No abstract

Photoluminescence is a radiative recombination process of electron–hole pairs. Self-trapped excitons (STEs), occurring in a material with soft lattice and strong electron–phonon coupling, emit photons with broad spectrum and large Stokes shift. Recently, series halide perovskites with efficient STE emission have been reported and showed promise for solid-state lighting. In this Perspective, we present an overview of various photoluminescence phenomena with the emphasis on the mechanism and characteristics of emission derived from STEs. This is followed by the introduction of STE emission in hybrid halide perovskites. We then introduce all-inorganic STE emitters and focus in particular on the mechanism of STEs in double-perovskite Cs2AgInCl6 and strategies for efficiency improvement. Finally, we summarize the current photoluminescence and electroluminescence applications of STE emitters as well as the potential in luminescent solar concentrators and provide an overview of future research opportunities.

Lead halide perovskite quantum dots (QDs) possess color-tunable and narrow-band emissions and are very promising for lighting and display applications, but they suffer from lead toxicity and instability. Although lead-free Bi-based and Sn-based perovskite QDs (CsSnX3, Cs2SnX6 and (CH3NH3)3Bi2X9) have been reported, they all showed low photoluminescence quantum yield (PLQY) and poor stability. Here we report the synthesis of Cs3Bi2Br9 perovskite QDs with high PLQY and excellent stability. Via a green and facile process using ethanol as the anti-solvent, as-synthesized Cs3Bi2Br9 QDs show a blue emission at 410 nm with a PLQY up to 19.4%. The whole series of Cs3Bi2X9 (X = Cl, Br, I) QDs by mixing precursors could cover the PL emission range from 393 to 545 nm. Furthermore, Cs3Bi2Br9 QDs show excellent photostability and moisture stability due to the all-inorganic nature and the surface passivation by BiOBr, which enables the one-pot This article is protected by copyright. All rights reserved. 3 synthesis of Cs3Bi2Br9 QDs/silica composite. A lead-free perovskite white light emitting diode (W-LED) is fabricated by simply combine the composite of Cs3Bi2Br9 QDs/silica with Y3Al5O12 (YAG) phosphor. As a new member of lead-free perovskite QDs, Cs3Bi2Br9 QDs open up a new route for the fabrication of optoelectronic devices due to their excellent stability and photophysical characteristics.