Solar energy conversion with high yield and cost-effective ratio requires use of materials which are easily available, stable within the time and flexible in structure in order to allow improvements in their intrinsic and surface properties. A class of such materials are perovskites with ABO₃ structure or kesterites. The basic structure of ABO₃, has a high structural tolerance factor and can be maintained with a wide variety of constituent elements. As a result, the composition-property relationship can be systematically investigated while keeping the same crystal structure. Also, due to the exceptional stability of the structure, the valency, stoichiometry, and vacancy of perovskite compounds can be varied widely in order to tune optical, electrical and catalytic properties. Therefore, the challenge is to couple the synthetic approach with an expected outcome resulting from the theoretical calculations.

In this presentation we will show the study on quaternary Ln_1-xNi_xTiO₃ that revealed the optical and electronic properties might be affected by varying La content in the matrix under employment of a reductive atmosphere of H₂. This constitutes a unique and advantageous feature for its use in solar energy conversion. Understanding the effect of La doping and Ni segregation occurring under the reductive atmosphere on the photoelectrochemical properties of the La_1-xNi_xTiO₃ will generate new set of knowledge while providing a facile route to tune photon absorption and charge transport properties. A similar study will be presented for kesterite Cu₂ZnSnS₄. The questions which will be undertaken are: does La doping favourably affect the electron-hole separation in addition to the enhancement of photon absorption?; how do oxygen vacancies created by ion doping and reduction in hydrogen affect the charge transport properties?; can Ni segregation affect the catalytic property of the Ln_1-xNi_xTiO₃ surface?. The same questions will be applied to kesterite based PEC system upon ion doping and applied atmosphere. We will try to answer these questions through use transient absorption spectroscopy approach allowing to follow changes in charge carrier dynamics from the sub nanoseconds up to seconds timescales upon introduction of any variable to the system.