RESEARCH

Exciton dynamics in quantum dots (QDs) and multiple exciton generation

In QDs the energy of an absorbed photon can via multiple exciton generation (MEG) be broken down into many electron-hole pairs thereby increasing the photocurrent. Alternatively, hot electron transfer can use the extra energy providing higher photovoltage. Both of these processes are capable of improving the solar cell efficiency beyond the Shockley-Queisser limit. In order to make use of the effects, the processes have to be followed by efficient charge stabilization with minimal back recombination. It is also vital to efficiently fill the holes left in QDs after electron injection. The purpose of the current project is to carry out a thorough study of the dynamic processes in the material to optimize the key components of QD solar cells (QDSC).

Physics of two-dimensional (2D) transition metal mono-/di-chalcogenides (TMCs)

Ultrathin two dimensional (2D) transition metal chalcogenides have recently emerged as a class of promising materials for electronic, optoelectronic and spintronic device applications. In layered transition metal dichalcogenides (TMDCs), band gap can be tuned by changing the number of layer. Strong spin orbit coupling and inversion symmetry breaking lead to valley (K or K') selective excitation in these materials. This valley selective excitation of electron makes TMDCs most suitable candidate for valleytronics. However, the physics of this kind of 2D layered materials is not completely understood. The aim of our group is to gain insight into electronic and optical properties of such materials using ultrafast spectroscopy. On the other hand, the coupling between two different layered TMCs forming heterostructure can enhance the optical and electrical properties making them useful for solar cell, photo detector and other optoelectronic devices. The study of exciton dynamics in such heterostructure will also be taken up in this project. Nonetheless, Z-scan technique will be employed to investigate nonlinear absorption and optical limiting behaviour of layered TMC materials.

Organic Photovoltaics: materials and devices

One of the major concerns about organic solar cells is their low efficiency. Recent studies have pointed out that poor absorption and low carrier mobility of organic materials are responsible for the limited performance of organic photovoltaic cells. Molecular orbital mismatch that governs the open circuit voltage is also an important factor. Therefore, synthesis of novel organic materials (polymers and small molecules), develop new device architectures, spectroscopic investigation on materials and electrical characterization of devices are some of the aims of this project to address the efficiency issue.

Metal Halide Perovskite: Material Properties to Device Applications

Research on metal halide perovskites (both inorganic and hybrid organic-inorganic) has largely arisen out of rapid progress in their photovoltaic applications. However, these materials are potentially suitable for a diverse optoelectronic application such as light emitting diodes, photodetectors and lasers. These applications are enabled by the favourable material properties, which include long charge carrier diffusion lengths, high absorption coefficients with a sharp absorption edge and remarkably high photoluminescence (PL) quantum efficiency. Understanding the excited state photo-carrier dynamics and interactions are crucial for elucidating the working mechanisms of optoelectronic devices. Thus, our research group is extensively involved to develop the fundamental understanding of important properties of these materials like electronic structure, absorption, emission, carrier dynamics and transport, and other relevant photophysical processes that have propelled these materials to the forefront of modern optoelectronics research. Moreover, we develop new perovskite materials and study their application possibility in optoelectronic devices.