Colloidal quantum dots (CQDs) represent a groundbreaking technology reshaping the landscape of commercial imaging and display solutions. This talk explores the rapid advancements in quantum-dot semiconductors, examining their unique properties and addressing the challenges they face in competing with state-of-the-art epitaxially grown compound semiconductors.  Among the critical factors for commercial viability are material selection, suitable photodiode architecture, and scalable production methods. The presentation will address the important question: "How can we create a high-performance semiconductor from quantum dots?" Special attention will be given to manufacturing techniques, discussing the economic feasibility of scaling up to large wafer processing. Highlighting recent breakthroughs, we will showcase successful integrations of PbS QDs into compact, lightweight, low-power, and cost-effective imaging systems, emphasizing their potential as ideal candidates for next-generation shortwave infrared (SWIR) cameras and advanced imaging applications. The talk will also cover the challenges and opportunities in the commercialization process, including regulatory nuances, safety considerations, and strategies for reducing production costs.

Near- and short-wave infrared (NIR/SWIR) active quantum dots have attracted considerable interest for applications in biotechnology, energy conversion and optoelectronics. Most research has been conducted on binary lead- and mercury-based QDs due to the comparable simplicity of their synthesis and their outstanding properties. RoHS (Restriction of Hazardous Substances in Electrical and Electronic Equipment)-compliant III-V compounds such as InAs and InSb are currently emerging, but their more covalent character, high oxidation sensitivity and scarcity of appropriate group-V precursors make it much more challenging to achieve precise control of their size, shape and surface state.

This presentation will focus on novel types of PbS-based core/shell structures. For the PbS core QD synthesis, a library of thioureas was synthesized as the sulfur precursors, which gave rise to a broad size range, excellent monodispersity and high reaction yield. This approach was also adapted to the continuous flow synthesis of larger amounts of QDs. A widely adopted strategy to enhance the PLQY of PbS QDs consists of their overcoating with a CdS shell using Pb/Cd cation exchange. Nonetheless, this procedure leads to a continuous blue-shift of the emission wavelength with proceeding cation exchange, while the PL intensity goes through a maximum, making it difficult to optimize the emission for a desired wavelength. To avoid cation exchange, we added an intermediate buffer shell of ZnS on the PbS core QDs before growing the CdS shell. We present the optical and structural properties of the novel PbS/ZnS/CdS core/shell/shell QDs as a function of the different shell thicknesses and compare them with results from ab-initio simulations on slabs of these structures. In an extension of this study, PbS/CdS QDs obtained via cation exchange have been overcoated using a reactive monomolecular precursor to obtain PbS/CdS/CdS thick-shelled QDs. Finally, recent advances in the synthesis of InAs-based core/shell structures will be presented.

Photodetectors in the short-wave infrared (SWIR: 1-1.7 µm) range have garnered significant attention due to the growing demand for 3D imaging and facial recognition technologies. The inherent transparency of silicon above 1 µm wavelength and the intricate integration processes of III-V materials restrict conventional technologies from effectively addressing this spectral region. In this context, it has become essential to explore alternative photodetector materials. Among the candidates for SWIR sensing, lead sulfide quantum dots (PbS QD) are very promising for integration as active material due to their strong, size-tuneable absorption at targeted infrared wavelengths. However, when exceeding a specific nanocrystal size, these QD are prone to surface oxidation and aggregation limiting their performances and integration in sensor devices. [1]

Among several strategies developed to passivate and deposit these QDs as thin layer, one of the most promising is to combine them with halogenated perovskites. [2] Inspired by this approach, we investigated and optimized all the steps, from the synthesis of the PbS QD to their integration in the perovskite matrix. An efficient solution exchange of long-chain ligands on the surface of QDs with perovskite precursors is performed and confirmed through FTIR, NMR, and XPS measurements. The relevance of this perovskite shell around the QD is explored optically (PL, Abs spectroscopy) revealing significantly improved luminescence stability under ambient atmosphere for more than 2 months in thin films. To facilitate thin film fabrication, we developed a stable ink based on the ligand-exchanged QDs and perovskite precursors. The optimized inks are stable for days in suitable solvents for film deposition. This new approach enables one-step thin film deposition compared to the multi-step approach required to manage organic ligand exchange. The solution-processed perovskite-exchanged PbS QD strategy was devised to produce reproducible and homogenous thin films absorbing in the desired NIR spectral region which are further integrated into devices. This study covers fundamental understanding of the exchanged quantum dot system and explores its photodetector performance.

