  Hybrid perovskites (CH3NH3PbI3) is one of the most promising novel materials
for solar harvesting. Toxicity of lead (Pb), however, has always remained a
concern. We investigated the electronic structure of complete replacement of Pb
by alkaline earths (Ca, Sr, Ba) and found it to be wide band gapped (Eg)
semiconductors (band gap ~ 3.7 to 4.0 eV), and hence not suitable as absorber
material. This opens up a new avenue to explore these materials as transparent
conductor (TC). We doped CH3NH3BaI3 (largest Eg) with La, which shifts its
Fermi level (EF) at conduction band bottom and induces states at EF for
conduction. This is precisely what is required for a transparent conductor.
Optical and transport properties simulated from linear response (within Density
Functional Theory (DFT)) calculations suggested it to be a very good TC
material with a high figure of merit ({\sigma}/{\alpha}), where {\sigma} is the
electrical conductivity and {\alpha} is the optical absorption coefficient.
This claim is also supported by our calculated results on density of states at
EF, effective mass, carrier concentration etc. at various La-doping. We propose
CH3NH3(Ba1-xLax)I3 (x~12.5%) to be a good TC material to be used in a all
perovskite solar cell.
