All Density Functional Theory (DFT) calculations were performed using the Vienna ab initio simulation package (VASP) code. Density functional perturbation theory (DFPT) and phonon dispersion calculations were performed using the Perdew-Burke-Ernzerhof for solids (PBEsol) exchange-correlation functional which adopts the Generalised Gradient Approximation (GGA). The rest of the calculations were performed using the PBE0 hybrid functional and has been shown to accurately predict the electronic structure of Sb(V)based oxides. Plane-wave cutoff and k -point sampling were tested and converged using vaspup2.0, with a cutoff energy of 500 eV and a k -point sampling of 6 × 6 × 5 for the 14-atom primitive cell of Sb 2 O 5 found to be sufficient for total energies converged to 1 meV/atom. The crystal structure of Sb 2 O 5 was visualised using vesta. The electronic band structure and density of states were plotted using the sumo package. Charge transport properties were obtained and plotted using amset and ThermoParser. Phonon dispersion curves were calculated using phonopy and plotted using ThermoParser. The band alignment of bulk Sb 2 O 5 was calculated using the core and vacuum energies from a 30 Å thick (001) surface slab with 20 Å of vacuum, using the surfaxe package. For defect calculations, a 112-atom supercell from a 1 × 2 × 2 expansion of the Sb 2 O 5 conventional cell was used to minimize the interactions between periodic defects. To sample the defect configuration landscape and search for ground and metastable defect structures, the ShakeNBreak approach was used to initially generate Γ-point-only relaxations for each defect with 10 different local distortions. The ground-state structure found in these initial relaxations was then selected for structural optimization with a converged Γ-centred 2 × 2 × 2 k-point mesh to obtain the total energy of the ground-state defective supercell.