Orientation Control of Two-Dimensional Perovskites by Incorporating Carboxylic Acid Moieties

Biomolecules incorporated in halide perovskite nanocrystals: synthesis, optical properties, and applications

Halide perovskite nanocrystals (HPNCs) have emerged at the forefront of nanomaterials research over the past two decades. The physicochemical and optoelectronic properties of these inorganic semiconductor nanoparticles can be modulated through the introduction of various ligands. The use of biomolecules as ligands has been demonstrated to improve the stability, luminescence, conductivity and biocompatibility of HPNCs. The rapid advancement of this field relies on a strong understanding of how the structure and properties of biomolecules influences their interactions with HPNCs, as well as their potential to extend applications of HPNCs towards biological applications. This review addresses the role of several classes of biomolecules (amino acids, proteins, carbohydrates, nucleotides, etc.) that have shown promise for improving the performance of HPNCs and their potential applications. Specifically, we have reviewed the recent advances on incorporating biomolecules with HP nanomaterials on the formation, physicochemical properties, and stability of HP compounds. We have also shed light on the potential for using HPs in biological and environmental applications by compiling some recent of proof-of-concept demonstrations. Overall, this review aims to guide the field towards incorporating biomolecules into the next-generation of high-performance HPNCs for biological and environmental applications.

Perpendicularly oriented 2D perovskite thin films prepared using the bar-coating method and DMSO additive

A 2D perovskite incorporating an amine moiety with a carboxy group exhibited orientation changes as the amount of DMSO additive varied. The degree of perpendicular orientation was increased by optimizing the amount of DMSO additive, while using the bar-coating method. Moreover, film thickness and the ratio of perpendicular orientation exhibited a positive correlation.

Directional Anisotropy of the Vibrational Modes in 2D-Layered Perovskites

The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes with respect to the main axes of the pseudocubic lattice in the octahedral plane. Here, we study the directionality of the fundamental phonon modes in single exfoliated Ruddlesden-Popper perovskite flakes with polarized Raman spectroscopy at ultralow frequencies. A wealth of Raman bands is distinguished in the range from 15 to 150 cm^-1 (2-15 meV), whose features depend on the organic cation species, on temperature, and on the direction of the linear polarization of the incident light. By controlling the angle of the linear polarization of the excitation laser with respect to the in-plane axes of the octahedral layer, we gain detailed information on the symmetry of the vibrational modes. The choice of two different organic moieties, phenethylammonium (PEA) and butylammonium (BA), allows us to discern the influence of the linker molecules, evidencing strong anisotropy of the vibrations for the (PEA)₂PbBr₄ samples. Temperature-dependent Raman measurements reveal that the broad phonon bands observed at room temperature consist of a series of sharp modes and that such mode splitting strongly differs for the different organic moieties and vibrational bands. Softer molecules such as BA result in lower vibrational frequencies and splitting into fewer modes, while more rigid molecules such as PEA lead to higher frequency oscillations and larger number of Raman peaks at low temperature. Interestingly, in distinct bands the number of peaks in the Raman bands is doubled for the rigid PEA compared to the soft BA linkers. Our work shows that the coupling to specific vibrational modes can be controlled by the incident light polarization and choice of the organic moiety, which could be exploited for tailoring exciton-phonon interaction, and for optical switching of the optoelectronic properties of such 2D layered materials.

Crystal Orientation Drives the Interface Physics at Two/Three-Dimensional Hybrid Perovskites

Combining halide perovskites with tailored dimensionality into two/three-dimensional (2D/3D) systems has revealed a powerful strategy to boost the performances of perovskite photovoltaics (PVs). Despite recent advances, a clear understanding of the intimate link between interface structure and physics is still missing, leading so far to a blind optimization of the 2D/3D PVs. Here, we reveal the impact of 2D/3D crystal alignment in driving interface charge-recombination dynamics. The 2D crystal growth and orientation are manipulated by specific fluorination of phenethylammonium (PEA), used here as the organic cation backbone of the 2D component. By means of time-resolved optoelectronic analysis from the femto- to microsecond regions, we demonstrate a static function of the 2D layer as an electron barrier and homogeneous surface passivant, together with a dynamic role in retarding back charge recombination. Our results reveal a crucial dependence of such beneficial effects with the 2D layer, leading to an enhanced open-circuit voltage (V_oc), mostly attributed to the 2D phase which orients parallel on the 3D layer. Such findings provide a deep understanding and delineate precise guidelines for the smart design of multidimensional perovskite interfaces for advanced PVs and beyond.

Novel Organic-Inorganic Perovskite Compounds Having Phosphonium Groups

Organic-inorganic perovskites are composed of organic cations and [PbX₆]^4- octahedra, and the properties change depending on the type of organic cations. To identify the effect of organic cations and control the properties of the perovskite, thin films were prepared using quaternary alkylammonium and quaternary alkylphosphonium cations, which have big steric effects. A big steric effect can generate the distortion of [PbX₆]^4- octahedra leading to changes in properties. A thin film of a Pb-based organic-inorganic perovskite having quaternary alkylphosphonium cations was prepared for the first time. An exciton absorption was observed at a lower wavelength than other perovskites prepared from primary and quaternary ammonium salts. The perovskite with phosphonium groups was thermally stable compared with ammonium groups.

Factors determining the vertical orientation of two-dimensional perovskites

Factors determining the orientation of two-dimensional perovskites were examined.

Tuning the Structures and Optical Properties of Perovskites by Varying the Alkylamine Type and Chain Length

Organic-inorganic perovskites, (RNH3)2PbX4, have attracted much attention as one of the most promising light-harvesting and light-emitting materials. The present work investigated the steric effects of the organic parts on the perovskites by varying the alkylamine type and chain length. Primary, secondary, and tertiary amines with various chain lengths were introduced into organic-inorganic perovskites. Extending the chain length raised the phase transition point and shortened the absorption wavelength. In addition, the introduction of secondary and tertiary amines resulted in red- and blue-shifting of the absorption peaks, respectively.

Two-dimensional halide perovskite nanomaterials and heterostructures

Novel two-dimensional halide perovskite nanomaterials and heterostructures enable next generation high performance electronics and photonics.