Browsing by Author "Sargent, E. H."

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Open Access
Giant alloyed hot injection shells enable ultralow optical gain threshold in colloidal quantum wells
(American Chemical Society, 2019) Altıntaş, Yemliha; Güngör, Kıvanç; Gao, Y.; Sak, Mustafa; Quliyeva, Ulviyya; Bappi, G.; Mutlugün, Evren; Sargent, E. H.; Demir, Hilmi Volkan
As an attractive materials system for high-performance optoelectronics, colloidal nanoplatelets (NPLs) benefit from atomic-level precision in thickness, minimizing emission inhomogeneous broadening. Much progress has been made to enhance their photoluminescence quantum yield (PLQY) and photostability. However, to date, layer-by-layer growth of shells at room temperature has resulted in defects that limit PLQY and thus curtail the performance of NPLs as an optical gain medium. Here, we introduce a hot-injection method growing giant alloyed shells using an approach that reduces core/shell lattice mismatch and suppresses Auger recombination. Near-unity PLQY is achieved with a narrow full-width-at-half-maximum (20 nm), accompanied by emission tunability (from 610 to 650 nm). The biexciton lifetime exceeds 1 ns, an order of magnitude longer than in conventional colloidal quantum dots (CQDs). Reduced Auger recombination enables record-low amplified spontaneous emission threshold of 2.4 μJ cm–2under one-photon pumping. This is lower by a factor of 2.5 than the best previously reported value in nanocrystals (6 μJ cm–2 for CdSe/CdS NPLs). Here, we also report single-mode lasing operation with a 0.55 mJ cm–2 threshold under two-photoexcitation, which is also the best among nanocrystals (compared to 0.76 mJ cm–2 from CdSe/CdS CQDs in the Fabry–Pérot cavity). These findings indicate that hot-injection growth of thick alloyed shells makes ultrahigh performance NPLs.
Open Access
Highly Efficient Visible Colloidal Lead-Halide Perovskite Nanocrystal Light-Emitting Diodes
(American Chemical Society, 2018) Yan, F.; Xing, J.; Xing, G.; Quan, L.; Tan S.T.; Zhao, J.; Su, R.; Zhang, L.; Chen, S.; Zhao Y.; Huan, A.; Sargent, E. H.; Xiong, Q.; Demir, Hilmi Volkan
Lead-halide perovskites have been attracting attention for potential use in solid-state lighting. Following the footsteps of solar cells, the field of perovskite light-emitting diodes (PeLEDs) has been growing rapidly. Their application prospects in lighting, however, remain still uncertain due to a variety of shortcomings in device performance including their limited levels of luminous efficiency achievable thus far. Here we show high-efficiency PeLEDs based on colloidal perovskite nanocrystals (PeNCs) synthesized at room temperature possessing dominant first-order excitonic radiation (enabling a photoluminescence quantum yield of 71% in solid film), unlike in the case of bulk perovskites with slow electron-hole bimolecular radiative recombination (a second-order process). In these PeLEDs, by reaching charge balance in the recombination zone, we find that the Auger nonradiative recombination, with its significant role in emission quenching, is effectively suppressed in low driving current density range. In consequence, these devices reach a maximum external quantum efficiency of 12.9% and a power efficiency of 30.3 lm W-1 at luminance levels above 1000 cd m-2 as required for various applications. These findings suggest that, with feasible levels of device performance, the PeNCs hold great promise for their use in LED lighting and displays.