Michael Worku

Mechanochemical synthesis has emerged as a facile method for the preparation of a wide range of organic, inorganic, and polymeric materials. Here, we report the use of mechanochemical synthesis for the preparation of ionically bonded organic metal halide hybrids with a zero‐dimensional (0D) structure at the molecular level. (Ph₄P)₂SbCl₅ and (Ph₄P)₂MnCl₄ were synthesized by grinding appropriate ratios of organic halide salt Ph₄PCl with inorganic metal halide salts SbCl₃ and MnCl₂, respectively. The structural and photophysical properties of mechanochemically synthesized (Ph₄P)₂SbCl₅ and (Ph₄P)₂MnCl₄ were characterized, which are almost identical to those of single crystals prepared by slow solution growth. By reacting Ph₄PCl with both SbCl₃ and MnCl₂, we have been able to produce a mixture of two 0D organic metal halide hybrids that exhibit a dual emission covering a wide range of the spectrum with Commission Internationale de l'Eclairage (CIE) coordinates of (0.4898, 0.4800). Our work has clearly established mechanochemical synthesis as an effective method to produce ionically bonded organic‐inorganic hybrids.

Zero‐dimensional (0D) organic metal halide hybrids, in which organic and metal halide ions cocrystallize to form neutral species, are a promising platform for the development of multifunctional crystalline materials. Herein we report the design, synthesis, and characterization of a ternary 0D organic metal halide hybrid, (HMTA)₄PbMn_0.69Sn_0.31Br₈, in which the organic cation N‐benzylhexamethylenetetrammonium (HMTA⁺, C₁₃H₁₉N₄⁺) cocrystallizes with PbBr₄²⁻, MnBr₄²⁻, and SnBr₄²⁻. The wide band gap of the organic cation and distinct optical characteristics of the three metal bromide anions enabled the single‐crystalline “host–guest” system to exhibit emissions from multiple “guest” metal halide species simultaneously. The combination of these emissions led to near‐perfect white emission with a photoluminescence quantum efficiency of around 73 %. Owing to distinct excitations of the three metal halide species, warm‐ to cool‐white emissions could be generated by controlling the excitation wavelength.

A hollow nanostructure enables color tuning of metal halide perovskites with efficient blue emissions from cesium lead bromide.

Optically pumped white light-emitting diodes (WLEDs), consisting of blue/ultraviolet LED chips and down conversion phosphors, have a wide range of applications in our daily life, such as full color display and solid-state lighting. While remarkable progress in light quality, device efficiency, and lifetime has been achieved during the last two decades, many challenges remain in optically pumped WLEDs, and searching for low cost high performance down conversion phosphors is still of great interest. Recently, metal halide perovskites have emerged as a highly promising new generation of light emitters for their exceptional optical properties with high quantum efficiencies and color tunability, which have also inspired researchers to investigate their derivatives. In this perspective, we briefly review the progress during the last few years in the development of metal halide perovskites and perovskite-related materials as down conversion phosphors for optically pumped WLEDs. We also highlight some major issues and challenges that need to be addressed to enable perovskite-based light emitters to possibly replace currently used rare-earth doped inorganic phosphors and quantum dots.

A new class of materials, phosphonium halide salts, are used as surface passivation agents for efficient and stable PSCs.

The family of molecular level low‐dimensional organic metal halide hybrids has expanded significantly over the last few years. Here a new type of 1D metal halide structure is reported, in which metal halide octahedra form a corrugated double‐chain structure via nonplanar edge‐sharing. This material with a chemical formula of C₅H₁₆N₂Pb₂Br₆ exhibits a broadband yellow emission under ultraviolet light excitation with a photoluminescence quantum efficiency of around 10%. The light‐yellow emission is considered to be attributed to self‐trapping excitons. Theoretical calculations show that the unique alignment of the octahedra leads to small band dispersion and large exciton binding energy. Together with previously reported 1D metal halide wires and tubes, this new bulk assembly of 1D metal halides suggests the potential to develop a library of bulk assemblies of metal halides with controlled structures and compositions.

Perovskite light‐emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi‐2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light‐emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi‐2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi‐2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi‐2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m⁻² and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs.