Multifunctional and Robust Optoelectronic Synapses Based on Metal Oxide/Metalcone Heterojunctions by Atomic/Molecular Layer Deposition

Optoelectronic synaptic devices, which integrate optical sensing and synaptic plasticity, are pivotal for emulating biological visual systems and advancing neuromorphic computing. Herein, we report versatile optoelectronic synapses based on SnO₂/titanicone (Ti-based hydroquinone, Ti-HQ) heterojunctions fabricated via atomic/molecular layer deposition (ALD/MLD). The SnO₂/Ti-HQ heterojunction structure introduces abundant charge trapping sites and a built-in electric field, significantly enhancing the optoelectronic response and relaxation time compared to a single inorganic SnO₂ device. Importantly, this ALD/MLD-enabled optoelectronic heterojunction strategy exhibits general applicability and can be successfully extended to other metal oxide/metalcone systems. The SnO₂/Ti-HQ device emulates a variety of synaptic behaviors, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), transition from short-term plasticity (STP) to long-term plasticity (LTP), and the learning-forgetting-relearning process. The extremely low energy consumption per spike is confirmed in this device with ∼1.13 fJ at 0.1 mV ultralow bias voltage. Notably, the hybrid device also exhibits exceptional air stability, retaining 90% of initial EPSC after ambient storage for 9 months. Furthermore, optical logic operations and image preprocessing capabilities have been realized in the hybrid heterojunction devices. Its wavelength-dependent responses from ultraviolet to red light enable color discrimination. A proof-of-concept intelligent vehicle system, controlled by light wavelength, validates its potential for artificial vision. This work highlights a feasible and effective route for artificial optoelectronic synapses based on inorganic-organic hybrid heterojunctions by powerful ALD/MLD technology, showing enormous potentials in energy-efficient neuromorphic devices for multifunctional applications, especially in the biomimetic visual system.