Photonic properties of organic nano-materials for light-beam control and energy

Speaker: Prof.Jean-Michel Nunzi (Queen’s University)

Time: December 11th , 10:00a.m

Location: Room -34, Building of Physics and Technology

Abstract: 

Several approaches are currently explored to build devices exploiting size-effects in nano-sciences. Self-assembling emerges as a master technique to enable applications in the real world. Nonlinear phenomena related to light-matter interactions open the door to new paradigms related to the self-organization of nano-photonic structures, improved light emitting and high efficiency photovoltaic devices.

Practically, photoactive molecules move like molecular motors into a glassy matrix when they are illuminated under resonant excitation conditions. The movement results in a macroscopic mass transport. The property was discovered in 1995 by research teams in Canada and USA. Authors named the resulting deformations Surface Relief Gratings. Over the years, we developed a microscopic picture of the origin of the phenomenon. We discovered later on that the same materials self-organized into robust photonic structures, meanwhile they were excited under a uniform light beam. We could attribute the process to the nonlinear optical interaction in which the movement of the molecules under light happens from regions of high excitation rate, to regions of lower excitation rate, in a totally reversible manner. The process stops when the excitation rate is minimized. This allows the collective fabrication of nano-structures that maximize light matter interaction. That is the desired property in order to harvest solar energy.

On a similar scale, a photovoltaic technology that is not limited to the Shockley–Queisser efficiency limit and that is amenable to low-cost and large-area production requirements is studied in our team. The physics does not rely on the photoelectric effect, which is at the origin of the efficiency limits of the photovoltaic conversion in semiconductor devices; it is based on optical rectification of sunlight. Antennas efficiently convert waves into a potential difference, which must be rectified to DC or low frequency current to be useable for energy production. This particular type of visible-light antenna was theoretically designed forty years ago; it was named a rectenna. EM-wave to DC conversion can in principle be done at solar frequencies with much higher conversion efficiency than present day photovoltaic technologies, but it suffers that rectification should be achieved at optical frequencies where diodes don’t exist. Self-assembling enables the design of large area-devices in which light rectification is achieved by metallic nano-antennas covalently coupled to molecular diodes. The nonlinear optical effects happening at the top of the antennas are the key ingredients that we explore in order to design ultra-high efficiency and low-cost next-generation photodetectors and photovoltaic devices.


CV - Dr. Jean-Michel Nunzi

Professor, Department of Physics, engineering Physics and Astronomy, Department of Chemistry, Queen’s University, Canada.

http://faculty.chem.queensu.ca/people/faculty/Nunzi/

My research interests are the optical and electronic properties of organic materials and devices:  photo-physics, nonlinear optics, self-organization under light, charge generation and transport, solar cells, plastic lasers, nano-materials, bio-compatible materials and devices. I also study the fabrication of chiral structures using light - matter interactions.


Research Specialization: Photonics, Nonlinear Optics, Organic Devices, Organic Electronics, Organic Semiconductors, Polymers, Nanomaterials.

Areas of Research: Optics and Photonics, Micro and Nanoelectronics, Renewable energies

11 patents, 240 peer-reviewed publications, 7000 citations, H-index 46

Member of the Editorial Board in Scientific Reports, European Physical Journal: Applied Physics, and Energies.