Flexible Phototransistors on Paper: Scalable Fabrication of PEDOT:PSS Devices Using a Pen Plotter

Phototransistors are used in plenty of diverse applications such as optical communication systems, light sensors, imaging devices, and biomedical instruments for detecting and amplifying light signals. Herein, an approach for the large-scale production of low-cost and flexible phototransistors by integrating the inks of PEDOT:PSS, and graphite with paper, which serves as an ionic conductor material to gate the PEDOT:PSS channel, is proposed. The fabrication of the devices is carried out by sequentially depositing the PEDOT:PSS channel and graphite electrodes onto paper using a benchtop XY plotter. To characterize device-to-device variability, 200 devices are fabricated and their electrical and optical properties are statistically analyzed. By performing a detailed characterization on the optical properties under varying wavelength, power, and bias conditions, it is found that devices exhibit good photoresponse across a wide spectrum range. Moreover, devices maintain their photoactive characteristics even when subjected to high mechanical tensile strain, indicating the suitability of these paper-supported devices for flexible electronic applications. Time and photocurrent magnitude can be tuned via gate voltages applied through the graphite-based back-gate configuration.