Additive manufacturing of transparent conductive indium tin oxide by sol-gel and multiphoton absorption polymerization

Many optoelectronic devices, such as solar cells and LEDs, require materials that possess both transparency and conductivity. Indium tin oxide (ITO), the most commonly used transparent conductor, is limited to flat thin films and, therefore, cannot be used in 3D electronics. Herein, we present the fabrication of complex 3D ITO structures at sub-micron resolution via multiphoton absorption polymerization (MAP), a vat photopolymerization technology, by combining sol-gel chemistry and radical polymerization. Following the MAP fabrication, heat treatment is applied to convert the gel into a ceramic ITO. The sintering temperature affects the porosity, electrical conductivity, and transparency of the printed ITO structures. Electrical conductivity was measured for printed objects sintered at temperatures starting at 700 °C up to 1150 °C with a maximum bulk conductivity of 14.47 ± 1.54 S/cm at 1000 °C and maximal transparency above 90 %. Enabling the fabrication of full 3D conductive ITO micro-structures via MAP, this work unlocks new possibilities and perspectives for the fabrication of 3D optoelectronic devices with transparent and conductive components.