Continuous Liquid Metal Printed 2D TCO Superlattices

Two-dimensional (2D) conducting metal oxides offer unprecedented control of thin film electrostatics at the nanoscale. We present a scalable, roller-based continuous liquid metal printing (CLMP) approach for fabricating large area (100 cm²) layered transparent conductive oxides (TCOs) via rapid low-temperature Cabrera-Mott oxidation of compliant liquid metals (Ga, In). We exploit repeating heterostructures of these 2D oxides (3 nm per layer) to produce TCOs at 180 °C with record conductivity while simultaneously raising visible range transmittance above 98%. HRTEM and XRD characterization reveal the unique 2D film morphology consisting of large grained cubic InO_x layered with amorphous GaO_x. To investigate the impact of modulation doping at the type I heterojunction between InO_x / GaO_x, we also present XPS, UV-Vis, and Hall characterization. Our rapid (6 m / min) low-temperature CLMP approach yields flexible TCOs that demonstrate 20X enhanced strain tolerance while requiring zero post-annealing and offering greater conductivity than low-temperature ITO, which is limited by poor dopant activation. These capabilities establish CLMP 2D TCOs as a promising set of transparent electrode materials for flexible optoelectronic devices such as photodetectors and displays.