G. A. Ozin

Band spectroscopy of colloidal photonic crystal films

Here we report on the optical properties associated with photonic bands of three-dimensional photonic colloidal crystals. Optical spectroscopy analysis shows fluctuations of the transmitted and reflected light intensity in photon frequency regions where no stop bands open up. The different optical features observed at low and high photon energy ranges are analyzed in terms of the band structure of the crystal. A relationship is found between dispersion of the bands and the features observed experimentally. On these premises, we show it is possible to map the higher-energy band region along nonprincipal directions of the first Brillouin zone by transmission spectroscopy.

Photonic crystal intermediate reflectors for micromorph solar cells: a comparative study

Wave-optics analysis is performed to investigate the benefits of utilizing Bragg-reflectors and inverted ZnO opals as intermediate reflectors in micromorph cells. The Bragg-reflector and the inverted ZnO opal intermediate reflector increase the current generated in a 100 nm thick upper a-Si:H cell within a micromorph cell by as much as 20% and 13%, respectively. The current generated in the bottom muc-Si:H cell within the micromorph is also greater when the Bragg-reflector is used as the intermediate reflector. The Bragg-reflector outperforms the ZnO inverted opal because it has a larger stop-gap, is optically thin, and due to greater absorption losses that occur in the opaline intermediate reflectors.

Selectively transparent and conducting photonic crystal rear-contacts for thin-film silicon-based building integrated photovoltaics

Wave-optics analysis is performed to show that selectively transparent and conducting photonic crystals (STCPCs) can be utilized as rear contacts to enhance the performance of building-integrated photovoltaics (BIPV). For instance, the current generated in an a-Si:H cell with an STCPC functioning as its rear contact is comparable to that of a similar cell with an optimized ZnO/Ag rear contact. However, the solar lumens (~3.5 klm/m2) and power (~430W/m2) transmitted through the cell with the STCPC rear contact can potentially provide indoor heating and lighting, respectively. Moreover, experimental results show that STCPC rear contacts could be used to control the color temperature of light transmitted through BIPV panels.

Electrical properties of p-type and n-type doped inverse silicon opals - towards optically amplified silicon solar cells

While the silicon photonic crystals have promised revolutionary developments in the field of optical telecommunications and optical computing, it has only recently been realized that their prowess to trap and slow photons could potentially and significantly improve the efficiency of silicon solar cells. In this work n-doped and p-doped inverse silicon opals are synthesized and processed to optimize their electrical charge transport properties, which are shown to be of semiconductor device quality. Moreover a prototype p-i-n junction solar cell based on the inverse silicon opal is reduced to practice and its optoelectronic behavior is evaluated.

Flash nano-welding: investigation and control of the photothermal response of ultrathin bismuth sulfide nanowire films.

Ultrathin Bi₂S₃ nanowires undergo a pronounced photothermal response to irradiation from a commercial camera flash. Controlled nano-welding was shown by using single walled carbon nanotube mats as an electrically and thermally conductive substrate. The resulting welded nanowire film is denser and has significantly lower resistance than unflashed bilayer films.

F2-laser digital etching of colloidal photonic crystals

We report on digital etching of silica colloidal photonic crystals by employing a pulsed deep-ultraviolet F2 laser at 157nm wavelength. When the laser fluence is above a microsphere-size-dependent threshold and within an appropriate fluence window, colloidal crystals can be etched in a digitized fashion, whereby a single microsphere layer can be removed upon exposure to a single laser pulse. Alternatively, single spheres or lines of spheres can be selectively ejected by patterning the laser beam. The results demonstrate a fast, noncontact, straightforward, and cost-effective approach for engineering extrinsic defects into colloidal photonic crystals.

Nanoporous transparent and conducting films and photonic crystals

Herein we present nanoporous transparent and conducting films prepared by sputtering controlled amounts of ITO onto and into the interconnected pores of SiO2 and SnO2 nanoparticle films. The sheet resistance of these nanoporous transparent conducting films made with either SiO2 or SnO2 nanoparticles is less than 103 Ω/□. Furthermore, we demonstrate entirely nanoporous one-dimensional photonic crystals by alternately stacking nanoporous transparent and conducting films made from SiO2 and SnO2 nanoparticles.

Three-Dimensional Lithography of Photonic Crystals

We present our work on the fabrication of three-dimensional Photonic Crystal templates by holographic lithography and direct laser writing. Both optical methods are highly qualified for the production of top-quality polymeric three-dimensional Photonic Crystals and allow in combination the controlled incorporation of defects and waveguides in large-area structures. Scanning electron micrographs and optical spectra of different Photonic Crystals are presented and compared with numerical simulations. Our roadmap to infiltrate the polymeric templates with high refractive-index materials is outlined.

Integrating photonic crystals in thin film silicon photovoltaics

Wave-optics analysis is performed to investigate the benefits of integrating photonic crystals into micromorph cells. Specifically, we theoretically investigate two novel micromorph cells which integrate photonic crystals and compare their optical performance with that of conventional micromorph cells. In the first innovative micromorph cell configuration the intermediate reflector is a selectively transparent and conducting photonic crystal (STCPC). In the second micromorph cell its bottom μc-Si:H cell is structured in the form of an inverted opal. Our results show that with the AM1.5 solar spectrum at normal incidence the current generated in a conventional micromorph cell is increased from 12.1 mA/cm2 to 13.0 mA/cm2 when the bottom μc-Si:H cell is structured in the form of an inverted opal. However, the current generated in the micromorph cell can be increased to as much as 13.7 mA/cm2 when an STCPC is utilized as the intermediate reflector. Furthermore, the thickness of the μc-Si:H opal must be relatively large in order to absorb a sufficient amount of the solar irradiance, which is expected to degrade the electrical performance of the device. In contrast, our results suggest that STCPC intermediate reflectors are a viable technology that could potentially enhance the performance of micromorph cells.

Er doped As 2 S 3 photoresist for 3-D direct laser fabrication of 3-D nanostructures

We present a novel high-index-of-refraction (2.45) photoresist material based on erbium doped arsenic trisulfide. It shows room temperature photoluminescence at 1.5 microns wavelength, and can directly be used for direct laser writing.