The colloidal synthesis of two-dimensional (2D) lead chalcogenide semiconductors yields near-infrared emissive materials with strong excitonic contribution at room temperature.^[1-4] They are model systems for efficient charge carrier multiplication and hold potential as intriguing candidates for fiber-based photonic quantum applications. However, synthetic access to the third family member, 2D lead telluride (PbTe), remains elusive due to a challenging precursor chemistry. Here, we report a direct synthesis for 2D PbTe nanoplatelets (NPLs) with tunable photoluminescence (PL, 910 – 1460 nm (1.36 – 0.85 eV), PLQY 1 – 15 %), based on aminophosphine precursor chemistry.^[1] Our NMR study underpins the synthetic importance of an ex-situ transamination of tris(dimethylamino)phosphine with octylamine to yield a reactive tellurium precursor for the formation of 2D PbTe NPLs at temperatures as low as 0 °C. Associated GIWAXS measurements confirm the 2D geometry of the NPLs and the formation of superlattices. The importance of a post-synthetic passivation of PbTe NPLs by PbI₂ to ensure colloidal stability of the otherwise oxygen sensitive samples is supported by X-ray photoelectron spectroscopy. Our results expand and complete the row of lead chalcogenide-based 2D NPLs, opening up new ways for further pushing the optical properties of 2D NPLs into the infrared and toward technologically relevant wavelengths.

Core/shell (c/s) semiconductor nanocrystals (NCs) are key building blocks in modern optoelectronic devices. The specific core and the shell materials determine the alignment between valence- (VB) and conduction-band (CB) energy levels. Because photogenerated electrons (e^-) and holes (h⁺) relax to their lowest and highest available energy levels, respectively, these carriers are confined to the core and away from the surface in type-I c/s NCs, resulting in high photoluminescence (PL) stability and efficiency. In contrast, c/s NCs with a reverse-type-I configuration are highly susceptible to the environment as both carriers localize on the shell and are easily extractable by charge scavengers. In a type-II configuration, one of the semiconductors has both higher (or lower) VB and CB values, resulting in one carrier being confined to the core and the other to the shell. The presence of physically separated e^-–h⁺ pairs (excitons) gives type-II c/s NCs long PL lifetimes. In the presence of quantum confinement, the exact size of the core and shell open a continuum between quasi-type-II—with only partial delocalization of one of the carriers, for example—and true type-II configurations.

Here, we report the synthesis and structural characterization of PbCh/AeCh core/shell nanocrystals (Ae = Ca, Sr, Ba; Ch = S, Se). Using a new synthesis developed by us, we have successfully passivated PbS or PbSe cores with alkaline-earth (Ae) chalcogenide shells. For example, PbS/SrS and PbSe/SrS are near-IR active NCs with PL maxima ranging between ~1000–2000 and 1500–2300 nm, respectively. Colloidal epitaxy in this system is possible thanks to both core and shell materials adopting identical rock salt crystalline structures, with a lattice parameter mismatch of ≤ 5% for SrS, CaSe, and SrSe (Figure). We predict that these materials will be more robust and, because the lead-based core is buried inside the NCs, potentially less toxic and more biocompatible compared to other bare lead-based materials.

