Alexander Skyrme Urban

Colloidal perovskite nanoplatelets offer thickness-tunable, directional emission, but maintaining narrow ensemble photoluminescence linewidths at greater thicknesses remains challenging. Here, we show that under selected reaction conditions, distinct CsPbBr3 nanoplatelet thickness populations emerge in succession during synthesis, each offering a transient window for isolation before further morphological evolution. By tuning growth kinetics through precursor composition and overall dilution under ambient conditions, we make these windows experimentally accessible. In situ photoluminescence monitoring tracks the successive populations and guides the time-selective isolation of 4- and 5-monolayer nanoplatelets. The resulting ensembles exhibit narrow cyan emission with linewidths down to 70 and 80 meV, respectively. Post-synthetic surface treatment increases the photoluminescence quantum yield to 70 % while preserving narrow emission, and halide exchange extends the approach to red-emitting iodide nanoplatelets. These findings demonstrate that favorable nanoplatelet morphologies can be accessed as transient populations along a growth trajectory, establishing control over growth kinetics and isolation time as a strategy for obtaining narrow-emitting colloidal nanostructures.

Colloidal quantum dots (QDs) are promising for light‐emitting applications, but their synthesis under ambient conditions remains challenging. Here we present a rapid, room‐temperature (RT) method that produces highly stable QDs within minutes using the zwitterionic ligand 2‐ammonioethyl 2‐octyl‐1‐dodecyl phosphate (OD‐PEA). The strong binding of OD‐PEA enables precise size control and effective passivation, yielding blue‐emitting QDs () with narrow linewidths () and high photoluminescence quantum yields (up to 86 %). The QDs retain their optical quality for months in air and offer tunable emission from blue–cyan through ligand concentration, and from ultraviolet to deep red via halide exchange. A proof‐of‐concept perovskite light‐emitting diode (PeLED) fabricated from these QDs exhibits appreciable electroluminescence (EL) at with a low turn‐on voltage. This work establishes a simple and scalable strategy for producing stable, strongly confined perovskite QDs, advancing their potential for next‐generation optoelectronic and photonic technologies.

Colloidal nanocrystals exhibit high tunability and low-cost solution processing attractive for next-generation electronic applications. However, colloidal nanocrystals are inherently heterogeneous and the impact of this heterogeneity on device performance has been largely disregarded, since analytical techniques cannot assess the functionality of individual nanocrystals on a large scale. Here we introduce a rapid, in situ method to determine the size and quantum yield of thousands of individual nanocrystals within minutes, based on interferometric scattering microscopy and photoluminescence imaging. Monitoring the life cycle of CsPbBr ₃ perovskite nanocubes, our approach uncovers phenomena masked by bulk averaging. We find a substantial performance spread across the nanocubes and an anticorrelation of quantum yield and size. During a subsequent solution-phase defect engineering process, we uncover size-dependent enhancement kinetics, which initially favour the enhancement of smaller nanocubes. Finally, we image light-induced degradation by tracking the size reduction and photobleaching of single sub-20-nm nanocrystals, finding material loss decreases at higher laser powers due to the trapping of photoinduced electrons by the formed metallic lead.

Lead halide perovskite nanocrystals (PNCs) exhibit outstanding optical and electronic properties for next-generation optoelectronics; however, their instability under ambient conditions severely hinders their practical implementation. Here, we demonstrate a versatile ligand cross-linking approach via electron-beam irradiation that effectively enhances nanocrystal stability without compromising their exceptional optical properties. Electron-beam exposure induces cross-linking reactions within the native oleylamine and oleic acid ligand shell, forming a robust, interconnected organic network that substantially increases hydrophobicity, long-term ambient stability, and resistance to various solvents. Unlike polymer or micelle encapsulation strategies, our cross-linking method preserves the structural integrity of the PNC layer and its optical properties without introducing additional layers or barriers that could impede charge transport. We further exploit this technique to create unprecedented heterostructures, achieving dual-emission spectra without ion exchange. Additionally, we present a novel method for producing mechanically stable, freestanding PNC films, which significantly simplifies device fabrication. These findings open up new avenues for integrating highly stable perovskite nanocrystal layers into commercial-scale photovoltaic and optoelectronic devices.

Colloidal CsPbBr ₃ quantum dots (QDs) are promising for light-emitting applications, but their synthesis under ambient conditions remains challenging. Here we present a rapid, room-temperature (RT) method that produces highly stable CsPbBr ₃ QDs within minutes using the zwitterionic ligand 2-ammonioethyl 2-octyl-1-dodecyl phosphate (OD-PEA). The strong binding of OD-PEA enables precise size control and effective passivation, yielding blue-emitting QDs (474 nm) with narrow linewidths (25 nm) and high photoluminescence quantum yields (up to 86 %). The QDs retain their optical quality for months in air and offer tunable emission from blue-cyan through ligand concentration, and from ultraviolet to deep red via halide exchange. A proof-of-concept perovskite light-emitting diode (PeLED) fabricated from these QDs exhibits appreciable electroluminescence (EL) at 480 nm with a low turn-on voltage. This work establishes a simple and scalable strategy for producing stable, strongly confined perovskite QDs, advancing their potential for next-generation optoelectronic and photonic technologies.

