Gate-reconfigurable metal-oxide/polymer heterojunction phototransistors for broadband photodetection and multifunctional opto-synaptic computing

Abstract

Reconfigurable optoelectronic devices capable of integrating broadband photodetection with neuromorphic computation are highly desirable for next-generation intelligent systems. Here, we demonstrate a bilayer heterojunction phototransistor comprising zinc-tin oxide (ZTO) and poly(3-hexylthiophene) (P3HT), which exhibits gate-tunable photoconductance and multifunctional opto-synaptic behavior. The device achieves broadband photoresponse across ultraviolet and visible wavelengths, with responsivities of 2.5 × 10⁻¹ A W⁻¹ at 365 nm and 1.6 × 10⁻² A W⁻¹ at 520 nm, accompanied by specific detectivities of 2.4 × 10¹² Jones and 1.5 × 10¹¹ Jones, respectively. Gate-controlled reversible switching between positive and negative photoconductance (PPC/NPC) is achieved within a single ZTO/P3HT heterojunction phototransistor. This dual behavior originates from the asymmetric charge dynamics within the bilayer architecture. Under illumination, photogenerated holes are confined within the P3HT layer, while photogenerated electrons are transferred and accumulated in the ZTO layer. This interlayer coupling between the polymer and oxide layers enables bias-dependent modulation of carrier transport pathways, allowing dynamic and reversible transition between PPC and NPC within the same device. Beyond photodetection, the phototransistor effectively emulates key synaptic behaviors, including paired-pulse facilitation (PPF), short-term plasticity (STP), long-term plasticity (LTP), and diverse spike-dependent plasticity rules. The underlying physical mechanism of positive and negative correlations in spike-rate-dependent plasticity (SRDP) is elucidated as a competition between fast and slow relaxation dynamics under optical–electrical co-stimulation. Furthermore, convolutional neural network (CNN) simulations based on the device demonstrate robust image recognition performance, with recognition accuracy exceeding 98% after reinforcement by optical pulse modulation. These results highlight the potential of the ZTO/P3HT heterojunction as a reconfigurable opto-synaptic platform, bridging broadband photodetection and neuromorphic computing for future intelligent vision and in-sensor processing systems.