Sustainable Multi-stack Printed Heaters on Paper with Efficient Heat Distribution

Printed heaters are emerging as a promising solution for flexible, sustainable, and eco-friendly applications, with potential uses ranging from wearable and portable devices to the automotive industry. This study addresses key challenges in heat uniformity and mechanical protection, by employing screen printing with water-based inks and biodegradable paper substrates. The multi-stack heater, composed of carbon, silver, and aluminum oxide (C/Ag/AlOx), demonstrates excellent electrical and thermal performance. At 5 V, the C/Ag/AlOx heater achieves a peak temperature of approximately 120 °C, with spatial temperature fluctuations within ±3 °C, offering superior thermal uniformity compared to bare Ag and Ag/AlOx heaters, which exhibit temperature gradients up to 10 °C. All configurations show robust durability during 6 h of 5 V cycling and minimal resistance changes during environmental stability tests under 80 °C and 80% relative humidity. In tape adhesion tests, the C/Ag/AlOx heater maintained nearly unchanged resistance after several peel cycles thanks to the protective AlOx coating. Finally, the ultralow cost multi-stack configuration (0.20 € per heater) embedded in a skin bandage reached a maximum temperature of 50 °C at 3.5 V, with a power density of 0.08 W/cm2, highlighting its potential for precise temperature control and homogeneous heating in thermotherapy applications.