Lead halide perovskite nanocrystals (LHP NCs) are of broad interest as classical light sources (LED/LCD displays) and as quantum light sources. Their surface chemistry overwhelmingly dominates the subsequent utility. The NC core, in this case, is structurally extremely soft and practically any covalent or strongly coordinating bonding to the surface competes with the internal bonding, posing a great surface capping dilemma. In particular, the solvates of the lead ions or haloplumbates may outcompete the internal bonding. The ligands known to attach but not ruin the LHP NC are mostly binding through ionic bonding. We will review the pros and cons. of thus far successfully used cationic ligands, including the latest generation of sulfonium and guanidinium long-chain molecules [1,2], as well as stronger-binding commercial and synthetic phospholipids [3]. We will review distinct four cases of these ligands based on their tightness of binding as well as the dynamicity of binding. We show that the binding dynamics is crucial for photocatalytic applications of these nanocrystals, relying on photoinduced charge-transfer to the substrate molecule [4]. We will then discuss the prospects of thus far underinvestigated anionic ligands, focusing on head-groups bearing multiple oxide ions, as well as the importance of ligand-tail engineering [5]. We aim to address an overarching question: which surface chemistry should be pursued for optimal retention of the LHP NC structural and colloidal integrity – does an ideal ligand even exist? And if not, what guideline can we offer for diverse applications, including quantum light sources? The presentation will encompass the work of my interdisciplinary team and diverse international collaborators, whose names will be appropriately mentioned in the presentation and footnotes.

1. O. Kolomiiets et al. ACS Nano, 2025, 19, 30, 27860–27872.  

2. Y. Berezowska et al. J. Am Chem. Soc. 2025, in print

3. V. Morad et al. Nature, 2024, 626, 542–548

4. V. M. Amberg et al. J. Am. Chem. Soc., 2025, 147, 10, 8548–8558

5. V. Morad et al. submitted

Lead halide perovskite nanocrystals have emerged as promising candidates for light-emitting devices and quantum light sources due to their high photoluminescence quantum yield, narrow emission linewidths, and tuneable emission. The chemistry of the ligand shell plays a critical role in stabilising the nanocrystal surface and governing their optoelectronic performance, yet directly assessing surface quality remains challenging. In this talk, we correlate vibrational fingerprints with charge-carrier dynamics to reveal a cohesive picture linking ligand-induced surface disorder to the photophysical performance of perovskite nanocrystals. We further demonstrate ultralow-frequency Raman spectroscopy as a powerful and surface-sensitive probe for resolving subtle changes arising from nanocrystal size and ligand chemistry.

By investigating a size series spanning the strong- (5 nm) to weak-confinement (28 nm) regimes, we show that the linewidths of Raman-active phonon modes provide a highly selective metric of surface disorder and structural quality. Extending this approach to a set of 28 nm nanocrystals capped with four different zwitterionic ligands, we uncover clear correlations between ligand steric effects, surface disorder, and phonon broadening observed in the Raman response.

Complementary photoluminescence and terahertz photoconductivity measurements reveal an evident correlation of charge-carrier dynamics and radiative emission yields with ligand chemistry and surface quality inferred from phonon broadening. In particular, we show that surface defects preferentially trap hot carriers, thereby diminishing exciton stability and radiative recombination.

This work offers powerful insights into optimising nanocrystal-ligand boundaries to enhance the performance of nanoscale quantum light sources and optoelectronic devices.

Metal halide hybrids (MHHs) have emerged as a versatile class of materials due to their distinctive electronic structures, which endow them with optoelectronic functionalities suitable for a broad spectrum of applications, including photovoltaics, solid-state lighting, scintillation, photodetection, lasing, and ferroelectric technologies. Zero-dimensional (0D) MHHs comprising discrete metal halide units spatially isolated within an organic cation matrix represent a promising subclass for solid-state lighting, owing to strong exciton confinement within individual halometallate units and the resultant high radiative recombination efficiencies. However, potential difficulties with solubility and chemical incompatibility hinder large-scale utility of 0D MHHs for device applications.

