Exploring the Influence of Cation and Halide Substitution in the Structure and Optical Properties of CH3NH3NiCl3 Perovskite

This manuscript details a comprehensive investigation into the synthesis, structural characterization, thermal stability, and optical properties of nickel-containing hybrid perovskites, namely CH3NH3NiCl3, CsNiCl3, and CH3NH3NiBrCl2. The focal point of this study is to unravel the intricate crystal structures, thermal behaviors, and optical characteristics of these materials, thereby elucidating their potential application in energy conversion and storage technologies. X-ray powder diffraction measurements confirm that CH3NH3NiCl3 adopts a crystal structure within the Cmcm space group, while CsNiCl3 is organized in the P63/mmc space group, as reported previously. Such structural diversity underscores the complex nature of these perovskites and their potential for tailored applications. Thermal analysis further reveals the stability of CH3NH3NiCl3 and CH3NH3NiBrCl2, which begin to decompose at 260 °C and 295 °C, respectively. The optical absorption properties of these perovskites studied by UV-VIS-NIR spectroscopy revealed the bands characteristic of Ni2+ ions in an octahedral environment. Notably, these absorption bands exhibit subtle shifts upon bromide substitution, suggesting that optical properties can be finely tuned through halide modification. Such tunability is paramount for the design and development of materials with specific optical requirements. By offering a detailed examination of these properties, the study lays the groundwork for future advancements in material science, particularly in the development of innovative materials for sustainable energy technologies.

Synthesis, Characterization, and Photoelectric and Electrochemical Behavior of (CH3NH3)2Zn1-xCoxBr4 Perovskites

We report the synthesis, characterization, and photoelectric and electrochemical properties of (CH3NH3)2Zn1-xCoxBr4 (x = 0.0, 0.3, 0.5, 0.7, and 1.0) samples. X-ray powder and single-crystal diffraction confirm the formation of solid solution across the entire range. Additionally, as the cobalt concentration increases, the crystallinity of the samples decreases, as indicated by the powder diffraction patterns. All samples remain stable up to 560 K, beyond which they decompose into CH3NH3Br and the respective bromide. The semiconductor behavior of the compounds is confirmed through optical absorption measurements, and band gap values are determined by using the Tauc method from diffuse reflectance spectra. Raman spectroscopy reveals a slight redshift in all vibration modes with increasing cobalt content. Finally, photovoltaic measurements on solar cells constructed with (MA)2CoBr4 perovskite exhibit modest performance, and electrochemical measurements indicate that the compound with the composition (MA)2Zn0.3Co0.7Br4 exhibits the highest current for electrochemical water reduction during oxygen evolution.

Zero- and One-Dimensional Lead-Free Perovskites for Photoelectrochemical Applications

The development of 100% lead-free perovskite materials for photoelectrochemical applications is a hot topic in the current research scenario. Herein, by varying the preparation strategy, we have synthesized two distinct lead-free manganese halide perovskite nanocrystals (NCs), CsMnCl₃(H₂O)₂ (1D-CMC₃H) and Cs₂MnCl₄(H₂O)₂ (0D-C₂MC₄H), by simple ultrasonication/crystallization and a modified ligand-assisted reprecipitation (LARP) approach (room temperature synthesis), respectively. For the first time, a polar solvent methanol was used instead of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) for the synthesis of perovskite NCs. These two manganese halide perovskites exhibit unique morphology-dependent photoluminescence properties. The photoelectrochemical properties of these two Mn-halide-based perovskite NCs were evaluated through electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). The as-prepared one-dimensional (1D) and zero-dimensional (0D) Mn-halide perovskites exhibit more effectual dissociation of photogenerated electron-hole pairs as well as the presence of more rapid interfacial charge transfer on the photoelectrodes under light irradiation. Further improvement in the photoelectrochemical behavior of the 1D-CMC₃H and 0D-C₂MC₄H perovskite photoelectrodes is achieved with eco-friendly ZnO. The overall photoelectrochemical performances of Mn-halide perovskites with ZnO afforded excellent light-harvesting and charge carrier properties.

