Crystallized Cu2O films fabricated at low substrate temperature of 50–90 °C by spin-spray method

Crystalline Cu2O films were fabricated via the spin-spray method at substrate temperature (Ts) below 90 °C, without the post heat treatment. Grain size, crystal orientation and optical band gap controls of Cu2O films were achieved by changing Ts. The film orientation was delicately tuned in sequence from {111} to {200} with Ts increasing from 50 to 90 °C. The Cu2O film fabricated at Ts of 70 °C had a film thickness of 1.19 µm and consisted of a columnar structure with an average diameter size of 0.8 µm. In contrast, the films fabricated at Ts of 90 °C were composed of nanoparticles with diameters less than 0.1 µm. It was observed that a smaller grain size on the film surface corresponded to a wider optical band gap. Notably, the film fabricated at Ts of 50 °C exhibited a relatively wide band gap of 2.97 eV due to the quantum size effect.