Optical Printing of Conductive Silver on Ultrasmooth Nanocellulose Paper for Flexible Electronics

The nanofibrillated cellulose paper (nanocellulose paper or nanopaper), which is flexible, transparent, ultrasmooth, and biodegradable, has emerged as a new substrate material for the next generation of paper‐based flexible electronics. Herein a visible light‐induced printing technique for depositing highly conductive silver (Ag) patterns on nanopaper is reported. The optical Ag printing process is simple to implement at room temperature and only requires nontoxic, low‐cost aqueous chemical solutions and an inexpensive light projection setup. The abundant carboxyl groups on the nanopaper enable efficient absorption of Ag⁺ ions on the nanopaper surface for light‐induced reduction of Ag⁺ into a thin film of densely packed silver nanoparticles (AgNPs). Chemical annealing of the deposited AgNPs further enhances the conductivity of the printed Ag patterns. The mechanical and electrical properties of the printed Ag patterns on nanopaper are characterized, and the application of the optical Ag printing technique fabricating the nanopaper‐based flexible circuits and electrochemical biosensors is also demonstrated. The optical printing technique will enable new designs and applications of nanopaper‐based flexible electronics.