The Role of Excitation Energy in Photobrightening and Photodegradation of Halide Perovskite Thin Films.

We study the impact of excitation energy on the photostability of methylammonium lead triiodide (CH3NH3PbI3 or MAPI) perovskite thin films. Light soaking leads to a transient increase of the photoluminescence efficiency at excitation wavelengths longer than 520 nm, whereas light-induced degradation occurs when exciting the films with wavelengths shorter than 520 nm. X-ray diffraction and extinction measurements reveal the light-induced decomposition of CH3NH3PbI3 to lead iodide (PbI2) for the high-energy excitation regime. We propose a model explaining the energy dependence of the photostability that involves the photoexcitation of residual PbI2 species in the perovskite triggering the decomposition of CH3NH3PbI3.

High-speed GaN/GaInN nanowire array light-emitting diode on silicon(111).

The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space.