White LED-assisted low-temperature sintering of paper electric circuits and their electronic application

Inkjet printed electronic devices, as a new kind of thin film electronics, have got much attention due to their advantages of fast manufacturing, flexibility and cost saving. The challenge of this field is efficient sintering at low temperature, which is necessary for the wearable and flexible electronic application, especially on heat-sensitive substrates, e.g. papers and plastics. To solve the cracking phenomenon at high-temperature sintering which is a common problem for photo paper substrate, we proposed an effective multiple-step method combining acetone washing with LED-assisted low-temperature heating. The sintering temperature was reduced dramatically through using this method, with the resistivity of silver tracks treated at 70 °C equal to that treated by thermal sintering at 150 °C. Thus, we broke through the bottleneck resulting from high-temperature sintering of cracking of long conductive tracks. The mechanisms of the capping agents' removal and LED-assisted low-temperature sintering were investigated by X-ray photoelectron spectra (XPS). Besides, the size of silver nanoparticles (NPs) was well controlled by adjusting the dropping speed of the solution, which helped improve the electrical performance of the ink. The surface properties including morphologic roughness, bonding strength and flexibility were also investigated. By combining inkjet-printing and post-processing method, we showed exemplary applications of paper electronics with fast-manufactured, no-mask-required, pattern-programmable and precisely-controlled characteristics. Our results provide a simple and convenient approach for developing high-performance flexible thin-film electronic devices based on inkjet printing technology.