The role of electron-hole recombination in organic magnetoresistance

TL;DR

This study demonstrates that organic magnetoresistance (MR) is directly caused by electron-hole pair formation, with MR disappearing when the probability of their meeting in space is reduced, highlighting the role of recombination in MR effects.

Contribution

It provides direct experimental evidence linking electron-hole recombination to organic MR, clarifying the underlying mechanism in organic thin film devices.

Findings

MR disappears when e-h meeting probability is reduced

MR line shape follows a B^0.5 power law at high fields

Electron-hole pair formation is essential for MR in organic devices

Abstract

Magneto-electrical measurements were performed on diodes and bulk heterojunction solar cells (BHSCs) to clarify the role of formation of coulombically bound electron-hole (e-h) pairs on the magnetoresistance (MR) response in organic thin film devices. BHSCs are suitable model systems because they effectively quench excitons but the probability of forming e-h pairs in them can be tuned over orders of magnitude by the choice of material and solvent in the blend. We have systematically varied the e-h recombination coefficients, which are directly proportional to the probability for the charge carriers to meet in space, and found that a reduced probability of electrons and holes meeting in space lead to disappearance of the MR. Our results clearly show that MR is a direct consequence of e-h pair formation. We also found that the MR line shape follows a power law-dependence of B0.5 at higher fields.