To overcome these challenges, low-temperature melt-processing has emerged as a viable alternative, wherein effective suppression of the melting temperature (Tm) relative to the decomposition temperature (Td) is required. Such Tm suppression can be achieved through judicious selection of organic cations that promote the formation of stable liquid melts.

Here, we report a targeted molecular design strategy that enables access to ambient-stable, melt-processable supercooled liquid (SCL) multimetallic bromide hybrids incorporating Mn²⁺/Cd²⁺ or Mn²⁺/Zn²⁺ metal centers with benzyltributylammonium cations. These systems exhibit markedly low glass transition temperatures (Tg = 15-16 °C), substantially reduced melting points (Tm = 90–100 °C), Mn²⁺-activated green photoluminescence, and high optical transparency. Comprehensive structural, optical, thermal, and electronic-structure analyses elucidate the chemical design principles governing phase behavior and confirm the dopant-mediated luminescence mechanism. Rheological characterization validates the presence of the SCL phase, revealing pronounced thermal hysteresis and enabling quantification of relaxation time scales characteristic of metastable liquid states.

Collectively, this work introduces a new class of phase-engineered MHH materials with enhanced melt-processability suitable for molding and device fabrication, while establishing fundamental correlations between chemical composition, phase stability, and functional properties. These findings expand the accessible phase space of MHHs and provide a framework for rational design of hybrid materials exhibiting SCL behavior.

Perovskite luminescent materials have been extensively investigated owing to their strong excitonic effects, high photoluminescence quantum yield, and simple processability. Among them, structures integrating organic and inorganic components, such as conventional Ruddlesden-Popper layered perovskites, offer a degree of structural versatility that is difficult to achieve in other classes of luminescent materials. This tunability arises largely from the crucial role of the organic molecules, which act as an effective channel for modifying the crystallographic framework and, consequently, enabling emission tunability. Through appropriate ligand selection, it becomes possible to control emission bandwidth, color purity, and even promote the emergence of broadband or white-light photoluminescence. In this work, we investigate a family of organic cations by systematically varying the alkyl-chain length and the number of aromatic rings, using a straightforward room-temperature synthesis to evaluate their influence on the optoelectronic properties of the resulting structures. Our results reveal a clear morphological switch from typical platelet-like crystals to elongated microstructures as the alkyl chain supporting the aromatic ring increases in length. This morphological evolution is reflected in the emission behavior of the samples, with a transition from narrow blue to broadband white light, and quantum yields reaching up to 10% in perovskite-related structures that exhibit terraces or grooved surfaces. The interplay between organic cation bulk and packing constraints emerges as key parameters leading to the observed structural and optical changes. Our findings, therefore, provide valuable guidelines for identifying molecular descriptors in organic cations that can disrupt the conventional layered architecture and enable white light emission across distinct crystalline morphologies.

Understanding the relationship between the structural and optical properties of lead halide perovskite quantum dots (QDs) is crucial for their use in optoelectronics. Achieving this requires precise control during synthesis. However, the fast growth of highly ionic perovskite QDs and their dynamic surface passivation present significant challenges in managing their size, shape, and impurity doping during production. Although considerable progress has been made in controlling the size of perovskite QDs, especially CsPbBr₃, regulation of surface morphology and impurity doping remains difficult. Here, we first explain the growth mechanism of CsPbBr₃ QDs under thermodynamic equilibrium control, allowing gram-scale synthesis of strongly size-confined, monodisperse QDs.[1] Next, we describe how the surface facets of CsPbBr₃ QDs can be adjusted by annealing them with facet-selective dicationic ligands designed to match the geometric arrangement of Cs⁺ vacancies. Finally, we present a doping mechanism based on electrostatic surface Mn²⁺ adsorption, which enables efficient dopant incorporation into strongly confined CsPbBr₃ QDs with a Cs-deficient stoichiometry compared to undoped ones.[2] Our synthesis achieves a Mn²⁺ doping/alloying concentration of up to ~44%, with Mn²⁺ photoluminescence efficiency exceeding 90%. This allows for the determination of the intrinsic exciton-to-dopant energy transfer rate. Additionally, we will explore single-particle spectroscopy of precisely controlled perovskite QDs for single-photon sources.

