The bistable effects of CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole (PVK) polymer layer by using flexible poly-vinylidene difluoride (PVDF) and polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that CdSe/ZnS nanoparticles were formed inside the PVK polymer layer. Current-voltage (I-V) measurement on the Al/[CdSe/ZnS nanoparticles+ PVK]/ITO/PVDF and Al/[CdSe/ZnS nanoparticles+ PVK ]/ITO/PET structures at 300 K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing and emission of charges in the electronic states of the CdSe nanoparticles. A bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results. These results indicate that OBDs fabricated by embedding inorganic CdSe/ZnS nanoparticles in a conducting polymer matrix on flexible substrates are prospects for potential applications in flexible nonvolatile flash memory devices.

The bistable effects of ZnO nanoparticles embedded in an insulating poly(methyl methacrylate) (PMMA) polymer single layer by using flexible polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that ZnO nanoparticles were formed inside the PMMA polymer layer. Current-voltage (I-V) measurement on the Al/ZnO nanoparticles embedded in an insulating PMMA polymer layer/ITO/PET structures at 300 K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the ZnO nanoparticles, indicative of trapping, storing, and emission of charges in the electronic states of the ZnO nanoparticles. The carrier transport mechanism of the bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results by analyzing the effect of space charge.

Capacitance-voltage (C-V) measurements on Au/a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer containing core/shell CdSe∕ZnS nanoparticles (hybrid layer)/indium tin oxide (ITO) coated glass and Al/hybrid layer/ITO coated glass capacitors at 300K showed metal-insulator-semiconductor behavior with a large flatband voltage shift. This shift was due to the existence of the CdSe∕ZnS nanoparticles, indicative of trapping, storing, and emission of charge carriers in the CdSe∕ZnS nanoparticles. Symmetric and asymmetric C-V characteristics appeared in the Al/hybrid layer/ITO coated glass and Au/hybrid layer/ITO coated glass capacitors, respectively. A dipolar carrier trapping model is proposed to explain the symmetric behavior in the C-V curve.

Current-voltage and conductance-voltage (G-V) measurements on three-layer Al∕C60∕CdSe nanoparticles∕C60∕indium tin oxide (ITO) structures fabricated by using a spin-coating method showed a nonvolatile electrical bistable behavior. Capacitance-voltage (C-V) measurements on Al∕C60∕CdSe nanoparticles∕C60∕ITO structures showed a clockwise hysteresis with a flatband voltage shift due to the existence of the CdSe nanoparticles, indicative of memory effects in the devices. Current-time measurements showed that the devices exhibited excellent memory retention ability at ambient conditions. Possible operating mechanisms for the memory effects in the Al∕C60∕CdSe nanoparticles∕C60∕ITO devices are described on the basis of the G-V and the C-V results.

A hybrid polymer-nanocrystal (NC) light-emitting diode (LED) device with a single active layer structure is simply fabricated by a spin coating. From a high-resolution transmission electron microscopy (HRTEM) study, each PVK polymer particle is observed to be capped with TPBi molecules and CdSe/ZnS NCs are mainly distributed along the circumference of PVK and TPBi surfaces, resulting in a core-shell polymer-NC hybrid of [CdSe/ZnS]/TPBi/[CdSe/ZnS]/PVK. An Al/[CdSe/ZnS]/TPBi/[CdSe/ZnS]/PVK/indium-tin oxide(ITO)/glass LED shows electroluminescence (EL) centered at around 585 nm at the forward bias of +10 V, which clearly reveals that CdSe/ZnS NCs existing at the interface between PVK and TPBi act as recombination centers for excitons. In particular, EL can be observed at both forward bias and reverse bias, and this means that this device with an isotropic distribution of NCs has an inversion symmetry.