Particle-free inkjet printing of nanostructured porous indium tin oxide thin films

Abstract

We report a simple, low-cost, single-step inkjet printing method for the fabrication of nanostructured, highly transparent and conductive ITO films, which completely avoids the use of ITO particles in the fabrication process. In our method, the inks are formed from a liquid solution presenting a properly selected mixture of indium and tin acetates. After jet printing, the ink is decomposed during a subsequent annealing step, in which the released CO₂ gas bubbles control the ITO nucleation process to provide a porous film texture. We show that the fabricated ITO films are highly crystalline, stoichiometric, and nanoporous with controlled porosity. Electrical measurements show relatively low resistivity values for the films (down to 0.029 Ω cm) comparable to those of the best ITO thin films fabricated by other methods. Optical ellipsometry tests demonstrate a relatively high refractive index (1.5–1.7) and high transparency of the films over a wide region of the spectrum ranging from 500 to 1700 nm. Since the method does not require any pre-fabricated ITO particles, masks or templates, and enables the deposition of films on substrates of various materials and shapes, it can be employed for fabrication of nanoporous ITO films for a diversity of applications, including solar cell, bio- and chemical sensing, etc.