The Electronic Disorder Landscape of Mixed Halide Perovskites.

Band gap tunability of lead mixed halide perovskites makes them promising candidates for various applications in optoelectronics. Here we use the localization landscape theory to reveal that the static disorder due to iodide:bromide compositional alloying contributes at most 3 meV to the Urbach energy. Our modeling reveals that the reason for this small contribution is due to the small effective masses in perovskites, resulting in a natural length scale of around 20 nm for the "effective confining potential" for electrons and holes, with short-range potential fluctuations smoothed out.

Tetrabenzo[a,c]phenazine Backbone for Highly Efficient Orange-Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation.

Three thermally activated delayed fluorescence (TADF) molecules, namely PQ1, PQ2, and PQ3, are composed of electron-accepting (A) tetrabenzo[a,c]phenazine (TBPZ) and electron-donating (D) phenoxazine (PXZ) units are designed and characterized. The combined effects of planar acceptor manipulation and high steric hindrance between D and A units endow high molecular rigidity that suppresses nonradiative decay of the excitons with improved photoluminescence quantum yields (PLQYs). Particularly, the well-aligned excited states involving a singlet and a triplet charge-transfer excited states and a localized excited triplet state in PQ3 enhances the reverse intersystem crossing rate constant (k ) with a short delay lifetime (τ ).

Ion Migration-Induced Degradation and Efficiency Roll-off in Quasi-2D Perovskite Light-Emitting Diodes.

Quasi-2D perovskites have attracted wide attention as the emitter of light-emitting diodes (LEDs) in recent years because of the ease of obtaining high external quantum efficiencies (EQEs). However, the quick degradation under continuous operation and significant EQE roll-off at high current densities are issues that need to be overcome for future practical applications using quasi-2D perovskite LEDs (PeLEDs). In this context, we discuss the mechanism of the degradation and EQE roll-off on the basis of ion migration.

Detrimental Effect of Unreacted PbI on the Long-Term Stability of Perovskite Solar Cells.

Excess/unreacted lead iodide (PbI ) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI crystals under continuous light illumination.

Detecting and identifying reversible changes in perovskite solar cells by electrochemical impedance spectroscopy.

The current status of electrochemical impedance spectroscopy (EIS) and related analysis on perovskite solar cells (PSC) is still unsatisfactory. The provided models are still vague and not really helpful for guiding the efforts to develop more efficient and stable devices. Due to the slow and complex dynamics of these devices, the obtained spectra need to be validated, which is hardly ever done.