Large magnetoresistance at room temperature in organic semiconductor devices

The magnetic field effect on the transport and efficiency of group III tris(8-hydroxyquinoline) organic light emitting diodes

“…The values of the critical field obtained for the two Lorentzians in this fit are 6.4 and 67 mT, which are comparable to the values obtained from the efficiency data for this sample. This result for Alq 3 suggests that if the mobility of the carriers is affected by the presence of triplets within the device, then there is also a B dependence of this interaction, which increases with increasing B field. For the Gaq 3 and Inq 3 samples, the B dependence of the OMR appears to be approximately linear and does not show the Lorentzian components, which are present in the efficiency data for these samples.…”

“…For the Gaq 3 and Inq 3 samples, the B dependence of the OMR appears to be approximately linear and does not show the Lorentzian components, which are present in the efficiency data for these samples. This implies that the interaction between the carriers and triplets at null field is weak for these materials, which suggests that for Gaq 3 and Inq 3 at null field, there is little energetic barrier for a carrier trapped at a triplet site, and so the increase in the triplet concentration has a negligible effect of the mobility at low magnetic fields. In addition, the observation that, for example, at a field of 30 mT, there is effectively no increase in the current through the device while there is a 1.5%-3% increase in the efficiency of the device is strong evidence that the change in efficiency cannot be a consequence of the OMR.…”

“…Mermer et al [2][3][4] showed that the effect of the magnetic field on the current through organic devices was a general phenomenon and could be observed in a range of both the small molecule and the polymer systems. They dubbed the effect of organic magnetoresistance ͑OMR͒.…”

Magnetoresistance in organic light-emitting diode structures under illumination

“…3 Recently, organic magnetoresistance ͑OMR͒ of up to ϳ15% has been observed in a number of organic materials commonly used for organic light-emitting diodes ͑OLEDs͒, and here the mechanism is still unclear. [4][5][6][7][8] These observations have been made in device structures with no magnetic components, and the effect is found to correlate with the onset of light emission from the device, which suggests that the effect is excitonic in nature. 9 The term organic magnetoresistance is something of a misnomer as the effect is seen in devices that exhibit highly nonlinear current-voltage characteristics and hence cannot be considered as a resistance in the classical sense.…”

The role of magnetic fields on the transport and efficiency of aluminum tris(8-hydroxyquinoline) based organic light emitting diodes

“…The effect of the magnetic field on the current through the device was attributed to an increase in the electron injection due to singlet excitons reaching the cathode and dissociating. The effect of a magnetic field on the current through organic materials was investigated further by Mermer et al [4][5][6] They observed that organic magnetoresistance ͑OMR͒ can be observed in a number of different systems and that the effect could be both positive and negative. Desai et al 7 investigated the role of the cathode material on the OMR of a typical Alq 3 based OLED structure and found that the OMR was intimately correlated with the light emission from the device so that at drive voltages below "turn on," no OMR was observed.…”