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Lead-free perovskites and their analogues have been extensively studied as a class of next-generation luminescent and optoelectronic materials. Herein, we report the synthesis of new colloidal Cs 4 M( ii )Bi 2 Cl 12 (M( ii ) = Cd, Mn) nanocrystals (NCs) with unique luminescence properties. The obtained Cs 4 M( ii )Bi 2 Cl 12 NCs show a layered double perovskite (LDP) crystal structure with good particle stability. Density functional theory calculations show that both samples exhibit a wide, direct bandgap feature. Remarkably, the strong Mn–Mn coupling effect of the Cs 4 M( ii )Bi 2 Cl 12 NCs results in an ultra-short Mn photoluminescence (PL) decay lifetime of around 10 μs, around two orders of magnitude faster than commonly observed Mn 2+ dopant emission in NCs. Diluting the Mn 2+ ion concentration through forming Cs 4 (Cd 1−x Mn x )Bi 2 Cl 12 (0 < x < 1) alloyed LDP NCs leads to prolonged PL lifetimes and enhanced PL quantum yields. Our study provides the first synthetic example of Bi-based LDP colloidal NCs with potential for serving as a new category of stable lead-free perovskite-type materials for various applications. 

Metal halide perovskites have witnessed great success in green, red, and near‐infrared light‐emitting diodes (LEDs), yet blue LEDs still lag behind. Reducing undesired energetic disorders – broadn‐phases and halide segregation – is considered as the most critical strategy to further improve the performances. Here, the study reports a newly designed and synthesized di‐ammonium ligand with rigidπ‐conjugated rings and additional methyl groups to construct Dion–Jacobson (DJ) structure. Augmented coordination from the extra ammonium site and increased effective bulkiness from methyl groups lead to better distribution control over conventional mono‐ammonium ligands. This enhances the radiative recombination of blue emissions in the film with homogeneous energy landscape and improved surface morphology, as evidenced by a series of imaging and mapping techniques. As a result, it demonstrates DJ perovskite LEDs (PeLEDs) with peak external quantum efficiencies of ≈4% at 484 nm and ≈11% at 494 nm, which are among the top reported for pure DJ phase‐based PeLEDs in the corresponding wavelength regions. The results deepen the understanding of regulating energetic disorders in perovskite materials via molecular engineering.

 

Lead halide perovskite (LHP) nanocrystals (NCs) have recently garnered enhanced development efforts from research disciplines owing to their superior optical and optoelectronic properties. These materials, however, are unlike conventional quantum dots, because they possess strong ionic character, labile ligand coverage, and overall stability issues. As a result, the system as a whole is highly dynamic and can be affected by slight changes of particle surface environment. Specifically, the surface ligand shell of LHP NCs has proven to play imperative roles throughout the lifetime of a LHP NC. Recent advances in engineering and understanding the roles of surface ligand shells from initial synthesis, through postsynthetic processing and device integration, finally to application performances of colloidal LHP NCs are covered here.

 

The development of halide perovskite (HP) based thin film solar cells has been unprecedented in the past few years, and there is significant ongoing effort aiming to make perovskite solar cells (PSCs) more efficient and stable. Parallel to the PSC research, there is growing interest in exploring the synthesis and physiochemical behaviors of HP nanocrystals (NCs). While these HP NCs inherently possess many unique properties that are suitable for the use in PSCs, the reported effort of incorporating HP NCs into PSCs is still highly limited. As a result, there is a gap between HP NC and PSC research. In this context, we provide here a brief review of the established HP NC synthesis and a discussion of the several recent studies pertaining to the use of HP NCs in PSCs. Based on these, we provide perspectives on promising directions for bridging the gap between HP NC and PSC research in the future.