Research

Overview

The Nanophotonic Energy Materials group explores new structures, materials, and devices utilizing nanophotonics for photovoltaics and other optoelectronic applications.

The group uses a combination of theory, simulations, experimental fabrication and characterization to design, optimize, create, and test devices. Our work range from basic science research, to fabrication of working proof-of-concept devices, cognizant of the need for scalable designs and techniques.

Nanophotonics

Our lab specializes in engineering the interaction of light with materials at the nanoscale, and works to better understand the basic principles controlling those interactions. We explore ways to use nanostructures with features at or below the wavelength of light (~500 nm) to create new functionality in devices. Because light operates as a wave at these lengthscales, the effects of interference are significant, along with the reflection, refraction, and absorption we experience in our macroscopic world.

Furthermore, nanophotonic interactions can induce plasmonic resonances in metals (collective oscillations of electrons), modify transition rates for emitters through changing the local density of optical states (LDOS), and be trapped inside cavities beyond millions of cycles. These provide a rich array of effects that can be utilized for designing devices with new or improved functionalities. 

 

Photovoltaics

While the deployment of solar energy has increased orders of magnitude in the previous decades, coupled to the decreased cost of silicon photovoltaics, currently the price of installed solar energy is dominated by not the solar cells themselves, but the connections to the grid, support structures, and other "balance of system" costs. In order to continue to decrease the cost per watt of solar energy, in particular to offset the substantial cost of energy storage, it is necessary to continue to increase photovoltaic efficiencies.

Two techniques to address this are coupling multiple absorber materials with different band gaps to create multi-junction devices, or controlling the absorption and emission of the device to couple exclusively with the sun. Both approaches require careful consideration of the optics involved, and stand to benefit greatly from nanophotonic optimization.

Algorithmic Optimization

Because of the complexity of nanophotonic interactions, traditional design methods are often difficult to apply to the creation of optimal structures. Many phenomena are quite counterintuitive, making "rational design" insufficient - for example, the positioning of a semiconducting nanowire behind a quantum emitter can cause the emitter to send more light either toward or away from the nanowire, depending on the relative distance between the two. This is not a phenomena that we regularly experience in the macroscopic world in which we develop our intuition, and so intuitive design often fails when applied to nanophotonic structures. 

Algorithmic design, or using computer software not only to assist in the creation, but to fully design the geometry, seeks to address this. By coupling optimization algorithms to full-wave simulations, these counter-intuitive phenomena can be fully accounted for, presenting great promise in improving the performance of nanophotonic devices.