Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called defect-tolerance—the apparently benign nature of structural defects, highly abundant in these compounds, with respect to optical and electronic properties. Here, we review the important differences that exist in the chemistry and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.

Properties and potential optoelectronic applications of lead halide perovskite nanocrystals

Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.

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Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals

Visible-light-driven photochemistry has continued to attract heightened interest due to its capacity to efficiently harvest solar energy and its potential to solve the global energy crisis. Plasmonic nanostructures boast broadly tunable optical properties coupled with catalytically active surfaces that offer a unique opportunity for solar photochemistry. Resonant optical excitation of surface plasmons produces energetic hot electrons that can be collected to facilitate chemical reactions. This review sums up recent theoretical and experimental approaches for understanding the underlying photophysical processes in hot electron generation and discusses various electron-transfer models on both plasmonic metal nanostructures and plasmonic metal/semiconductor heterostructures. Following that are highlights of recent examples of plasmon-driven hot electron photochemical reactions within the context of both cases. The review concludes with a discussion about the remaining challenges in the field and future oppor...

Surface-Plasmon-Driven Hot Electron Photochemistry

Metal halide perovskites represent a flourishing area of research, driven by both their potential application in photo-voltaics and optoelectronics, and for the fundamental science underpinning their unique optoelectronic properties. The advent of colloidal methods for the synthesis of halide perovskite nanocrystals has brought to the attention inter-esting aspects of this new type of materials, above all their defect-tolerance. This review aims to provide an updated survey of this fast-moving field, with a main focus on their colloidal synthesis. We examine the chemistry and the ca-pability of different colloidal synthetic routes to control the shape, size and optical properties of the resulting nano-crystals. We also provide an up to date overview of their post-synthesis transformations, and summarize the various so-lution processes aimed at fabricating halide perovskite-based nanocomposites. We then review the fundamental optical properties of halide perovskite nanocrystals, by focusing on their linear optical properties, on the effects of quantum confinement and, then, on the current knowledge of their exciton binding energies. We also discuss the emergence of non-linear phenomena such as multiphoton absorption, biexcitons and carrier multiplication. At last, we provide an outlook in the field, with the most cogent open questions and possible future directions.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications and Their Optical Properties

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we...

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties.

Mn2+ ions doped in high-energy absorbing semiconductor host nanocrystals take away the exciton energy and result in spin-polarized d–d emission. For the last three decades this has been widely studied on group II–VI semiconductors. Recently, the doping has been extended to CsPbX3 perovskite nanocrystals. Although the optical transition follows a similar principle, in which the exciton energy is transferred to dopant Mn d-state, doping in perovskite also revealed several new fundamental aspects of doping and dopant-induced new optical properties. Here, anions which mostly tune the band gap controlled the fate of the appearance of Mn emission. Also, the doping process was observed to be different than traditional growth doping. Hence, in perovskite host nanocrystals, while some aspects of Mn doping are found to be in agreement with previous findings, some new facts also surfaced. Combining all these facts, this Perspective focuses on the journey of Mn doping from group II–VI semiconductors to lead halide pe...

Doping Mn2+ in Lead Halide Perovskite Nanocrystals: Successes and Challenges

Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots The fast formation of perovskites makes the dopant insertions more competitive and challenging Introducing alkylamine hydrochloride (RNH3 Cl) as a promoting reagent, precise controlled doping of MnII in CsPbCl3 perovskite nanocrystals is reported Simply, by changing the amount of RNH3 Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d-d emission intensities are tailored Investigations suggested that RNH3 Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared

Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals

Doping Mn2+ in semiconductor nanocrystals is widely known for its long-lifetime Mn d–d orange emission. While this had been extensively studied for chalcogenide nanostructures, recently this was al...

Insights of Doping and the Photoluminescence Properties of Mn-Doped Perovskite Nanocrystals

In nanoscale, with size variation, Au shows different optical behaviors. For the small size clusters (sub-5 nm), it behaves more like semiconductors having sp and d band electronic energy levels splitting and also do not show the characteristic plasmon. However, for larger size particles (>5 nm), it shows the plasmonic absorption. Considering these two structures of Au0, we report here their coupling with a low bandgap semiconductor SnS and study the difference in their formation chemistry and materials’ properties. Following a common synthetic approach in which a smaller size SnS cube and tetrahedron shapes result in Au cluster decorated Au-SnS heterostructures, larger size SnS cubes form coupled Au-SnS nanostructures. Contrastingly, the nonplasmonic Au0 cluster-SnS hinders the photocatalytic activity, whereas the plasmonic coupled Au-SnS enhances the catalytic activity toward reduction of organic dye methylene blue. However, both types of heterostructures show enhanced photocurrent as well as photorespo...

Au-SnS Hetero Nanostructures: Size of Au Matters

Considering the chemistry of the formation and physics at interfaces, we report on the heterostructure of a promising new energy material, Au–Cu2ZnSnS4 (Au-CZTS), and investigate the impact of coupling on Au on improving both the photostability and the photoresponse behavior. We focus primarily on the fundamental issues involved in bringing together two dissimilar materials having different chemical and physical properties in a single building block where one is a multinary semiconductor nanomaterial and the other is a plasmonic noble metal. The formation of heteroepitaxy at the junction of Au and CZTS was investigated for two different phases of CZTS. Considering epitaxy formation along the {111} planes of Au, it was observed that the wurtzite and tetragonal phases of CZTS exhibit coincident site epitaxy with different periodic intervals. A detailed study of this epitaxy formation with Au in both phases of CZTS has been carried out and reported. Because Au-CZTS is a promising new material, we have furthe...

Amit K. Guria

Papers

Doping Mn2+ in Lead Halide Perovskite Nanocrystals: Successes and Challenges

Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals

Insights of Doping and the Photoluminescence Properties of Mn-Doped Perovskite Nanocrystals

Au-SnS Hetero Nanostructures: Size of Au Matters

Coincident Site Epitaxy at the Junction of Au–Cu2ZnSnS4 Heteronanostructures