Pure white-light emitting ultrasmall organic–inorganic hybrid perovskite nanoclusters

Abstract

Organic-inorganic hybrid perovskites, direct band-gap semiconductors have shown tremendous promise for optoelectronic device fabrication. We report the first colloidal synthetic approach to prepare ultrasmall (~1.5 nm diameter), white light emitting, organic-inorganic hybrid perovskite nanoclusters. The nearly pure white-light emitting ultrasmall nanoclusters were obtained by selectively manipulating the surface chemistry (passivating ligands and surface trap-states) and controlled substitution of halide ions. The nanoclusters displayed a combination of band-edge and broadband photoluminescence properties, covering a major part of the visible region of the solar spectrum with unprecedentedly large quantum yields of ~12% and photoluninescence lifetime of ~20 ns. The intrinsic white light emission of perovskite nanoclusters makes them ideal and low cost hybrid nanomaterials for solid-state lighting applications.The ever-increasing global demand for energy drives the need to discover highly efficient materials capable of saving energy in solid-state lighting (SSL) applications, such as light-emitting diodes (LEDs). 1,2 In this context, pure white-light emitting materials, and their subsequent uses in LED fabrication, will be a most effective way to reduce global power consumption. Currently, white-light LEDs are prepared by: (i) mixing single wavelength emitting organic phosphors, 3 and (ii) constructing multi-layer films composed of blue, green, and red color emitting semiconductor quantum dots (QDs). 4,5 However, the self-absorption process between different organic phosphors reduces device efficiency, a similar device characteristic that has also been observed for QD-based LEDs. Ultrasmall semiconductor nanoclusters (e.g., CdSe) display white-light, but they require expensive, complicated and high temperature synthetic methods. [6][7][8] Recently, white-light emitting bulk organic-inorganic perovskites were synthesized, 9,10 which would not only expand SSL research but also facilitate inexpensive LED fabrication. Scheme 1. Schematic Presentation of the Synthesis of White-Light Emitting Organolead Bromide Perovskite NanoclustersIn this communication, we report the first colloidal synthetic method to prepare white-light emitting, ultrasmall (~1.5 nm diameter) methylammonium lead bromide (MAPbBr3) perovskite nanoclusters (PNCs). Their synthesis is outlined in Scheme 1 and the detailed procedure is provided in the Electronic Supplementary Information (ESI) file. These PNCs display a combination of band-edge and broadband photoluminescence (PL) with a quantum yield (QY) of ~5% and PL lifetime of ~7 ns. We hypothesize that the broad emission properties originate from the presence of surface-related midgap trap-states. Furthermore, we showed selective manipulation of band-gap and trap-states via the preparation of mixed halide (MAPbClxBr3-x) PNCs through controlled anion exchange reactions enhanced both QY and PL lifetime at least two-fold. We believe these ultrasmall PNCs will provide fundamentally important informati...

Giant five-photon absorption from multidimensional core-shell halide perovskite colloidal nanocrystals

“…The NC size is determined by the reaction temperature, where larger NCs are obtained at higher temperature. However, below 140 °C, nanoplatelets (not NCs) are formed instead5455. Moreover, at the current stage, despite MAPbBr 3 NCs with small sizes can be obtained5253, various problems associated with high density surface defects, low sample crystalline quality, low reaction yield and non-uniform size distribution need to be further addressed5253.…”

“…Given that both our MAPbBr 3 and CsPbBr 3 NCs are in the weak confinement regime ( d B ∼4 nm<<8–9 nm diameter for MAPbBr 3 and d B ∼7 nm<9 nm side for the cubic CsPbBr 3 ), it is possible to enhance these σ n values further through even smaller strongly confined MAPbBr 3 NCs, their core–shell counterparts (that is, NCs' diameter <4 nm) and CsPbBr 3 NCs (that is, NCs' side <7 nm). However, it is presently extremely challenging to synthesize small MAPbBr 3 (refs 52, 53) and CsPbBr 3 NCs5455 with high crystalline quality, low surface defects, uniform size distribution and relatively high reaction yield, which are needed to conduct detailed investigations of the quantum confinement effect on the MPA of lead bromide perovskite NCs. The all-inorganic CsPbBr 3 NCs were prepared via the hot-injection method39 at temperatures between 140–180 °C.…”

Ultrathin Highly Luminescent Two‐Monolayer Colloidal CdSe Nanoplatelets

“…The Stokes‐shifted emission also in some cases can be attributed to the self‐trapped excitons (STE) associated with the strong electron–phonon coupling . In the case of STEs, due to the strong electron–phonon coupling, the peak intensity of the PL increases linearly with the excitation intensity without any saturation or deviation till the photodegradation of the material, while the PL emission originating from defect sites can be saturated or can deviate from linear behavior under high excitation intensities due to the limited number of permanent defect sites . Figure a shows the excitation power density (up to ≈300 W cm −2 ) dependence of PL emission from 2ML CdSe NPLs dispersed in hexane solution.…”

Synthesis and characterization of Mn-doped CsPb(Cl/Br)3 perovskite nanocrystals with controllable dual-color emission

“…Solution-processed hybrid and inorganic lead halide perovskites have attracted much attention in the past several years due to their excellent emission properties, high photoluminescence quantum yields (PLQY), small exciton binding energy and balanced electron and hole mobility lifetime, [1][2][3][4][5][6][7][8] which means that these materials have great potential in photophysical applications, including light emitting diodes, lasers and photodetectors. [9][10][11][12][13][14][15][16][17][18][19] However, the hybrid lead halide perovskites are extremely sensitive to oxygen and moisture, [20][21][22] which greatly restricts their applications. Compared with the organicinorganic perovskite nanocrystals, the all-inorganic cesium lead halide (CsPbX 3 , X ¼ Cl, Br, I) nanocrystals are much more stable.…”