ITO and AZO films for low emissivity coatings in hybrid photovoltaic-thermal applications

We report on the electrical and optical properties of ITO and AZO films fabricated directly on silicon substrates under several growth and annealing temperatures. We use broadband spectroscopic ellipsometry measurements (from 300 nm to 20 μm) to obtain a consistent model for the permittivity of each of the films. The results are then used to design an optimized, single layer, high transparency, high conductivity film, suitable as front transparent electrode and low thermal emissivity coating for silicon based solar cells. The best performance is found using the properties of the ITO film grown at 250 °C, with a state of the art resistivity of 0.2 mΩ cm and an optimized thickness of 75 nm which leads to 0.79 average absorptivity in the solar range (300-2000 nm) and 0.21 average emissivity in the thermal range (5-20 μm). The structural characterization of the films using X-Ray diffraction, and the Hall mobility and resistivity measurements of all the films are also provided, complementing and supporting the observed optical properties.