Crystal structure, stability and optoelectronic properties of the   organic-inorganic wide bandgap perovskite CH3NH3BaI3: Candidate for   transparent conductor applications
  Structural stability, electronic structure and optical properties of CH3NH3BaI3 hybrid perovskite is examined both from theory as well as experiment. Solution-processed thin films of CH3NH3BaI3 exhibited a high band gap of approximately 3.87 eV, which is in excellent agreement with the theoretical estimate of 4 eV. Also, the XRD patterns of the thin films match well with the l-peaks of the simulated pattern obtained from the relaxed unit cell of CH3NH3BaI3, crystallizing in the I4/mcm space group, with lattice parameters, a = 9.30 A, c = 13.94 A. Atom projected density of state and band structure calculations reveal the conduction and valence band edges to be comprised primarily of Barium d-orbitals and Iodine p-orbitals, respectively. The larger band gap of CH3NH3BaI3 compared to CH3NH3PbI3 can be attributed to the lower electro-negativity coupled with the lack of d-orbitals in the valence band of Ba{2+}. A more detailed analysis reveals the excellent chemical and mechanical stability of CH3NH3BaI3 against humidity, unlike its lead halide counterpart, which degrades under such conditions. The dopability of the CH3NH3BaI3 compound e.g. by doping La on the Ba site combined with its structural and mechanical stability under the ambient conditions, suggests this compound as a promising candidate for transparent conductor applications, especially for all perovskite solar cells. 
Akash Kumar, K. R. Balasubramaniam, Jiban Kangsabanik, Vikram, Aftab   Alam
cond-mat.mtrl-sci