Interfacial Chemistry Limits the Stability of Deep Blue Perovskite LEDs Revealed by Operando Characterization.

To commercialize lead halide perovskites as light-emitting diodes (LEDs), the operational device lifetime needs to be drastically improved. For this to be achieved, an understanding of degradation behavior under bias is crucial. Herein, we perform operando measurements of the structural, chemical, and electronic changes using synchrotron-based grazing-incidence wide-angle X-ray scattering and hard X-ray photoelectron spectroscopy on full-stack deep blue mixed bromide/chloride lead halide perovskite LEDs.

Dynamic nanodomains dictate macroscopic properties in lead halide perovskites.

Lead halide perovskites have emerged as promising materials for solar energy conversion and X-ray detection owing to their remarkable optoelectronic properties. However, the microscopic origins of their superior performance remain unclear. Here we show that low-symmetry dynamic nanodomains present in the high-symmetry average cubic phases, whose characteristics are dictated by the A-site cation, govern the macroscopic behaviour.

The impact of interfacial quality and nanoscale performance disorder on the stability of alloyed perovskite solar cells.

Microscopy provides a proxy for assessing the operation of perovskite solar cells, yet most works in the literature have focused on bare perovskite thin films, missing charge transport and recombination losses present in full devices. Here we demonstrate a multimodal operando microscopy toolkit to measure and spatially correlate nanoscale charge transport losses, recombination losses and chemical composition. By applying this toolkit to the same scan areas of state-of-the-art, alloyed perovskite cells before and after extended operation, we show that devices with the highest macroscopic performance have the lowest initial performance spatial heterogeneity-a crucial link that is missed in conventional microscopy.

Strain Heterogeneity and Extended Defects in Halide Perovskite Devices.

Strain is an important property in halide perovskite semiconductors used for optoelectronic applications because of its ability to influence device efficiency and stability. However, descriptions of strain in these materials are generally limited to bulk averages of bare films, which miss important property-determining heterogeneities that occur on the nanoscale and at interfaces in multilayer device stacks. Here, we present three-dimensional nanoscale strain mapping using Bragg coherent diffraction imaging of individual grains in CsFAPb(IBr) and CsFASnI (FA = formamidinium) halide perovskite absorbers buried in full solar cell devices.

Composition Dictates Octahedral Tilt and Photostability in Halide Perovskites.

Halide perovskites are excellent candidate materials for use in solar cell, LED, and detector devices, in part because their composition can be tuned to achieve ideal optoelectronic properties. Empirical efficiency optimization has led the field toward compositions rich in FA (formamidinium) on the A-site and I on the X-site, with additional small amounts of MA (methylammonium) or Cs A-site cations and Br X-site anions. However, it is not clear how and why the specific compositions of alloyed, that is, mixed component, halide perovskites relate to photo-stability of the materials.

Imaging Light-Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping.

In recent years, halide perovskite materials have been used to make high-performance solar cells and light-emitting devices. However, material defects still limit device performance and stability. Here, synchrotron-based Bragg coherent diffraction imaging is used to visualize nanoscale strain fields, such as those local to defects, in halide perovskite microcrystals.