Band gap tuning of ferroelectric PbTiO3 by Mo doping

Tuning the band gap of ferroelectric materials to visible region without reducing the polarization can provide an ideal photovoltaic material for solar energy harvesting, significantly efficient than the conventional p-n junction-based cells. In the present work, we have tried to achieve this elusive goal by doping Mo at the Ti ionic site in proper ferroelectric PbTiO3 which is known to have very large polarization. A significant reduction of band gap is achieved from 3.14 eV (un-doped PbTiO3) to 2.41 eV for 10% Mo doping concentration. In this doping, Mo-4d states which are lower in energy than Ti-3d states introduce an intermediate state below conduction band edge leading to band gap reduction. Analysis of the XRD patterns reveals that the Mo-doped PbTiO3 retains tetragonal structure and tetragonality increases with increasing the doping concentration of Mo. It is also found that increase of Mo concentration in PbTiO3 tends to enhance the conductivity suitable for transport of charge carriers. This finding may help to discover and design optical perovskite oxides for light energy harvesting application.