Metal-halide perovskites exhibit bright and sharp luminescence, with optoelectronic and structural properties that can be tuned over a wide range through solution processing [1,2]. In this talk, I will discuss our realisation of linearly polarised luminescence from perovskite light-emitting diodes (LEDs) [3]. This is achieved by self-assembling CsPbI₃ nanoplatelets into an edge-up orientation. Through strong dielectric and quantum confinement, there is a large exciton fine structure splitting. As a result, we achieve strong emission from out-of-plane dipoles for the optically bright excitons in these superlattices. In light-emitting diodes, this leads to a high degree of polarisation (DOP) of 74.4% in electroluminescence [3]. I will discuss the design principles for passivating ligands to improve the luminescent properties [4], how the bulk composition could be engineered to improve stability [5], and how the coordinating ligands could be tuned to control the orientation of these nanoplatelet superlattices [6].

High-entropy alloying (HEA) has recently emerged as a powerful strategy for engineering structural stability and electronic functionality across a wide range of materials. While HEA concepts have been successfully applied to metallic alloys and oxide ceramics, their implementation in halide perovskite nanocrystals (PNCs) remains at an early stage. In particular, the potential of HEA to benefit quantum-light technologies, especially single-photon sources (SPSs) operating at room temperature (RT), has not yet been explored. 

Here, we report the first demonstration that HEA engineering intrinsically enhances radiative recombination, exciton coherence, and single-photon purity in PNCs. By incorporating transition metals (Mn, Zn, Ni) onto the B-site of CsPb(Cl/Br)₃ PNCs, we create a high-entropy crystal lattice that provides a fundamentally altered excitonic environment. Systematic photophysical measurements reveal that HEA-PNCs exhibit significantly faster radiative decay, suppressed trap-assisted recombination, and reduced electron-phonon coupling. In addition, we conducted ab initio molecular dynamics simulations that show that high-entropy incorporation leads to reduced phonon interactions and enhanced exciton coherence. Our HEA-PNCs achieve a single-photon emission purity of 96%, nearly complete blinking suppression, and excellent photostability at room temperature, representing the strongest intrinsic SPS performance ever reported for PNCs. Unlike previous approaches requiring plasmonic Purcell enhancement, ligand engineering, or low-temperature operation, our strategy uses a materials-intrinsic mechanism that is fully compatible with scalable colloidal synthesis. Overall, this work demonstrates that HEA is a powerful, generalizable design principle for achieving robust room-temperature quantum-light emission in perovskite nanocrystals.

Two-dimensional perovskite nanoplatelets (NPLs) promise atomically precise emission control—but achieving that precision in the flask is anything but trivial. Their formation teeters on a fine balance between solvent polarity, precursor chemistry, and the split-second timing of an antisolvent drop. In this talk, I will show how data and diffraction together can turn this delicate art into a predictable science. Using in situ X-ray scattering and photoluminescence, we uncover how emissive nanocluster intermediates evolve into either rods or platelets depending solely on the antisolvent’s dipole moment and hydrogen-bonding strength—essentially, how chemistry “decides” the dimensionality.[1] Building on this mechanistic insight, our machine-learning platform Synthesizer transforms these parameters into predictive maps of color, linewidth, and quantum yield.[2] Within just a few syntheses, it delivers nm-level precision over emission and aspect ratio, all under ambient conditions. Together, these studies define a quantitative recipe for crafting bright, narrow, and stable 2D NPLs—and hint at a future where algorithms, not trial-and-error, steer nanocrystal growth.