In recent years, metal chalcogenides have emerged as prominent candidates as low-cost catalysts in renewable green technology applications. The scientific community has expressed significant interest in hydrogen production due to its potential as a clean alternative to fossil fuels, devoid of CO₂ emissions, and its impressive energy density. ¹

This project focuses on investigating NiSe, CoSe, and their ternary compounds, selected for their noteworthy electro-catalytic and photothermal properties, which raise the ability to generate a substantial increase in temperature, and enhance reaction kinetics (as per Arrhenius). ²

Previous efforts in this project concentrated on synthesizing, characterizing, and examining the basic electrochemical and photothermal properties of nanostructures. Synthesis of NiSe, CoSe, and ternary compounds with varying metal ratios yielded hexagonal nanoparticles in the 15-30 nm size range. These nanoparticles exhibited enhanced electro-catalytic activity in the hydrogen evolution reaction and demonstrated significant heating performance across different solvents and electrolytes. Furthermore, these nanoparticles were employed in advancing solar-driven membrane distillation technology, as part of a collaborative endeavor with Italian researchers. ³

Subsequently, the focus shifted to developing stable and suitable fluorine-doped tin oxide (FTO) electrodes for a new system, allowing the investigation of how the photothermal properties of nanoparticles influence the kinetics of the electrochemical hydrogen evolution reaction under illumination. A comprehensive analysis of kinetic parameters, including the activation energy of nanoparticles under various conditions, was conducted. These values offer insights into the degree to which temperature variations can impact the kinetics of an electrochemical reaction. Moreover, they can provide additional explanations for the differences in the activity observed among various catalysts. ⁴ In some instances, the nanoparticles exhibited lower activation energy than platinum (Pt). Additionally, an initial experiment was conducted integrating the new electrodes and the new system. Future work will focus on optimizing the new setup and exploring catalytic activity under illumination by leveraging the photothermal effect.

Wet chemical synthetic routes for transition metal dichalcogenides (TMDCs) of the composition MX₂ (M = Mo, W; X = S, Se), which have been studied extensively in the past, yield colloidal inks of ultrathin (mono- and bilayer) laterally smaller nanoplatelets (NPLs) and laterally larger nanosheets (NSs) with interesting photophysics.[1-5] In contrast, the telluride analogues remain elusive, with only MoTe₂ nanocrystals being synthetically accessible in the semimetallic 1T' phase,[6] despite the fact that their direct band gap in the NIR region (0.95 eV[7]) make semiconducting MoTe₂ monolayers a promising candidate for fibre-optic applications in the O-band.

One major challenge in synthesizing semiconducting MoTe₂ is the small difference of only 35 meV between the semiconducting (stable) 2H phase and the semimetallic 1T' phase,[8] making it difficult to target one phase over the other during the reaction. Meanwhile the transformation between the 1T' and 2H phase is unfavored at typically accessible reaction temperatures in colloidal systems (~ 300 °C).[6,8]

In addition, reactive tellurium sources are scarce and often require more sophisticated tailoring of the precursor chemistry in comparison to sulfur and selenium. Here we adapt a synthesis using TeO₂ and thiol precursor chemistry[9] to yield MoTe₂ and WTe₂ NPLs primarily consisting of the 2H phase, which we substantiate using insights from spectroscopic and microscopic analyses.

The electrochemical reduction of nitrate (NO_₃^⁻) to ammonia (NH_₃) offers a sustainable approach to minimize nitrate pollution while generating valuable chemicals. This study focuses on the functionality of copper-based catalysts, specifically Cu₃N, Cu₂O, CuO, and Cu₃P, in promoting this reaction. Utilizing 0.1 M phosphate-buffered saline (PBS) as the electrolyte, a systematic investigation of the performance and stability of these catalysts is conducted. It was revealed that Cu₃N’s surface was modified during catalysis to CuO. Post-catalysis characterizations were conducted to understand these transformations, revealing significant insights into the stability and activity of the oxidized forms. The findings indicate that Cu_₂O and CuO exhibited comparable activity to Cu_₃N after the oxidation process. Additionally, the relatively unexplored realm of transition-metal nitrides and phosphides presents a fertile ground for further research. The inclusion of Cu_₃P highlighted its distinct potential in nitrate reduction applications, demonstrating greater activity in hydrogen evolution compared to the other copper species. The comprehensive evaluation of Cu_₃N, Cu_₂O, CuO, and Cu_₃P provided a nuanced understanding of copper-based catalysts, laying the groundwork for future advancements in electrochemical nitrate reduction studies.

