Our research focuses on the next generation technology in the fields of nanophotonics, polarization-selective photonics, bioelectronics, biophotonics, pulsed laser-based deposition, and many other photonic applications.

Nanocrystal Quantum Dot-based Photovoltaics

The Photonic and Optoelectronic Devices Group is committed to improving the performance of renewable energy technologies. Research is being conducted on plastic solar cells which utilize the novel properties of semiconducting nanocrystals, or quantum dots, to improve solar cell efficiency.

By employing the use of PbSe quantum dots in plastic solar cells we have enhanced the harvest of the infrared portion of the solar energy spectrum. The nanocrystal quantum dots sensitize the conjugated polymer poly-3(hexylthiophene) used in our hybrid photovoltaic devices to work with infrared light.

PbSe/PbS Nanocrystal quantum dots of the core-shell configuration also feature high photoluminescence efficiency, enhanced photochemical stability and structural robustness, and show great potential in the development of even-more efficient colloidal quantum dot-based hybrid solar cell devices.

This work is supported by a grant from the US Army Research Office (ARO).

Selected Publications:

Applied Physics Letters, vol.88, 2006, p.183111; Journal of Applied Physics, Vol.104, 2008, p.044306

Nanotechnology, vol.17, 2006, p.5428; Journal of Experimental Nanoscience, vol.2, 2007, p.13

Colloidal Quantum Dot-based Light Emitting Diodes, Flexible Displays, and Solid State Lighting

Due to the high brightness, high efficiency, and solution processibility of colloidal quantum dots, they have many advantages for next-generation lighting technologies. Our group has fabricated red, green and blue light emitting diodes (LEDs) from Cd(S,Se)/(Zn,Cd)S quantum dots. Currently, we hold the record for brightness and color purity in our quantum dot-LEDs.

Additionally, we use a proprietary mist-deposition technique for patterning and assembling multicolor quantum dot-LEDs with monolayer precision. The quantum dot-LEDs can be deposited onto flexible substrates of poly(ethylene terephthalate), or PET, paving the way for the development of matrix array-based quantum dot-LED displays that are rugged, lightweight, and conformable.

Our quantum dot-LEDs also show promise in the areas of biochemical sensing and white LED lighting. The development of our electrically pumped-microcavity quantum dot-LED has resulted in high control over the spectral output and polarization of devices.

This work is supported by grants from the US National Science Foundation.

Selected Publications:

Applied Physics Letters, vol.92, 2008, p.023111

Journal of Applied Physics, Vol. 105, 2009, p. 034312

Applied Physics Letters, vol.91, 2007, p.023102;

IEEE Photonics Technology Letters, vol.17, 2005, p.2008;

IEEE Photonics Technology Letters, vol. 20, 2008, p. 1998

Semiconductor Nanostructure-based Lasers and Optical Amplifiers

Multi-photon pumped nanoscale lasers have been considered as a promising approach for the frequency up-conversion of coherent light. The potential applications are widespread, ranging from tunable short-wavelength light sources, on-chip nanolasers, biomedical sensing and diagnostics, to quantum computing and communication.

In our lab, we study frequency up-converted lasers with two different types of microcavities: the nanostructure self-formed microcavities (like nanowires and nanodisks) with wide band gap semiconductors (ZnS, ZnO, GaN, …) and the external cavities with colloidal semiconductor nanocrystal quantum dots (CdSe, InP,…). Experimental techniques including single nanostructure emission measurement, fluorescence imaging, and picosecond time-resolved photoluminescence spectroscopy are employed.

This work is supported by the US Army Research Office (ARO) and the Penn State Center for Multiscale Wave-Materials Interactions (CMWMI).

Selected Publications:

Optics Letters Vol. 33, 2008, pp. 2437;

Applied Physics Letters, vol.92, 2008, p.233116;

Optics Express, Vol. 17, 2009, 7893;

Applied Physics Letters, vol.92, 2008, pp.261110;

Applied Physics Letters, vol.90, 2007, p.171105;

Bioelectronics and Biosensors

Cell–based biosensing is an emerging technology that can be used to detect chemical and biological agents. Our research focuses on the development of single–cell–based and multiple–cell–based microelectrode array impedance sensors for toxin detection and anti–cancer drug screening. We are also integrating ultrasonic micro–transducers to cell–based sensors so that they can be employed in single–/multiple–cell level drug delivery studies with high–throughputs.

Our micro–fabricated biosensors, optimized with surface–engineering techniques, show high sensitivity, high–throughputs, high reproducibility, and large SNR. We are also developing theoretical models for cell–based impedance sensors, which explain changes in cell–electrode hetero–junction and cell membrane structures due to external and/or internal stimuli. These models provide insights into biosensing mechanics and are successfully implemented in our cell–based impedance sensing.

This work is supported by two NIH sub-contracts via Dr. Xu's collaborations with the University of Washington and TRS Ceramic, Inc.

Selected Publications:

Biosensors and Bioelectronics, vol.23, 2008, p.1307