Low-dimensional perovskites, such as zero-dimensional nanocrystals and two-dimensional perovskites, are of great interest for various photonic applications. In this talk, I will highlight how the synthesis of such materials can impact their structural, optoelectronic, and stability properties. I will also present various methods for microstructuring low-dimensional perovskites into photonic structures, either by template-assisted self-assembly or dry processing onto pre-designed micropatterns.

Halide perovskites are fascinating semiconductors for light-emitting applications. Compared to conventional inorganic covalent semiconductors like silicon or GaAs, perovskites are structurally soft and often more disordered. Understanding the consequences of this remains a key challenge for commercialization but offers also opportunities for tailoring properties to target applications.

Here I will present our recent mechanistic insights from spectroscopy on the role of composition, doping and dimensionality to control light emission through localization effects in low-dimensional halide perovskite emitters.

I will present the intriguing photophysics of a new 2D germanium perovskites, with properties in some respects even outshining their lead analogues, and then will introduce a new synthesis route to ambient doping of 0D nanocrystals in the strong confinement regime, giving for the first time access to strongly confined, yet transition-metal doped perovskite nanocrystals, with profound consequences for the light-emitting properties of the resulting materials. Overall I will highlight the promise these solution-processable materials hold for low-cost optoelectronic technologies with custom-tailored properties.

As a novel light source technology, perovskite light-emitting diodes (PeLEDs) have achieved external quantum efficiencies comparable to OLEDs, and with superior colour space coverage. In this talk, we discuss some key considerations behind the high efficiencies and the potential mechanisms that may approach or exceed the efficiency limits. We focus on the critical challenges in this field, including device instability, brightness and downscaling. We have demonstrated, for the first time, that ultralong operational lifetimes satisfying the practical demands can be achieved in perovskite LEDs. We show that it is possible to control the p- and n-type behaviours in emissive perovskite semiconductors, enabling ultra-high brightness of 1.16 million nits in perovskite LEDs, setting a brightness record for solution-processed LEDs. Our efforts of downscaling micro- and nano-perovskite LEDs to below the size limit of conventional LEDs are presented, showcasing the potential of micro/nano-PeLEDs for next-generation display technologies. Finally, we present our results on the first electrically-driven perovskite laser and its potential as a new semiconductor laser technology.

Lead-halide perovskites have rapidly established themselves as a new class of semiconductor materials with outstanding optical properties and technological promise [1,2]. Nanoplatelets (NPLs) of these materials exhibit extreme quantum and dielectric confinement, resulting in strongly modified exciton manifolds compared to their bulk and nanocrystal counterparts. Understanding the fine structure and optical selection rules of these excitons is essential for advancing perovskite-based quantum photonic devices.

Here, we investigate the electronic structure and excitonic emission pathways of single 2-monolayer CsPbBr₃ nanoplatelets, combining polarization-resolved micro-PL spectroscopy at 10 K with variational and k·p modeling that explicitly incorporates finite-well confinement, dielectric contrast, Coulomb interaction, and crystal-field contributions.

Our calculations predict a four-level band-edge exciton manifold composed of one dark state and three bright states, split by a combination of orthorhombic crystal field terms, extreme confinement, and anisotropic dielectric screening. The bright manifold divides into two strongly allowed in-plane dipole states and a suppressed out-of-plane exciton whose oscillator strength is quenched by dielectric screening effects [3-5].

Experimentally, single-NPL µ-PL spectra reveal polarization-orthogonal bright doublets with ≈2 meV splitting, unambiguously resolving the in-plane exciton states in the orthorhombic phase. Temperature-dependent time-resolved PL, interpreted through a two-phonon bright–dark mixing model, yields bright–dark splittings consistent with our theoretical predictions and recent high-resolution studies [6].

This combined theoretical–experimental approach provides a comprehensive picture of exciton fine structure under ultra-strong confinement, revealing the emergence of anisotropic emission channels and the suppression of out-of-plane excitonic transitions. These insights establish atomically thin CsPbBr₃ nanoplatelets as promising platforms for polarization-defined light sources, quantum emitters, and engineered excitonic materials in next-generation optoelectronic and quantum technologies.