Group V (bismuth and antimony) containing copper chalcogenide-based nanostructures are an environmentally benign class of compounds for employment in potential energy storage and conversion applications. We investigate the mechanistic insights in the colloidal synthesis of this class of materials and harness them in various applications. The colloidal approach for synthesis of most heterostructured/ multicomponent nanocrystals (NCs) typically proceeds via the formation of binary semiconductor NC seeds. Contrary to this, a lesser explored pathway involves liquid droplets for catalysing the growth of the semiconductor NCs, known as the solid-liquid-solid (SLS) mechanism This offers facile control over the reaction kinetics with the variation of the nature of the metal seed catalysing the growth process. Using this approach, we synthesized Bi-Cu_2-xS heterostructures with tuneable Cu_2-xS stem. The stability of the Cu thiolate intermediate formed in the reaction could be varied by modification of the alkyl phosphonic acid used, which in turn controls the number of Cu_2-xS stems in the heterostructures. The advantages of the branched morphology were examined by assessing the electrochemical performance of the single stem and multi stem Bi-Cu_2-xS NCs anodes in K⁺ ion batteries. Multiple stem NCs show enhanced cycling stability and rate capability with higher specific capacity (∼170mAh·g−1 after 200 cycles) than the single pods (∼111mAh·g−1 after 200 cycles).[1] Following this work, we synthesized multinary anisotropic Cu-Bi-Zn-S nanorods (NRs) via the SLS mechanism wherein in situ generated Bi NCs catalyses the formation of Bi-Cu_2-xS heterostructures which eventually transforms into homogeneously alloyed quaternary Cu-Bi-Zn-S NRs. We observe that the reaction proceeds through the dissolution of the metallic bismuth seed into a trisegmented heterostructure with a Bi-rich BixCuySz phase, a Cu-rich BixCuySz stem, and an alloyed transitional BixCuySz segment present at the heterointerface. Finally, the formation of the homogenous NRs is facilitated by the gradual dissolution of the Bi-rich seed and recrystallization of the Cu-rich stem into the transitional segment. The NRs exhibit promising thermoelectric properties with very low thermal conductivity values of 0.45 and 0.65 W/mK at 775 and 605 K, respectively, for Zn-poor and Zn-rich NRs.[2]

Our interest in exploring multinary group V containing colloidal nanostructures also led to the direct synthesis of quaternary compositions of Cu-Sb-S-based NCs. We developed a hot injection synthetic pathway for three substituted tetrahedrites compositions i.e., Cu₁₀Zn₂Sb₄S₁₃, Cu₁₀Ni₂Sb₄S₁₃, Cu₁₀Co₂Sb₄S₁₃. Balancing the precursor reactivities of constituent species was crucial for obtaining phase pure and better size distribution of the NC ensemble. All the synthesized substituted tetrahedrites exhibited lower thermal conductivity while Cu₁₀Ni₂Sb₄S₁₃ exhibited the highest electrical conductivity thus making them promising candidates for thermoelectric applications. [3]

Our quest for developing compositionally complex nanostructures led to pushing our limits from quaternary nanostructures to emerging high entropy materials. High entropy materials are defined as materials containing more than 5 constituent elements with 5-35% of each element and crystallizing in a single phase stabilized by a high configurational entropy. The presence of multiple cations with different reactivities towards the chalcogenide species results in the formation of additional byproducts in the reaction leading to the emergence of a multiphase system in a conventional hot injection or heat-up colloidal synthesis pathway for high entropy materials. Therefore, the design of these nanostructures requires strategic techniques to avoid phase separation. Using cation exchange as a tool we use our preformed multicomponent group V containing copper chalcogenide-based NCs as templates for the subsequent diffusion of additional cations in the chalcogenide phase resulting in the synthesis of the target single-phase high entropy NCs.

