High-Field Magnetoresistance of Organic Semiconductors

Abstract

The magneto-electronic field effects in organic semiconductors at high magnetic fields are described by field-dependent mixing between singlet and triplet states of weakly bound charge carrier pairs due to small differences in their Landé g-factors that arise from the weak spin-orbit coupling in the material. In this work, we corroborate theoretical models for the high-field magnetoresistance of organic semiconductors, in particular of diodes made of the conducting polymer poly(3,4ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) at low temperatures, by conducting magnetoresistance measurements along with multi-frequency continuous-wave electrically detected magnetic resonance experiments. The measurements were performed on identical devices under similar conditions in order to independently assess the magnetic field-dependent spin-mixing mechanism, the socalled Δ mechanism, which originates from differences in the charge-carrier g-factors induced by spinorbit coupling.

Isotope Effect in the Magneto‐Optoelectronic Response of Organic Light‐Emitting Diodes Based on Donor–Acceptor Exciplexes

“…Following the MEL studies at low temperature, we consider that the "Δg-mechanism" of spin-1/2 polaron pairs dominates the MEL response at cryogenic temperatures, as concluded in previous studies. [32,33,38] This mechanism should not be strongly isotope dependent though, in contrast to our observations shown in Figure 3c,d. The FWHM of the MEL(B) is generally not determined by the HFI when the Δg-mechanism governs the MEL response.…”

Temperature and current dependence of the magnetoresistive behavior of poly(styrene-sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS)

“…To our knowledge, the experimental data presented above reflects the most comprehensive study of PEDOT:PSS magnetoresistance. It is consistent with previously reported behavior of magnetoresistance of PEDOT:PSS thin-film diodes, 14,23 and it reveals the full complexity of the PEDOT:PSS magnetoresistance due to its nontrivial dependence on the device operating point. Although it has been previously concluded that intermediate and ultrasmall magnetic field effects have to originate from different microscopic effects, given the strong differences in the evolution of the magnitude with magnetic field, the clear correlation of the FWHM of the intermediate magnetic field effect ΔB and the minimum of magnetoresistance attributed to the ultrasmall magnetic field effect B m put the interpretation of magnetoresistance data based on these phenomenological characteristics in question.…”

Correlation between bias-dependent ESR signals and magnetic field effects in organic light emitting diodes

“…The MC and MEL curves of organic materials have been shown to be well reproduced empirically by the non-Lorentzian function {H/(|H| + H 0 )} 2 (H 0 is the quarter-saturation field) 2,41 typically in the magnetic field region much lower than a few thousand gauss, over which the contribution from Δg-dependent MC could be dominant (Δg is the difference of the g-factor between the hole and electron carriers). 42 Actually, the obtained MC and MEL curves were found to match the function using the following parameters: H 0 values for MC are 20G (3.5 V) and 18G (4 V) and H 0 values for MEL are 30G (3.5 V) and 35G (4 V), as shown in Figs. 3(a) and 3(b).…”

“…We note here that, in the low magnetic field region typically below 50G, MC could include a low field effect indicated by the function of H 2 /(H 2 + H 0 0 2 ) (H 0 0 is a constant). 42,43 This effect is typically observed with the opposite sign to the contribution from the non-Lorentzian function. Yet, the MC in Fig.…”

“…It has been recently proposed that the spinmixing between S and T 0 is associated with Δg. 42 Thus, Δg could affect the competition relation between the spin-mixing and the dissociation /recombination processes. The present model is partly similar to those proposed previously for the MFEs of OLEDs.…”