In recent years, there have been rapid advances in the synthesis of lead halide perovskite nanocrystals (NCs) for use in solar cells, light emitting diodes, lasers, and photodetectors. These compounds have a set of intriguing optical, excitonic, and charge transport properties, including outstanding photoluminescence quantum yield (PLQY) and tunable optical band gap. However, the necessary inclusion of lead, a toxic element, raises a critical concern for future commercial development. To address the toxicity issue, intense recent research effort has been devoted to developing lead‐free halide perovskite (LFHP) NCs. In this Review, we present a comprehensive overview of currently explored LFHP NCs with an emphasis on their crystal structures, synthesis, optical properties, and environmental stabilities (e.g., UV, heat, and moisture resistance). In addition, strategies for enhancing optical properties and stabilities of LFHP NCs as well as the state‐of‐the‐art applications are discussed. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high‐quality LFHP NCs for a broader range of fundamental research and practical applications.

ganic CsPbX 3 QDs possess narrow full width at half maximum (FWHM) of emission (as small as 12 nm) and excellent quantum yield (QY: 50-90%). [1,8] They have a Bohr diameter up to 12 nm, [1] exhibiting a size-tunable bandgap in the visible region. It is also notable that the exchange of halide ions (Cl − , Br − , and I − ) in as-synthesized perovskite QDs is highly effective, rendering easy and rapid access to a wide range of perovskite QDs with tunable absorption and photoluminescence (PL) spectra. [1] In spite of significant advances in perovskite research noted above, a key to the success of perovskite-based materials and devices is the stability of perovskites as they are susceptible to decomposition due to their ionic crystal nature. [7,9] Recently, several methods including coating with alumina by atomic layer deposition, [10] partial coating with SiO 2 via sol-gel process, [11] physical mixing with hydrophobic polymers, [12] and encapsulation within mesoporous silica [7] or polymer beads [13] have proven to be effective in improving stability in polar and ambient environments. However, nearly all approaches described above for stability enhancement result in nanocomposites with multiple perovskite QDs encapsulated in microscopic protective matrices. These microscale nanocomposites may be disadvantageous for biomedical applications where cellular uptake is more feasible for smaller nanoscopic particles, [14] or LEDs where the processing of nanoscopic luminescent particles often leads to low scattering loss, higher loading and packing density, and thus film uniformity. [11] Clearly, the ability to deliberately and reliably improve the stability of perovskite QDs (e.g., against humidity and polar solvents) while retaining their individual nanometer size represents a critical step that underpins future advances in optoelectronic and biological applications.Herein, we report a general and robust strategy by capitalizing on judiciously designed amphiphilic star-like diblock copolymers with well-controlled molecular weight and low polydispersity of each block as molecularly engineered nanoreactors to craft uniform perovskite QDs. Remarkably, these QDs simultaneously possess precisely tunable dimensions Instability of perovskite quantum dots (QDs) toward humidity remains one of the major obstacles for their long-term use in optoelectronic devices. Herein, a general amphiphilic star-like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite QDs with precisely tunable size and exceptionally high water and colloidal stabilities is presented. The selective partition of precursors within the compartment occupied by inner hydrophilic blocks of star-like diblock copolymers imparts in situ formation of robust hairy perovskite QDs permanently ligated by outer hydrophobic blocks via coprecipitation in nonpolar solvent. These size-and compositiontunable perovskite QDs reveal impressive water and colloidal stabilities as the surface of QDs is intimately and permanently ligated by a layer of outer ...

In recent years, halide perovskite materials have sparked intensive research, including their burgeoning development in the field of photo(electro)chemical catalysis. Halide perovskite materials are based on abundant and low‐cost elements with a rich structural composition and a variety of molecular and morphological dimensionalities. They possess versatile advantages over other photo(electro)catalytic materials owing to the facile adjustment of electronic properties via molecular and compositional engineering. Thus, the rapid development of perovskite photo(electro)catalysts in the past 4–5 years has opened up new opportunities for diverse photo(electro)chemical applications, ranging from photocatalytic organic reactions (e.g., chemical transformations, photopolymerization, and degradation) to solar‐to‐chemical fuel conversion (e.g., water splitting and CO2 reduction). This review aims to provide an up‐to‐date discussion on recent applications of halide perovskite photo(electro)catalytic materials, emphasizing their crystal and morphological dimensionality, synthetic methodologies, heterojunction structures, and fundamental structure‐activity relationships. Furthermore, current challenges and future research directions for the rational design of halide perovskite materials to boost their overall catalytic performance and stability are identified and envisaged respectively.

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature-sensitive polymer ligands.S trikingly,s ignificant discrepancies in optical and catalytic properties of thermoresponsive noble-metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM), in situ using as tarlike blockc opolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises,p lasmonic absorption of PNIPAM-capped Au NPs red-shifts with increased intensity in the absence of free linear PNIPAM, whereas ag reater red-shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably,t he absence or addition of free linear PNIPAM also accounts for non-monotonic or switchable on/off catalytic performance,respectively,ofPNIPAM-capped Au NPs.

Cocrystallization involving two or more components aggregating into cocrystals allows the preparation of materials with markedly improved charge mobility. This approach however, is little explored in all-conjugated block copolymers (BCPs). Herein, we report the first investigation into the correlation between cocrystals and charge mobility in a series of new all-conjugated BCPs: poly(3-butylthiophene)-b-poly(3-hexylselenophene) (P3BT-b-P3HS) for high-performance field-effect transistors. These rationally synthesized rod-rod BCPs self-assemble into cocrystals with high charge mobilities. Upon one-step thermal annealing, their charge mobilities decrease slightly despite their increased crystallinities. After two-step thermal annealing, P3BT-b-P3HS (P3BT/P3HS=2:1) and (1:1) cocrystals disappear and phase separation occurs, leading to greatly decreased charge mobilities. In contrast, P3BT-b-P3HS (1:2) retains its cocrystalline structure and its charge mobility.

Despite recent progress in producing perovskite nanowires (NWs) for optoelectronics, it remains challenging to solution‐print an array of NWs with precisely controlled position and orientation. Herein, we report a robust capillary‐assisted solution printing (CASP) strategy to rapidly access aligned and highly crystalline perovskite NW arrays. The key to the CASP approach lies in the integration of capillary‐directed assembly through periodic nanochannels and solution printing through the programmably moving substrate to rapidly guide the deposition of perovskite NWs. The growth kinetics of perovskite NWs was closely examined by in situ optical microscopy. Intriguingly, the as‐printed perovskite NWs array exhibit excellent optical and optoelectronic properties and can be conveniently implemented for the scalable fabrication of photodetectors.

No abstract

No abstract