This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.

triphenylamine-containing polymer (BTPA-F) organic redox system ( Figure 1 a). The conjugated copolymer of BTPA-F with a closed ring and steric crowded triphenylamine (TPA) group was used in the present study for its rich electrochemical redox behavior, [ 31,32 ] while the ethyl viologen diperchlorate (EV(ClO 4 ) 2 ) acted as the counter-electrode material for BTPA-F oxidation and a source of the mobile perchlorate ions to stabilize the charged form of the polymer. [ 20,[33][34][35] Sandwiched between two metal electrodes, the EV(ClO 4 ) 2 /BTPA-F bilayer structure exhibits history-dependent memristive behaviors, which meet the fundamental requirements for mimicking the potentiation and depression processes of a biological synapse. Consequently, a series of synaptic behaviors, including the spike-ratedependent and spike-timing-dependent plasticity (SRDP and STDP) characteristics, the transition from short-term memory (STM) to long-term memory (LTM), as well as the "learningforgetting-relearning" process, are successfully emulated in the present organic redox system. These demonstrations show the possibility of using organic materials for the construction of neuromorphic information storage and processing systems. Results and DiscussionPrepared via Suzuki coupling polymerization reaction (see Scheme S1 and the Supporting Information for details), the successful synthesis of the conjugated copolymer of BTPA-F was verifi ed through 1 H NMR, UV-vis absorption spectroscopy and electrochemistry analyses (Figures S1-S3, Supporting Information). When sandwiched between metal electrodes, the 450 nm EV(ClO 4 ) 2 /90 nm BTPA-F bilayer structure (Figure 1 b and Figure S4, Supporting Information) exhibits a distinctive history-dependent asymmetric resistive switching behavior at room temperature, as plotted in the current-voltage ( I -V ) characteristics of Figure 1 c. Initially, the Ta/EV(ClO 4 ) 2 /BTPA-F/Pt memristor shows a small conductivity of ≈ 0.03 S m −1 (read at 0.2 V). Upon being subjected to four consecutive positive voltage sweeps of 0 V → 1 V → 0 V, the device conductivity increases incrementally to 0.09 S m −1 . Afterward, fi ve consecutive negative voltage sweeps of 0 V → −1 V → 0 V have been applied onto the bilayer structure, while the device conductivity decreases continuously from 0.25 to 0.13 S m −1 (read at −0.2 V). The small rectifying effect may be ascribed to the difference in the molecular orbital energy levels of the BTPA-F polymer and the EV(ClO 4 ) 2 counter-electrode material, which in turn infl uences the charge transport across the EV(ClO 4 ) 2 /BTPA-F junction under electric fi elds of different polarities. Nevertheless, such a rectifying effect is useful for the single-direction

No abstract