Direct-Writing Meets Spin Coating: Hybrid Process for High-Performance, Low-Voltage OTFTs on Flexible Substrates

Flexible organic thin film transistors (OTFTs) offer a compelling pathway towardsnext-generation wearable and large-area electronics due to their mechanical flexibility, lightweight nature,and compatibility with low processing temperature. However, realizing scalable fabrication strategies thatdeliver both low-voltage operation and high performance remains a critical challenge. Conventional deposi-tion techniques, such as thermal evaporation and photolithography, although effective, require high-vacuumand cleanroom environments, making them unsuitable for cost-effective, large-area flexible electronics.Similarly, inkjet printing, while promising as an additive deposition technique, often suffers from nozzleclogging due to stringent ink requirements and limited viscosity ranges, which in turn limit material selection.Many OTFTs also exhibit high operating voltages due to low gate capacitance arising from low-permittivitydielectric layers. In this work, we present a fully solution-processable bottom-gate bottom-contact (BGBC)OTFT fabricated on a flexible Polyethylene Terephthalate (PET) substrate using a hybrid approach thatintegrates direct-write printing for electrode patterning and spin coating for active and dielectric layersdeposition. Silver nanoparticle (AgNP) ink was used to deposit the conductive electrodes, while Poly(Vinyl)Alcohol (PVA) and TIPS-pentacene were employed as the gate dielectric and organic semiconductor,respectively. The BGBC OTFT demonstrated a saturation mobility μ_sat of 9.91 × 10⁻² cm²/Vs, a thresholdvoltage V_th of –5 V, a subthreshold swing S of 75.5 mV/dec, and an on/off current ratio ION/IOFF of 104.All processing steps were conducted below 150 ◦C. These results validate the effectiveness of this hybridfabrication strategy for realizing high-performance, low-voltage OTFTs compatible with flexible substrates,advancing the pathway towards scalable wearable devices.