A physical explanation to the controversial Urbach tailing universality

Structural, opto-thermal and electrical properties of ZnO:Mo sprayed thin films

“…On the contrary, to understand the Urbach tailing distortion, which is due to Mo content, at relatively high amount (3%), it is important to point out the fact that Mo element has relatively high atomic radius against zinc one. This probably leads to an escape from ZnO matrix of some Mo x O y entities in these films [52]. Indeed, as reported elsewhere [53], it is known that Mo oxide can be found in various oxidation states with high oxygen index (Mo x O y , with 1ox o3 and 3oyo9).…”

Effect of Spinel Inversion on (CoxFe1−x)3O4 All‐Oxide Solar Cell Performance

“…At Fe ion compositions of above 41 %, the E opt1 band gap disappears and E opt2 increases, indicating that the concentration of Co 3+ decreases with increasing Fe cation incorporation, whereas Co 2+ maintains its concentration regardless of Fe ion levels. In Figure c, a tail states energy (Urbach energy) map shows that with Co ion incorporation from 85 % to 43 %, the Urbach energy increases from 0.32 to 0.61 eV. This means that as Fe ion incorporation increases, the material's structure becomes more disordered, as confirmed in both XRD and Raman results.…”

Defect generation, d-d transition, and band gap reduction in Cu-doped TiO2 nanoparticles

“…This defect tail is known as the Urbach tail, and the energy associated with this defect tail is referred to as Urbach energy. The equation for Urbach energy is given by α ¼ α 0 exp E E U , where α is the absorption coefficient, E is the photon energy, and E u is the Urbach energy [41,42]. The Urbach energy is calculated by plotting lnα vs. E. The reciprocal of the slopes of the linear portion, below the optical band gap, gives the value of E u .…”