Center for EXcitonics

projects

Our efforts are divided into four working groups, each containing between three and five faculty devoted to key scientific problems confronting the development of more efficient solar cells and solid state lighting.

(I) Coherence and Disorder

 

Leaders: Alan Aspuru-Guzik & Keith Nelson

Faculty team: Vladimir Bulovic, Jianshu Cao, Moungi Bawendi

The aim of this working group is to understand and control coherence in excitonic antennas and exciton polaritons – coherent combinations of excitons and photons. Key topics in this group are coherent multi exciton spectroscopy, photosynthetic antennas, and J-aggregates.  This faculty team has been working on this topic since the inception of the center, and covers all aspects of the theory (Aspuru-Guzik,Cao ), materials (Bulovic, Bawendi) and characterization (Nelson, Bawendi) of coherent excitonic systems.

 

Text Box:    Figure 1. The Fenna Matthews Olson complex is an example of an excitonic circuit in photosynthesis. Like our nanostructured devices, photosynthesis exploits excitons and exhibits much larger levels of long range disorder than conventional solar cells. Image: Alán Aspuru-Guzik .                        Figure 1. The Fenna Matthews Olson complex is an example of an excitonic circuit in photosynthesis. Like our nanostructured devices, photosynthesis exploits excitons and exhibits much larger levels of long range disorder than conventional solar cells. Image: Alán Aspuru-Guzik .           (II) Semiconductor Nanocrystals

 

Leader: Moungi Bawendi

Faculty team: Karl Berggren, Chuck Black, Vladimir Bulovic, Silvija Gradecak, Marko Loncar, Eric Stach

 

 

The aim of this working group is to understand exciton dynamics in semiconductor nanocrystals using multiexciton spectroscopy and photonic interrogation of single quantum dots in the visible and infrared. Key topics in this group are superconducting nanowire single photon detectors for single dot spectroscopy in the infrared, and extreme nanolithography for managing the interaction between individual semiconductor nanocrystals and photons. This team complements the spectroscopic and synthetic capabilities of the Bawendi group with nano-scale fabrication (Berggren and Black) and novel detectors (Berggren).

 

(III) Solar Antennas

 

Leader: Marc Baldo

Faculty team: Moungi Bawendi, Vladimir Bulovic, Tim Swager, Harry Tuller, Troy Van Voorhis

This working group seeks to use excitonics to collect, concentrate, and wavelength-convert sunlight for single junction solar cells, thereby increasing their efficiencies beyond conventional limits. Key topics for this team are: singlet exciton fission and solar-powered lasers for coherent upconversion. This team centers on the organic materials expertise in the Baldo group, with complementary efforts in inorganic luminescent materials from Harry Tuller. The major focus on singlet exciton fission is assisted by theory in the Van Voorhis and Cao efforts. 

 

(IV) Hybrid Excitonics

 

Leader: Vladimir Bulovic

Faculty team: Alan Aspuru-Guzik, Ken Crozier, Keith Nelson

This working group combines excitons with photons to form ‘exciton polaritons’ - new states of matter and energy.  The combination of excitons and photons has important new properties that may be exploited in new classes of energy conversion devices, especially ultralow threshold lasers which may be the foundation of future solid state lighting.  Optical outcoupling is a major loss in modern LEDs, but this loss can be eliminated in lasers.  

 

Seed programs

We are also supporting three seed programs. These are independent from the working groups. The seeds cover topics that we believe could grow into crucial contributions to the central research thrusts of the EFRC. Both seeds focus on new materials synthesized by junior faculty.

 

(i) Artificial Chlorosomes for Controlled Exciton Transport

Alfredo Alexander-Katz & Bradley Olsen propose to develop antenna structures that are hierarchically structured to maximize exciton flows. By exploiting the amphiphilicity and structure forming capabilities of block copolymers (BCPs), we will be able to recreate in a synthetic manner the confinement found in nature, and self-assemble “Artificial Chlorosomes” within one of the microdomains of the BCP.

 

(ii) Vectorial Energy Transfer in Nanoporous Metal-Organic Frameworks 

Mircea Dincă is studying novel classes of nanoporous metal-organic frameworks that may exhibit superior transport through dyes confined within the nanopores. Ultimately, these materials may find application in the solar antenna working group.

 

(iii) Spin transport influence on organic semiconductors and spin filtering

Jagadeesh Moodera proposes to investigate spin polarized current in organic semiconductors towards high efficiency light emission in organic field effect transistors (LE-OFETs), including spinexcitonic studies. We will be combining spin filters, and barriers with organic materials, to reach our goal of efficient spin transport and also improved LE-OFETs.

(iv) Spatially resolved exciton dynamics in quantum dot thin films.

Will Tisdale is using tip-enhanced near-field optical microscopy to investigate exciton dynamics within interacting QD assemblies. A central goal of this work is to probe heterogeneity on sub-diffraction limited length scales in order to understand the impact of structural ordering and film morphology on sub-ensemble behavior.



The Center for Excitonics is an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science and Office of Basic Energy Sciences

 

 

©2012 Massachusetts Institute of Technology

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