Karl “Jet” Meitzner – The Richmond Lab @ UO

EDUCATION

B.S. in Chemistry (2010)

University of Wisconsin, Eau Claire

RESEARCH PROJECT

As part of the quest for increased solar cell efficiency, my research project focuses on fabricating and analyzing thin-film photovoltaic materials. We hope to discover material combinations that will increase the quantum efficiency of the absorption of high energy solar photons by promoting the process of impact ionization (II). This process produces two or more electron-hole pairs per absorbed photon, thus resulting in an internal quantum efficiency (IQE) > 1 and a greater solar cell photocurrent. While II occurs to a small extent in existing silicon solar cells, maximizing its probability increases the theoretical solar cell efficiency from 30% to 42%. With the eventual possibility of global assimilation in mind, our current focus is to build upon well-established silicon solar technology.

Working closely with undergraduate Brock Tillotson, the chemical bath deposition method is used to deposit thin films of crystalline zinc sulfide (ZnS) on Si. These thin films produce a ZnS/Si interface that is theoretically capable of promoting impact ionization. The thin film deposition process is complicated by the ease with which Si oxidizes, thus producing a layer of SiO₂ that electrically isolates the ZnS film from the Si substrate. An air-free method with microwave heating is used in order to deposit thin films under optimal conditions.

ZnS film on silicon substrate — This is a scanning electron microscope (SEM) image of ZnS on a silicon substrate. The white/gray particles are ZnS while the black background is the silicon.

Carrier dynamics (including impact ionization, diffusion, recombination, and free carrier absorption) within the materials are analyzed by an ultrafast pump-probe laser experiment in which electron-hole pairs are generated by an energetic pump beam and monitored via free carrier absorption (FCA) of a low energy, time-delayed probe beam. With a temporal resolution of ~100fs, both ultrafast carrier dynamics and quantum efficiencies are observed simultaneously.

pic for website laser expt — Internal quantum efficiency for carrier generation in Si at three different excitation wavelengths. The decays in traces (a) and (b) correspond to carrier diffusion from regions of high carrier density to regions of lower carrier density. The IQE is the value at which the traces flatten (recombination is slow relative to the timescale of this measurement). The dashed lines are at IQE values of 1.00 and 1.25. The inset is zoomed in around time t=0.

A paper on this laser experiment has been published in Applied Physics Letters:

http://apl.aip.org/resource/1/applab/v103/i9/p092101_s1

If you don’t have access to the journal, you can still view the paper! Just click Here

PERSONAL INFO

It’s the beginning of my 4th year in the Richmond lab and I couldn’t ask for a better project, coworkers, and boss. After graduating I’d like to move to Portland or Bend and work R&D at a solar company. Meanwhile, I very much enjoy shooting lasers at stuff (silicon or ZnS, mostly) and playing golf, frolf, guitar or Halo 4. Quack