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Ultralow trap densities, exceptional optical and electronic properties have been reported for lead halide perovskites single crystals; however, ambiguities in basic properties, such as the band gap, and the electronic defect densities in the bulk and at the surface prevail. Here, we synthesize single crystals of methylammonium lead bromide (CH3NH3PbBr3), characterise the optical absorption and photoluminescence and show that the optical properties of single crystals are almost identical to those of polycrystalline thin films. We observe significantly longer lifetimes and show that carrier diffusion plays a substantial role in the photoluminescence decay. Contrary to many reports, we determine that the trap density in CH3NH3PbBr3 perovskite single crystals is 1015 cm-3 , only one order of magnitude lower than in the thin films. Our enhanced understanding of optical properties and recombination processes elucidates ambiguities in earlier reports, and highlights the discrepancies in the estimation of trap densities from electronic and optical methods. [ABSTRACT FROM AUTHOR]

A new class of highly fluorescent 9,9′-bis-(alkyl)-2,7-diarylfluorene having electron withdrawing or electron donating groups on the p-phenyl positions were synthesized and characterized. The highly luminescent fluorene derivatives, 1-6 showed blue emission (376-416 nm), narrow FWHM (∼ 50 nm), high quantum yield (ϕF = 0·12-0·87) and short fluorescence lifetimes, τF = 0·23-1·14 ns. The HOMO levels of 9,9′-bis-(alkyl)-fluorene were tuned by the p-substituents at 2,7-phenyl group. Hammett correlation with EHOMO of these new molecules provides an effective tool to predict the HOMO level of similar molecules prior to the synthesis. These data indicate that they are useful as emitting materials for organic light emitting devices, OLEDs. [ABSTRACT FROM AUTHOR]

The article reports on creation of tandem cells through putting perovskite cells by the materials scientists at the University of Oxford and Stanford University and illustrates production of perovskite crystal by rapid crystallization technique.

The article presents research on perovskites.