The potential profile and the energy level offset of core/shell heterostructured nanocrystals (h-NCs) determine the photophysical properties and the charge transport characteristics of h-NC solids. However, limited material choices for heavy metal-free III-V/II-VI h-NCs pose challenges in comprehensive control of the potential profile. Herein, we present an unprecedented approach to such control by steering dipole moments at the interface of III-V/II-VI h-NCs. The controllable heterovalency at the interface is responsible for interfacial dipole moments that result in the vacuum-level shift, providing an additional knob for the control of optical and electrical characteristics of h-NCs. We capitalize on the atomic precision with which to synthesize h-NCs by correlating interfacial dipole moments to photochemical stability and optoelectronic performance of resulting h-NCs.

Colloidal Ag(In,Ga)S2 nanocrystals (AIGS NCs) with the band gap tunability by their size and composition within visible range have garnered surging interest. High absorption cross-section and narrow emission linewidth of AIGS NCs make them ideally suited to address the challenges of Cd-free NCs in wide-ranging photonic applications. However, AIGS NCs have shown relatively underwhelming photoluminescence quantum yield (PL QY) to date, primarily because coherent heteroepitaxy has not been realized. Here, we report the heteroepitaxy for AIGS-AgGaS2 (AIGS-AGS) core-shell NCs bearing near-unity PL QYs in almost full visible range (460 to 620 nm) and enhanced photochemical stability. Key to the successful growth of AIGS-AGS NCs is the use of the Ag-S-Ga(OA)2 complex, which complements the reactivities among cations for both homogeneous AIGS cores in various compositions and uniform AGS shell growth. The heteroepitaxy between AIGS and AGS results in the Type I heterojunction that effectively confines charge carriers within the emissive core without optically active interfacial defects. AIGS-AGS NCs show higher extinction coefficient and narrower spectral linewidth compared to state-of-the-art heavy metal-free NCs, prompting their immediate use in practicable applications including displays and luminescent solar concentrators (LSCs).

ZnSe 1−X Te X nanocrystals (NCs) are promising photon emitters with tunable emission across the violet to orange range and near-unity quantum yields. However, these NCs suffer from broad emission line widths and multiple exciton decay dynamics, which discourage their practicable use. Here, we explore the excitonic states in ZnSe 1−X Te X NCs and their photophysical characteristics in relation to the morphological inhomogeneity of highly mismatched alloys. Ensemble and single-dot spectroscopic analysis of a series of ZnSe 1−X Te X NC samples with varying Te ratios coupled with computational calculations shows that, due to the distinct electronegativity between Se and Te, nearest-neighbor Te pairs in ZnSe 1−X Te X alloys create localized hole states spectrally distributed approximately 130 meV above the 1S h level of homogeneous ZnSe 1−X Te X NCs. This forms spatially separated excitons (delocalized electron and localized hole in trap), accounting for both inhomogeneous and homogeneous line width broadening with delayed recombination dynamics. Our results identify photophysical characteristics of excitonic states in NCs made of highly mismatched alloys and provide future research directions with potential implications for photonic applications.

Auger recombination (AR), whereby the electron−hole recombination energy is transferred to a third charge carrier, prevails in nanocrystal quantum dots (QDs) and governs the performance of QD-based devices including light-emitting diodes and lasers. Thus, precise AR evaluation of QDs is essential for understanding and improving the characteristics of such applications. So far, conventional charging approaches, such as the stir-versus-static method, photochemistry, or electrochemistry, have been able to assess the AR decay rate of either positively (two holes and one electron, X + ) or negatively (one hole and two electrons, X − ) charged excitons, and the decay dynamics of the other type of charged exciton is presumably estimated by the superposition principle of the biexciton Auger process. Herein, we demonstrate an opto-electrical method that enables us to precisely assess AR rates of X + and X − in core/shell heterostructured QDs. Specifically, we devise electron-only devices and hole-only devices to inject extra charge carriers into QDs without unwanted side reactions or degradation of QDs and probe AR characteristics of these charged QDs via timeresolved photoluminescence measurements. We find that AR rates of charged excitons, both X + and X − , gained from the present method agree well with those attained from conventional approaches and the superposition principle, corroborating the validity of the present approach. This present method permits us to comprehend multicarrier dynamics in QDs, prompting the use of QDs in light-emitting diodes and laser devices based on QDs.

Improving operational stability is one of the most crucial issues for the practical application of quantum-dot (QD)-based light-emitting diodes (QLEDs), particularly in devices with heavy-metal-free QDs. Although a few potential reasons for their operational instability have been suggested, such as poor charge balance and surface defects of QDs, the origin of degradation needs to be disclosed more clearly to achieve higher device stability. Here, we systematically investigate the effect of excess charges on the degradation of InP-based QLEDs. For this, we intentionally designed charge-imbalanced QLEDs, i.e., hole-excess and electron-excess devices, by inserting an insulating layer adjacent to QDs, and measured their lifetime discharging the devices at regular intervals to observe the effect of each excess carrier separately. Based on multilateral analysis, we found that excess holes cause rapid deterioration of QDs and resultant permanent degradation of QLEDs at an early stage, whereas excess electrons temporarily charge the QDs. To minimize the permanent degradation of QDs, we adopted an electrochemically robust ligand for QDs by ligand exchange, enabling QLEDs to exhibit improved lifetime (by a factor of ∼109) with no notable permanent degradation. We believe that our device design, analysis methods, and strategies for better stability would not only expand the fundamental understanding of QLEDs but also contribute to the development of highly stable InP-based QLEDs.