Structure-Function Coupling in Pyridyl Triazole Copolymers for Neuromorphic Synaptic Transistors

Organic ferroelectric transistors are excellent candidates as low-cost alternatives for synaptic devices. Specifically, interfaces with donor-acceptor semiconducting polymers and copolymers of poly-(vinylidene fluoride) (PVDF) are attractive for mimicking synaptic responses. By tailoring the linking unit between the pyridyl triazole (PyTr) acceptors and thiophene donors, three copolymers are synthesized incorporating selenium-substituted thiophene, benzothiadiazole, and fluorine-substituted thiophene linkers. Using the hexafluoropropylene copolymer of PVDF (PVDF-HFP) as the dielectric layer, the three PyTr semiconductors show p-type transport in transistor architectures with carrier mobilities between 0.1 and 0.2 cm² V^-1 s^-1. The synaptic plasticity is investigated by applying long-term pulsed voltages at the gate electrode to emulate potentiation and depression processes. To assess their neuromorphic functionality, the synaptic responses of the devices are tested for image recognition in a multilayer perceptron neural network. The copolymer with the benzothiadiazole linker achieved recognition accuracy close to 80%, whereas the one with a fluorine-substituted thiophene linker shows no synaptic behavior, highlighting the critical role of the semiconductor-dielectric interface. A detailed study of the interface trap density and morphology is performed to identify how interfacial properties directly influence synaptic device performance.