fig3

Figure 3. Heterojunction-based zero-power optoelectronic synapses. (A) Schematic illustrations of the working mechanism in heterojunction-based zero-power optoelectronic synapse correspond to the (i) original, (ii) illumination, and (iii) dark state, respectively. E_{c, p}, E_{c, n}, E_{v, p}, E_{v, n}, E_{F, p} and E_{F, n} represent the bottom of conduction band, top of valence band and Fermi levels of p-type and n-type semiconductors, respectively; (B) Schematic illustration of the vertically structured zero-power artificial photoreceptor based on the GaN/BiFeO₃ heterojunction; (C) UV light-induced learning-forgetting-relearning behavior, demonstrating visual memory emulation in the GaN/BiFeO₃-based neuromorphic sensor; (D) Visual memory emulation in a UV-sensitive artificial neuromorphic sensor. Subfigures (B-D) Reproduced with permission^[37]. Copyright 2025, John Wiley & Sons; (E) Schematic illustration of the F₁₆CuPc/C₈-BTBT heterojunction-based zero-power artificial optoelectronic synapse; (F) SRDP triggered by ten consecutive light pulses, with a duration of 50 ms under different pulse frequencies; (G) Schematic illustration of an artificial visual system, in which the front-end signal processing units are integrated within the image sensor array. Subfigures (E-G) Reproduced with permission^[38]. Copyright 2022, John Wiley & Sons; (H) Cross-sectional SEM image of the ZnO/WO_X heterojunction-based zero-power optoelectronic memristor; (I) Photocurrent under constant light stimuli on a dark background; (J) Photocurrent response of the device under background illumination and flash stimulation, demonstrating Weber’s law behavior; (K) Schematic diagram of the neuromorphic visual system, consisting of adaptive image preprocessing using a visual adaptive neuron and image recognition using a spiking neural network; (L) Spontaneous adaptation of overexposed images based on the experimentally observed frequency-dependent relaxation dynamics of the visual adaptive neuron. Subfigures (H-L) Reproduced with permission^[39]. Copyright 2025, John Wiley & Sons. UV: Ultraviolet; C₈-BTBT: dioctylbenzothienobenzothiophene; SRDP: spike-rate-dependent plasticity; EPSC: excitatory postsynaptic current; PMMA: poly(methyl methacrylate); ITO: indium tin oxide.