Electrical, optical, and structural characteristics of perovskite light-emitting diodes (PeLEDs) are investigated. The PeLED consisting of ITO/ZnO/MAPbI 3 (CH 3 NH 3 PbI 3 )/spiro-OMeTAD/Ag structures shows a peak emission wavelength of 766 nm, turn-on voltage of 1.7 V, reverse breakdown voltage of À5.4 V, current efficiency of 1.5 Â 10 À4 cdA À1 , maximum luminance of 0.1 cdm À2 , and an external quantum efficiency of 0.2% at bias voltage of 3 V (or a current density of 617 mA cm À2 ). The PeLED also shows a significant output drop at higher bias voltage. According to the analyses of forward J-V curves and structural studies, this could be associated with the anomalously large ideality factor of 12.8 and the high series resistance of 2.8 Ω cm 2 , that is, the leakage current through parasitic shunt path (possibly through pinholes in the perovskite) and accelerated Joule-heating result in a significant output degradation.

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The growth of one-dimensional nanostructures without a metal catalyst via a simple solution method is of considerable interest due to its practical applications. In this study, the growth of amorphous silicon (a-Si) nanotips was investigated using an aqueous solution dropped onto the Si substrate, followed by drying at room temperature or below for 24 h, resulting in the formation of a-Si nanotips on the Si substrate. Typically, the a-Si nanotips were up to 1.6 μm long, with average top and middle diameters of 30 and 80 nm, respectively, and contained no metal catalyst in their structure. The growth of a-Si nanotips can be explained in terms of the liquid–solid mechanism, where the supercritical Si solution (liquid) generated on the Si substrate (after reaction with the aqueous solution) promotes the nucleation of solid Si (acting as seeds) on the roughened surface, followed by surface diffusion of Si atoms along the side wall of the Si seeds. This is very similar to the phenomenon observed in the growth of snow ice crystals in nature. When photoexcited at 265 nm, the a-Si nanotips showed blue luminescence at around 435 nm (2.85 eV), indicating feasible applicability of the nanotips in optoelectronic functional devices.