A-Site Cation Functional Engineering Enables Lead-free Perovskite Photosynapse for Neuromorphic Visual Computing

Optoelectronic synapses that directly couple light sensing with memory and computing functions offer a promising route toward energy-efficient neuromorphic vision systems. However, the development of high-performance perovskite synapses remains heavily reliant on lead-based perovskites, raising sustainability and toxicity concerns. Herein, we report a previously unexplored lead-free antimony halide perovskite, Cs₂AgSb₂I₉, and demonstrate its application as an ultralow-power optoelectronic photosynapse, enabled by A-site cation functional engineering. Specifically, incorporation of Ag into the perovskite lattice fundamentally modulates the electronic structure, suppressing excitonic confinement, enhancing carrier transport, and introducing energetically favorable Ag interstitial states that act as reversible charge trapping/detrapping centers to enable short-term memory. As a result, Cs₂AgSb₂I₉ devices exhibit extensive synaptic behaviors, including paired-pulse facilitation and spike-intensity-, spike-duration-, and spike-number-dependent plasticity, as well as Hebbian-like learning characteristics. Notably, the photosynapse can operate with an ultralow energy consumption of 6.18 × 10^-14 J per synaptic event, approaching the energy scale of biological synapses. Artificial neural networks based on Cs₂AgSb₂I₉ devices further demonstrate a high accuracy of 97.5% for image recognition. Overall, this work introduces a new lead-free perovskite platform and highlights A-site cation functional engineering as an effective strategy for realizing sustainable and low-power neuromorphic visual computing.