Colloidal semiconductor Quantum Dots (QDs), often considered as artificial atoms, have reached an exquisite level of control, alongside gaining fundamental understanding of their size, composition and surface-controlled properties, as recognized by the Nobel prize in Chemistry 2023. Their tuned characteristics and scalable bottom-up synthesis accompanied by the applicability of solution based manipulation, have led to their wide implementation in displays, lasers, light emitting diodes, single photon sources, photodetectors and more.

For the next step towards enhancing their functionalities, inspired by molecular chemistry, we introduce the controlled linking and fusion of two core/shell quantum dots creating an artificial molecule manifesting two coupled emitting centers. Accordingly, the coupled colloidal quantum dot molecules (CQDMs) present novel behaviors differing than their quantum dot building blocks. First, two types of biexcitons coexist as observed via heralded spectroscopy. Moreover, such CQDMs open the path to a novel electric field induced instantaneous color switching effect, allowing color tuning without intensity loss, that is not possible in single quantum dots. All in all, such quantum dot molecules, manifesting two coupled emission centers, may be tailored to emit distinct colors, opening the path for sensitive field sensing and color switchable devices such as a novel pixel design for displays or an electric field color tunable single photon source

Semiconductor quantum dots and quantum shells with complex confinement potentials are promising scintillators. They can demonstrate intense, fast, and durable scintillation under X-ray or electron excitation. Photon yields can reach greater than 100 photons/keV, exceeding typical scintillation standards, driven by structurally-engineered slowed Auger recombination and consequent radiative biexciton emission. This remains true even with several electron-hole pairs in the nanoshell. The single nanosecond lifetime of the quantum dot and quantum shell scintillators is much faster than typical standards with no afterglow. Fast scintillation improves frame rates in imaging, potential in tomography imaging, and typically also improves energy resolution. The samples can maintain bright scintillation performance under intense synchrotron X-ray excitation for at least 10 hours, equivalent to c. 1 million hours with a normal laboratory source. Using micrometer thick films to perform imaging, resolution of 20 lines/mm can be achieved. Based upon these results and performance metrics reported in literature, some general design strategies will be discussed with particular attention to materials which are strong performers as laser media and single photon sources. Furthermore, the predictive capacity of using more accessible laser-based spectroscopy experiments will be highlighted.

The direct wet-chemical synthesis of 2D lead chalcogenide nanoplatelets yields photoluminescent materials with strong excitonic contribution at room temperature. [1-4] In the spirit of the recent Nobel prize for the discovery and synthesis of quantum dots (QDs) we report herein on our studies of strongly confined wet-chemically synthesized flat 2D PbSe QDs. These 2D nanocrystals have lateral dimensions of e.g. 6 x 5 nm^2, a thickness of 1-3 PbSe monolayers and exhibit PL in the NIR between 860 – 1510 nm with a PL quantum yield of up to 60 %. [2,3] The highly efficient PL at fiber-optics-relevant telecommunication wavelengths renders colloidal lead chalcogenide 2D semiconductors intriguing materials for future solution-processable optics. Scanning tunnelling spectroscopy (STS) of single flat PbSe QDs revealsa conduction and valence band density of states that is typical for QDs rather than a steplike function linked to 2D nanoplatelets and substantiates the strong confinement in the flat PbSe QDs. Our experimental observations are supported by theoretical calculations of the electronic band structure using the tight-binding approach. 

