Nano-Enabled Energy

The Lieber group is focused on several areas of nano-enabled energy with an emphasis on defining the fundamental limits that can be achieved using nanoscale structures. Current efforts include the design of novel nanowire materials and assemblies for next-generation solar cells to the development of nanoelectrode platforms for elucidating fundamental mechanisms of and enhancing electron transfer mechanisms at work in microbial fuel cells. Specific research areas being pursued include the following:

Nanowire photovoltaics. We are exploring two central nanowire motifs involving p-i-n dopant modulation in axial and coaxial geometries as platforms for fundamental studies at the single nanowire level. Current work is focused on controlled synthesis of core/multi-shell nanowires with in situ doping of the core and heteromorphic, crystalline shells to define optimized structure and electronic properties to maximize open circuit voltage in subwavelength diameter structures. We are also using a combination of experiments and simulations to define the unique absorption and photocurrent response achievable from designed core/multi-shell nanowire structures. In addition, the lateral and vertical assembly of nanowires elements, together with studies of the unique photovoltaic properties of devices configured from these assemblies, is being explored.

Microbial fuel cells. The mechanisms of electron transfer between microbes and electrodes in microbial fuel cells (MFCs), which ultimately limit power extraction, remain controversial. The Lieber group is pursuing the development of novel nanoelectrode structures combined with in-situ optical imaging as platforms to define extracellular electron transfer down to the level of single microbes, as well as in controlled microbe-microbe assemblies. In addition, work is focused on the development of novel nanostructures that facilitate both extracellular and intracellular electron transfer from bacteria as well as mammalian cells.

Bottom-up Design of NW Based Solar Cells
Schematic of coaxial NW building blocks (blue indicates p-type doped core and beige indicates n-type doped shells); Schematic of typical silicon core/shell NW device fabricated from one NW building block on arbitrary substrate with integrated back-side reflector; Schematic illustrating potential for new device architecture using distinct NW building blocks within each layer. Colors indicate peak wavelength of light absorbed for particular NW morphology.
FDTD simulations of resonant mode spatial profiles for p/in (profiles 1-3) and p/pin (profiles 4-6) structures.
DTD simulations of resonant mode spatial profiles for p/in (profiles 1-3) and p/pin (profiles 4-6) structures. All profiles are for TM polarizations and use a linear color scale representing absorption (not electric field intensity) within the mesoscopic structures. Resonant modes labeled 3 and 6 correspond to whispering-gallery type modes while all others correspond to Fabry-Perot resonances.