Agenda
13:30–14:45 - Session 3: Electro-Optical properties of Nanostructures
Dr. Bill Mitchel (AFRL Materials and Manufacturing Directorate), Chair
-
13:30–13:45
High Efficiency and Long Life Photovoltaic Research for Space Applications
Wei-Fang Su,* Chun-Wei Chen, Lee-Yi Wang, Chi-An Dai
Department of Materials Science and Engineering, National Taiwan University, 1, Roosevelt Road, Sec. 4, Taipei, Taiwan
Polymer photovoltaic device is favored over wafer based semiconductor photovoltaic device due to its light weight and flexible behavior. However, the polymer photovoltaic device usually has shortcomings in low efficiency and short life. We are proposing to make high efficiency and long life photovoltaic devices from aromatic polymer-oxide nanoparticle hybrid material containing ordered nanostructure for space applications. We have established time resolved photoluminescence spectroscopy to measure exciton life time and time of flight photoluminescence spectroscopy to measure charge carrier mobility. By inclusion CdSe nanoparticles into MEHPPV conducting polymer in the hybrid solar cell increases the ordering in polymer. The absorption spectrum was red shifted for hybrid system as compared with neat polymer. The hybrid system also exhibits an order increase in power efficiency (2006 Nanotechnology 17, 1260). The exciton life time of hybrid material can be decreased to less than half of the neat polymer by inclusion low cost and nontoxic TiO2 nanorod into MEHPPV conducting polymer (2006 Nanotechnology, 17, 5781-5785). The TiO2 nanorod-MEHPPV solar cell has been fabricated. The efficiency of cell can be increased by 2.5 times by inserting a TiO2 nanorod electron transport layer between the hybrid active layer and metal electrode (2006 Nanotechnology 17, 5387-5392). The charge carrier mobility of P3HT polymer can be increased at least an order by blending TiO2 nanorods into P3HT. The carrier mobility can be further increased using column structured ZnO electron transport layer infiltrated with the TiO2-P3HT hybrid. Environmental friendly, red absorbing and water soluble polythiophene (poly [2- (3-thienyl) ethyloxy-4-butyl sulfonate]) (PTEBS) and spectrum tunable homogeneous TiO2-P3HT hybrid have been synthesized for high efficiency solar cell.
-
13:45–14:00
Shell/Core Nanoparticles for Optoelectronic Applications
T. Randall Lee
Department of Chemistry, University of Houston, 4800 Calhoun Road, Houston, TX 77204-5003
The optical absorbances of monometallic nanoparticles with core-shell geometries can be tuned from the visible to near infrared by varying the core size and shell thickness in a systematic fashion. These nanoparticles, called “nanoshells”, typically consist of a dielectric silica core (≥ 100 nm diameter) surrounded by a gold shell (≤ 30 nm thick). As such, they have been targeted for use in a variety of applications, including Raman-based imaging, cancer therapy, and optical shielding. Here, we wish to report the preparation and characterization of discrete metallic silver core particles that are coated with a thin metallic gold shell. At selected dimensions, these composite particles absorb strongly in the visible and/or near infrared spectral regions. Importantly, they can be prepared with substantially greater ease and markedly smaller sizes than the previous generation gold-coated silica nanoshell particles.
-
14:00–14:15
Novel carbon-Al complex nanolayer in efficient organic/polymer light-emitting diodes
Tzung-Fang Guo,*, † Fuh-Shun Yang,† Zen-Jay Tsai,† and Ten-Chin Wen‡
†Institute of Electro- Optical Science and Engineering
‡Department of Chemical Engineering
National Cheng Kung University
Tainan, Taiwan 701
Incorporating a thin organic-oxide functionalized nanolayer with Al yields a composite cathode structure for the fabrication of high-performance organic/polymer light-emitting diodes (O/PLEDs). The electroluminescence (EL) efficiency of phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLEDs with an organic oxide/Al composite cathode, reaches 12.20 cd/A, which is markedly higher than those, 5.26 cd/A and 0.11 cd/A, of devices with Ca/Al and Al cathodes, respectively. The improved device performance is due to the instant formation of a specific carbon-Al complex nanolayer at the cathode interface during the deposition of Al. As characterized through the depth-profile measurement of X-ray photoelectron spectroscopy, an Al-C interlayer is found at the cathode interface, which works as a medium enabling the efficient injection of electrons through the Al electrode and eliminating the metal-induced quenching sites of luminescence in the EL layer near the recombination region.
-
14:15–14:30
Plasma-like negative capacitance in nano-colloids
Jason Shulman, S. Tsui, F. Chen, and Y. Y. Xue
Texas Center for Superconductivity at the University of Houston, 202 UH Science Center, University of Houston, Houston, TX 77204
C. W. Chu
Texas Center for Superconductivity at the University of Houston, 202 UH Science Center, University of Houston, Houston, TX 77204
Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720
Hong Kong University of Science and Technology, Hong Kong
Recently, there has been a rapid increase in the number of reports describing negative capacitance (NC) in various nanostructures. In order to explore the conditions and possible mechanisms responsible for such observations we have investigated several nano-colloids which exhibit NC. The response of these systems is linear over a broad range of conditions. The low frequency dispersions of both the resistance and capacitance are consistent with the free-carrier plasma model. Furthermore, we observe that the phenomenon is sensitive to the surface/volume ratio of the nanoparticles and the possible interfacial water. The possible mechanisms, ranging from a negative dielectric constant to nonlinear resistance with relaxation, are explored. It appears that plasma-like excitations and a new energy storage mechanism are needed to interpret the data.
-
14:30–14:45
Controlled Zn/ZnO transformation and doped ZnO nanostructures with tunable optical properties
Wei-Yu Chen1, Ruey- Chi Wang2, and Chuan- Pu Liu1, 3,*
1 Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan
2 Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung, 81148, Taiwan
3 Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan
Diverse Zn, Zn/ZnO polyhedral particles and doped ZnO single-crystalline nanostructures with tunable optical properties were synthesized on Si substrates via a combination of thermal chemical vapor deposition, oxidation annealing and alloying vapor deposition (AVD). The single-crystalline Zn polyhedral particles with size larger than several microns could be grown on the Si substrate where the possible epitaxial planes with Si(111) could be ZnO (0001), (011–0), and (011–1) facets. The novel phase transformation from Zn to ZnO were studied systematically by controlled annealing treatments, where the optical properties of the polyhedral particles and the interfaces between Si (111) and different Zn facets were studied by cathodoluminescence (CL) and high-resolution transmission electron microscopy (HRTEM), respectively. Besides, Al: ZnO and Co: ZnO 1D nanostructures with tunable doping concentration were synthesized by varying the alloying treatment temperature of AVD. HRTEM results show that the doped nanostructures are single-crystalline wurtzite structures growing along the <0001> direction. Room-temperature CL measurements show that both the ZnO polyhedral particles and doped ZnO nanostructures exhibit strong ultraviolet (UV) emissions with negligible green emissions. The UV emission of the ZnO polyhedral particles shifts to a lower energy from 3.38 to 3.33eV by increasing oxidation annealing temperature from 450 to 600°. However, the UV emission of the Al doped 1D nanostructures shift to a higher energy from 3.29 to 3.34eV due to Al incorporation.
