No abstract

Double perovskites are promising candidates for less toxic and highly stable metal halide perovskites, but their optoelectronic performances still lag behind those of the lead halide counterpart, due to the indirect nature of the bandgap and the strong electron–phonon coupling. Reducing the dimensionality of Cs2AgBiBr6 down to a 2D layered form is strategic in order to tune the band gap from indirect to direct and provides new insights into the structure–property relationships of double perovskites. Herein, we report on a series of monolayer 2D hybrid double perovskites of formula (RA)4AgBiBr8, where RA represents different primary ammonium large cations with alkyl- and aryl-based functionalities. An in-depth experimental characterization of structure, film morphology, and optical properties of these perovskites is carried out. Interestingly, the variation of the ammonium cation and the interplanar distance between adjacent inorganic monolayers has peculiar effects on the film-forming ability and light emission properties of the perovskites. Experiments have been combined with DFT calculations in order to understand the possible origin of the different emissive features. Our study provides a toolbox for future rational developments of 2D double perovskites, with the aim of narrowing the gap with lead halide perovskite optoelectronic properties.

Emphasis was recently placed on the Cs2AgBiBr6 double perovskite as a possible candidate to substitute toxic lead in metal halide perovskites. However, its poor light-emissive features currently make it unsuitable for solid-state lighting. Lanthanides doping is an established strategy to implement luminescence in poorly emissive materials, with the additional advantage of fine-tuning the emission wavelength. We discuss here the impact of Eu-and Yb-doping on the optical properties of Cs2AgBiBr6 thin films, obtained from solution-processing of hydrothermally synthesized bulk crystalline powders, by combining experiments and density functional theory calculations. Eu(III) incorporation does not lead to the characteristic 5 D0→ 7 F2 emission feature at 2 eV, while only a weak trap-assisted sub band-gap radiative emission is reported. Oppositely, we demonstrate that incorporated Yb(III) leads to an intense and exclusive photoluminescence emission in the nearinfrared as a result of the efficient sensitization of the lanthanide 2 F5/2→ 2 F7/2 transition.

A method which is able to produce different types of nano-structured materials, namely nano-particles, nano-structured surfaces and nano-porous membranes, from two-phase metallic alloys is reviewed. The new process first establishes nano-structures in the bulk alloy and then separates them by selective phase dissolution. Variation in processing makes it possible to produce different types of nano-structure even from the same alloy. The process can be applied to many different alloy systems. An overview is presented emphasizing the versatility of the process with examples of different nano-structure types that can be produced. Further, the new method is discussed in relation to similar processes (specifically, electrochemical processes) which have been used for nano-structure synthesis.

Invited for this month cover is the group of Teresa Gatti at the Justus Liebig University (JLU) in Giessen, Germany, the group of Federico Bella at Politecnico di Torino (POLITO), Italy, and the group of Francesco Lamberti at the University of Padova (UNIPD), also in Italy. The image shows how waste tires can be converted in a conductive carbon powder that undergoes a green processing step to produce carbon electrodes for lead‐free perovskite solar cells. Similar devices can be employed to harvest indoor light in order to power the Internet of Things (IoT) ecosystem. The Research Article itself is available at 10.1002/cssc.202201590.