Fabrication and characterization of metal halide perovskite-based memristors: integration of an ionic buffer layer to control the hysteretic behaviour

The intrinsic hysteresis of perovskites in the current-voltage response can be exploited for memory devices like memristors. Since controlling the hysteresis is a fundamental point, the purpose of the this work was to study the effect on the device response due to the integration of an ionic buffer layer in an already studied configuration. The memristor configuration considered as reference was FTO/PEDOT:PSS/MAPbI3/Au. The material chosen for the buffer layer was poly(ethylene glycol) (PEG), doped with 1-buthyl-3- methylimidazolium idide (IL). Both the TOP configuration FTO/PEDOT:PSS/MAPbI3 /PEG+IL/Au, and the BOTTOM one FTO/PEG+IL/MAPbI3/Au have been tested. In order to obtain a thin film of good quality, different solvents and concentrations of ionic liquid in the polymer have been tested, as well as different conditions for the layer depo- sition. Once the optimal conditions were found, the electrical response and the structure of the devices were studied. The device activation was studied via cyclic voltammetry, finding different behaviours in each of the three cases. In order to see morphological changes in the perovskite, Scanning Electron Microscopy was performed with secondary and backscattered electron detection, while Grazing Incidence Wide Angle X-Ray Scat- tering measurements allowed to determine structural changes and different crystallites orientation with respect to the reference case. The three different devices that have been tested showed significant differences. The BOTTOM device exhibited a larger hysteresis than the reference but it was not possible to deactivate it after the first cycle, and the perovskite crystallization appeared different in this case. A more interesting case is represented by the TOP device which was the only one exhibiting activation for negative voltage. Moreover, not only the functionality but also the perovskite crystalline structure was deeply modified by the presence of the buffer layer.