A systematic strategy for effectively engineering the charge extraction in inverted structured perovskite solar cells based on CH3NH3PbI3−xClxis provided. An optimized power conversion efficiency of 20.5% is realized.

A broad absorption band around 500 nm is observed in ZnS nanoparticles. The absorption becomes more intensive and shifts to the blue as the particle size is decreased. The absorption energy is lower than the band gap of the particles and is considered to be caused by the surface states. This assignment is supported by the results of the fluorescence and of the thermoluminescence of the surface states. Both the absorption and the fluorescence reveal that the surface states are size dependent. The glow peak of the semiconductor particles is not varied as much upon decreasing size, indicating the trap depth of the surface states is not sensitive to the particle size. Considering these results, a new model on the size dependence of the surface states is proposed, which may explain our observations reasonably.

Zinc oxide flower-like bunches were directly synthesized on indium-doped tin oxide (ITO) glass substrates through a simple chemical bath deposition process. By adjusting precursor concentration, other morphologies (spindles and rods) were also obtained. All of them are hexagonal and single crystalline in nature and grow along the [0001] crystallographic direction. The possible growth mechanisms for these nano-and microcrystals were proposed. It was revealed that both the inherent highly anisotropic structure of ZnO and the precursor concentration play crucial roles in determining final morphologies of the products. In addition, vibrational properties of ZnO crystals with different morphologies were investigated by Raman spectroscopy.

The thermoluminescence (TL) of ZnS nanoparticles is reported. The TL intensity increases as the particle size is decreased. The consistency of the size dependence of the TL with that of the surface fluorescence indicates that the TL may be related to the surface states. TL may be caused by the recombination of carriers released from the surface states or defect sites by heating. Smaller particles have higher surface/volume ratio and more surface states, therefore contain more accessible carriers for TL. Besides, the carrier recombination rate increases upon decreasing size due to the increase of the overlap between the electron and hole wave functions. These two effects may make the TL increase upon decreasing size of the particles. The appearance of TL prior to any radiation reveals that trapped carriers have pre-existed. The investigation of TL may provide some useful information about the surface states that may explain the size dependence of the surface fluorescence.

A simple one-pot method is developed to prepare size- and shape-controlled copper(I) sulfide (Cu(2)S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethiol and oleylamine at a relatively high temperature. The crystal structure, chemical composition and morphology of the as-obtained products are characterized by powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The morphology and size of the Cu(2)S nanocrystals can be easily controlled by adjusting the reaction parameters. The Cu(2)S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The spherical Cu(2)S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shape of the Cu(2)S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time, accompanied by the diameter and thickness increasing. More interestingly, the nanodisks are inclined to self-assemble into face-to-face stacking chains with different lengths and orientations. This one-pot approach may extend to synthesis of other metal sulfide nanocrystals with different shapes and sizes.

Using the measured capacitance-voltage curves of Ni Schottky contacts with different areas on strained AlGaN∕GaN heterostructures and the current-voltage characteristics for the AlGaN∕GaN heterostructure field-effect transistors at low drain-source voltage, we found that the two-dimensional electron gas (2DEG) electron mobility increased as the Ni Schottky contact area increased. When the gate bias increased from negative to positive, the 2DEG electron mobility for the samples increased monotonically except for the sample with the largest Ni Schottky contact area. A new scattering mechanism is proposed, which is based on the polarization Coulomb field scattering related to the strain variation of the AlGaN barrier layer.

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By inserting a PCBM (phenyl-C61-butyric acid methyl ester) layer between a P3HT (poly(3-hexylthiophene)):PCBM blend and a Ca/Al