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Research

Cable Supercapacitors

Currently, millions of miles of electrical cables have been used for providing electrical connections in machineries, equipment, buildings and other establishments. Energy storage devices are completely separated from these electrical cables if used. However, it will revolutionize energy storage applications if both electrical conduction and energy storage can be integrated into the same cable. Here, a dual-function coaxial supercapacitor cable (CSC), which has the capability to be used as an electrical cable and an energy storage device, is demonstrated. Similar to typical coaxial cables, the inner core is used for electrical conduction and the overlying layer is used for energy storage. The integrated CSC device shows excellent flexibility and bendability, long and stable cycle lifetimes, and high energy and power densities. All these remarkable results demonstrate a clear technological advance achieved by clubbing electrical conduction and energy storage into one cable.

For details: “Highly Ordered MnO2 Nanopillars for Enhanced Supercapacitor Performance” Adv. Mater. 26, 4279-4285 (2014). (Highlighted by Nature in News & Views).

Plasmonic Structures

We have developed a facile fabrication technique for producing tunable plasmonic substrates. With this technique, we are able to tune the plasmon resonance of the substrate to match the molecular resonance of an organic dye with a simple additional fabrication step. Two oscillators can exchange their energies and become coupled when placed in the vicinity of each other. Our nanohole structures are very promising candidate for photon-exciton coupling. This is because nanoscale light confinement is possible with their plasmon resonances. Moreover, since our structures are open cavities, accessing the mode volume in which the coupling take place is relatively easy. This allows us to probe physical/chemical properties of the coupled states. We have found that when we match the plasmon resonance of the nanohole structure to an organic dye such as R6G, Raman scattering signal from the sample is significantly enhanced. Our ongoing research is to explore the use of our fabrication technique to fabricate plasmonic structures with unique properties.

For details: Chantharasupawong, P.; Tetard, L.; Thomas, J., Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of Tunable Plexcitonic Substrates. The Journal of Physical Chemistry C 2014, 118, 23954-23962.

Semitransparent Organic Solar Cells

We develop a facile and efficient approach to fabricate highly ordered ZnO nanorods (NRs) on top of rough silver nanowire (AgNW) surface. Prepared by an all-solution process, this nanostructure composite of ZnO-AgNW-ZnO film shows a 77% optical transmission at 550nm with 30 Ω/□ sheet resistance when measured from the surface of the top ZnO layer. Moreover, this well-ordered ZnO NR layer on top of AgNW is highly beneficial for organic solar cells as a multifunctional layer since it provides protection for AgNW against oxidation and moisture. With the use of this nanostructured composite electrode, we have observed a 14% improvement of Jsc over the control device.

Optical Limiting

Lasers are currently indispensable for many applications in a variety of fields. This includes military, telecommunications, manufacturing and medicine. Although lasers are a very powerful source of energy, at times, they can be damaging. Laser systems are so powerful that industries often utilize high power laser systems for cutting and drilling. For humans, unintended laser irradiations can damage eyes or other body parts. This poses high health threat to those who are working with such laser systems. In military applications, lasers are incorporated in many types of weaponry. These lasers can damage sensors or blind military personals. Therefore, there is a considerable need for a device to protect people and optoelectronic devices from laser threats. We are developing and testing materials which can diffuse high intensity laser lights while allowing low intensity laser lights to pass through it.

Details are given in:

  • SPIE Newsroom report
  • “Evolution of Nonlinear Optical Properties: From Gold Atomic Clusters to Plasmonic Nanocrystals”, Nano Letters, 12, 4661−4667 (2012)
  • “Optical power limiting in fluorinated graphene oxide: An insight into the nonlinear optical properties”, J. Phys. Chem. C, 116, 25955 (2012)
  • “Enhanced optical limiting in nanosized mixed zinc ferrites”, Appl. Phys. Lett. 100, 221108 (2012)

OPAZ-scan

We have developed a measurement technique, by combining Optical Z-scan and Photoacoustic Z-scan, called OPAZ-scan. This technique benefits from the advantages of both measurements. With this system nonlinear absorption of both optically light and dark sample can be measured. Furthermore, it is also found that the simultaneous measurement of the optical and photoacoustic signals gives enhanced insight into optical nonlinearity, especially ones with mixed nonlinear scattering and absorption.

For details: “Simultaneous optical and photoacoustic measurement of nonlinear absorption”, Appl. Phys. Lett. 102, 041116 (2013).

Highly Sensitive Photorefractive Polymers

Photorefractive composites derived from conducting polymers offer the advantage of dynamically recording holograms without the need for processing of any kind. Thus, they are the material of choice for many cutting edge applications, such as updatable 3D displays and imaging through a scattering medium. Photorefractive polymers sensitive to visible light have evolved to a state of high performance and reliability. Organic polymer materials also have the inherent advantages of ready manipulation of component formulations to suit a given application and low cost. Unlike many other permanent recording materials such as photopolymers, holograms can be written and erased in PR materials many times without the need of chemical processing. Our current focus is the development of highly sensitive polymers for video-rate holographic 3D display applications. Our group is developing photorefractive polymers using highly efficient new sensitizers.

For details: “Photoconducting polymers for photorefractive 3D display applications” (invited review article) Chem. Mater. 23, 416 (2011)

Wearable Energy Storage and Harvesting Ribbons (2016)

Wearable technology has been in the lime light ever since the electronics started becoming smaller and smaller. The miniaturization of gadgets became even easier with the introduction of nanoscience and technology. We have fabricated a flexible and wearable integrated device in the form of thin ribbons which can simultaneously harvest and store energy. An array of such devices are woven into a textile form that can be knitted on clothes. The integrated device consists of a perovskite solar cell on a copper ribbon to harvest the light energy and a thin film supercapacitor on the other side of the ribbon is used to store the charges generated.

Superstructures for Photodetectors and Synapses

The human brain has the power to process and memorize information simultaneously. Neuromorphic computing is designed based on this principle. We recently developed optoelectronic synapsis using a superstructure, which is a baby step in this direction. This superstructure is developed by growing highly photosensitive methylammonium lead bromide perovskite quantum dots (PQDs) on graphene, by a defect-mediated process. Graphene, a two-dimensional sheet of carbon atoms, is a dream material for electronic and optoelectronic applications due to its interesting properties such as broad bandwidths, very high electron mobility and high transparency besides outstanding flexibility and stability. However, a major disadvantage of graphene is the low charge generation efficiency, with only 2.3% of incident light being converted to electric charge. This low charge generation limits its applications in optoelectronic and photonic devices. Contrarily, PQDs have emerged as attractive materials for optoelectronic devices due to their high extinction coefficients, bandgap tunability, high photoluminescence quantum yield, and narrow emission spectrum. However, the charge transport properties of these PQDs are inferior when compared to graphene. By combining these two materials in a superstructure enabled us to achieve high optical absorption and charge transport in an extremely thin medium. The neuromorphic computing ability of our device was tested via face recognition experiments.