Donor–acceptor conjugated polymers of arylene vinylene with pendent phenanthro[9,10-d]imidazole for high-performance flexible resistor-type memory applications

Abstract

We report the synthesis and resistive memory device characteristics of new donor–acceptor (D–A) conjugated poly(arylene vinylene) polymers, PVC-PI, PVT-PI, and PVTPA-PI, consisting of carbazole (C), thiophene (T), and triphenylamine (TPA) with pendent phenanthro[9,10-d]imidazole (PI). PVC-PI, PVT-PI, and PVTPA-PI synthesized by Stille coupling reaction have the optical band gaps of 2.86, 1.68, and 2.58 eV, respectively. These polymers possess similar HOMO energy levels (−5.08 to −5.18 eV), but different LUMO energy levels (−2.24, −3.40, and −2.60 eV for PVC-PI, PVT-PI, and PVTPA-PI, respectively). The PVC-PI flexible device with the sandwich configuration of PEN/Al/polymer/Al reveals the volatile static random access memory (SRAM) characteristic while the PVTPA-PI device exhibits the nonvolatile write-once-read-many-times (WORM) switching behavior. The above two devices could operate at low voltages (less than 2.5 V) with high ON/OFF current ratios (over 10⁴) and exhibit excellent durability upon repeated bending tests. However, the PVT-PI device only shows a diode-like electrical behavior. The polymer conformation affects the strength of D–A electrical polarization and charge trapping ability, leading to the variation of the volatility of the memory devices. The present study demonstrates that the prepared vinylene-based donor–acceptor conjugated polymers have excellent memory characteristics with reproducibility and reliability for advanced flexible organic electronics.