Photocatalytic self-cleaning properties of thin films of photochromic yttrium oxyhydride

Oxyhydride of yttrium (YHO) belongs to an emerging class of materials, with oxide and hydride anions sharing the same sites in the lattice. Under sunlight irradiation, the material is transparent to visible light with transparency exceeding 85% and can absorb about 10% of sunlight. Furthermore, increasing light transmittance in the visible light enhanced the self-cleaning properties of the coated materials, making these materials promising candidates for smart windows applications. However, the light-absorbing properties of the materials were increased with exposure time, and in the photodarkening state, they can absorb about 40% of sunlight. Kelvin probe measurements show work function values between 2.9 and 4.2 ​eV for YHO, depending on the H₂/Ar pressure in the deposition chamber. Using the Kelvin probe, we demonstrate that the work function decreases with decreasing deposition pressure and hydrogen flow. Measurements under solar light reveal a decrease of work function by 0.2 ​eV followed by a slow relaxation with the light off. Moreover, the self-cleaning test shows that the oxyhydroxide thin films have excellent photocatalytic activity and total self-cleaning in 40 ​h.