Controlled aqueous synthesis of ultra-long copper nanowires for stretchable transparent conducting electrode

The environmentally benign synthesis of ultra-long copper nanowires with successful control of diameter and length for stretchable transparent conducting electrodes (TCEs) is reported. Ultra-long copper nanowires (CuNWs) with an average length of 92.5 μm (maximum length up to 260 μm) and an average diameter of 47 nm were synthesized using environmentally friendly water-alcohol mixtures and l-ascorbic acid as a reducing agent. A facile removal of insulating surface layers, such as organic capping molecules and copper oxide/hydroxide, by short-chain organic acid treatment allowed low contact resistance between the CuNWs without post-reductive treatment at elevated temperatures. The CuNWs were directly spray-coated on glass or polydimethylsiloxane (PDMS) at a low processing temperature of 130°C. The CuNW TCE on a glass substrate exhibited a low sheet resistance of 23.1 Ohm sq^-1 and a high optical transmittance of 84.1% at 550 nm. Furthermore, the CuNWs were directly spray-coated on stretchable PDMS, which showed a low sheet resistance of 4.1 Ohm sq^-1 and a high optical transmittance of 70% at 550 nm.