**4.2 Organics materials**

Organic active layer materials are generally small organic molecules, polymers (synthetic and natural), etc. These materials have gained a great deal of interest from researchers for resistive switching due to their attractive properties compared to


### **Table 1.**

*Summary of reported materials for memristors.*

#### **Figure 3.**

*Illustrations of types of active materials used in memristors.*

traditional metal oxides [61]. The properties include easy solution processing and good chemical, mechanical and morphological properties; also, it possesses high intrinsic flexibility. Although some of the organic molecules lack in stability portion; they overcome it by having a low operating voltage as well as a good memory window. These materials can serve as a good candidate for low-power operating memory systems. Some materials, such as poly(3-hexylthiophene) (P3HT) [50], poly(,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) [51], phenyl-C61-butyric acid methyl ester (PCBM) [62], phenanthrol [9,10-d] imidazole (PFT− PI) [53, 63], cobalt(III)-containing conjugated and nonconjugated polymers [63], polyaniline (PANI) [64], coppertetracyanoquinodimethane (Cu-TCNQ ) [54], etc., have shown good performance not only as the active layer but also as electron transfer layer in transistors, light-emitting diodes, and photovoltaic devices. These materials usually have shown the dual filament formation as an RS mechanism including the phase change, redox reactions, conformation change, and charge transfer mechanism. Due to the advantages of small organic molecules, such as easy modification in electronic properties and easy processing, these molecules can be used as an active medium in synaptic as well as memory devices.
