Ga³⁺ and Y³⁺ Cationic Substitution in Mesoporous TiO₂ Photoanodes for Photovoltaic Applications

The optoelectronic properties of transparent nanocrystalline TiO2 films were modified by the incorporation of a low level of Ga3+ or Y3+ cations. After optimizing their relative concentration level, we were able to increase in a noticeable manner the power conversion efficiency from 7.4% to 8.1% for gallium and even to 9.0% in the case of yttrium where all three photovoltaic (PV) performance parameters were improved simultaneously. The beneficial effect of gallium and yttrium on the PV characteristics is attributed to a lower electrical resistance and longer electron lifetime enhancing the charge collection efficiency in the transparent layer. We also herein demonstrate that the substitution of the titanium site by a trivalent element in the benchmark TiO2 enables the disposal of the “magic” TiCl4(aq) post-treatment. The potential of this approach was also confirmed in solid-state PbS quantum-dot (QD) solar cells. In particular, a gallium-containing TiO2 anatase photoanode generated twice as much short-circuit photocurrent density as the standard electrode. A 1.9% power conversion efficiency has been achieved by using a solid-state heterojunction of the doped TiO2 with a 100 nm of PbS QD overlayer and using a gold back contact.