Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

State of the Art and Prospects for Halide Perovskite Nanocrystals.

Further enhancing the performance and stability of inverted perovskite solar cells (PSCs) is crucial for their commercialization. We report that the functionalization of multication and halide perovskite interfaces with an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate (FcTc2), simultaneously enhanced the efficiency and stability of inverted PSCs. The resultant devices achieved a power conversion efficiency of 25.0% and maintained >98% of their initial efficiency after continuously operating at the maximum power point for 1500 hours under simulated AM1.5 illumination. Moreover, the FcTc2-functionalized devices passed the international standards for mature photovoltaics (IEC61215:2016) and have exhibited high stability under the damp heat test (85°C and 85% relative humidity). Description Organometallics stabilizing perovskites Perovskite solar cells with inverted (p-i-n) structure can have greater stability and lifetimes than conventional n-i-p structures but usually have somewhat lower power conversion efficiencies (PCEs). Li et al. report that an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate, can stabilize a multication perovskite layer of an inverted perovskite solar cells. After 1500 hours of maximum power point operation, 98% of the 25.0% PCE was maintained. The solar cell also exhibited high stability in damp heat tests. —PDS Functionalizing interfaces with an organometallic compound created an efficient and stable inverted perovskite solar cell.

Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

Polymer-guided assembly of inorganic nanoparticles.

Lanthanides have been widely explored as optically active dopants in inorganic crystal lattices, which are often insulating in nature. Doping trivalent lanthanide (Ln3+) into traditional semiconductor nanocrystals, such as CdSe, is challenging because of their tetrahedral coordination. Interestingly, CsPbX3 (X = Cl, Br, I) perovskite nanocrystals provide the octahedral coordination suitable for Ln3+ doping. Over the last two years, tremendous success has been achieved in doping Ln3+ into CsPbX3 nanocrystals, combining the excellent optoelectronic properties of the host with the f-f electronic transitions of the dopants. For example, the efficient quantum cutting phenomenon in Yb3+-doped CsPb(Cl,Br)3 nanocrystals yields a photoluminescence quantum yield close to 200%. Other approaches of Ln3+ doping and codoping have enabled promising proof-of-principle demonstration of solid-state lighting and solar photovoltaics. In this perspective article, we highlight the salient features of the material design (including doping in Pb-free perovskites), optical properties and potential optoelectronic applications of lanthanide-doped metal halide perovskite nanocrystals. While review articles on doping different metal ions into perovskite nanocrystals are present, the present review-type article is solely dedicated to lanthanide-doped metal halide perovskite nanocrystals. Methods for integrating lanthanide materials into light-emitting devices to improve their performance have been reviewed by scientists from India and China. Semiconductors create light when the energy of a high-energy electron is converted to a single photon. Conventionally, the minimum energy of this photon is determined by an intrinsic material property known as the bandgap. Wasim Mir from the Indian Institute of Science Education and Research Pune, and colleagues, summarize developments in using lanthanide ions to enable the generation of lower-energy light. Lanthanide ions provide an energy “step” within the bandgap that means the electron is converted to two low energy photons rather than a single high energy one. The authors review how embedding lanthanum ions within nanoparticles made from so-called metal-halide perovskites makes them easier to integrate into common optoelectronic semiconductors such as silicon. Metal halide perovskites are extraordinary defect-tolerant semiconductors. A unique structural aspect of perovskites is the octahedral coordination for (B-site) metal ions, unlike other semiconductors that exhibit tetrahedral coordination. This octahedral coordination helped to achieve lanthanide doping in halide perovskite nanocrystals in 2017. Fundamental understanding of material design, luminescence and quantum cutting phenomena in lanthanides (with focus on Yb3+) doped in CsPbX3 (X = Cl, Br, I) and Cs2AgInCl6 nanocrystals are reported. Subsequently, these doped systems are applied for solar energy harvesting and lighting in both visible and near infrared region. This perspective article summarizes everything important that has happened so far in field and discusses about the future research directions.

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Lanthanide doping in metal halide perovskite nanocrystals: spectral shifting, quantum cutting and optoelectronic applications

Besides widely used surface passivation, engineering the film crystallization is an important and more fundamental route to improve the performance of all-inorganic perovskite solar cells Herein, we have developed a urea-ammonium thiocyanate (UAT) molten salt modification strategy to fully release and exploit coordination activities of SCN- to deposit high-quality CsPbI3 film for efficient and stable all-inorganic solar cells The UAT is derived by the hydrogen bond interactions between urea and NH4 + from NH4 SCN With the UAT, the crystal quality of the CsPbI3 film has been significantly improved and a long single-exponential charge recombination lifetime of over 30 ns has been achieved With these benefits, the cell efficiency has been promoted to over 20 % (steady-state efficiency of 192 %) with excellent operational stability over 1000 h These results demonstrate a promising development route of the CsPbI3 related photoelectric devices

Efficient (>20 %) and Stable All-Inorganic Cesium Lead Triiodide Solar Cell Enabled by Thiocyanate Molten Salts.

Two-dimensional (2D) lead halide perovskites represent an emerging class of materials given their tunable optoelectronic properties and long-term stability in perovskite solar cells. In order to as...

Suppressed Halide Ion Migration in 2D Lead Halide Perovskites

In metal halide perovskite solar cells, electron transport layers (ETLs) such as TiO2 dictate the overall photovoltaic performance. However, the same electron capture property of ETL indirectly imp...

TiO2-Assisted Halide Ion Segregation in Mixed Halide Perovskite Films.

The strong binding between CsPbBr3 nanocrystals and methyl viologen induces a long-lived charge-separated state following band gap excitation with important implications in photocatalytic processes...

Perovskite Photocatalysis. Methyl Viologen Induces Unusually Long-Lived Charge Carrier Separation in CsPbBr3 Nanocrystals

The suppression of halide ion exchange between CsPbBr3 and CsPbI3 nanocrystals achieved through capping with PbSO4–oleate has enabled us to deposit different perovskite nanocrystals as aligned arrays on the electrode surfaces without intermixing of species. The electrophoretic deposition of PbSO4–oleate-capped CsPbX3 (X = Cl, Br, I) nanocrystals suspended in hexane solution on mesoscopic TiO2 films allows the design of controlled architecture with single or multiple layers of perovskite films. The hierarchy in the assembly of these nanocrystals is seen first through the linearly organized nanocrystals in hexane followed by the deposition of larger linear rods ∼500 nm in length. Since most of the photophysical properties of nanocrystals are retained in these aligned arrays, we can design films with tunable luminescence including white color. The electrophoretic deposition of layered films of perovskites in a controlled fashion opens up new ways to design tandem perovskite solar cells and tunable display de...

Hierarchical Arrays of Cesium Lead Halide Perovskite Nanocrystals through Electrophoretic Deposition.

The photocatalytic properties of cesium lead bromide (CsPbBr3) perovskite nanocrystals make them attractive for designing light harvesting assemblies. Often ignored, the surface chemistry can dicta...

Jeffrey T. DuBose

Papers

Suppressed Halide Ion Migration in 2D Lead Halide Perovskites

TiO2-Assisted Halide Ion Segregation in Mixed Halide Perovskite Films.

Perovskite Photocatalysis. Methyl Viologen Induces Unusually Long-Lived Charge Carrier Separation in CsPbBr3 Nanocrystals

Hierarchical Arrays of Cesium Lead Halide Perovskite Nanocrystals through Electrophoretic Deposition.

Surface Chemistry Matters. How Ligands Influence Excited State Interactions between CsPbBr3 and Methyl Viologen