Microwave calcination of electrospun ITO nanofibers and improvement of transparent electrode characteristics through vacuum rapid thermal annealing

In this study, we applied microwave annealing (MWA) to calcinate indium tin oxide (ITO) nanofibers synthesized by electrospinning and evaluated the potential of the process by comparison with conventional thermal annealing (CTA). The MWA calcination was carried out for 2 min at 1800 W (processing temperature of 530 °C) with microwave at the frequency of 2.45 GHz, and CTA calcination was carried out for 30 min at 600 °C. We found that ITO nanofiber electrodes calcined by MWA have nearly equivalent physical properties as those calcined by CTA despite a lower processing temperature and shorter processing time. Subsequently, we applied vacuum rapid thermal annealing (RTA) at 300 °C for 30 s to the calcined nanofibers, which increased the crystallite size and created vacancy-like oxygen defects, thereby increasing the electron concentration and further reducing the resistance of the ITO nanofiber electrodes. Therefore, low-thermal-budget MWA calcination and vacuum RTA can effectively improve the properties of ITO nanofibers and contribute to the development of transparent and flexible electrodes.