Our lab focuses on ultraviolet (250 nm - 400 nm), visible (400 nm - 700 nm), and infrared (700 nm - 25 µm) photonics research.
Selected Research Nuggets:
Bifacial PV System Performance Modeling
Unlike conventional monofacial photovoltaic (PV) cells, bifacial PV cells convert light hitting the both sides of them to electricity. However, partly due to lack of accurate bifacial PV system modeling, methods to predict system performance of bifacial systems have remained limited. In collaboration with Sandia National Laboratories and National Renewable Energy Laboratory (NREL), we are developing a model using reverse ray tracing method to accurately estimate the performance of bifacial PV systems. The model is based on RADIANCE and Python software. Furthermore, we are studying the impact of different installation parameters such as system configuration and size, and weather conditions, on the performance of bifacial PV systems. We are also validating our ray tracing model by comparing modeled vs. measured irradiance data from multiple bifacial and monofacial PV test arrays across the country.
The project is funded by the U.S. Department of Energy SunShot National Laboratory Multiyear Partnership (SuNLaMP) program. For more details on the team and project please also visit the PV Performance Modeling Collaborative's website.
Silicon Nanowire based Optoelectronic Biosensors
Current cancer detection methods are insufficient for early detection; at present, cancer detection is performed using a combination of physical examination and CT scans or MRIs. Early detection both lowers the cost of treatment and increases survival rates. Nanowires (NWs) are effective sensing structures due to their large surface area to volume ratio. However, contacting the NW arrays is challenging. Our silicon (Si) NW optoelectronic biosensor is made by a bundle of vertically oriented NWs, allowing us to electrically contact millions of NWs per cm2 simultaneously, compared to 10’s of NWs in other state-of-the-art NW biosensors.
The project is in collaboration with a Massachusetts-based start-up, Advanced Silicon Group, and Professor Aliasger Salem's lab at UIowa, and funded by the National Science Foundation STTR and I-Corps programs.
III-V Nanowire Optoelectronics
Nanohole Arrays for Nanowire Growth
Selective Area Epitaxy (SAE) inherently requires some area to be available for epitaxy while other areas are covered. One such method it to create nanoholes in SiNx/Si. Our lab employs electron beam lithography and nanoimprint lithography of a polymeric mask to form the nanohole pattern. Once etched, the sample contains nanoscale holes ready for Molecular Beam Epitaxy (MBE). After MBE, the NWs are ready to be used in novel devices.
Our team’s goal is to use NWs to develop novel semiconductor optoelectronics devices, such as, transistors, solar cells, lasers, and LEDs. One such device is a NW metal-oxide-semiconductor field effect transistor (MOSFET) where the NW is used to connect the source and drain while a global gate is under the entire structure. NWs are horizontally oriented on the structure so that they can form a circuit between source and drain, but the spacing between devices is large enough that a single nanowire cannot short the circuit.
This project is in collaboration with Professor John Prineas' lab at UIowa and is funded by the National Science Foundation Electronics, Photonics and Magnetic Devices (EPMD) program.
High Efficiency and Low Cost Solar Cells
We are utilizing various low cost chemical texturing techniques to develop high efficiency silicon-based solar cells. One such technique is the formation of nanoporous silicon surface (often termed as black Si (bSi)) by metal assisted catalyzed etching (MACE), where the metal catalysts are copper (Cu) or silver (Ag). Our goal is to make high-efficiency bSi single and tandem junction solar cells.
This project is funded by an Iowa Energy Center Opportunity grant. The collaborators for tandem junction solar cell work include Professors Michael Flatté and Markus Wohlgenannt.
We are developing metal-dielectric metamaterials and metasurfaces for various applications, including window coatings and ophthalmological optical components. For example, we are designing and nanofabricating a spectrally-selective solar window coating that consists of a nanostructured metallic layer. This solar window coating not only resolves the delamination problem by reflecting the infrared radiation, but also is easier and less expensive to manufacture using nanoimprint lithography.
Our research sponsors to-date include: