Electrical Engineering Seminar: Heayoung Yoon
(Lectures and Seminars)
"Fabrication, integration, and electrical/spectroscopic characterizations of nanoscale molecular electronics and solar energy devices"
Dr. Heayoung P. Yoon, Center for Nanoscale Science and Technology (CNST) National Institute of Standards and Technology (NIST)
Considerable attention has been devoted to developing nano-electronic devices and solar cells that use unique properties of nanowires. Such example includes nanoscale molecular junction devices that function as nonlinear circuit elements and nanowires interconnect these circuit elements. A crossed-nanowire device is comprised of self-assembled molecular junctions that are sandwiched between a lithographically-defined bottom contact and a metal nanowire top contact. The flexibility of the fabrication process offers rapid integration of junctions with different molecules and metal contacts. Temperature dependent current-voltage (I-V-T) characteristics and inelastic electron tunneling (IET) spectra at 4 K of the crossed-nanowire junctions of OPE (oligo phenylene ethynylene) and thiol-substituted oligoaniline switching molecules will be presented. For low-cost, high-efficiency energy harvesting devices, micro/nanowires solar cells have shown enhanced photovoltaic (PV) performance comparing to that of the planar solar cells fabricated using the same material. Unlike planar cells, where the light absorption and carrier collection are in competition, the radial junction architecture provides the advantage of decoupling the processes. This talk will discuss the design, fabrication, and characterization of radial n+-p+ junction solar cells composed of densely-packed c-Si pillar arrays.
As the last part of the talk, local PV characterizations using a low energy electron beam (< 5 keV) will be presented. Using a commercial thin film solar cell (n-CdS / p-CdTe), local current-voltage measurements were performed using nano-contacts in conjunction with local carrier generation using electron beams. Electron beam induced current was used to measure local efficiency with a spatial resolution as high as ≈20 nm both on the top surface and in cross-section of the device. The results show that a large fraction of grain boundaries displays higher photocurrent as compared to grain bulk effectively serving as a three-dimensional distributed photocurrent collector.