Halide Double-Perovskite Semiconductors beyond Photovoltaics

Halide double perovskites, A₂M^IM^IIIX₆, offer a vast chemical space for obtaining unexplored materials with exciting properties for a wide range of applications. The photovoltaic performance of halide double perovskites has been limited due to the large and/or indirect bandgap of the presently known materials. However, their applications extend beyond outdoor photovoltaics, as halide double perovskites exhibit properties suitable for memory devices, indoor photovoltaics, X-ray detectors, light-emitting diodes, temperature and humidity sensors, photocatalysts, and many more. This Perspective highlights challenges associated with the synthesis and characterization of halide double perovskites and offers an outlook on the potential use of some of the properties exhibited by this so far underexplored class of materials.

Lead-Free, Water-Stable A3 Bi2 I9 Perovskites: Crystal Growth and Blue-Emitting Quantum Dots [A=CH3 NH3 + , Cs+ , and (Rb0.05 Cs2.95 )+ ]

Despite the great success in the increase in the power conversion efficiency of lead halide perovskite solar cells, the toxicity of lead and the unstable nature of the materials are still major concerns for their wider implementation at the industrial level. Herein, large-size single crystals (SCs) are developed in HI solution by using a temperature lowering method and nanocrystals (NCs) of A₃ Bi₂ I₉ perovskites [where A=CH₃ NH₃ ⁺ (MA)⁺ , Cs⁺ , and (Rb_0.05 Cs_2.95 )⁺ ] are formed in ethanol (EtOH) and toluene (TOL). The stability of A₃ Bi₂ I₉ perovskite is investigated by immersing the SCs for 24 h and pellets for 12 h in water. Moreover, the A₃ Bi₂ I₉ perovskite NCs displays a promising photoluminescence quantum yield of 17.63 % and a long lifetime of 8.20 ns.

Exploring Organic Metal Halides with Reversible Temperature-Responsive Dual-Emissive Photoluminescence

The exceptional structural tunability of organic metal halides endows them with fascinating electronic and photophysical properties, providing much scope for applications. In this work, single crystals of the organic metal halide (C₄ H₉ NH₃ )₂ MnI₄ are found to show reversible thermo-induced luminescent chromism within a wide temperature range. The (C₄ H₉ NH₃ )₂ MnI₄ single crystal exhibits two emission peaks at 550 and 672 nm, which are assigned to a d-d transition of Mn²⁺ -centered tetrahedra and self-trapped excitons, respectively. The temperature-dependent emission color change is attributed to the thermo-induced trapping and detrapping process of the self-trapped exciton. (C₄ H₉ NH₃ )₂ MnI₄ exhibits a maximum photoluminescence quantum efficiency of up to 68 % at 70 °C. The disclosed interacted photoluminescence decay mechanisms may prove useful for the further design of organic metal halides for optical thermometry.

Study on Paramagnetic Interactions of (CH3NH3)2CoBr4 Hybrid Perovskites Based on Nuclear Magnetic Resonance (NMR) Relaxation Time

The thermal properties of organic-inorganic (CH3NH3)2CoBr4 crystals were investigated using differential scanning calorimetry and thermogravimetric analysis. The phase transition and partial decomposition temperatures were observed at 460 K and 572 K. Nuclear magnetic resonance (NMR) chemical shifts depend on the local field at the site of the resonating nucleus. In addition, temperature-dependent spin-lattice relaxation times (T1ρ) were measured using 1H and 13C magic angle spinning NMR to elucidate the paramagnetic interactions of the (CH3NH3)+ cations. The shortening of 1H and 13C T1ρ of the (CH3NH3)2CoBr4 crystals are due to the paramagnetic Co2+ effect. Moreover, the physical properties of (CH3NH3)2CoBr4 with paramagnetic ions and those of (CH3NH3)2CdBr4 without paramagnetic ions are reported and compared.