Solution-Processed Multi-Junction Optoelectronic Synapses for Mode-Switchable SWIR Neuromorphic Vision Sensing

Shortwave infrared (SWIR) optoelectronics are the main pillars for machine vision and perception. However, conventional photodetectors and neuromorphic sensors with complementary characteristics are more challenging to integrate into a single device architecture in the SWIR band. Herein, a bias-programmable back-to-back rectifying junction is designed to switch between high-speed photodetector and persistent optoelectronic synapse modes. Numerical models demonstrate how bias tunes the relative barrier heights of the multi-junction stack, thereby modulating the carrier dynamics and triggering transitions among different operation modes. This concept is experimentally implemented using IR-absorbing colloidal lead sulfide (PbS) quantum dots (QDs) assembled into anti-series p-n and Schottky junctions. For 1550 nm operation, cascaded p-n QD homojunctions effectively improve photodetector performance while strengthening the synaptic plasticity of photocurrent. The programmable device states enable image denoising and motion trajectory tracking. Notably, a unique synapse regime is identified to suppress static IR background and enhance the signal-to-noise ratio (SNR) of dynamic events, achieving static-dynamic fusion in SWIR vision. This solution-processable and voltage-controlled multi-junction design provides a scalable route toward spatiotemporal SWIR vision sensing systems.