Correlation between the width and the magnitude of magnetoconductance response in π-conjugated polymer-based diodes

Hyperfine interaction (HFI) has been considered as a dominant spin mixing mechanism in conventional semiconducting polymers causing large magnetoconductance (MC) in organic diodes. However, the relationship between the MC width or HFI strength and the MC magnitude has not been investigated. We studied the correlation between the width and the magnitude of the MC response in organic diodes made by several conventional π-conjugated semiconducting polymers. First, by comparing the MC responses in electron- and hole-only unipolar devices made by the same polymer, we found that the electron-only device with a larger MC width always show a larger MC magnitude than that in the corresponding hole-only device. Second, we intentionally decreased and increased the charge localization or HFI strength in these unipolar devices by controlling their annealing temperature and UV irradiation, respectively. We found that the MC magnitude in these unipolar devices generally increases when the HFI strength increases but with different rates. We conclude that the width of MC or HFI strength is a crucial but not a unique factor that influences the MC magnitude. Finally, although the HFI in bipolar devices is smaller than that in the corresponding electron-only devices, the MC magnitude in bipolar devices is always larger than that in the electron-only devices suggesting that their underlying mechanisms are different.