Magnetoresistance in organic semiconductors: including pair correlations in the kinetic equations for hopping transport

TL;DR

This paper develops a self-consistent kinetic model for polaron hopping in organic semiconductors that incorporates pair correlations and spin dynamics, elucidating the origins of organic magnetoresistance.

Contribution

It introduces a novel kinetic framework that explicitly includes double occupation and intersite correlations, advancing understanding of the bipolaron mechanism in organic magnetoresistance.

Findings

Correlations are essential for magnetoresistance; without them, it vanishes.

The model reduces to an effective resistor network at low voltages.

Spin relaxation influences the system's resistivity.

Abstract

We derive the kinetic equations for polaron hopping in organics that explicitly take into account the double occupation possibility and pair intersite correlations. The equations include simplified phenomenological spin dynamics and provide a self-consistent framework for the description of the bipolaron mechanism of the organic magnetoresistance. At low applied voltages the equations can be reduced to effective resistor network that generalizes the Miller-Abrahams network and includes the effect of spin relaxation on the system resistivity. Our theory discloses the close relationship between the organic magnetoresistance and the intersite correlations. Moreover, in the absence of correlations, as in ordered system with zero Hubbard energy, the magnetoresistance vanishes.