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Two-dimensional (2D) Ruddlesden-Popper hybrid organic-inorganic perovskites are the most promising candidates for highly efficient optoelectronic devices due to their remarkable exciton characteristics, adjustable band structure and long-term environmental stability. However, excitons emission behavior of 2D Ruddlesden-Popper perovskites is still unclear. Here we theoretically-experimentally decoupled the excitons behavior in 2D Ruddlesden-Popper PEA 2 PbI 4 nanosheets. Theoretically, the Elliott theory was used to separate exciton and band edge absorptions of PEA 2 PbI 4 nanosheets and determine an exciton binding energy of about 274 meV. Experimentally, spectral-dependent photoluminescence lifetime and excitation powder density-dependent photoluminescence spectra revealed that a distinct photoluminescence tail emission should be derived from localized excitons with lower emission energy than free excitons. Further, the luminescent component of the free excitons and localized excitons with their corresponding densities of states was theoretically decoupled by line-shape analysis of PEA 2 PbI 4 nanosheets photoluminescence spectra, which is consistent with the experimental results demonstrating the existence of localized excitons. Hence, our work provides understanding on the exciton behavior and luminescence mechanism of 2D Ruddlesden-Popper perovskites, which would benefit the prediction of high-performance excitonic devices based on 2D Ruddlesden-Popper perovskites. • Excitons behavior in 2D Ruddlesden-Popper PEA 2 PbI 4 nanosheets was decoupled. • A band tail state emission derived from localized excitons. • The luminescent component of the free excitons and localized excitons was separated. [ABSTRACT FROM AUTHOR]

All-inorganic halide perovskites have attracted great attention by virtue of the merits of bright emission, tunable wavelength and narrow-band emission. Despite the excellent optical features, all-inorganic halide perovskite materials have suffered from intrinsic instability, which has limited their applications in various optoelectronic devices. To mitigate the intractable issue, we demonstrated the CsPbBr3 nanoparticles decorated with smaller SiO2 nanocrystals to passivate the surface defects; SiO2 nanoparticles were applied as a barrier layer to maintain the optical property and enhance environmental stability. A facile in situ method was proposed to prepare CsPbBr3/SiO2 nanocomposites, in which an environmental ethanol/water solvent system was needed with the addition of tetraethyl orthosilicate (TEOS) as a silicon precursor. The obtained CsPbBr3/SiO2 nanocomposites have better optical characteristic and stability than bare CsPbBr3 nanoparticles. Even 70% photoluminescence intensity of as-prepared CsPbBr3/SiO2 nanocomposites can be maintained after 168 h storage in ethanol. This newly developed synthesis will open up a new route for the fabrication of optoelectronic devices in an environmentally friendly way, and the as-obtained perovskite materials with improved stability will make them great potential for multifunctional optoelectronic devices. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite nanocrystals have held great promise as incredibly effective luminescent materials and also have been synthesized efficiently by room temperature approaches. Toluene, a high toxicity solvent, is often used as a valid antisolvent in ligand-assisted reprecipitation strategy, which badly restricts the commercial application of this convenient method. Here, aiming to address the toluene toxicity issue, the low toxic tetraethyl orthosilicate (TEOS) is employed as a new alternative antisolvent to achieve high uniform and composition dependent luminescent all-inorganic perovskite Cs 4 PbX 6 (X = I, Br, Cl) combined with CsPbX 3 (X = I, Br, Cl) nanocrystals with tunable emission large-span wavelengths (626–437 nm) and remarkably narrow full width at half-maximum (FWHM) monochromaticity (down to 19 nm). Meanwhile, the ratio of CsBr to PbBr 2 is proved to be a critical factor to control the crystalline phase of the resulting perovskite nanocrystals. Additionally, one monochromatic light-emitting diode (LED) lamp with brightly pure green emission is fabricated based on bromine-based perovskite nanocrystals. This newly developed low toxicity antisolvent synthesis (LTaS) is suitable candidate for commercial production in an environmentally-friendly way, and the as-obtained perovskite materials with superior optical merits will be brought to the forefront of lighting and displays. [ABSTRACT FROM AUTHOR]

• The electron injection of ETL/perovskite of PeLEDs at molecular level is studied. • The molecular planarity bridging effects are discovered. • Superior molecular planarity of ETL enhances electron transport ability of ETL. • Superior molecular planarity of ETL improves carrier injection of ETL/perovskite. • Superior molecular planarity of ETL leads to superior performances of PeLEDs. Effectively balancing carrier injection of perovskite LEDs (PeLEDs) for next-generation display and illumination urgently needs for molecularly understanding carrier injection behavior of electron transport layer (ETL)/perovskite toward further developing high performance PeLEDs. Here, we molecularly reveal the electron injection behaviors of PeLEDs by theoretically-experimentally decoupling the electron transport of ETLs and electron injection of TmPyPB/perovskite and TPBi/perovskite. Resulted, the better molecular planarity bridging effect (MPBE) of TmPyPB than TPBi can effectively increase electronic-coupling for the improved electron transport ability and significantly decrease injection barrier for the enhanced electron injection capability, intrinsically leading to a more balanced carrier injection and a less electron accumulation of PeLEDs. Compared to TPBi-based PeLEDs, the TmPyPB-based PeLEDs present the obviously-increased average EQE, current efficiency, power efficiency and luminance by 44 %, 63 %, 43 % and 100 %, respectively. Meanwhile, this PeLED shows a higher voltage tolerance characteristic of 7.5 V than that of TPBi-based PeLEDs (6.25 V). Therefore, this work may provide a fundamental insight into carrier injection behavior of PeLEDs for effectively-regulating its carrier injection balance and further for its greatly-facilitated commercialization. [ABSTRACT FROM AUTHOR]