A Facile Method Based on Oxide Semiconductor Reduction for Controlling the Photoresponse Characteristic of Flexible and Transparent Optoelectronic Devices

A facile method is presented involving a reducing agent, sodium dithionite (Na2S2O4), to control the photoresponse characteristics of oxide semiconductors that detect visible‐light. The method exhibits extraordinary potential for fabricating a diverse range of optoelectronic devices. Due to its weak S–S bond, Na2S2O4 generates excessive subgap states and oxygen vacancies in hafnium–indium–gallium–zinc oxide (HIGZO) thin‐film during the reduction treatment (RDT). It is achievable to finely tune the photoresponse characteristic by adjusting the molarity of Na2S2O4, implying superior applicability of RDT into various applications. First, HIGZO phototransistors with photoresponsivity of 626.32 A W−1, photosensitivity of 3.32 × 107, and detectivity of 7.18 × 1011 Jones under 10 mW mm−2 of red light illumination are fabricated using 0.1 m Na2S2O4. Second, 0.5 m Na2S2O4 is chosen for photomemory‐based neuromorphic devices with a paired‐pulse facilitation index of 142.6% when the input pulse of red light with an intensity of 1 mW mm−2 is introduced. In addition, major synaptic functions such as short‐term memory and long‐term memory behaviors, originated from persistent photoconductivity and depending on sequential pulse condition, are successfully emulated. These results indicate that RDT can control the photoresponse of oxide semiconductors to expand the applicability of oxide semiconductors without using a light absorption layer. A facile method is developed using sodium dithionite (Na2S2O4) as a reducing agent for controlling the photoresponse characteristic of oxide semiconductors that detect visible light. The method has extraordinary potential for the fabrication of diverse optoelectronic devices, including phototransistors and photomemory‐based neuromorphic devices. Reduction treatment controls the photoresponses of oxide semiconductors, thus increasing their applicability without any need for a light‐absorbing layer.