The main issue in developing a quantum dot light-emitting diode (QLED) display lies in successfully replacing heavy metals with environmentally benign materials while maintaining high-quality device performance. Nonradiative Auger recombination is one of the major limiting factors of QLED performance and should ideally be suppressed. This study scrutinizes the effects of the shell structure and composition on photoluminescence (PL) properties of InP/ZnSeS/ZnS quantum dots (QDs) through ensemble and single-dot spectroscopic analyses. Employing gradient shells is discovered to suppress Auger recombination to a high degree, allowing charged QDs to be luminescent comparatively with neutral QDs. The “lifetime blinking” phenomenon is observed as evidence of suppressed Auger recombination. Furthermore, single-QD measurements reveal that gradient shells in QDs reduce spectral diffusion and elevate the energy barrier for charge trapping. Shell composition dependency in the gradience effect is observed. An increase in the ZnS composition (ZnS >50%) in the gradient shell introduces lattice mismatch between the core and the shell and therefore rather reverses the effect and reduces the QD performance.

Polymer/lead halide perovskite composites are a promising platform for wearable optoelectronic devices. In particular, one-dimensional nanocomposites are considered core materials for solar energy conversion textiles and optical sensors. Herein, we designed stretchable photodetectors incorporating thin and uniform polymer/perovskite composite nanofibers produced by electrospinning of a polymer/perovskite precursor solution.During the reaction of precursors in the as-spun nanofiber, protruding perovskite nanoplates on the fiber surface and embedded nanoparticles within the fiber were formed, showing double photoluminescence emissions. Furthermore, the mechanical behavior of the nanofibers on a rubbery substrate strongly depends on their orientation angle (α) with respect to the applied tensile force. As α decreases, the loaded stress is significantly reduced, which contributes to a stretchability of up to 15% strain for any orientation. The excellent percolation of perovskite nanoparticles leads to high photocurrents under green and red light illumination. At 15% strain, the responsivity and detectivity of the stretchable photodetector at λ = 550 nm were 51.2 mA W −1 and 2.23 × 10 11 Jones, respectively. The device performance was well retained during mechanical deformation and stability tests. This thin and stretchable device was also applied to a wearable photodetector to demonstrate its great potential as a wearable image sensor.

As attractive photoactive materials, metal halide perovskites demonstrate outstanding performance in a wide range of optoelectronic applications. Among the various compositions studied, mixed-halide perovskites have a finely tunable band gap that renders them desirable for targeted applications. Despite their advantages, photoinduced halide segregation often deters the photoelectric stability of the materials. Herein, we adopt a strategy of post-treating the perovskite surface with an organic spacer to generate a two-dimensional (2D) perovskite passivating layer. Trap-assisted recombination pathways can be selectively modulated by passivating the surface halide defects that cause photoinduced halide segregation. Fluorescence lifetime imaging of flat and bent surfaces of perovskites reveals that the perovskite lattice tolerates mechanical strain via the neutralizing passivation of ionic halide defects. Upon bending, the photocurrent response of the flexible photodetector is maintained over 83% for 2D passivated perovskite and drops to 23% for pristine perovskite. A flexible photodetector array built with 2D passivated perovskite, in combination with a deep learning algorithm, demonstrates excellent accuracy in determining letters of the alphabet for both flat (>96%) and bent (>93%) states. The connection of chemically modified charge carrier dynamics and mechanical properties revealed in this study offers valuable guidance for developing next-generation optoelectronic applications.

As the properties of a semiconductor material depend on the fate of the excitons, manipulating exciton behavior is the primary objective of nanomaterials. Although nanocrystals exhibit unusual excitonic characteristics owing to strong spatial confinement, studying the interactions between excitons in a single nanoparticle remains challenging due to the rapidly vanishing multiexciton species. Here, a platform for exciton tailoring using a straightforward strategy of shape‐tuning of single‐crystalline nanocrystals is presented. Spectroscopic and theoretical studies reveal a systematic transition of exciton confinement orientation from 3D to 2D, which is solely tuned by the geometric shape of material. Such a precise shape‐effect triggers a multiphoton emission in single nanotetrapods with arms longer than the exciton Bohr radius of material. In consequence, the unique interplay between the multiple quantum states allows a geometric modulation of the quantum‐confined Stark effect and nanocrystal memory effect in single nanotetrapods. These results provide a useful metric in designing nanomaterials for future photonic applications.

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