This work investigates the growth mechanisms and optimization of optical properties in block copolymer (BCP)‐templated MAPbBr ₃ perovskite nanocrystals (PeNCs). Neutron scattering, transmission electron microscopy, and in situ optical spectroscopy studies combined with confinement‐model‐based size estimation of the nanocrystals during the perovskite formation revealed a complex multispecies growth behavior of BCP‐templated PeNCs, which was significantly influenced and could be controlled by systematically varying the stoichiometry between polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) and PbBr ₂ in the precursor, and the manner of adding the A‐cation either as a dispersion in a polymer solution or dissolved in methanol. The combination of optimized precursor stoichiometry and methanol‐based A‐cation addition yielded narrow emission linewidths of 83 meV and photoluminescence quantum yields of up to 87%. These findings provide new mechanistic insights and practical levers for improving BCP‐templated perovskite nanocrystals, paving the way for their application in future optoelectronic devices.

Single-particle optical spectroscopy has revealed the intrinsic photophysics of nanoscale materials, yet it remains largely confined to emission-based measurements. Direct and quantitative absorption spectroscopy at the level of individual nanosystems has been limited by insufficient sensitivity, leaving non-emissive and higher-lying electronic states experimentally inaccessible. Here, we introduce imaging cavity-enhanced absorption spectroscopy (iCEAS), a high-finesse microcavity platform that amplifies light–matter interaction by orders of magnitude and enables hyperspectral extinction imaging with parts-per-million sensitivity and sub-nanometer spectral precision. Using CsPbBr3 perovskite nanocubes as a model system, we directly measure spectrally resolved absorption cross-sections of clusters containing as few as three nanocubes and demonstrate linear scaling over nearly two orders of magnitude. Correlative atomic force microscopy enables extraction of an absolute single-nanocube absorption cross-section of (6.5 ± 0.6) × 10 ^-14 cm ² at 460 nm, in agreement with independent transient-absorption measurements. Beyond absolute quantification, iCEAS reveals size-dependent spectral shifts and degradation dynamics inaccessible to photoluminescence alone. By enabling correlative access to morphology, absorption, and emission within the same nanoscale object, iCEAS establishes a general framework for quantitative single-particle absorption spectroscopy across a broad range of nanomaterials.

Asymmetric photoluminescence (PL) lineshapes are a ubiquitous and defining feature of semiconductor nanocrystal ensembles, yet their microscopic origin has remained unresolved for decades. Here we show that ensemble PL can be quantitatively described by three statistically independent contributions: a Gaussian component encoding size dispersion, an exponential high-energy wing reflecting a Boltzmann-distributed exciton population, and a low-energy tail governed by exciton-phonon coupling and radiative recombination from disorder-localized states. This minimal formulation yields a generalized Gaussian asymmetric Laplace (GaLa) lineshape that accurately reproduces PL spectra across materials, morphologies, and temperatures. In the strongly confined two-dimensional limit, the low-energy wing transitions to a Lorentzian form, indicating the onset of a distinct exciton-phonon interaction regime captured by a second member of the same statistical family (GaLx). The parameters extracted from GaLa and GaLx provide direct, quantitative access to exciton thermodynamics and intrinsic energetic disorder from a single steady-state measurement. Together, these results establish a unifying statistical framework that reproduces the full ensemble PL lineshape from the strongly confined to the bulk-like limit, enabling predictive materials diagnostics and emission engineering across quantum-emitter platforms.

Precise and reproducible control over nanocrystal synthesis is essential for tailoring optical properties, yet remains a long‐standing challenge in halide perovskites. A broadly adoptable machine learning–guided framework, the Synthesizer, is introduced that combines Gaussian Process regression and Bayesian optimization with chemistry‐aware molecular encodings and systematic feature engineering. Rather than new algorithms, the advance lies in translating interpretable machine learning tools into a practical, benchtop platform for nanocrystal optimization under ambient conditions. Using CsPbBr ₃ as a model system, nm‐level precision in photoluminescence peak tuning (430 nm to 520 nm) is achieved, along with benchmark narrow linewidths down to 70 meV via lateral confinement control, and robust photoluminescence quantum yield optimization linked to surface trap density. Mapping the two‐dimensional parameter space (Cs/PbBr ₂ and antisolvent/PbBr ₂ ratios) across multiple antisolvents enables predictive optimization and identifies the antisolvent/PbBr ₂ ratio as a previously underappreciated mechanistic parameter, offering a quantitative basis for antisolvent‐accelerated nanocrystal growth. Transfer tests across distinct chemical spaces, including alcohols and cyclopentanone, confirm generalizability to unseen molecules, while application to CsPbI ₃ demonstrates extension to new material systems. These results establish an adoption‐ready platform for data‐efficient, uncertainty‐aware synthesis design, providing reproducible pathways to accelerate materials discovery beyond halide perovskites.