Remarkable Black‐Phase Robustness of CsPbI₃ Nanocrystals Sealed in Solid SiO₂/AlO_x Sub‐Micron Particles

Abstract

applications, [6] X-ray detectors, [7] potential color conversion layers in visible light communication, [8,9] and mini and micro light-emitting diode (mini-and micro-LED) displays. [10][11][12] Among them, the CsPbI 3 processes the lowest bandgap, which attracts a vast interest from the community. [13] It absorbs the largest portion of solar light in solar-cells, compared to its counterparts; [14] it emits the deepest red light, constituting the largest gamut in the micro-LED display; [12,15] however, it is the least stable member of the lead-halide PNCs family. In addition to the degradation induced by external factors, which are shared among all PNCs, [11] the CsPbI 3 suffers undesirable intrinsic phase transition when the temperature is changing. So far, four phases of CsPbI 3 have been identified. They fall into two categories. The first category, being of the perovskitetype and fluorescently active, contains three phases: α (cubic), β (tetragonal), and γ (orthorhombic) phases. These three phases are collectively denoted as "black" phases. On the contrary, the second category, the "yellow" phase -δ-CsPbI 3 (non-perovskite type), is fluorescently inactive, due to its indirect bandgap. In ambient room temperature (RT), it has been proven that the γ-CsPbI 3 exhibits the highest stability among three black phases, but is still less stable than the thermodynamically favored δ-CsPbI 3 . [16] Phase transitions can be observed at changing temperature, as sketched in Figure 1. At 1 atm, the CsPbI 3 exists in the form of α phase when the temperature is higher than 320 °C, but this critical temperature depends on the pressure. [17] Upon cooling, the CsPbI 3 PNCs either turn directly into δ phase, in the case when no constraint or pressure is exerted, [17,18] as sketched in the Route (1) in Figure 1, or into β and γ phases in succession and temporarily maintains in black phase at RT, in cases where there exist constraints of proper degree [17,19] or crystal grains are sufficiently small, [4] as sketched by Route (2) in Figure 1, but under some triggers, such as environmental humidity in ambient, the meta-stable γ-CsPbI 3 would eventually turn into δ-CsPbI 3 (Route (3), Figure 1). [13,17,20] During heating, if starting from the yellow phase at RT, the δ-CsPbI 3 phase turns to α-CsPbI 3 when the temperature approaches the range from 300 to 450 °C (route (4), Figure 1). [17,[21][22][23] If starting from the black phases at RT (commonly γ-CsPbI 3 ), although it would end up α-CsPbI 3 at temperatures beyond 300 °C, according to literature published, the γ-CsPbI 3 will first transfer to δ-CsPbI 3 This work combines the high-temperature sintering method and atomic layer deposition (ALD) technique, and yields SiO 2 /AlO x -sealed γ-CsPbI 3 nanocrystals (NCs). The black-phase CsPbI 3 NCs, scattered and encapsulated firmly in solid SiO 2 sub-micron particles, maintain in black phases against water soaking, ultraviolet irradiation, and heating, exhibiting remarkable phase stability. A new phase-transition route, from γ via β to α ...

High-Reliability Perovskite Quantum Dots Using Atomic Layer Deposition Passivation for Novel Photonic Applications

“…The PeQDs were uniformly mixed with KSF red phosphors having an emission wavelength of 630 nm and UV glue and then excited by blue LEDs (446 nm) to make white LEDs. This strategy, however, is ineffective since the reabsorption effect is caused by the self-aggregation of the nanoscale PeQD powder [ 5 , 24 , 29 , 53 ]. The light scattering is enhanced by adding a light scatterer, i.e., TiO 2 nanoparticles, to the mixture.…”

“…Because of their exceptional qualities, including their narrow emission bandwidth, high fluorescent quantum yield, tunable emission color, and wide color gamut, QDs are the leading candidate for the field of next-generation solid-state lighting and displays. QDs have recently gained considerable interest as a promising contender for a wide variety of optoelectronic applications, including light-emitting diodes (LED) [ 1 , 5 ], solar cells [ 6 , 7 ], photodetectors [ 8 ], lasers [ 9 ], photocatalysis [ 10 ], biomedical imaging [ 11 ], lighting [ 12 ], and visible-light communication (VLC) [ 13 , 14 ]. The commercialization of QDs in the display sector is attributed, in particular, to conventional CdSe QDs from the II-VI group, which exhibit a high photoluminescence quantum yield (PLQY) in addition to other exceptional optical properties.…”

“…Studies have demonstrated that ALD growth can protect QDs against environmental degradation, oxidation, ripening, and sintering [ 37 , 38 ]. Moreover, ALD growth can enhance the performance of QDs and QD layers, which will result in increased charge carrier mobility and charge carrier multiplication [ 1 , 5 , 39 ]. As a result, the ALD process has enormous potential as a method for post-functionalizing QDs in addition to encapsulating and protecting them from oxidation.…”

The synthesis of metal halide perovskite nanocrystals: surface and interface engineering

“…Moreover, their condensed amorphous structures prevent the permeation of H 2 O and oxygen molecules and result in a higher thermal stability. 19,20…”

“…Moreover, their condensed amorphous structures prevent the permeation of H 2 O and oxygen molecules and result in a higher thermal stability. 19,20 The improved performance of MHPs would increase possibilities for MHP NC-based optoelectronic and photocatalytic applications. And it is well perceived that the dynamics of the photogenerated electron-hole pairs are the important operating parameters of the relevant optoelectronic devices.…”