It has been experimentally discovered that a low magnetic field (less than 500 mT) can substantially change the electroluminescence, photoluminescence, photocurrent, and electrical-injection current in nonmagnetic organic semiconducting materials, leading to magnetic-field effects (M FEs). Recently, there has been significant driving force in understanding the fundamental mechanisms of magnetic responses from nonmagnetic organic materials because of two potential impacts. First, MFEs can be powerful experimental tools in revealing and elucidating useful and non-useful excited processes occurring in organic electronic, optical, and optoelectronic devices. Second, MFEs can lead to the development of new multifunctional organic devices with integrated electronic, optical, and magnetic properties for energy conversion, optical communication, and sensing technologies. This progress report discusses magnetically sensitive excited states and charge-transport processes involved in MFEs. The discussions focus on both fundamental theories and tuning mechanisms of MFEs in nonmagnetic organic semiconducting materials.

Magnetic‐Field Effects in Organic Semiconducting Materials and Devices

Molecular spintronics is recognized to as an attractive new research direction in a field of spintronics, following to metallic spintronics and inorganic semiconductor spintronics, and attracts many people in recent decades The purpose of this manuscript is to describe the history of molecular spintronics by introducing important achievements and to show the current status of this field In addition, the authors briefly introduce several theories for implementing studies in molecular spintronics

Molecular Spintronics

We studied magnetoconductance (MC) and magnetoelectroluminescence (MEL) in organic diodes from blends of pi-conjugated polymers and fullerenes at various concentrations, c The MC response is composed of several components that depend on the applied bias voltage and c A dominant positive low-field (LF) component, which also governs the MEL response, dramatically decreases and broadens in the blends, thus unraveling a positive high-field and negative LF components The positive MC components are caused by electrostatically bound e-h polaron pairs in unblended devices, and charge transfer pairs in the blends, which are dominated by two different field-induced spin sublevel mixing mechanisms In contrast, the negative LF response is due to e-e and h-h pairs; this is confirmed by studying MC in electron- and hole-unipolar devices, which lack positive MC response

/pdf/magnetic-field-effects-in-p-conjugated-polymer-fullerene-2jtuulb1lz.pdf

Magnetic Field Effects in π-Conjugated Polymer-Fullerene Blends: Evidence for Multiple Components

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-003859.pdf

Magnetic field effects in $\pi $-conjugated polymer/fullerene blends; evidence for multiple components

Single-layer polymer light-emitting field-effect transistors (LEFETs) that yield EQEs of >8% and luminance efficiencies >28 cd A(-1) are demonstrated. These values are the highest reported for LEFETs and amongst the highest values for fluorescent OLEDs. Due to the electrostatics of the ambipolar LEFET channel, LEFETs provide an inherent advantage over OLEDs in terms of minimizing exciton-polaron quenching.

Highly Efficient Single‐Layer Polymer Ambipolar Light‐Emitting Field‐Effect Transistors

The effect of magnetic field on the intensity of electroluminescence from devices made of a poly-$p$-phenylenevinylene (PPV) copolymer was investigated. The emission intensity was enhanced by the application of magnetic field, and the magnitude of the increase depended on operational voltages. When the device was operated under application of low voltages, the intensity increased with magnetic field and reached an 8.5% increase at about $100\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$. With the increase of the operational voltage, the effect of magnetic field was lessened. In addition, when measured at high voltages with increasing magnetic field, the emission intensity started to decrease after passing a maximum, then leveled off. This saturation value was slightly higher than that observed in the absence of magnetic field. These findings suggest that two processes sensitive to magnetic field are included in the emission processes. They are assigned to the charge recombination (CR) of anion and cation radicals and triplet-triplet annihilation (TTA) processes. From the analysis of the effects of magnetic field on the emission intensity based on a kinetic model, we quantitatively determined the fractions of singlet and triplet excitons generated through the CR process to be 0.17 and 0.83, respectively. With the increase of the concentration of triplet excitons in the organic layer, production of singlet excitons through the TTA process was enhanced, and the total yield of the singlet excitons exceeded 0.5 under normal device operational conditions. We conclude that this high yield is responsible for the high emission efficiency observed in the light-emitting devices based on PPVs.

Yoshio Sakaguchi

Papers

Fractions of singlet and triplet excitons generated in organic light-emitting devices based on a polyphenylenevinylene derivative