Core/shell (pseudo type-II) CsPbBr3/ZnS nanocrystals are prepared, showing ∼15 times enhancement in average photoluminescence lifetime compared to CsPbBr3 nanocrystals. The nanocrystal films (without external encapsulation) retain intense luminescence even after being dipped in water for more than 2 days.

In layered hybrid perovskites, such as (BA)2PbI4 (BA=C4H9NH3), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb–I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.

Lead halide perovskites are seriously considered for next generation photovoltaic technology. They have a unique combination of easy synthesis, high efficiency, and cost-effective techniques. Still, the major concern is the toxicity of lead used in perovskite devices. The research community is still debating whether the amount of lead used in a solar cell really poses a danger or not. However, it is pretty clear that mitigating the lead leakage from the lead halide perovskite device is of utmost importance. In this review, we discuss new material chemistry approaches that can be applied to reduce the lead leakage/wastage from damaged lead halide perovskite solar cells. ECR (encapsulate, capture, and recycle) approaches have the potential to significantly reduce the environmental and health hazard risks of lead halide perovskite devices. Encapsulation by a self-healing material and rigid glass can help the perovskite survive the extreme conditions and avoid exposure of the perovskite layer to the external environment. Capturing of lead can also be done by an encapsulant layer that can very quickly and efficiently bind to lead, in the case that it leaks from the damaged perovskite device. Moreover, the recycling of damaged or decommissioned devices helps to avoid the lead wastage and contamination in the environment. Finally, we also discuss the potential of lead-free perovskite for optoelectronic applications.

Layered two-dimensional (2D) lead halide perovskites are already an important class of optoelectronic materials. Layered 2D tin-halide perovskites are also now emerging. Unlike lead analogs, tin-halide perovskites are environmentally benign. Furthermore, compared to three-dimensional (3D) tin-halide perovskites, 2D layered tin-halide perovskites show improved moisture stability. However, a better understanding of electronic and optical properties, along with novel material design approaches, are required to realize the potential layered tin-halide perovskites for optoelectronic applications. Here, we prepare a series of 2D layered tin-halide perovskite single crystals and find that all of the samples exhibit two excitonic emissions. Similar to the Ruddlesden−Popper phase, A 2 SnI 4 (with A = phenylethylammonium, butylammonium, hexylammonium, and octylammonium monovalent cations) is prepared. Furthermore, A′SnI 4 (similar to the Dion−Jacobson phase) (with A′ = 4-(aminomethyl)piperidinium divalent cation) is prepared. All of the samples show two sharp photoluminescence (PL) peaks. Two absorption features are also observed corresponding to the two PL peaks. The time-resolved PL studies show that both emissions have a nearly similar and short (few nanoseconds) PL lifetimes. The two absorption features and short nanosecond PL lifetimes suggest that the two emissions are excitonic in nature. While dual excitonic emission is rather unusual for a typical semiconductor, recent studies showed such dual emissions from layered lead halide perovskites as well.

In layered hybrid perovskites, such as (BA)2PbI4 (BA=C4H9NH3), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb–I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.