Electronic structure and optical properties of Bi,N co-doped SnO₂

The geometry, electronic structure, and optical properties of Bi and N co-doped SnO₂ are investigated by first-principles calculations. The calculated results show that the N and Bi atoms can be introduced to intrinsic SnO₂ with reasonable formation energy (8.95–9.61 eV/cell) at different sites. Interestingly, the BiSn₁₅O₃₁N presents the character of indirect gap semiconductor with n-type conductivity. Increasing the doping concentration of N or Bi, BiSn₁₅O_32−x N _x (x = 2,3) behaves like a hole-rich semiconductor, while Bi_ySn_16−y O₃₁N (y = 2,3) possesses the characteristic of metal. Moreover, the band gap of doped structures becomes smaller than intrinsic SnO₂ due to the emergence of energy bands contributing from doping elements near the Fermi level. The absorption intensity is enhanced in UV region, and the optical absorption edge shows red-shift phenomenon for all the doped systems. Our results on Bi,N co-doped SnO₂ display the improved capacity of absorption and broadened absorption region. These findings can be utilized in light sensor and solar cell.