Solid-state lighting has made tremendous progress over the past decade, with the potential to make much more progress over the coming decade. In this talk, we review the current status of solid-state lighting relative to its ultimate potential to be "smart" and ultra-efficient. Smart, ultra-efficient solid-state lighting would enable both very high "effective" efficiencies, as well as potentially large increases in human productivity.

Multijunction solar cells are the first photovoltaic technology to surpass single-junction Shockley-Queisser theoretical efficiency limits, and represent the highest efficiency of any solar cell technology. Recent experimental results on high-efficiency solar cells with 3-, 4-, and 5- junctions will be presented. Many challenges remain to develop new semiconductors with lower rates of carrier recombination at the bandgaps needed to push toward still higher efficiencies.

In solar cells, free charge carriers can recombine both via bimolecular (Langevin) and trap-assisted recombination (Shockley-Read-Hall). Trap-assisted recombination of electrons and holes is governed by capture coefficients that are thermally activated with an identical activation energy as measured for the hole mobility μp. To elucidate which recombination mechanism is dominant in organic solar cells, we investigated Charge-transfer (CT) state electroluminescence in several polymer:fullerene bulk heterojunction solar cells.

This seminar will cover a few topics we are working on to understand and engineer solar and thermal radiation. The seminar will start with a discussion on near-field radiation heat transfer. Max Planck himself realized that the blackbody radiation law that now bears his name was limited to geometries much larger than the wavelength of thermal radiation. Theory has predicted that thermal radiation heat transfer between two surfaces separated by tens of nanometers can exceed that of Planck’s blackbody radiation law by several orders of magnitude.

WiFi interface is known to be a primary energy consumer in mobile devices, and idle listening (IL) is the dominant source of energy consumption in WiFi.  Most existing protocols, such as the 802.11 power-saving mode (PSM), attempt to reduce the time spent in IL by sleep scheduling.   However, through an extensive analysis of real-world traffic, we found more than 60% of energy is consumed in IL, even with PSM enabled. 

The scalability of CMOS technology has driven computation into a diverse range of applications across the power consumption, performance and size spectra. Communication is a necessary adjunct to computation, and whether in the context of high-performance computing, mobile devices or biomedical implants, chip-to-chip communication can take up a significant portion of the overall system power budget. A single interconnect methodology cannot address such a broad range of requirements efficiently.

Although my career has focused on advancing science and engineering in its more basic aspects, I have had several opportunities to also advance energy sustainability, which is a central goal of Energy Frontier Centers. In my talk I will give some examples of how this has happened in my case and ideas for how my personal experience can be generalized by others.

The conventional approach to building physics models is based on physical intuition gained in prior studies of similar systems. Unfortunately, intuition is often faulty. We show that a recently developed technique from information science, compressive sensing (CS), provides a simple, efficient, and systematically improvable way of constructing models in a numerically robust and conceptually simple way. CS is a new paradigm for model building in physics - its models are sparse and just as robust or better than those built by current state-of-the-art approaches.

Like a tuning fork for light, optical resonators have a characteristic set of frequencies at which it is possible to confine light waves. At these frequencies, optical energy can be efficiently stored for lengths of time characterized by the resonator Q factor, roughly the storage time in cycles of oscillation. In the last ten years there has been remarkable progress in boosting this storage time in micro and millimeter-scale optical resonators. Chip-based devices have attained Q factors of nearly 1 billion and micro-machined crystalline devices have provided Qs exceeding 100 billion.

Nanoparticles form the cornerstone in many applications of nanotechnology, and their properties are highly dependent on specific particle characteristics. We have focused on synthesis in supercritical fluids since this approach offers an energy efficient green route for the production of nanomaterials with a very high degree of control of the particle characteristics. However, in order to tailor nanoparticle characteristics insight into their formation and growth is vital and this can be achieved through in situ studies.