In the second part of the talk I will focus on colloidal 2D PbS nanoplatelets (NPLs) with a thickness of 1-2 nm. [4] The PbS NPLs exhibit excitonic PL at 720 nm, directly tying to the typical PL limit of unmodified CdSe NPLs. In the first comprehensive study of the low-temperature PL from PbS NPLs we observe unique PL features in single PbS NPLs at 4 K, including narrow zero-phonon lines widths down to 0.6 meV. Time-resolved measurements identify trions as the dominant emission source with a 2.3 ns decay time. Sub-meV spectral diffusion and no immanent blinking over minutes is observed, as well as discrete jumps without memory effects. These findings advance the understanding and underpin the potential of colloidal PbS NPLs for optical and quantum technologies. [5]

Transition metal dichalcogenides (TMDCs) are highly researched photonic two-dimensional (2D) semiconductors. Among other members of the TMDC group, WS₂ shows remarkably high nonlinear susceptibility owing to its lack of inversion symmetry.^[1] This effect is observed for all odd-numbered WS₂ layers but is especially strong in monolayers and can be further increased by strain,^[2] while defective crystal structures lead to inversion symmetry breaking of even-layered WS₂.^[3]
The ability of TMDCs to yield stable monolayers with rich exciton physics^[4] inspired the wet-chemical synthesis of MoS₂^[5,6,7] and WS₂^[6,8] as well as their respective Mo1-xWxS2 alloys^[9] and heavier chalcogenides (Se ^[10] and Te). With the scalable bottom-up approach, predominantly atomically thin^[9] nanosheets (NSs) with controlled crystal phase-^[5,6], size^[5]- and composition^[9] are obtained and can be readily processed in solution or after precipitation. Comprehensive characterization via HR-TEM, Raman spectroscopy, and steady-state absorption spectroscopy confirms the synthesis of primarily monolayered semiconducting NSs with a narrow lateral size distribution (5-25 nm).

Here, we investigate the non-linear optical response of colloidal WS₂ with a femtosecond-laser-pulsed confocal mirror microscope. Our study includes one- and two-photon photoluminescence and efficient second harmonic generation (SHG) of colloidal WS₂ monolayers. The power-dependent SHG intensities from the colloidal WS₂ monolayers show steeper slopes than the commercially available CVD-grown WS₂ flakes, indicating a higher non-linear susceptibility for colloidal WS₂.
These results highlight the exceptionally high non-linear response in colloidal WS₂, underscoring the potential of colloidally synthesized WS₂ as functional 2D semiconductors.

Forming complex structures of functional materials in a controlled and reproducible fashion is a well-known challenge. [1,2] Specifically, bimetallic phosphides are of interest for energy-related applications; however, a satisfactory structure-function relationship has not been fully deciphered yet. In this work, we show that a colloidal chemistry approach produces bimetallic phosphides electrocatalysts of Co and Cu, size range 40-100 nm, where segregation and phase transformation induce significant changes in morphology compared to solid solutions. Their complexity permits the tuning of the catalytic sites to the hydrogen and oxygen evolution reactions (HER and OER), allowing the bimetallic phosphides to catalyze the full water splitting reaction. The experimental results show that in alkaline medium water cleavage is particularly favorable on CuxCoyP catalysts (and especially when x = 50%), enhancing their HER performance with an overpotential of 184 mV @ 10 mA/cm2. As for the OER enhancement, the results show that the bimetallic phosphides undergo a surface transformation during the OER, whereby (oxy)hydroxides form at anodic potentials in alkaline solution and serve as the actual electrocatalysts. The best OER performance was displayed by Cu25Co75P having an overpotential of 283 mV @ 10 mA/cm2. [3] Additionally, these CuxCoyP catalysts offer promising functionality towards methanol oxidation reaction (MOR) without fully oxidizing it to CO2 and rather producing beneficial product formate (HCOO-), displaying a lower overpotential by up to 180 mV as compared to OER and a higher mass activity. At 1.52 V and on passing 300 C charge the Faradaic efficiency for formate production is 100% in case of both the bimetallic and monometallic phosphides. This kind of selective oxidation of methanol is highly desired in direct alcohol fuel cell applications. [4]

