Fig. 1. (Color online) (a) Four basic circuit elements: resistor, capacitor, inductor and memristor. Reprinted from Ref. [28]. (b) The variable resistance model of memristor proposed by Strukov et al. Reprinted from Ref. [29]. (c) Schematic diagram of a typical sandwich structure memristor of Au/MAPbI_3−xCl_x/ITO. Reprinted from Ref. [14]. (d) Ta/Ta₂O₅:Ag/Ru high resolution transmission electron microscope (HRTEM) image and typical abrupt I–V curve. Reprinted from Ref. [30]. (e) Schematic of vertical structure Au/MAPbI₃/PEDOT:PSS/ITO and dark current of memristor. Reprinted from Ref. [32]. (f) Schematic diagram of synaptic working principle. Reprinted from Ref. [35]. (g) Diagram of atomic switches in ON and OFF states via ECM mechanism. Reprinted from Ref. [44]. (h) Schematic diagram of VCM-induced resistance switching behavior. Reprinted from Ref. [45]. (i) Schematic diagram of Schottky barrier for TiN/SiO₂/Si structure. Reprinted from Ref. [53].

Fig. 2. (Color online) (a) Atomic structure diagram of perovskite. Reprinted from Ref. [60]. (b) Structure of CsPbBr₃ nanocrystals. Reprinted from Ref. [64]. (c) Au/CH₃NH₃PbI_3–xCl_x/FTO device structure chemical diagram and voltage application diagram. (d) Scanning electron microscope (SEM) image of the surface morphology of the CH₃NH₃PbI_3–xCl_x film. (e) Cross-sectional SEM image of Au/CH₃NH₃PbI_3–xCl_x/FTO. Reprinted from Ref. [67].

Fig. 3. (Color online) Properties of halide perovskites. (a) Tunable bandgap. Reprinted from Ref. [72]. (b) Variable structure. Reprinted from Ref. [76]. (c) High carrier mobility. Reprinted from Ref. [71]. (d) Good light absorption. Reprinted from Ref. [79]. (e) Ultra-high flexibility. Reprinted from Ref. [80].

Fig. 4. (Color online) (a) Schematic diagram of Ag/PMMA/MA₃Sb₂Br₉/ITO device structure. (b) Crystal structure of MA₃Sb₂Br₉. (c) Cross-sectional SEM image. (d) I–V characteristics of a memristor based on MA₃Sb₂Br₉. (e) Durability. (With a write voltage of −0.5 V, a reset voltage of 1.2 V, and a read voltage of 0.01 V, the pulse width is 1 ms.) (f) Retention time. (Write voltage is −0.5 V, and read voltage is 0.01 V.) (g) Measure of the HRS and LRS data reliability of 30 units at 0.01 V. (h) X-ray diffraction pattern of the MA₃Sb₂Br₉ layer deposited on ITO. (i) Absorption spectrum of MA₃Sb₂Br₉ film. (j) Device resistance-switching at different compliance currents. (k) Sb 3d XPS spectra of MA₃Sb₂Br₉ film on the ITO substrate. Reprinted from Ref. [86].

Fig. 5. (Color online) STDP for OTP synaptic devices. (a) Schematic representation of biological synapses. (b, f) Asymmetric Hebbian rules. (c, g) Asymmetric anti-Hebbian rules. (d, h) Symmetrical Hebbian rules. (e, i) Symmetrical anti-Hebbian rules. Reprinted from Ref. [95].

Fig. 6. (Color online) (a) I–t response of the device under ON/OFF switch lighting (at a read voltage of 10 mV). (b) I–t response of the device under ON/OFF switch lighting at reading voltages of 0.1, 1, or 10 mV, respectively. (c) A schematic diagram of a logical OR with two input sources and one output. (d) Schematic diagram of the light-induced structure of the device and the schematic of the logical OR gate. Reprinted from Ref. [103]. (e) A schematic diagram of a logical OR gate structure with two input signals and one output signal. (f) Logarithmic I–V curve of a two-layer device measured in the dark and under a wavelength of 442 nm (1.01 mW/cm²). (g) I–t curve of the device at 0 V. (h) Resistance-switching speed of the device at a light intensity of 1.01 mW/cm². Reprinted from Ref. [104].

Fig. 7. (Color online) (a) Schematic diagram of PPF measurement. (b) PPF ratios measured at different illumination intensities (0 to 0.38 µW/cm²). Inset: PPF ratio and fit normalized using function. (c) Correlation between the decay time constant measured in the dark and light exposure and the number of stimulation pulses. (d) When the device is repeatedly stimulated with electrical pulses under dark (upper) and light (0.19 µW/cm²) (lower), the conductivity maintains the curve. (e) The conductance retention curve of the device in LTM mode in which light is applied and removed alternately (1.29 µW/cm²). (f) Evolution of device conductance of devices that have been programmed in the LTM scheme in the dark. Under dark and light conditions (1.29 µW/cm²), the device was stimulated with electrical pulses. Reprinted from Ref. [107]. (g) Schematic representation of biological synapses. The synaptic device is shown in the upper right corner. The illustration in the upper left corner is the crystal structure of 2D layered (C₆H₅CH₂CH₂NH₃)₂SnI₄. (h) Photocurrents of (PEA)₂SnI₄ film (red line) and (PEA)₂SnI₄-based photoconductor at the same 5 µW/cm² irradiation at 470, 590, and 660 nm, respectively (blue asterisk). (I) A cross-sectional view of an artificial synaptic device. The inset is an example of input light spikes and output PSC. (j) PSC changes (∆PSC) triggered by a spike pulse (wavelength = 470 nm, duration = 20 ms, power density = 11.6 µW/cm²) at a bias voltage (V_bias) of 2 V. (k, l) STP and LTP behaviors obtained by variable frequency light stimulation devices. Reprinted from Ref. [110].

Fig. 8. (Color online) (a) Processing metal halide perovskites with semiconductor technologies. (b) Optical photographs of MAPbI₃ and CsPbBr₃ under parylene thin layers before and after water immersion. (c) 3D schematic of the memristor structure. (d) Optical micrograph of the fabricated CsPbBr₃-based memristor; the scale bar is 10 μm. (e) I−V characteristics of the device. The inset shows the logarithmic scale of the I–V curve. Reprinted from Ref. [113].

Fig. 9. (Color online) (a) Schematic diagram of preparing a perovskite microplate array on a substrate. (b–d) Optical images of growth after the substrate was seeded for 1 minute and 2 minutes. Reprinted from Ref. [118]. (e) Schematic outline of the preparation procedures. (f–i) PDMS-CHT restricts the growth of the CsPbCl₃ solution. Bright-field and fluorescent microscope overlay images of exposure to UV light (360–380 nm) are shown. Reprinted from Ref. [119].

Fig. 10. (Color online) Morphology of solution on (a) isotropic substrate and (b) anisotropic MicroCP substrate with –NH₂. (c) High-speed camera observation and SEM images of the perovskite transformation process. Reprinted from Ref. [124].

Table 1. A summary of the electrical performance of HP-based RS devices.