Search

A facile and reproducible method for scalable synthesis of high‐quality core/shell quantum dots (QDs) is a prerequisite to facilitate their versatile applications. Herein, a seed‐mediated heat‐up approach is developed for the preparation of high‐quality core/shell QDs with variable shell composition and continuously tunable shell thickness by selection of conventional salts as the precursors. The method is very simple and highly reproducible and, therefore, can be easily scaled up to get gram‐level product. The as‐obtained CdSe/CdS and CdSe/ZnCdS core/shell QDs exhibit intriguing optical properties, that is a narrow photoluminescence (PL) emission peak and near‐unity PL quantum yield. Importantly, the CdSe/ZnCdS core/shell QDs with a size of 11.4 nm exhibit obviously suppressed blinking behavior, and the fraction of nonblinking QDs (defined by an on‐time fraction ≥ 0.95) can reach as high as 96.0% on the measurement of more than 200 QDs. Moreover, quantum‐dot light‐emitting diodes (QLEDs) based on CdSe/ZnCdS core/shell QDs show a peak external quantum efficiency of 14.8% and low efficiency roll‐off at luminance ranging from 1000 to 25 000 cd·m−2. It is anticipated that the presented work will pave a novel way for the large‐scale production of high‐quality QDs and further boost their applications in light‐emitting diodes, lasing, and biological imaging. [ABSTRACT FROM AUTHOR]

According to the thinner emitting layer and stronger electric field in perovskite light‐emitting diodes (PeLEDs) than those in perovskite solar cells, the strong electric‐field‐driven ion‐migration is a key issue for the operational stability of PeLEDs. Here, a methylene‐bis‐acrylamide cross‐linking strategy is proposed to both passivate defects and suppress ion‐migration with an emphasis on the suppressing mechanism via in situ investigations. As typical results, in addition to the enhanced external quantum efficiency (EQE, 16.8%), PeLEDs exhibit preferable operational stability with a half lifetime (T50) of 208 h under continuous operation with an initial luminance of 100 cd m−2. Moreover, the EQE of cross‐linked LEDs can maintain above 15% during 25 times scanning as the devices are measured every 4 days. To the authors' knowledge, this is the highest stability published until now for high‐efficiency PeLEDs with EQE over 15%. The in situ/ex situ mechanism investigation demonstrates that such cross‐linking increases binding energy from 0.54 to 0.92 eV and activation energy from 0.21 to 0.5 eV. Hence, it suppresses ligands breaking away and ion migration, which prevents ions from moving inside and across crystals. The proposed cross‐linking passivation strategy thus provides an effective methodology to fabricate stable perovskites‐based photoelectric devices. [ABSTRACT FROM AUTHOR]

A hydrogen-bonded amine-group doping strategy is proposed for effectively suppressing color-shift of blue PeLEDs. The theoretical and experimental results demonstrated that the N−H⋯X interaction between −NH 2 dopants and Pb−X lattices can increase the potential barriers of halide ion migration and hence stabilize the emitting wavelength even at high voltage loads, making the strategy attractive for developing color-stable perovskite optoelectronic devices for lighting and display applications. [Display omitted] Voltage loading-induced change in the electroluminescence (EL) wavelength of mixed halide perovskite light-emitting diodes (PeLEDs), so-called color-shift, has become an inevitable phenomenon, which is seriously unfavorable to their applications in lighting and display. Here, we achieve color-stable blue PeLEDs via a hydrogen-bonded amine-group doping strategy. Selecting guanidine (GA) or formamidinium (FA) as amine-group (−NH 2) doping source for CsPbBr x Cl 3− x quantum dots (QDs), experimental and theoretical results reveal that the strong N−H⋯X (X = Br/Cl) bonding can be produced between −NH 2 dopants and Pb−X lattices, thereby increasing the migration barrier of halide anions. Resultantly, color-stable sky-blue devices were realized with emission peaks fixed at 490.5 (GA) and 492.5 (FA) nm without any obvious shift as the voltage increases, in sharp contrast devices without N−H⋯X producing a 15 nm red-shift from 487 to 502 nm. Not only that, maximum external quantum efficiency is improved to 3.02% and 4.14% from the initial 1.3%. This finding offers a convenient boulevard to achieve color-stable PeLEDs with high efficiency. [ABSTRACT FROM AUTHOR]

• The reaction yield of DBSA-QDs is 68 %, which is close to the theoretical limit. • The DBSA capped PQDs exhibit suppressed growth under various conditions. • An ion migration suppression mechanism was proposed. • The blue DBSA-QDs exhibit a steady spectrum under UV light and bias. Surface ligands play important roles in synthesis, surface passivation, colloidal stability, and modulation of optoelectronic properties for quantum dots (QDs). It is well known that conventional ligands exhibit weak binding on the surface of perovskite QDs (PQDs), resulting in uncontrolled growth and unsatisfied stability during purification and operation. This impedes the device performance progress and practical applications severely. Stronger ligands anchoring on PQDs tightly and passivating surface defects efficiently have been reported to solve the problems. Herein, we choose a representative strong ligand, dodecylbenzene sulfonic acid (DBSA), to investigate its influence on PQD growth, stability under high-temperature with various solvents and additives, and the possibility of core–shell structure construction. Interestingly, the DBSA capped PQDs exhibit abnormally ripening under above conditions. Besides, a new mechanism for ion migration suppression is proposed based on internal lattice relaxation and inter-particle migration pathway elimination. Although DBSA-PQDs can be purified several times and maintain a high quantum yield, the corresponding light-emitting diodes show poor external quantum efficiency, which might be assigned to the unbalanced colloidal stability and film conductivity. This work indicates that strong ligands provide wider space for PQD modulation and the balance between stability and device performance should also be considered. [ABSTRACT FROM AUTHOR]