Direct Printing of Electronics on Flexible Porous Substrates

ABSTRACT 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.