Electrical conductivity switching and memory effects in poly(N-vinylcarbazole) derivatives with pendant azobenzene chromophores and terminal electron acceptor moieties

Bistable electrical conductivity switching and non-volatile memory effects were demonstrated in Al/polymer/indium-tin oxide sandwich structure devices, constructed from two poly(N-vinylcarbazole) derivatives with pendant azobenzene chromophores and terminal electron acceptor moieties (–NO2 or –CN). Both polymers (PVK-AZO-NO2 and PVK-AZO-2CN) exhibit write-once read-many-times (WORM) type memory effects, with low switching threshold voltages below −2 V and high ON/OFF current ratios of ∼105–106. The observed electrical bistability in both polymers can be attributed to the field-induced charge transfer interaction between carbazole electron donor and terminal electron acceptor (–NO2 or –CN) moieties, and subsequent charge trapping at the intermediate azobenzene chromophores. The proposed switching mechanism is supported by the changes in the UV-visible absorption spectra of the polymer film upon transition from the OFF to the ON state.