Low-temperature sintering of silver-ammonia complex organic composite ink shows high conductivity for humidity sensors

The development of flexible electronic devices is faced with the challenge of difficult fabrication of complex functional structures on flexible substrates. In this paper, a high viscosity ink of silver-ammonia complex was developed based on the reductive ink principle. Using the electrohydrodynamic direct writing, composite fiber patterned printing was achieved on a flexible substrate. By low-temperature sintering of precursor fibers for reduction, a dense silver structure was formed on the surface, resulting in the formation of Ag/PEO conductive fibers. This approach avoided the high temperature damage to the flexible substrate and the adhesion of materials, while demonstrating good conductivity. The Ag/PEO conductive fibers exhibited different sensitivities to H2O molecules in low, medium, and high humidity environments, which were used to design a flexible Ag structure humidity sensor (ASHS) as a functional material. The ASHS showed a linear response relationship and a fast response speed in an environmental humidity range of 11% to 75%RH, enabling real-time monitoring of human respiration. This study demonstrates a promising application prospect of the silver-ammine complex ink in the field of flexible electronic devices.