Broadband High-Gain Phototransistors Enabled by Interfacial Charge Transfer in ZTO/PM6:Y6 Composite Channels

Interfacial charge transfer in composite semiconductor channels provides a powerful and physically transparent route to achieving broadband and high-gain phototransistors, yet remains insufficiently explored in indium-free oxide-organic systems. Here, we report a broadband-responsive hybrid phototransistor based on an all-solution-processed composite channel composed of zinc-tin oxide (ZTO) and an organic bulk heterojunction PM6:Y6. In this architecture, amorphous ZTO serves primarily as a high-mobility, low-noise electron transport channel with excellent gate controllability, while the PM6:Y6 bulk heterojunction supplies strong and broadband optical absorption, enabling efficient photocarrier generation from the ultraviolet to the near-infrared region. Efficient interfacial charge transfer at the oxide/organic interface allows photogenerated electrons in the PM6:Y6 layer to be injected into the ZTO channel, where they are rapidly transported and amplified by the field-effect conduction pathway. Systematic optoelectronic characterizations reveal that the resulting high gain originates from interfacial carrier separation and accumulation at the composite channel, rather than from direct charge transport within the organic layer alone. As a result, the device exhibits pronounced photocurrent enhancement across the ultraviolet-visible-near-infrared spectral range, with a photosensitivity exceeding 5 orders of magnitude, a maximum responsivity of 9.13 × 10³ A/W, and a specific detectivity on the order of 10¹⁵ Jones. By replacing indium-containing oxides with solution-processed ZTO, this work demonstrates that broadband high-gain photodetection can be realized without relying on indium-specific electronic properties. These results establish interfacial charge transfer as a general and scalable physical mechanism for designing indium-free, broadband, and high-performance oxide-based phototransistors.