Electronic and optical properties of broad-spectrum transparent and conductive oxide films

As one of the most popular transparent conductive materials, tin-doped indium oxide (ITO) films have been widely applied in various optoelectronic devices operating within the visible spectrum. However, the optical transparency of ITO films in the middle and far-infrared wavelength ranges is ultralow, which limits the development of infrared optoelectronic devices. Studies on transparent and conductive ITO films with a broad spectrum are rare at present. In this work, we synthesized a series of high-performance ITO films at low temperatures, showing high transmittance and conductivity across the wavelength range from 300 to 10 000 nm, which is rarely reported. The crystal structures, electronic properties, and optical bandgaps of the ITO films were characterized using synchrotron-based x-ray diffraction, x-ray photoemission spectroscopy, low-temperature electrical transport, and optical spectroscopies. These ITO films can achieve transmittance of 99% at 536 nm, 88% at 2500 nm, and 46.5% at 6000 nm, while maintaining high conductivity. It is indicated that this high optical transmittance across the wavelength range from 300 to 10 000 nm may result from the red shift of the plasmon energy and the narrowed metallic band near the Fermi level. Moreover, these outstanding properties remain highly stable even after annealing at 600 °C in ambient conditions. Our work provides an approach to prepare highly stable, low optical loss, infrared-transparent, and conductive ITO films, which is important for advancing infrared optoelectronic technology.