Electrical Bistability and WORM Memory Effects in Donor–Acceptor Polymers Based on Poly(N‐vinylcarbazole)

Bistable electrical conductivity switching behavior and write‐once, read‐many‐times (WORM) memory effects have been demonstrated in Al/polymer/ITO sandwich devices. These devices were constructed from two poly( N ‐vinylcarbazole) derivatives with pendant donor–trap–acceptor (D‐T‐A) structures. The observed electrical bistability can be attributed to the field‐induced charge‐transfer interaction between the carbazole electron‐donor unit and the terminal electron‐acceptor unit, and subsequent charge trapping at the intermediate azobenzene chromophores. The charge‐transfer and trapping processes are further stabilized by the conformational relaxation of the total energy of the D‐T‐A system through donor–acceptor electrostatic interaction. The proposed switching and conduction mechanism is supported by density functional theory calculations, UV/Visible absorption spectra, core‐level X‐ray photoelectron spectra, and high‐resolution transmission electron microscopy images of the polymer thin films. The influence of the charge‐trapping effect of the azobenzene mediator is further explored by studying the electronic properties of two other poly( N ‐vinylcarbazole) derivatives as the control samples, in which nitro or cyano acceptor groups are directly bonded to the carbazole electron‐donor moieties.