The safety and stability concerns with liquid electrolytes of Li batteries are prompting their replacement by solid-state conductors; however, ion mobilities of conventional solid electrolytes do not match up to their liquid counterparts. To address this challenge, we have been exploring fast-ion or superionic solids based on earth abundant selenides and sulfides, where cations form a “liquid-like” network within a rigid anion cage allowing cation mobilities rivaling those of liquid electrolytes. Whereas superionicity is attained in these materials only at elevated temperatures, we find that in nanocrystals of copper selenide and sulfide the superionic phase is attained at lower temperatures than in the bulk. From electronic structure investigations and in-situ electron microscopy studies of copper selenide, we find that the key factor in this effect is compressive strain prevalent in nanocrystals, which also makes ion-transport pathways energetically feasible. Superionic transport achieved in nanostructures can be extended to macroscopic length scales by assembling solids from the nanostructures. Copper selenide nanowires exhibit an ionic conductivity of 4 S/cm which is an order-of-magnitude higher than that in bulk copper selenide. This record high conductivity results from the combination of crystalline paths for conduction in the axial direction with nanoscale confinement in the radial direction. These advances pave the way for fast-ion solid electrolytes.

Electrochemical nitrogen reduction reaction (NRR) is an environmentally friendly alternative strategy to the high energy consumed and high carbon released Haber–Bosch process for NH₃ production. Nevertheless, it is limited by a low ammonia yield and faradaic efficiency (FE) due to (i) the complexity associated with the breaking of the N≡N bond and (ii) the competing hydrogen evolution reaction. The primary challenge for NRR is the development of highly efficient electrocatalysts which will be able to tackle these hindrances effectively and convert N₂ to NH₃ under benign conditions, with minimal energy input. This presentation will dive into the concept of exploring surface engineering strategies of 2D materials such as defect engineering and heterojunction formation that can enhance the catalytic activity of the NRR process. We will showcase two main examples: the electrochemical dealloying of exfoliated 2D-PdBi₂ nanoflakes into palladium hydride (PdH_x, x ≤ 2) in addition to the formation of the MoS2/rGO heterostructure which significantly enhance NRR and dwell on the mechanisms. The applied design ideas, synthetic methods, and catalytic performance of the 2D catalysts will be described with the fabrication of mechanisms to inspire more practical design strategies for NRR electrocatalysts.

In the last decade, lead halide perovskites have revolutionized material science with their remarkable charge mobility, light absorption, and adjustable band gaps, all achieved through low-temperature processing.[1] However, their instability and toxicity limit their broader application. Despite these challenges, perovskites hold great potential for future energy technologies, spurring the development of "perovskite-inspired" materials (PIMs). In this aspect, the scientific interest has recently shifted to alkali metal-based chalcogenides, which represent a new category of semiconducting inorganic compounds and are being explored as potential candidates in the quest for novel energy materials. Recently, the focus has shifted to alkali metal-based chalcogenides as promising semiconductors for energy materials. Ternary alkali-metal dichalcogenides {AMeE (A = Li, Na, K, Rb, Cs; Me= Metals E = S, Se, Te} are identified as potential candidates for energy conversion and storage.[2] While high-temperature solid-state synthesis often results in limited phase control, wet chemical synthesis offers a promising alternative by producing uniform nanoscale particles and providing insights into their formation.[3,4]

Building on several theoretical and experimental studies on cesium copper-based chalcogenides, we present the synthesis of cesium copper selenide on a nanoscale regime with precise control over dimension, morphology, and phase.[5,6] The influence of key reaction variables, such as precursor’s reactivity, ligands, reaction temperature, and reaction time, on the size and shape of the nanocrystals was demonstrated, showcasing the flexibility of the wet chemical synthesis. An ex-situ mechanistic investigation reveals that NC formation is driven by the dissolution of binary Cu_2-xSe, followed by incorporating Cs⁺ to form the ternary CsCu₅Se₃. The current study also reveals that variation in the alkyl chain length of amines influences the size, shape, and formation of distinct phases. The structural, electronic, and thermoelectric characteristics were experimentally evaluated and further corroborated by computational analysis. The experimental results revealed the material's ultralow thermal conductivity of 0.6 W.M^-1.K^-1 and a good thermoelectric figure of 0.3 at 720 K, providing concrete evidence of its potential. The detailed mechanistic insights presented in this study will significantly advance the development of cutting-edge functional materials in the field of alkali metal chalcogenides for various applications.

