that the classic Einstein relation $\frac{D}{\mu}=\frac{kT}{q}$ is still valid in disordered semiconductors in thermal(quasi)equilibrium by studying the diffusion-driven currents of single-carrier diodes. This is in contrast to the previous theoretical prediction [2] and experiment observation from Leo et.al. [3] where the Einstein relation increases with 1/T. We will discuss the reason for this discrepancy here and suggest that one-carrier diodes experiment might nor be suitable for verifying Einstein relation in organic semiconductors.