Jaehoon Lim

Realizing high-resolution stretchable displays requires emissive materials that combine photopatternability with intrinsic stretchability. In colloidal nanocrystal films, however, the network formation needed for precise patterning often restricts molecular mobility, creating a fundamental trade-off with mechanical compliance. Here, we address this challenge using a benzophenone-based dual-crosslinker strategy that forms an elastomeric nanocrystal network. The tetrafunctional small-molecule crosslinker promotes efficient photopatterning, whereas the benzophenone-terminated polybutadiene crosslinker provides mechanical compliance. By tuning the crosslinker composition, the dual-crosslinking system enables direct optical patterning with line widths down to 2 μm and crack-free deformation up to 36% uniaxial strain. Both perovskite and InP-based nanocrystals largely retain their photoluminescence after processing, while the dual-crosslinking platform enables multicolor patterning and transfer to elastomeric substrates. QLEDs incorporating strained emissive layers maintain more than 90% of the maximum luminance of their unstretched counterparts. This dual-crosslinker design offers a general route to intrinsically stretchable, directly photopatternable colloidal nanocrystal emission layers.

ZnSe is a cornerstone shell material for enhancing the efficiency and stability of quantum dots (QDs). However, the chemical mechanisms governing detrimental zinc vacancy (VZn) formation remain unclear, limiting the predictive synthesis of high-quality heterostructures. Herein, we demonstrate that rational manipulation of ZnxSey intermediates via free oleic acid (OA) effectively suppresses both VZn and morphological inhomogeneity in CdSe/ZnSe core/shell QDs. Under OA-deficient conditions, sluggish precursor conversion yields a broad distribution of ZnxSey intermediates, including Zn-deficient heavy clusters like Zn2Se3(TOP), that lead to VZn incorporation. Conversely, excess OA shifts the intermediate landscape toward Zn-rich light species and suppresses the shift of intermediates into oxidized forms. This intermediate-level control enables the growth of VZn-free, morphologically uniform ZnSe shells with near-unity photoluminescence quantum yield. Our findings establish intermediate stoichiometry as a deterministic handle for the defect-free heteroepitaxy.

This paper proposes a doping‐based strategy to fabricate dual‐functional hole injection layers (HILs) for high‐performance quantum‐dot light‐emitting diodes (QLEDs). Specifically, the HIL is created by introducing a p‐type dopant, 4‐isopropyl‐4′‐methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (TPFB), into N4,N4′‐Di(naphthalen‐1‐yl)‐N4,N4′‐bis(4‐vinylphenyl) biphenyl‐4,4′‐diamine (VNPB), the host material. Due to its strong electron‐accepting character, TPFB promotes efficient hole injection, while the vinyl groups in VNPB enable the formation of robust crosslinked thin films upon thermal annealing. Furthermore, through precise control of the doping concentration, the HIL's highest occupied molecular orbital level can be tuned, which lowers the hole injection barrier effectively; simultaneously, the robust crosslinked network structure substantially suppresses leakage current. Consequently, InP‐based red QLEDs incorporating the proposed HIL exhibit enhanced external quantum efficiency and operational stability compared with conventional devices employing poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid). This dual‐function HIL strategy simultaneously addresses hole injection and solvent resistance issues, offering a promising route toward high‐efficiency QLEDs with minimal leakage current.

We report a xanthene-based polymeric hole transport material (HTM), poly(XBC-co-PBCB), incorporating a benzocyclobutene crosslinkable unit (PBCB) for solution-processed quantum dot light-emitting diodes (QLEDs). Notably, although this polymer features a non-conjugated backbone system similar to conventional poly(9-vinylcarbazole) (PVK), the incorporation of a rigid π-conjugated xanthene pendant unit enables superior charge transport. This unique structural design provides a deep highest occupied molecular orbital (HOMO) energy level perfectly suited for the deep HOMO of QDs, while maintaining enhanced thermal stability. As a result, it achieves a hole mobility of 1.51 × 10–5 cm2 V–1s–1 after cross-linking, which is significantly higher than that of PVK. Upon thermal treatment, it forms a cross-linked network, providing excellent solvent resistance that enables robust multilayer device fabrication. Furthermore, a bilayer hole transport structure combining the cross-linked HTM with a thin PVK interlayer enables cascade-aligned energy levels, facilitating efficient hole transport. As a result, QLED devices employing the bilayer HTL exhibit enhanced performance, achieving a maximum external quantum efficiency (EQE) of 16.27%, a maximum current efficiency (CE) of 19.04 cd A–1, and an extended operational lifetime (T50) of 10.69 h at an initial luminance of 50,000 cd m–2, representing a sixfold improvement compared to PVK-based devices. These results highlight the effectiveness of crosslinkable xanthene-based HTMs in enabling balanced charge transport and improving device stability in solution-processed QLEDs.

