Anisotropic Lead-Free CsCu₂I₃ Based Optoelectronic Synapse for Polarization-Sensitive Neuromorphic Vision

Polarization provides a critical yet often overlooked dimension of visual information, enabling enhanced perception of scattering, object orientation, and material anisotropy. However, conventional polarization-sensitive photodetectors are limited to passive sensing and lack the capability directly encode and retain polarization information in a neuromorphic manner. Here, we report a polarization-sensitive optoelectronic synaptic device based on lead-free anisotropic CsCu₂I₃ single crystals. Benefiting from the intrinsic one-dimensional chain-like crystal structure of CsCu₂I₃, the device exhibits pronounced polarization-dependent photoresponses with a high dichroic ratio of up to 2.71, together with broadband UV–Vis sensitivity. More importantly, the polarization state of incident light directly modulates the synaptic response (ΔEPSC), enabling device-level coupling between polarization-sensitive photodetection and synaptic-state modulation. The device successfully emulates essential synaptic behaviors, including pair-pulse facilitation and spike-dependent plasticity modulated by pulse width, frequency, intensity, and number. In addition, polarization-dependent image reconstruction and contrast enhancement are demonstrated based on the experimentally measured polarization-dependent synaptic responses. This work establishes anisotropic lead-free halide single crystals as a promising material platform for energy-efficient and polarization-aware neuromorphic optoelectronic devices.