Halide perovskites exhibit remarkable optoelectronic properties that make them exceptional candidates for high-performance absorbers in perovskite photovoltaics and for bright emitters in light-emitting devices, lasers, and quantum photonic applications. Power-conversion efficiencies in perovskite solar cells have now surpassed 25%, and external quantum efficiencies in perovskite LEDs have exceeded 20%. These rapid advances are driven by their extraordinary intrinsic attributes, including strong optical absorption, defect tolerance, substantial spin-orbit coupling, long and balanced charge-carrier diffusion lengths, slow hot-carrier cooling, ion transport, and radiation hardness.

As a result, the scope of perovskite applications has expanded far beyond solar cells and LEDs to encompass spintronics, radiation detection, memristor devices, bioimaging, and quantum light sources such as single-photon emitters. Their structural versatility and diverse dimensionalities offer powerful handles for tailoring photophysical behavior ranging from surface engineering of colloidal perovskite nanocrystals via a rich ligand toolbox to energy-landscape manipulation in layered perovskites using a wide variety of large organic cations.

In this talk, I will discuss key photophysical mechanisms in low-dimensional perovskite emitters, focusing on colloidal nanocrystals and layered perovskites. I will also highlight our recent progress in engineering perovskite single-photon emitters and perovskite superlattice superfluorescence.

Understanding and controlling interfacial photophysics in perovskite nanocrystal (NC) hybrids is essential for designing next-generation light-harvesting and energy-conversion systems [1]. Metal halide perovskite NCs offer defect-tolerant electronic structures, sizeable oscillator strengths, and tunable excitonic properties that make them ideal donors for driving interfacial energy or charge transfer events. However, the rational design of functional NC–acceptor hybrids requires elucidating how surface chemistry, electronic coupling, and exciton dynamics govern these processes. Herein, we present two complementary works in which CsPbBr₃ NCs are interfaced with molecular acceptors to enable unidirectional transfer of energy or charge to surface-immobilized functional dyes.

In the first approach, CsPbBr₃ NCs are coupled to carboxylated zinc phthalocyanines (ZnPc), yielding a hybrid that mediates an unusual Dexter-type singlet energy transfer (DET) from the NCs to the dye. The strong NC–dye interaction induces, on one hand, the disaggregation of ZnPc molecules on the NC surface—enhancing the inherent photophysical properties of the dye—and, on the other hand, the creation of new surface trap states that open nonradiative pathways, partially reducing energy transfer efficiency. Nonetheless, the resulting CsPbBr₃@ZnPc hybrid operates as an efficient photosensitizer, prolonging triplet-state lifetimes and generating singlet oxygen almost quantitatively upon selective NC excitation [2].

In a second approach, surface-engineering CsPbBr₃ NCs with functional perylenediimides (PDIs) bearing phenyl or phenylpropyl carboxylic spacers produces hybrid systems, that is, NC@PDI-Ph and NC@PDI-PhPr, with well-defined spacer-dependent charge-separation and recombination dynamics. Global target analyses of transient absorption data demonstrate unidirectional electron transfer from the NCs to the PDIs upon excitation of either component. The resulting charge-separated states (CSS) persist on the tens-of-microseconds timescale (34 µs for NC@PDI-Ph and 63 µs for NC@PDI-PhPr), and spacer tuning provides precise control over recombination kinetics [3].

A comprehensive temporal and mechanistic picture of both hybrid systems is established using an arsenal of spectroscopic techniques—steady-state optical spectroscopy, ultrafast, nanosecond, and microsecond transient absorption, time-correlated single-photon counting, and global target analyses—all of which reveal how distinct excitonic components in the NCs drive the observed transfer pathways.

Taken together, these results establish metal halide perovskite NCs as versatile platforms for programming interfacial photophysics, enabling the rational design of hybrid materials for photocatalysis, energy harvesting, and optoelectronic architectures.