Organic–inorganic hybrid perovskite solar cells (PSCs) have made immense progress in recent years, owing to outstanding optoelectronic properties of perovskite materials, such as high extinction coefficient, carrier mobility, and low exciton binding energy. Since the first appearance in 2009, the efficiency of PSCs has reached 23.3%. This has made them the most promising rival to silicon-based solar cells. However, there are still several issues to resolve to promote PSCs’ outdoor applications. In this review, three crucial aspects of PSCs, including high efficiency, environmental stability, and low-cost of PSCs, are described in detail. Recent in-depth studies on different aspects are also discussed for better understanding of these issues and possible solutions.

All-silicon terahertz absorbers have attracted considerable interest. We present a design and numerical study of an all-silicon polarization-insensitive terahertz metamaterial absorber. The meta-atoms of the metamaterial absorber are square silicon rings which can be viewed as gratings. By properly optimizing the structure of the meta-atom, we achieve a broadband absorptivity that is above 90% ranging from 0.77 THz to 2.53 THz, with a relative bandwidth of 106.7%. Impedance matching reduces the reflection of the terahertz waves and the (0, ±1)-order diffraction induce the strong absorption. The absorption of this absorber is insensitive to the polarization of the terahertz wave and has a large incident angle tolerance of up to 60 degrees. The all-silicon metamaterial absorber proposed here provides an effective way to obtain broadband absorption in the terahertz regime. Metamaterial absorbers have outstanding applications in terahertz communication and imaging.

Gallium nitride nanowires (GaN NWs) were successfully grown on silicon substrates deposited with a thin gold film by plasma-assisted hot filament chemical vapor deposition (CVD), where GaN powder was used as the Ga source and nitrogen and hydrogen gases were used for the reactive gases. The diameters of synthesized GaN NWs are in a range of 40–150 nm and the lengths of some of the NWs are up to over 10 μm. The GaN NWs crystallize in a wurtzite structure and they are grown in alignment or bending modes depending on the growth conditions. The photoluminescence spectra exhibit five emission bands at about 379, 396, 467, 481 and 491 nm, which are related to the band edge emission, defects and impurities of GaN NWs, respectively. Furthermore, the excellent field emission (FE) properties of GaN NWs were observed, and the FE results reveal that the GaN NWs have a low turn-on field of 1.66 V μm⁻¹. It supplies a simple strategy to prepare GaN NW films for optical and electrical applications.