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 TiO 2 is herein studied for the photothermal conversion process. We found that N-doped TiO 2 can show an increased photothermal internal conversion efficiency from 65% for TiO 2 to 82% for N-TiO 2 in the UV range. Hall tests ( N T, trap density) and DFT simulations ( E T, 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 ( N T ) and defect energy states ( E T ). Furthermore, this understanding of defect-correlated photothermal conversion could extend to other nonmetallic dopant systems (i.e., S dopants and the O vacancy).