Hybrid two-dimensional (2D) lead halide perovskites have been employed in optoelectronic applications, including white light emission for light emitting diodes (LEDs). However, until now, there have been limited reports on white light emitting lead halide perovskites with experimental insights into the mechanism of the broad band emission. Here, we present white light emission from a 2D hybrid lead chloride perovskite, using the widely known phenethylammonium cation. The single crystal X-ray structural data, time-resolved photophysical measurements, and DFT calculations are consistent with broad band emission arising from strong exciton-phonon coupling with the organic lattice, which is independent of surface defects. The phenethylammonium lead chloride material exhibits a remarkably high color rendering index of 84, CIE coordinate of (0.37,0.42), CCT of 4426, and photostability, making it ideal for natural white LEDs applications.
Mechanochemistry is a green, solid-state, re-emerging synthetic technique that can rapidly form complex molecules and materials without exogenous heat or solvent(s). Herein, we report the application of solvent-free mechanochemical ball milling for the synthesis of metal halide perovskites, to overcome problems with solution-based syntheses. We prepared phase-pure, air-sensitive CsSnX 3 (X = I, Br, Cl) and its mixed halide perovskites by mechanochemistry for the first time by reactions between cesium and tin(II) halides. Notably, we report the sole examples where metastable, high-temperature phases like cubic CsSnCl 3 , cubic CsPbI 3 , and trigonal FAPbI 3 were accessible at ambient temperatures and pressures without post-synthetic processing. The perovskites can be prepared up to ''kilogram scales.'' Lead-free, all-inorganic photodetector devices were fabricated using the mechanosynthesized CsSnBr 1.5 Cl 1.5 under solvent-free conditions and showed 10-fold differences between on-off currents. We highlight an essentially solvent-free, general approach to synthesize metastable compounds and fabricate photodetectors from commercially available precursors.
In an artificial photosynthetic system,
separation of the catalytic
sites for water oxidation from those of carbon dioxide reduction by
a gas impermeable physical barrier is an important requirement for
avoiding cross and back reactions. Here, an approach is explored that
uses crystalline Co3O4 as an oxygen evolving
catalyst and a nanometer-thin dense phase silica layer as the separation
barrier. For controlled charge transport across the barrier, hole
conducting molecular wires are embedded in the silica. Spherical Co3O4(4 nm)–SiO2(2 nm) core–shell
nanoparticles with p-oligo(phenylenevinylene) wire
molecules (three aryl units, PV3) cast into the silica were developed
to establish proof of concept for charge transport across the embedded
wire molecules. FT-Raman, FT-infrared, and UV–visible spectroscopy
confirmed the integrity of the organic wires upon casting in silica.
Transient optical absorption spectroscopy of a visible light sensitizer
(ester derivatized [Ru(bpy)3]2+ complex) indicates
efficient charge injection into Co3O4–SiO2 particles with embedded wire molecules in aqueous solution.
An upper limit of a few microseconds is inferred for the residence
time of the hole on the embedded PV3 molecule before transfer to Co3O4 takes place. The result was corroborated by
light on/off experiments using rapid-scan FT-IR monitoring. These
observations indicate that hole conducting organic wire molecules
cast into a dense phase, nanometer thin silica layer offer fast, controlled
charge transfer through a product-separating oxide barrier.
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