Modeling and first-principles computations of silicon/oxide and silicon/metal interfaces for photovoltaic applications
The interface between silicon and the electrodes or buffer layers in a solar cell can have an enormous and often unpredictable effect on efficiency. While this is partially a result of trap states due to defects at these interfaces, it is also due to the fact that we simply do not have a good understanding of the interface atomic structure, slight changes in which can dramatically affect band alignments. Further, it is very difficult to precisely control the atomic structure of these interfaces, so properties can change from sample to sample.
During her stay at MIT, Dr. Wajood and Prof. Kolpak will work together to expand upon the current model for band alignment at silicon/metal interfaces to enable incorporation of the effects of non-ideal interface structure and stoichiometry (for example, reconstructions, inter-diffusion, or formation of a thin oxide layer between the silicon and the metal). Dr. Wajood will use density functional theory (DFT) calculations to compute the stoichiometry-dependent charge transfer, dipole formation, and band alignment at silicon/metal interfaces with various degrees of oxidation, and use the results to help identify relationships between these properties and fundamental atomic and/or bulk materials properties, with the ultimate objective of developing a chemical/physical model for analytic prediction of band alignments at complex interfaces.
Dr. Wajood will be introduced to DFT computations and the science of atomic-scale interface structure-property prediction, both of which are at the core of my group's research. Her physics background and experience in developing analytical physical models are highly complementary and ideal for pursuit of the project described above.