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 (-NO(2) or -CN). Both polymers (PVK-AZO-NO(2) 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 similar to 10(5)-10(6). 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 (-NO(2) 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.