Direct Printing of Electronics on Flexible Porous Substrates

Porous substrates such as paper and fabric are foundational to the future of flexible electronics. Over 60% of flexible electronics applications, including wearable health monitors, environmental sensors, and e-textiles, rely on porous substrates due to their breathability, flexibility, and affordability. However, ink spreading, solvent penetration, and substrate swelling significantly challenge their large-scale fabrication. Here, we utilize Drop Impact Printing (DIP), a nozzle-free technique that reliably deposits highly concentrated inks (up to 70% mass loading) onto untreated porous substrates, preserving their intrinsic properties. DIP effectively reduces lateral ink spread and penetration by precisely ejecting microdroplets via a sieve-impact mechanism, enhancing particle retention, conductivity, and mechanical durability under bending. Microsupercapacitors and humidity sensors fabricated using DIP exhibit remarkable performance improvements. Specifically, the 70% mass-loaded microsupercapacitor shows approximately a 41-fold increase in areal capacitance compared to the 10% loading at high scan rates, while humidity sensors demonstrate nearly a 60% increase in maximum response when ink concentration rises from 10% to 55%. Furthermore, we demonstrate an integrated, self-powered humidity-sensing system, along with a wireless humidity-sensing setup fabricated entirely using DIP, underscoring its applicability to real-world flexible electronics.