The efficiency of a solar cell is directly related to the charge carrier lifetime in the light absorbing material. Therefore, in order to better understand and improve the efficiency of solar cells, it is essential to be able to effectively characterize the lifetime of their charge carriers. In Sher's lab, lifetime measurements are typically conducted using time-resolved terahertz spectroscopy (TRTS). In TRTS, an optical laser pumps (i.e. excites the electrons of) the sample, while terahertz (THz) waves simultaneously probe the conductivity of the sample. The conductivity measurements can then be used to infer the sample's lifetime. However, the traditional pump laser is a poor imitation of actual sunlight conditions, both in wavelength and intensity. The main motivation of this thesis is to design a new THz setup that excites samples with a wavelength and intensity closer to sunlight, so that lifetime measurements are more representative of operation conditions. This involved installing a new pump source: a laser mount with interchangeable laser diodes of various wavelengths. Using lenses and a pinhole, we optimized the laser spot size and quality at a wavelength of 450 nm. For probing with THz waves, we adjusted the duty cycle and amplitude of the THz generation voltage, in order to maximize detection signal. Using our new THz set-up, we measured the lifetime of a lightly doped silicon sample to be 2.63 ± 0.04 μs, which is consistent with values expected from literature. We discuss the sources of uncertainty in our measurement, including drift in our signal. We also discuss future improvements upon our new THz set-up, which would allow for more accurate lifetime measurements. Finally, we explore the exciting new research that is made possible by our multi-wavelength laser diode.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Administrative Note","value":"Drupal Node ID: 24191