Tuning organic magnetoresistance in polymer-fullerene blends by controlling spin reaction pathways

Abstract

Harnessing the spin degree of freedom in semiconductors is generally a challenging, yet rewarding task. In recent years, the large effect of a small magnetic field on the current in organic semiconductors has puzzled the young field of organic spintronics. Although the microscopic interaction mechanisms between spin-carrying particles in organic materials are well understood nowadays, there is no consensus as to which pairs of spin-carrying particles are actually influencing the current in such a drastic manner. Here we demonstrate that the spin-based particle reactions can be tuned in a blend of organic materials, and microscopic mechanisms are identified using magnetoresistance lineshapes and voltage dependencies as fingerprints. We find that different mechanisms can dominate, depending on the exact materials choice, morphology and operating conditions. Our improved understanding will contribute to the future control of magnetic field effects in organic semiconductors.

Traps and trions as origin of magnetoresistance in organic semiconductors

“…11 A similar theoretical framework has been applied to account for other microscopic mechanisms and their effect on the magnetic-field dependent current, i.e., magnetoconductance (MC). 12 In recent work 13 we have shown that the dominant mechanism for OMAR in a real device depends on the operating conditions and morphology. Inspired by pioneering work from Wang et al, 8 we blended a polymer and a fullerene and showed that the MC and the underlying spin-based reactions could be tuned.…”

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

“…Finally, it was shown that the magnetic field effect on the current in pristine organic semiconductors is predominantly governed by the reactions between triplet excitons and polarons. 18,20,22,23,25 Moreover, Cox et al recently proposed an analytical model where these reactions are described by the spin-selective formation of socalled metastable trions from triplet exciton-polaron pairs. 23 Their model provides an intuitive explanation of the MC(V) dependence.…”

“…Accurately measuring and understanding the exact lineshapes of the LFE and HFE is therefore of major importance since the lineshapes can be correlated to the dominant underlying mechanism. 20 In this chapter, we present a detailed study on the voltage and temperature dependence of OMAR, aiming to unravel the magnetic field effects on the current in pristine conjugated polymer devices. Even though OMAR has been studied extensively, there are only a few detailed reports on its temperature dependence.…”

“…18 Very recently, we have shown that the dominant mechanism for OMAR depends on the exact material choice and operating conditions of the device. 20 Therefore, a thorough investigation of all relevant operating conditions is crucial in understanding magnetic field effects (MFEs) in organic semiconductors.…”

Recent progress in organic spintronics

“…Recent studies show that a general explanation of the MR effect cannot be given based on a single mechanism. Rather, the dominating mechanism depends not only on the materials and device parameters, but also on operation conditions [35,36]. (a) Possible quasi-particle pairs in organic semiconductors versus energy.…”