Optically resonant donor polymers can exploit a wider range of the solar spectrum effectively without a complicated tandem design in an organic solar cell. Ultrafast Förster resonance energy transfer (FRET) in a polymer-polymer system that significantly improves the power conversion efficiency in bulk heterojunction polymer solar cells from 6.8% to 8.9% is demonstrated, thus paving the way to achieving 15% efficient solar cells.

One dimensional (1D) anatase Co doped TiO2 nanostructures such as nanorods, nanowires, and nanotubes were synthesized by a simple solvothermal method using CoCl2·6H2O as the cobalt source. The effect of the different solvents on the crystal structures, morphologies, and sizes of the Co doped 1D nanostructures was investigated. The doping concentration of the samples primarily depends on the solvents. The X-ray photoelectron spectroscopy studies clearly showed that the Co was incorporated into the TiO2 lattice as Co2+ and oxygen vacancies were created due to the substitution of the Ti4+ ions by Co2+ ions. Optical absorption measurements showed additional absorption bands that are due to the ligand field transitions, 4T1g(4F) → 4T1g(4P) of Co2+ and also due to the transitions from different trap states related to the oxygen vacancies. The effects of the doping concentration on the defect structures and oxygen vacancies of the 1D nanostructures were mainly investigated using steady state photoluminescence (PL) and PL decay.

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Photocatalytic reduction of CO 2 is a promising strategy to alleviate the global energy crisis and environmental problems. Recently, metal halide perovskites with tunable bandgaps, large diffusion length, and abundant surface sites have drawn immense research interest for photocatalytic CO 2 reduction reactions. In this work, we develop an amorphous TiO 2 (aTiO 2 )encapsulated Cs 2 AgBiBr 6 double-perovskite nanocrystal (NC) by a room-temperature anti-solvent recrystallization method. Subsequently, we demonstrate the photocatalytic reduction of CO 2 to CH 4 (8.46 μmol g −1 h −1 ) and CO (5.72 μmol g −1 h −1 ) using this nanocomposite, where CH 4 is the dominant product. The Cs 2 AgBiBr 6 −aTiO 2 nanocomposite exhibits an 11-fold enhancement in the CH 4 yield compared to pristine Cs 2 AgBiBr 6 with prolonged stability of 16 h and higher selectivity of CH 4 over harmful CO production. The reason for the product selectivity is attributed to the presence of adventitious Ti 3+ on the surface of perovskite, which accelerates the CO 2 activation mechanism. The solvent effect on the product formation is also studied with ethyl acetate, acetonitrile, and dioxane. CH 4 becomes the dominant product in all of the cases, with an impressive evolution rate of 10.96 μmol g −1 h −1 in acetonitrile only. Impedance spectroscopy and ultrafast femtosecond transient absorption spectroscopy were used to establish the mechanism of CO 2 reduction. It was also confirmed that aTiO 2 helps in a faster and smoother charge transport at the interface by passivating the surface defects of the perovskite NCs. Our work provides a simple, highly efficient, and selective strategy for photocatalytic CO 2 reduction using doubleperovskite-based nanomaterial.

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We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C) than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.