Optically Switchable Organic Field Effect Transistor via Intensity Modulated Single Near‐IR Source

Optically switchable organic field effect transistors (OFETs) offer an additional modality for conventional electronic devices, allowing their electrical output to be switched via a specific optical input. Previously, optically switchable OFETs employing photochromic molecules such as diarylethenes (DAEs) incorporated into the active layer have demonstrated the ability to remotely modulate charge transport via light stimuli. However, these require intense, high‐energy UV irradiation and a complex dual‐wavelength setup for reversible photoisomerization. An upconverting photonic field effect transistor (UPFET) is introduced that addresses these challenges by integrating multicolor upconversion nanoparticles (UCNPs) with a poly(3‐hexylthiophene) (P3HT)/DAE blended active layer. These UCNPs convert a single 980 nm NIR source into UV or visible emission, enabling bidirectional photoisomerization of DAE without harmful high‐energy UV exposure. Based on spectroscopic and morphological analyses of the P3HT/DAE blend film, 20 wt.% DAE is identified as the composition that preserves molecular mixing and maximizes interaction between P3HT and DAE, yielding up to approximately 40% drain‐current modulation. Consequently, the optimized UPFET exhibits stable and reversible drain current modulation with high on/off ratios, solely controlled by NIR light intensity. By combining a power‐tunable single NIR source, the UPFET offers a pathway toward low‐power optical memory, sensor, and logic circuits with simplified operation.