The structural, electronic, and optical properties of organic-inorganic mixed halide perovskites CH₃NH₃Pb(I_1-y X_y)₃ (X=Cl, Br)

Methylammmonium lead iodide perovskites (CH₃NH₃PbI₃) have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH₃NH₃Pb(I_1-yX_y)₃ (X=Cl, Br; y=0, 0.33, 0.67). Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl^-/Br^- at I^-. Electronic structure calculations indicate that the valance band maximum (VBM) is mainly governed by the halide p orbitals and Pb 6s orbitals, Pb 6p orbitals contribute the conduction band minimum (CBM) and doping does not change the direct semiconductor material. The organic cationCH₃NH₃⁺ does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y=0 (0.793 eV) to y=0.33 (0.953 eV) then to y=0.67 (1.126 eV). The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.