Research
It is no secret that sooner we start relying majorly on renewable energy is better. Among all the renewable energy options that nature has generously provided, the sun stands out as the most easily accessible and enormous source of energy. Nanostructured electronic materials such as perovskites, organic semiconductors (OSCs) and 2D semiconductors offer great promise for applications in optoelectronic devices, such as photovoltaics (PVs), light emitting diodes (LEDs) and photodetectors. Devices, those make use of solar energy, have fundamental and practical limitations on their functionality. Therefore, it is extremely important to understand the fundamental physics of underlying processes in these materials in order to overcome the limitations. Efficiency of these devices depends on several processes such as carrier transport, thermalization, and spatial heterogeneity of the material. Better understanding of these fundamental processes will lead us to design and engineer the materials which in turn shall enable devices with better power conversion efficiency.
We are developing and utilising optical spectroscopic and microscopic methods, ranging from femtoseconds (fs) to seconds (s), to build a nanoscale understanding of carrier transport, thermalization and their correlation with spatial heterogeneity in molecular and inorganic semiconductors. This will enable the rational design and engineering of energy materials for high performance devices. We are also exploring molecular dynamics in biomacromolecules.
Themes
We are interested in understanding fundamental processes in variety of systems using different experimental and analysis methods. Selected themes as the following.
Relaxation-Rate Heterogeneity: Even for apparently simple condensed-phase processes, bulk measurements of relaxation often yield nonexponential decays; the rate appears to be dispersed over a range of values. Taking averages over individual molecules is an intuitive way to determine whether heterogeneity is responsible for such rate dispersion. However, this method is in fundamental conflict with ergodic behavior and often yields ambiguous results. Using novel analysis methods coupled with single-molecule spectroscopy we are trying to determine the underling mechanism of relaxation rate-dispersion in a variety of systems.
Examples: Power-law blinking dynamics in semiconducting nanostructures, molecular rotational rate-dispersion in complex liquids, anomalous molecular diffusion in biological systems.
Excited-State Dynamics: Optical excitation of semiconductors generates charge carriers. Carrier excitation with excess energy, i.e., excitation energy higher than the band gap, produces a nonequilibrium distribution of carriers. Subsequently, carriers undergo carrier− carrier scattering, which results in a quasi-equilibrium distribution of hot carriers having carrier temperature higher than the lattice temperature. These hot carriers then go through carrier-optical phonon scattering and cool down to the band extrema by dissipating their excess energy as heat to the lattice via phonon emission, carrier recombination follows. This whole cooling process is a major loss channel in PVs and partly contributes to the Shockley−Queisser limit. We aim to understand carrier thermalisation and recombination to provide fundamental insights into material properties.
Spatio-Temporal Dynamics: Charge-carrier diffusion, energy transport, effect of micro-scale spatial inhomogeneity in energy nanomaterials.
Coming soon...
Methods
Fluctuation Correlation Spectroscopy
Multidimensional Correlation Analysis Methods
Ultrafast Spectroscopy
Ultrafast Microscopy
Materials
Energy Nanomaterials: Perovskites, 2D Materials, Organic Semiconductors.
Biomacromolecules: DNAs, Proteins, Lipids.