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Laser Spectroscopy for Characterizing Metals, Organic/Inorganic Semiconductors and Photovoltaics

Laser Spectroscopy for Characterizing Metals, Organic/Inorganic Semiconductors and Photovoltaics

Monday, February 3, 2025 at 4:00 pm
Weniger 116
Dr. Getasew Admasu Wubetu

This research originated from my PhD work and was further developed during my tenure track at Bahir Dar University (BDU) in collaboration with Dublin City University (DCU), Ireland. Laser-Induced Breakdown Spectroscopy (LIBS) is widely used analytical techniques for the classification and quantification of target materials, such as aluminum and Cu targets. Polarization-resolved LIBS is a simple way to enhance the signal-to-background ratio (SBR) by placing a polarizer in front of a detector that suppresses the continuum radiation during the early stages of plasma emission. The main driving for polarization radiation is the electron velocity distribution function (EVDF) translated to radiative recombination of plasmas emission. In addition, nanosecond pump-probe absorption spectroscopy has been utilized to investigate wide bandgap semiconductors, such as chromium-doped bismuth sillenite (Bi12SiO20) (BSO). High- and low-temperature measurements were conducted in collaboration with the University of Antwerp, Belgium. The relaxation dynamics of both non-doped and doped BSO were investigated. The optical density relaxation was accurately modeled using the fitting of double and stretched exponential decay curves, revealing the positions of shallow and deep traps in BSO. The stretched exponential decay was well fitted on the Cr doped BSO crystal is attributed to quantum tunneling probability rather than trapping mechanisms. In my current experimental work at Oregon State University, within the Micro and Femto Energetics Lab in the Department of Physics, we have fabricated perovskite solar cells in n-i-p and p-i-n configurations with varying proportions in collaboration with Oxford University, UK. Over the past six months, we have been characterizing these devices using ultrafast photocurrent mapping to analyze fill factors, efficiencies, and, more importantly, the sub-band states associated with defects and grain boundaries in the perovskite solar cells, utilizing their unique setup. Additionally, we determined the energy band gap of 1.6 eV under different excitations by measuring the device's emission spectrum using Fluorometer Spectroscopy across a broad wavelength range, from UV to NIR. Furthermore, ongoing ultrafast transient absorption spectroscopic studies are examining carrier relaxation and exciton recombination dynamics on perovskite solar cell devices.

Matthew Graham