Research Areas

Research in AITG

The research activities in our group fall under three broad categories : electronic and structural phase transitions in solids, ferroelectric and multiferroic surfaces and interfaces and photo-induced phenomena in chemical systems. Some current themes are outlined below.

Electron Transfer Dynamics in Dye-Sensitized Solar Cells

We are investigating electron transfer mechanisms in Dye-Sensitized Solar Cells (DSSCs) from dyes to the semiconductor nano-particles. As a first phase of this project we are currently studying the ultrafast ET dynamics in the solution phase, occurring in the sub-picosecond regime - much faster than solvent relaxation.

This work was motivated by time-resolved and Resonance Raman experiments performed by our collaborators at TIFR, Mumbai aimed at establishing the role of vibrations in the electron transfer. Their work has revealed that ET from the solvent to the solute in the excited state drastically quenches the fluorescence, and these ultrafast transfer events maybe mediated by vibrational motions of the solute. We are modeling these transfer events using real-time ab initio molecular dynamics and time-dependent density-functional theory (TDDFT).

Photo-induced electronic and optical effects in amorphous materials chalcogenide glasses

Chalcogenide glasses are a very interesting class of semiconductors that display a variety of photo-induced phenomena owing to their amorphous nature and disordered electronic structure.

Motivated by nano-second pump-probe experiments on chalcogenide glasses at IISER Bhopal we are investigating the photo-induced transparency and dynamics of the transient defect states in GeSe2 and its compositional variants. Using a combination of classical molecular dynamics and excited-state dynamics via real-time TDDFT we are modeling the femto-second regime photo-induced changes in the semiconductors.

Electronic transitions in metals and alloys at high-pressures

At high pressures metals like Zn and Cd undergo a series of iso-structural phase transitions characterized by anomalous elastic constants and transport properties.

The origin of these transitions is in the sudden change in the topology of the Fermi surface of these metals referred to as a Lifshitz transition or electronic topological transitions (ETT). While such extreme conditions of pressure present severe challenges to experimental methods measuring such changes, the regime is quite accessible to theoretical tools.

In particular, ab initio electronic structure theory affords the study of electronic structure at high-pressures via variable-cell methods. We employ such tools to investigate the Fermi surface topology of metals and alloys at high pressures and predict ETTs. The theoretical discovery of such transitions is key to the justification of experimental explorations to confirm these transitions.

Electrode interfaces in solar cells

The overall efficiency of a solar cell depends on, among other factors, the charge collection efficiency of the electrode materials used. This factor in turn depends on the nature of the interface between the metals employed and the photo-active material (typically an inorganic semiconductor or a polymer). The formation of a work-function independent Schottky barrier at this interface is often detrimental to the efficiency of the cells as it can lead to lowered photo-voltages and currents. This is all the more crucial in nano-material based cells where the interfaces can be quite different from the bulk counterparts.

By employing density-functional theoretical methods we model accurately the electronic structure at some common interfaces. Ab initio modeling can provide valuable insights into the mechanism of barrier formation as well as the creation of charge-traps at the interface. The theoretical studies then provide a way to carefully engineer these interfaces and harness the full potential of the solar cell.