In this article, we present a new paradigm for organometallic hybrid perovskite solar cell using NiO inorganic metal oxide nanocrystalline as p-type electrode material and realized the first mesoscopic NiO/perovskite/[6,6]-phenyl C61-butyric acid methyl ester (PC61BM) heterojunction photovoltaic device. The photo-induced transient absorption spectroscopy results verified that the architecture is an effective p-type sensitized junction, which is the first inorganic p-type, metal oxide contact material for perovskite-based solar cell. Power conversion efficiency of 9.51% was achieved under AM 1.5 G illumination, which significantly surpassed the reported conventional p-type dye-sensitized solar cells. The replacement of the organic hole transport materials by a p-type metal oxide has the advantages to provide robust device architecture for further development of all-inorganic perovskite-based thin-film solar cells and tandem photovoltaics.

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ZnO quantum dots ͑QDs͒ of controlled sizes have been fabricated by a simple sol-gel method. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed decreasing with the QD size that is ascribed to the quantum confinement effect. From the resonant Raman scattering, the coupling strength between electron and longitudinal optical phonon, deduced from the ratio of the second-to the first-order Raman scattering intensity, diminishes with reducing the ZnO QD diameter. The size dependence of electron-phonon coupling is principally a result of the Fröhlich interaction.

We report room-temperature ultraviolet stimulated emission and lasing from optically pumped high-quality ZnO nanowires. Emission due to the exciton-exciton scattering process shows apparent stimulated-emission behavior. Several sharp peaks associated with random laser action are seen under high pumping intensity. The mechanism of laser emission is attributed to coherent multiple scattering among the random-growth oriented nanowires. The characteristic cavity length is determined by the Fourier transform of the lasing spectrum.

Optical phonon confinement and efficient UV emission of ZnO nanowires were investigated in use of resonant Raman scattering (RRS) and photoluminescence (PL). The high-quality ZnO nanowires with diameters of 80-100 nm and lengths of several micrometers were epitaxially grown through a simple low-pressure vapor-phase deposition method at temperature 550 degrees C on the precoated GaN(0001) buffer layer. The increasing intensity ratio of n-order longitudinal optical (LO) phonon (A(1)(nLO)/E(1)(nLO)) with increasing scattering order in RRS reveals the phonon quantum confinement as shrinking the diameter of ZnO nanowires. The exciton-related recombination near the band-edge transition dominate the UV emissions at room temperature as well as at low temperature that exhibits almost no other nonstoichiometric defects in the ZnO nanowires.

Both band gap engineering and spatial confinement of optical phonon were observed depending upon the size of ZnO quantum dots at room temperature. Size-dependent blueshifts of photoluminescence and absorption spectra reveal the quantum confinement effect. The measured Raman spectral shift and asymmetry for the E2(high) mode caused by localization of optical phonons agree well with that calculated by using the modified spatial correlation model.

ZnO nanowires have been synthesized on porous silicon substrates with different porosities via the vapour-liquid-solid method. The texture coefficient analysed from the XRD spectra indicates that the nanowires are more highly orientated on the appropriate porosity of porous silicon substrate than on the smooth surface of silicon. The Raman spectrum reveals the high quality of the ZnO nanowires. From the temperature-dependent photoluminescence spectra, we deduced the activation energies of free and bound excitons.

Self-assembled secondary ZnO nanoparticles, recognized with the agglomeration of crystalline subcrystals, are successfully synthesized by a simple sol-gel method. TEM images display that one artificial cluster behaves in a single-crystal-like wurtzite structure because subcrystals coagulate as the same crystal orientation. Moreover, from the resonant Raman scattering, the as-grown sample exhibits phonon red shift; meanwhile, the coupling strength between electron and longitudinal optical phonon, determined by the ratio of secondto first-order Raman scattering cross sections, diminishes compared with the samples after postannealing at 350 and 500°C. The size dependence of electron-phonon coupling is principally as a result of the Fröhlich interaction.