Abstract: The ability to spectrally-tune the response of semiconductors is of interest for optoelectronic devices in which wavelength-selectivity of the photoactive material is necessary for applications such as multi-junction solar cells, narrow-band photodetectors, transparent photovoltaics, tailored emission sources, and photo-chargeable batteries. Here, we introduce several nanostructured semiconductor materials and how their quantum nature can be exploited for spectral selectivity. Colloidal quantum dot thin films are a particularly promising material for these applications due to their tunable absorption throughout the near-infrared; their earth-abundant materials basis; and their amenability to a variety of solution-processed, scalable fabrication methods. We discuss several avenues for achieving controlled transparency or opacity within multiple wavelength bands in the absorption, reflection, and transmission spectra of colloidal quantum dot films, as well as multi-modal spatially-resolved characterization methods that can be used to train machine learning models for parameter prediction and underlying physics elucidation in materials and devices. We also discuss how colloidal quantum dots can be integrated with redox-active metal-organic frameworks to form hybrid materials that can both generate and store charge for applications in photobatteries and catalysis. Finally, we introduce a second semiconductor system of interest, 2D transition metal dichalcogenides (TMDs). 2D TMDs exhibit tunable electronic and optical properties at monolayer and few-layer thicknesses, as well as high absorption coefficients and carrier mobilities. However, unlike traditional semiconductors, TMD films cannot simply be made thicker to increase their absorptivity for applications, because their spectral response is a function of their thickness. We will discuss several enhancement strategies, using both dielectric and plasmonic metasurfaces, that allow for greater device performance and expand the functionality of TMDs in flexible solar cells and photosensors.

Susanna M. Thon is an Associate Professor of Electrical and Computer Engineering, with a secondary appointment in Materials Science and Engineering, and the Marshal Salant Faculty Scholar at Johns Hopkins University. She also serves as the associate director of the Ralph O'Connor Sustainable Energy Institute (ROSEI). Her research is in nanomaterials engineering for optoelectronic devices, with a focus on solar energy conversion and sensing.Thon's work has received funding from the National Science Foundation, Maryland Energy Innovation Institute, TEDCO Maryland Innovation Initiative, American Chemical Society, and the Department of Defense. She is the recipient of Johns Hopkins' Catalyst and Discovery awards and the National Science Foundation CAREER award and a past chair of the Optica Optics for Energy Technical Group. Thon received her bachelor's degree from MIT in 2005 and her master's and Ph.D., all in Physics, from the University of California Santa Barbara in 2008 and 2010, respectively. Prior to joining Johns Hopkins in 2013, she worked as a postdoctoral fellow at the University of Toronto.