Colloidal quantum dots (QDs) offer size-tunable optoelectronic properties and solution processability, yet achieving uniformly packed emissive layers remains a bottleneck for high-performance quantum-dot light-emitting diodes (QLEDs). Here, we report a machine learning -guided solvent optimization strategy to produce homogeneous QD films. Five representative solvent parameters are evaluated, and multiple regression models are trained against film uniformity derived from atomic force microscopy. Among them, support vector regression provides the highest predictive accuracy for film homogeneity. Guided by these predictions, we formulate a mixed solvent that closely matches the target profile, yielding superior packing homogeneity, which is confirmed by grazing-incidence small-angle x-ray scattering. QLEDs fabricated with this formulation exhibit an external quantum efficiency of 20.6% and an operational lifetime of 468.5 h at 20 000 cd m ⁻² , surpassing all single-solvent controls. These findings establish packing homogeneity as a decisive factor for device performance and introduce a generalizable and scalable framework for data-driven design of solution-processed devices, holding strong potential for next-generation optoelectronic systems.

Colloidal quantum dot light‐emitting diodes (QD‐LEDs) offer narrowband, color‐pure emission, solution processability, and wavelength tunability for next‐generation displays. However, commercialization is hindered by positive aging—a storage‐driven drift in which device external quantum efficiency (EQE) increases for several days before peaking, reflecting slow interfacial trap passivation in oxide electron‐transport layers (ETLs). This drift delays qualification, complicates calibration, and degrades device‐to‐device uniformity because the as‐fabricated performance does not represent the final state. Here, we suppress positive aging by pre‐stabilizing ZnMgO ETLs via single‐source chloride doping (MgCl ₂ ), which mitigates oxygen vacancy (OV)‐related defect signatures. Time‐dependent X‐ray photoelectron spectroscopy, single‐carrier device measurements, and steady‐state/time‐resolved QD photoluminescence show that undoped ZnMgO undergoes gradual defect passivation during storage, whereas Cl‐doped ZnMgO remains nearly time‐invariant. As a result, devices with Cl‐doped ZnMgO reach peak EQE at day 0 and maintain it during storage, while devices with undoped ZnMgO require several days to reach peak efficiency. In addition, as‐fabricated QD‐LEDs employing Cl‐doped ZnMgO exhibit ≈1.8× higher peak EQE and ≈1.3× longer operational lifetime than undoped controls, with negligible positive aging signatures. This intrinsic ETL stabilization enables day‐0 calibration, improves uniformity and yield, and removes the need for storage‐driven conditioning—identifying single‐source chloride doping as a practical route to robust ZnMgO ETLs for display applications.

Memristors enable parallel computation in next‐generation memory systems. Among the materials investigated, colloidal quantum dots (QDs) are attractive owing to their size‐tunable electronic structure, solution processability, and versatile surface chemistry. Nevertheless, most QD‐based memristors exhibit digital resistive switching (D‐RS) with abrupt binary transitions, limiting their neuromorphic potential. Here, an InP/ZnSe/ZnS QD‐based memristor exhibiting analog resistive switching (A‐RS) is demonstrated through a multilayer ZnO/QD/ZnO architecture engineered to promote uniform areal charge trapping. ZnO nanoparticle interlayers enhance electron transport, block hole injection to suppress recombination, and induce interfacial trap sites via controlled oxidation of the QD surface. Additional thinning of the QD layer mitigates vertical trap accumulation, ensuring stable and spatially distributed conduction. The resulting device exhibits robust trap‐controlled A‐RS and reproduces synaptic behaviors, including excitatory/inhibitory postsynaptic currents and long‐term potentiation/depression. Benchmarking with hardware‐level neural network simulations demonstrates excellent performance, achieving recognition accuracies of 92% in the multilayer perceptron model and 87.3% in the convolutional neural network trained on the CIFAR‐10 dataset, both approaching the performance of an ideal memristor. These results establish a viable pathway for exploiting the intrinsic properties of colloidal QDs in high‐performance memristors, demonstrating clear advantages over conventional D‐RS counterparts and underscoring their potential for neuromorphic compute‐in‐memory architectures.

This work establishes dual design criteria for HTL-blended QD-LEDs: efficient hole transport and tolerance to local HTL/ETL electron leakage.

Quantum dot light‐emitting diodes (QD‐LEDs) have struggled with charge imbalance due to inefficient hole injection. Traditional strategies focus on enhancing the hole transport layer (HTL) and reducing the injection barrier at the HTL‐QD interface. Although these approaches improve hole injection at specific interfaces, they fail to ensure efficient hole injection across all interfaces in QD‐LEDs. Therefore, engineering the hole injection layer (HIL) is required to comprehensively address these challenges. Optimized HIL designs align the energy levels of the anode/HIL and the HTL, enable efficient hole injection, and suppress leakage current—thereby improving both performance and stability of QD‐LEDs. These findings highlight the importance of comprehensive HIL engineering. In this study, a multilayered HIL structure composed of a poly(9‐vinylcarbazole) (PVK): phosphomolybdic acid (PMA) layer coupled with MoO ₃ is proposed. The PVK:PMA layer forms charge‐transfer complexes (CTCs), enhancing hole injection into the HTL, while MoO ₃ scavenges excess electrons, thereby reducing non‐radiative recombination. Additionally, the high ionization potential (IP) of PVK:PMA alleviates the hole injection barrier that may arise from the MoO ₃ and the organic HTL. This HIL structure doubles the power efficiency and extends the device lifetime by six times compared with conventional designs, demonstrating its potential for high‐efficiency, stable QD‐LEDs.