Hybrid halide perovskites have become the “next big thing” in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH3NH3PbI3. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the “perovskite fever”, and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites f...

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises.

Complexes of heterocyclic thione donors

Hybrid halide perovskites are now superstar materials leading the field of low-cost thin film photovoltaics technologies. Following the surge for more efficient and stable 3D bulk alloys, multilayered halide perovskites and colloidal perovskite nanostructures appeared in 2016 as viable alternative solutions to this challenge, largely exceeding the original proof of concept made in 2009 and 2014, respectively. This triggered renewed interest in lower-dimensional hybrid halide perovskites and at the same time increasingly more numerous and differentiated applications. The present paper is a review of the past and present literature on both colloidal nanostructures and multilayered compounds, emphasizing that availability of accurate structural information is of dramatic importance to reach a fair understanding of quantum and dielectric confinement effects. Layered halide perovskites occupy a special place in the history of halide perovskites, with a large number of seminal papers in the 1980s and 1990s. In ...

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Quantum and Dielectric Confinement Effects in Lower-Dimensional Hybrid Perovskite Semiconductors.

Two-dimensional (2D) perovskites have attracted considerable interest for their promising applications for solar cells and other optoelectronics, such as light-emitting diodes, spintronics, and photodetectors. Here, we review the recent achievements of 2D perovskites for various optoelectronic applications. First, we discuss the basic structure and optoelectronic properties of 2D perovskites, including band structure, optical properties, and charge transport. We then highlight recent achievements using 2D perovskites in solar cells and beyond solar cells, including progress on various synthesis strategies and their impact on structural and optoelectronic properties. Finally, we discuss current challenges and future opportunities to further develop 2D perovskites for various applications.

Advances in two-dimensional organic–inorganic hybrid perovskites

Two-dimensional (2D) halide perovskites have emerged as outstanding semiconducting materials thanks to their superior stability and structural diversity. However, the ever-growing field of optoelectronic device research using 2D perovskites requires systematic understanding of the effects of the spacer on the structure, properties, and device performance. So far, many studies are based on trial-and-error tests of random spacers with limited ability to predict the resulting structure of these synthetic experiments, hindering the discovery of novel 2D materials to be incorporated into high-performance devices. In this review, we provide guidelines on successfully choosing spacers and incorporating them into crystalline materials and optoelectronic devices. We first provide a summary of various synthetic methods to act as a tutorial for groups interested in pursuing synthesis of novel 2D perovskites. Second, we provide our insights on what kind of spacer cations can stabilize 2D perovskites followed by an extensive review of the spacer cations, which have been shown to stabilize 2D perovskites with an emphasis on the effects of the spacer on the structure and optical properties. Next, we provide a similar explanation for the methods used to fabricate films and their desired properties. Like the synthesis section, we will then focus on various spacers that have been used in devices and how they influence the film structure and device performance. With a comprehensive understanding of these effects, a rational selection of novel spacers can be made, accelerating this already exciting field.

The 2D Halide Perovskite Rulebook: How the Spacer Influences Everything from the Structure to Optoelectronic Device Efficiency.

The synthesis and the structural, thermal, and electrical characterization of haloplumbate(II) systems are described. The counterions are diprotonated linear aliphatic amines, such as the 2-methylpentane-1,5-diamine (2meptH2) and propane-1,3-diamine (pnH2) dications. The (2meptH2)[PbCl4] and (2meptH2)[PbBr4] are isostructural, space group Cc, with a = 24.140(4) A, b = 7.720(2) A, c = 7.795(2) A, β = 98.1(1)°, Z = 4 for the chlorine compound and a = 24.539(4) A, b = 8.031(2) A, c = 8.198(2) A, β = 99.6(1)°, Z = 4 for the bromine compound; the (2meptH2)[Pb1.5I5] crystallizes in the triclinic P1 space group, with a = 11.803(3) A, b = 12.565(3) A, c = 8.494(8) A, α = 106.2(1)°, β = 100.5(1)°, γ = 117.4(1)°, Z = 2; the crystals of (pnH2)[PbCl4] are orthorhombic, space group P212121, a = 19.247(4) A, b = 7.862(2) A, c = 7.581(2) A, Z = 4; the (pnH2)2[Pb1.5Br7]·H2O crystallizes in the triclinic P1 space group, with a = 11.517(3) A, b = 14.122(3) A, c = 8.149(2) A, α = 104.1(1)°, β = 109.8(1)°, γ = 77.5(1)°, Z ...

Structural and Electrical Characterization of Polymeric Haloplumbate(II) Systems

The reactions of ketones and N-substituted thioureas, in the presence of HCl (or HBr) and DMSO afford mixtures of the title compounds which are easily separated on a silica gel column. This method avoids the classical use of α-haloketones. The mechanism of these reactions involves the enolization of ketones and the activation of thiourea sulfur, probably by oxygen transfer from DMSO.

Condensation of thiourea derivatives with carbonyl compounds: one-pot synthesis of N-alkyl-1,3-thiazol-2-amines and of 3-alkyl-1,3-thiazolimines

Monomeric and oligomeric phosphates as deflocculants of concentrated aqueous clay suspensions

The crystal structure of the title compound has been determined from x-ray diffractometer data by the heavy-atom method and refined anisotropically by least-squares calculations. Crystals are monoclinic, space groupP 21/c, with unit cell dimensions:a=7.321(1),b=14.622(2),c=14.827(2) A,β=92.95(2)∘, Z=4. The finalR index is 4.6%. The copper coordination is trigonal, involving the sulphur atoms of twoN-ethyl-1,3-imidazolidine-2-thione molecules and one chlorine atom. The structure is held together by two intramolecular N-H⋯Cl hydrogen bonds and by normal van der Waals interactions.

Anna Bonamartini Corradi

Papers

Structural and Electrical Characterization of Polymeric Haloplumbate(II) Systems

Condensation of thiourea derivatives with carbonyl compounds: one-pot synthesis of N-alkyl-1,3-thiazol-2-amines and of 3-alkyl-1,3-thiazolimines

Monomeric and oligomeric phosphates as deflocculants of concentrated aqueous clay suspensions

The crystal and molecular structure of chlorobis(N-ethyl-1 3-imidazolidine-2-thione)copper(I)

Mechanism of the formation of 1,2,4‐thiadiazoles by condensation of aromatic thioamides and of N‐substituted thioureas