Defect States-Related Photothermal Conversion of UV Photons in TiO₂-Based Materials

Conversion of solar spectrum to heat has attracted widespread attentions. However, the efficient transformation of light in the ultraviolet region to heat is a great challenge. UV light-responsive TiO2 is herein studied for the photothermal conversion process. We found that N-doped TiO2 can show an increased photothermal internal conversion efficiency from 65% for TiO2 to 82% for N-TiO2 in the UV range. Hall tests (NT, trap density) and DFT simulations (ET, trap position) revealed that the defect density of deep-level defect states is greatly increased upon N doping. Accordingly, it is deduced that the photo-to-thermal process occurs through a defect-related nonradiative transition, and its efficiency (η) is strongly correlated with the defect states density (NT) and defect energy states (ET). Furthermore, this understanding of defect-correlated photothermal conversion could extend to other nonmetallic dopant systems (i.e., S dopants and the O vacancy).