  We report calculations of the electronic structure and optical properties of
doped $n$-type perovskite BaSnO3 and layered perovskites. While doped BaSnO$_3$
retains its transparency for energies below the valence to conduction band
onset, the doped layered compounds exhibit below band edge optical conductivity
due to transitions from the lowest conduction band. This gives absorption in
the visible for Ba2SnO4. Thus it is important to minimize this phase in
transparent conducting oxide (TCO) films. Ba3Sn2O7 and Ba4Sn3O10 have strong
transitions only in the red and infrared, respectively. Thus there may be
opportunities for using these as wavelength filtering TCO.
