UV-visible absorption and cathodoluminescence spectra of phase-pure epitaxial BiFeO3 thin films grown on SrTiO3(001) substrates by ultrahigh vacuum sputtering reveal a bandgap of 2.69–2.73eV for highly strained ∼70nm thick BiFeO3 films. This bandgap value agrees with theoretical calculations and recent experimental results of epitaxial BiFeO3 films, demonstrating only minimal bandgap change with lattice distortion. Both absorption and cathodoluminescence spectra show defect transitions at 2.20 and 2.45eV, of which the latter can be attributed to defect states due to oxygen vacancies.
Organic photovoltaic cells containing electron-transporting organic nanofibers in the form of "nanofabrics" are investigated. Nano-fabric heterojunctions of poly(3-hexylthiophene) and electron-transporting nanofibers significantly improve short-circuit current density in organic photovoltaic cells. The nanofibers and nanofabric are synthesized from organic electrontransporting material bis(octyl)-perylenediimide (PDI-C 8). The PDI-C 8 based nano-fabric's electron mobility is measured to be 0.08 cm 2 /V s. The nanofabric improves charge collection by expanding the interfacial acceptor-donor area while simultaneously providing dedicated electron transport pathways to the LiF/Al electrodes. An increase in fill factor is observed for photovoltaic cells incorporating the nanofabric heterojunctions and is attributed to efficient removal of space charge. V
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