This group focuses on the design, synthesis and characterization of novel hybrid organic-inorganic materials. Emphasis is on the synthesis of tailor-made organic ligands designed to control, enhance or mediate the optoelectronic properties of nanocrystals (NCs). The use of synthetic organic chemistry in ligand design enables desired properties to be embedded in a modular and scalable manner. These ligands allow the size, shape and material dependent properties of the NCs to be harnessed for energy, metamaterial and optoelectronic applications. The synthetic expertise in this group is complemented by single molecule spectroscopic and thin-film current-voltage measurements. Specific research directions are outlined below:
Plasmon Induced Triplet Energy Transfer (PITET)
The goal is to use the light captured by metal nanoantennas for photon upconversion, where low energy photons (e.g. from incoherent sources like the sun) are converted to useful high energy photons. In this project, novel light absorbing nanostructures based on noble metals will absorb near-infrared photons to produce violet photons emitted by organic chromophores. Specifically, silver nanoprisms or gold nanorods with their localized surface plasmon resonance tuned between 1.5 and 1.8 eV, resonant with the lowest excited triplet states of perylene and anthracene will photosensitize these molecular triplet states across an oxide barrier. Steady-state photon upconversion measurements will quantify the efficiency of plasmon-induced triplet energy transfer. Time resolved photoluminescence and transient absorption measurements will provide independent measurements of the yield and rate of triplet energy transfer.
Singlet fission sensitized nanocrystals for next-generation photovoltaics.
The aim here is to obtain a molecular level understanding on the energy transfer of triplet excitons derived from singlet fission (SF) to inorganic semiconductor NCs. With SF, photons more energetic than the bandgap are collected, thus vastly increasing photovoltaic efficiency. Specifically, SF materials with near unity yield of SF in the single crystal form; and acceptor NCs with band gaps in the infra-red will be studied. The conclusions are expected to be applicable to the SF-sensitization of any inorganic semiconductor, like silicon.
Photon upconversion with a nanocrystal-molecular hybrid system
This group discovered a new molecular-nanocrystal system for photon upconversion that can potentially have significant impact in several fields. Such a system can increase the efficiency of solar cells by 15%, and thus provide an inexpensive way to produce clean energy. If used for bioimaging, it may offer all the advantages of two-photon emission microscopy at a fraction of the cost. The key concept of this novel system is the use of a nanocrystal to absorb light and transfer the energy to a triplet state of a molecule. Two triplets then combine to emit light of higher energy. The beauty of this system is the tunability of both the nanocrystal light absorber and molecular fluorophore. This allows upconversion to be engineered between arbitrary wavelengths for various applications.
Photo: Excitation with a cw near-infrared beam produces yellow light. We can even use sunlight for this! Credit: M. Mahboub
This is a great advantage compared to existing methods for photon upconversion.
This work has been highlighted by various news outlets, e.g. the Huffington Post gives us a nod:
It was one of the Five Best Ideas of the Day by the Aspen Institute: