Optical band-gap and cathode luminescence (CL) properties of anatase TiO2 nanopowders mixed with γ- Al2O3 powders by planetary ball mill were evaluated as a function of a powder mass ratio (x=Al2O3/TiO2) of 0 to 0.5 and their correlation with XRD spectra was also investigated. The optical band-gap of TiO2 increased from 3.36 eV to 3.41eV with increasing milling time (tm) up to 600 min, which was in good agreement with the blue shifts observed in the CL spectra with increasing tm and it was interpreted as a quantum size effect. In addition, the optical band-gap of TiO2 powders mixed with Al2O3 with tm=60min greatly increased from 3.36 eV to 3.48 eV with increasing x up to x=0.5. On the other hand, the optical band-gap of all the powders was decreased by annealing at temperatures above 600°C, which was evidenced by the XRD spectra to be due to the growth of grain size.

Wehave investigatedthe thickness dependence of air exposure of copper phthalocyanine (CuPc) layerson molybdenum trioxide (MoO3) with ultraviolet photoemission spectroscopy (UPS). It was found that after the air exposure, the WF of MoOx dropped severely. Meanwhile, with ∼10 ÅCuPcthin films covered on the top, there is no big change of the MoOx WF before and after the air exposure.

Inverse-photoemission spectroscopy (IPES) in the near-ultraviolet range is a new tool for investigating the LUMO levels of organic materials. Previous IPES methods have had two serious weaknesses, i.e. low energy resolution and sample damage to organic materials. In the present method, on the other hand, the irradiation damage to the organic sample is significantly reduced by decreasing the kinetic energy of electrons below the damage threshold. The energy resolution of the instrument is improved by a factor of two to 0.3 eV by using multilayer band pass filters. Acceptor materials widely used in organic photovoltaic cells, C60 and phenyl-C61-butyric acid methyl ester (PC61BM), are measured with this new technique to determine the electron affinities.

Organic solar cells consisting of Phthalocyaninatocopper (PcCu) as donor and the Buckminsterfullerene C60 as acceptor molecule were prepared by physical vapor deposition as planar or bulk heterojunctions. The devices were studied by IV-characterization as well as intensity-modulated photovoltage spectroscopy to determine the average lifetime of charge carriers formed subsequent to light absorption. An increasing charge carrier lifetime was determined for an increasing PcCu-content in the films. Back transfer of electrons at the undesired contact of C60 with PEDOT:PSS as well as recombination following hole trapping in interface states in the contact of PcCu with C60 or in isolated domains of PcCu are discussed as possible origins.

A MATLAB program is developed to help analyze single molecule spectroscopic data obtained with a standard inverted optical microscope. The described software has provisions to mitigate the effects of high background signals present in such data sets and greatly streamlines their analysis. Efficient single molecule image analysis and statistical blinking analysis are enabled with these programs to support single molecule imaging in an inverted configuration.

Despite organic solar cells have recently shown remarkable high power conversion efficiencies approaching 10%, further improvements are required to provide a low-cost alternative to inorganic photovoltaics. Optical losses related to insufficient light trapping and parasitic absorption of the contact layers limit drastically the photocurrent delivered by the cells. Textured surfaces, such as V-grooves (2D) and pyramids (3D), can provide better light coupling into the conformally deposited solar cells. In this work, we analyze the enhancement in light absorption in textured solar cells based on copper phtalocyanine (CuPc) and fullerene (C60) on the micro- and submicroscale. The analysis is carried out with the aid of the finite element method in 2D and 3D, taking into account interference as well as reflection and refraction of the incident AM1.5G spectrum. The results show that both type of structured cells perform better than planar cells reaching up to 23% improvement in maximum photocurrent for normal incidence. We also explore the lateral inhomogeneities of the generation rate within the active layers and their potential effect on the exciton collection efficiency.

This report will demonstrate broadband, wide-angle, and polarization-insensitive absorption enhancement in ultra-thin films resting on metal substrates that have been etched with arrays of shallow sub-wavelength cylindrical holes. Absorption enhancement will be studied as a function of array geometry, with particular emphasis given to quasiperiodic arrays (a class of deterministic aperiodic arrays that were originally developed to tessellate 2-D planes with regular polygons). Through simulations and experimental data, it was found that absorption enhancement is heavily dependent on the rotational symmetry of the pattern of holes, as well as the inter-hole distance.