Manipulation of ionic transport in anisotropic silver-based lead-free perovskite analogue with interstitial-iodide for enabling artificial synaptic functions

Halide perovskites have been emerging as attractive candidates for artificial synapses due to their intriguing and unique ionic transport behaviors. However, lead toxicity in commonly studied lead-based perovskites is still a serious constraint and potential lead-free perovskite alternatives with comparable properties are highly sought-after. Here, we demonstrate a lead-free perovskite analogue CsAg 2 I 3 as the active material in artificial synapses for the first time. The solution-processed CsAg 2 I 3 thin film shows long-term stability in ambient conditions, low surface roughness and interesting dual-ion diffusion behaviors. We identified that a small amount of hydroiodic additive can effectively tune the anisotropic crystal orientation of the CsAg 2 I 3 thin-film and introduce interstitial iodide dopants, which further enabled a reversible analog switching and a variety of synaptic behaviors, including analog switching, paired-pulse facilitation, and spike-dependent plasticity. Unlike typical mechanisms in the previous perovskite artificial synapses, the interstitial iodide dopants and the intrinsic silver ions in the CsAg 2 I 3 contribute to the formation and rupture of conductive filaments due to much lower diffusion energy barriers, leading to a distinct dual-ion resistive-switching phenomenon. Collectively, these findings provide insights into the unique ionic transport properties of lead-free silver halide materials and demonstrate their capacity toward brain-inspired neuromorphic computing applications. A lead-free perovskite analogue CsAg 2 I 3 has been demonstrated for artificial synapse applications. The hydroiodic additive induced anisotropic crystal orientation and interstitial-iodide doping are critical for enabling the reversible analogue switching of the artificial synapse device. A dual-ion diffusion behavior is observed, attributable to the interstitial iodide and intrinsic silver due to their low defect formation energies and ion-migration energy barriers. • A lead-free perovskite analogue CsAg 2 I 3 is reported as the active layer in artificial synapses for the first time. • A facile additive strategy is employed to induce anisotropic crystal orientation and interstitial iodides in the thin film. • The CsAg 2 I 3 thin film shows promise for artificial synapses with a variety of demonstrated synaptic behaviors. • The switching mechanism involves a unique dual-ion effect contributed by interstitial iodide and intrinsic silver. • Crossbar simulation for image recognition of the CsAg 2 I 3 -based artificial synapse show a high accuracy of 93 %.