Chiroptical Synaptic Heterojunction Phototransistors: Noise-Reduced Detection of Circularly Polarized Light via Self-Assembled Supramolecular Nanohelix of π-Conjugated Molecules

Chiroptical photodetectors have become increasingly important in a range of fields, including chiral imaging, spintronics, and quantum optics. To enable practical chiroptical optoelectronics, it is essential to develop high-performance chiroptical photodetectors with high responsivity, sensitivity, polarization direction identification, and device integration feasibility. This study presents the successful demonstration of high-performance chiroptical synaptic phototransistors utilizing heterojunctions comprising a self-assembled nanohelix of a π-conjugated molecule and a metal oxide semiconductor. In this work, heterojunction devices consisting of a chiral nanomaterial and semiconductor offer a promising strategy for developing high-performance chiral optoelectronic devices. To impart strong chiroptical activity, a novel diketopyrrolopyrrole-based, donor-acceptor type π-conjugated molecule decorated with chiral glutamic acid was newly synthesized, capable of supramolecular self-assembly through noncovalent intermolecular interactions. Through hydrogen-bonding-driven, gelation-assisted self-assembly, we obtained supramolecular nanohelix structure consisting of intertwining fibers with strong and stable chiroptical activity in solid-film form. Phototransistors based on interfacial charge transfer at the heterojunction from the chiroptical nanohelix to the metal oxide semiconductor exhibited exceptional chiroptical detection, with a high photocurrent dissymmetry factor and remarkable photoresponsivity. Interestingly, the chiroptical phototransistor displayed photonic synapse-like behavior, generating time-dependent photocurrents and persistent photoconductivity attributed to interfacial charge trapping. Leveraging the synaptic functionality advantage, a trained convolutional neural network achieved over 89 % accuracy in recognizing noise-reduced circularly polarized images of handwritten alphabetic characters.