Halide perovskite materials offer an ideal playground for easily tuning their color and, accordingly, the spectral range of their emitted light. In contrast to common procedures, this work demonstrates that halide substitution in Ruddlesden–Popper perovskites not only progressively modulates the bandgap, but it can also be a powerful tool to control the nanoscale phase segregation—by adjusting the halide ratio and therefore the spatial distribution of recombination centers. As a result, thin films of chloride‐rich perovskite are engineered—which appear transparent to the human eye—with controlled tunable emission in the green. This is due to a rational halide substitution with iodide or bromide leading to a spatial distribution of phases where the minor component is responsible for the tunable emission, as identified by combined hyperspectral photoluminescence imaging and elemental mapping. This work paves the way for the next generation of highly tunable transparent emissive materials, which can be used as light‐emitting pixels in advanced and low‐cost optoelectronics.

Improving the perovskite/electron transporting layer (ETL) interface is a crucial task to boost the performance of perovskite solar cells (PSCs). This is utterly fundamental in the inverted (p-i-n) configuration using...

Layered lead halide perovskites (2D LHPs) are attracting considerable attention as a promising material for a new generation of solar cell devices. LHPs have been presented as a more stable alternative to the more widespread 3D bulk perovskite materials; however, a critical analysis of their photostability is still lacking. In this work, we perform a comparative study between BA 2 MA n−1 Pb n I 3n+1 (BAbutylammonium and MAmethylammonium) 2D LHPs with different dimensionalities (n = 1−3) and MAPbI 3 3D perovskites. We compare different stability testing protocols including photometrical determination of iodine-containing products in nonpolar solvents, X-ray diffraction, and photoluminescence (PL) spectroscopy. The resulting trends of the photostability in an inert atmosphere based on PL spectroscopy measurements demonstrate a nonmonotonic dependence of the degradation rate on the perovskite layer thickness n with a "stability island" at n ≥ 3, which is caused by a combination of antibate factors of electronic structures and chemical compositions in the family of 2D perovskites. We also identify a critical oxygen concentration in the surrounding environment that affects the mechanism and strongly enhances the rate of layered perovskite photodegradation.