RESUMO
This work combines the high-temperature sintering method and atomic layer deposition (ALD) technique, and yields SiO2 /AlOx -sealed γ-CsPbI3 nanocrystals (NCs). The black-phase CsPbI3 NCs, scattered and encapsulated firmly in solid SiO2 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 ß to α phase without transferring into δ phase, has been discovered upon temperature increasing. The phase stability is ascribed to the high pressure exerted by the rigid SiO2 encapsulations, and its condensed amorphous structures that prevent the permeation of H2 O molecules. Nanoscale coating of Al2 O3 thin films, which are deposited on the surface of the CsPbI3 -SiO2 by ALD, enhances the protection against O2 infiltration, greatly elevating the high-temperature stability of CsPbI3 NCs sealed inside, as the samples remain bright after 1-h annealing in air at 400 °C. These fabrication and encapsulation techniques effectively prevent the formation of δ-CsPbI3 under harsh environment, bringing the high-pressure preservation of black-phase CsPbI3 from laboratory to industry toward potential applications in both photovoltaic and fluorescent areas.
RESUMO
The metal halide perovskite nanocrystal (MHP-NC), an easy-to-fabricate and low cost fluorescent material, is recognized to be among the promising candidates of the color conversion material in the micro light-emitting diode (micro-LED) display, providing that the stability can be further enhanced. It is found that the water steam, oxygen, thermal radiation and light irradiation-four typical external factors in the ambient environment related to micro-LED display-can gradually alter and destroy the crystal lattice. Despite the similar phenomena of photoluminescence quenching, the respective encroaching processes related to these four factors are found to be different from one another. The encroaching mechanisms are collected and introduced in separate categories with respect to each external factor. Thereafter, a combined effect of these four factors in an environment mimicking real working conditions of micro-LED display are also introduced. Finally, recent progress on the full-color application of MHP-NC is also reviewed in brief.
RESUMO
The low luminance efficiency, poor reliability and parasitic peaks have greatly limited the commercialization of deep ultraviolet (DUV) light-emitting diodes. Tasks of identifying the culprits of these deficits are of paramount importance but remains unaccomplished. We employ the full-range temperature (20 K -300 K) measurement on 275-nm DUV devices that subjected to a 15-hour current-stress aging. The results suggest that the primary culprit of fast luminous decay is the proliferation of non-radiative centers. The origins of two main parasitic peaks are identified. The 310-nm peak is considered to solely come from deep-level radiative centers (DLRCs) that only dwell in the active region. Whereas, the 400-nm peak is proven to be dual-sources. One is related to the DLRCs in the active region, which only can be observed at very low currents; the other emerging at higher currents are associated with similar kinds of DLRCs located in the p-region, which only are excited when electrons overflow. This new discovery also demonstrates that a thorough investigation on the interplay among carriers and various types of defects should be conducted on the basis of the measurement that is taken under a wide temperature range, as well as under a proper forward voltage. This is to let the quasi-Fermi level shift across deep defect levels, the band-edge, and to over-band, whereby these recombination sites are exposed to deficit, moderate and saturated electron environment so that their natures can be well tested.