Selective Absorbers / Emitters for Thermophotovoltaic Energy Conversion

LEFT: Schematic diagram of a solar thermophotovoltaic system which converts solar energy into heat and then into electricity. RIGHT: Schematic diagram of a dielectric filled metallic photonic crystal with radius r, period a, and depth d.

Nanophotonic cavities can greatly enhance solar absorbers/emitters for the application of thermophotovoltaic devices. However, the actual fabrication of such devices has remained costly and non-scalable. Our goal is to create low-cost and scalable nanophotonic devices by using traditional CMOS/MEMS compatible fabrication methods. The goal of the research is to allow for deployable nanophotonic devices for energy conversion. The goal of this research is to simultaneously solve the several critical issues of nanoophotonic based absorber/emitters, such as 1) optimal absorption, 2) high temperature stability, 3) wafer-scale fabrication, and 4) wide angle absorption/emission.

Selected Publications

Jeffrey B. Chou, Yi Xiang Yeng, Yoonkyung E. Lee, Andrej Lenert, Ivan Celanovic, Marin Soljacic, Evelyn N. Wang, Nicholas X. Fang, and Sang-Gook Kim, "Enabling Ideal Selective Solar Absorption with 2D Metallic Dielectric Photonic Crystals" Advanced Materials, 2014.

Jeffrey B. Chou, Yi Xiang Yeng, Andrej Lenert, Veronika Rinnerbauer, Ivan Celanovic, Marin Soljacic, Evelyn N. Wang, and Sang-Gook Kim, "Design of Wide-Angle Selective Absorbers / Emitters with Dielectric Filled Metallic Photonic Crystals for Energy Applications" Opt. Express, vol. 22, no. S1, pp. A144-A154, Jan. 2014, (2014)

Heon-Ju Lee, Katherine Smyth, Stephen Bathurst, Jeffrey Chou, Michael Ghebrebrhan, John Joannopoulos, Nannaji Saka, and Sang-Gook Kim, "Hafnia-plugged microcavities for thermal stability of selective emitters" Appl. Phys. Lett. 102, 241904 (2013), DOI:10.1063/1.4811703

Katherine Smyth, Jeffrey Chou, Sang-Gook Kim, "HfO2 Plugged Optical Nanostructures for High Temperature Photonic and Plasmonic Applications," ASME Society-Wide Micro and Nanotechnology Forum, IMECE 2013, San Diego, CA

Hot-Electron Water Splitting via Metallic Photonic Crystals

LEFT: Image of metallic photonic crystal. RIGHT: Band diagram of hot electron process for water splitting.

The intermittency of solar energy conversion via photovoltaics presents a major obstacle to their extensive penetration into the grid. Thus, despite major advances in solar cell efficiency, the path to fully integrated solar energy remains incomplete without solar energy storage solutions. Hot-electron based water splitting can allow for efficient, solar-powered conversion of water to hydrogen fuel. In combination with our large scale fabrication method, we hope to develope low-cost and widely distributed energy conversion technology.

Selected Publications

J.B. Chou, D.P. Fenning, Y. Wang, M.A. Polanco, J. Hwang, A. El-Faer, F. Sammoura, J. Viegas, M. Rasras, A.M. Kolpak, Y. Shao-Horn, S.G. Kim, "Broadband Photoelectric Hot Carrier Collection with Wafer-Scale Metallic-Semiconductor Photonic Crystals" 42nd IEEE PVSC Conference, New Orleans, LA, USA, June 2015

Spoof Plasmonics for Near-Field Heat Transfer

LEFT: Band diagram simulation of the dielectric filled metallic photonic crystal (MPhC) with a Lorentz-Drude model of Tungsten, which shows the spoof plasmon mode exists below the light line. Simulation was performed via rigorous coupled-wave analysis (RCWA). RIGHT: Scanning electron microscope (SEM) image of the fabricated MPhC with a period of 800 nm.

Dielectric filled metallic photonic crystals support surface "spoof" plasmons which can be frequency tuned by altering the geometry of the cavities. By tuning the frequency of the spoof plasmons to match the bandgap of a photovoltaic, extremely efficient thermal energy conversion can be achieved. The evanescent modes of the spoof plasmons allow for thermal radiative heat transfer to surpass the blackbody limit.

Nano-Electro Mechanical Systems (NEMS) with Nanophotonics

Nanophotonic structures, such as photonic crystals, plasmonics, and nano-metallic cavities have demonstrated remarkable properties for a wide variety of applications. However, the static nature of the devices limits any tunability of the structures. By combining NEMS with new nanophotonic properties, new novel, high-speed devices can be made to manipulate light in new novel ways.

Optical MEMS for optical interconnects

LEFT: Schematic diagram of two blades in a server communicating via a free-space, high-speed optical link. RIGHT: A to-scale schematic diagram of the fabricated electrothermal lens scanner capable of latching in at fixed positions for a zero power hold.

Optical interconnects can greatly enhance the bandwidth of traditional electrical interconnects. Specfically, free-space optical interconnects allow for a wireless solution to reduce clutter in server cluster type systems. However, precise optical alignment is critical in free-space systems. We present several optical MEMS based auto-aligners for free-space interconnects. Among the devices successfully demonstrated are electrostaticly and electrothermally actuated lens scanners, with electronic feedback loops to maintain alignment in both high-speed and low-speed alignment schemes.

Selected Publications

J. B. Chou, N. Quack, and M. C. Wu, "Integrated VCSEL-Microlens Scanner with Large Scan Range," Journal of Microelectromechanical Systems, 2014.

J. B. Chou, K. Yu, and M. C. Wu, "Electrothermally Actuated Lens Scanner and Latching Brake for Free-Space Board-to-Board Optical Interconnects," Journal of Microelectromechanical Systems, vol. PP, no. 99, pp. 1 -10, 2012.

Jeffrey Chou, Kyoungsik Yu, David A. Horsley, Brian Yoxall, Sagi Mathai, Michael R. T. Tan, Shih-Yuan Wang, Ming C. Wu, "Robust Free Space Board-To-Board Optical Interconnect with Closed Loop MEMS Tracking", Special Issue on Photonic Interconnect, Applied Physics-A, Dec 2008, pp. 973-982.