A thermoelectric cooler is a solid-state device that transfers heat from one side to another when an electrical current passes through it. This technology is appealing because it can provide precise and localized cooling and heating without using hazardous liquids or gases commonly found in traditional vapor compression refrigeration. These devices are compact, customizable in size, work in any orientation, operate noiselessly, and require minimal maintenance. Even though thermoelectric coolers could be transformative for many advanced thermal management applications, their widespread adoption is hindered by the low efficiency of the thermoelectric materials and costly manufacturing processes.
 In this work, we use extrusion-based 3D printing techniques to fabricate high-performance thermoelectric materials using nanomaterial-based ink. The ink formulation is optimized to ensure structural integrity and particle interfacial bonding during annealing, providing p- and n-type materials with record-high zT values of 1.46 and 1.35 at room temperature, respectively. Moreover, we integrate the printed materials into a 32-pair device and achieve a significant cooling temperature gradient of 50 °C and a coefficient of performance of 3.8, comparable to best-performing thermoelectric coolers, avoiding material waste, and the energy-intense and inefficient steps, such as high-temperature synthesis, pressure-assisted sintering, and cutting and dicing ingots, commonly used in conventional manufacturing processes.

Metal chalcogenides are key material enablers for renewable energy technologies to decrease the current global reliance on fossil fuels and reduce greenhouse gas emissions.^[1,2] However, there is a persistent demand for the development of advanced materials that offer improved efficiency and performance. These innovations are essential for enhancing sustainability and tackling critical global challenges. In the current decade, high entropy chalcogenide nanocrystals (HECh NCs) have emerged as fascinating new materials with remarkable mechanical properties, offering significant potential for a wide range of sustainable energy applications. ^[3] This class of advanced nanomaterials typically comprise five or more principal elements with nearly- equimolar compositions, that utilizes a high configurational entropy to stabilize multiple elements within a single crystal lattice or sublattice. ^[4]

Motivated by the growing demand for HEChs, we present the synthesis of 5 and 6 component high entropy metal telluride with Pd_xCu_yTe₂ as the principal base. Using Pd_xCu_yTe₂ as seed, we design the dimension-controlled colloidal synthesis of (Ni,Cu,Pd,In,Sb)Te and (Ni,Cu,Pd,Ga,Sb,Sn)Te by two-pot diffusion-mediated synthesis at relatively low temperature. The key reaction variables such as precursor reactivity, capping ligands, reaction temperature, and reaction time have been shown to influence the size and shape of the NCs, highlighting the flexibility of the wet chemical synthesis method. The structural and electronic attributes of these materials were evaluated experimentally by XRD, TEM, XPS and UV-Vis spectroscopy. Combined instrumental analyses aided in elucidating the atomic-scale nucleation and growth mechanisms. The synthesized NCs demonstrated exceptional catalytic performance for hydrogen evolution reaction in acidic electrolyte, achieving a current density of 10 mA/cm² at much lower overpotential. The mechanistic insights detailed in this study expands the scope of synergistic properties exhibited by HEChs and will be crucial for advancing the development of innovative, functional HEChs for diverse applications.

Electrochemical water splitting represents one of the most advanced technologies to provide clean and renewable energy. [1] In this process, oxygen evolution reaction (OER) requires four electrons,[2] which is known as a complex and pivotal step that controls the water splitting efficiency. Up to now, the most popular and efficient catalyst for OER is an Iridium-based electrode. [3] However, the cost of Ir makes the process expensive, and finding cheaper material based on earth-abundant metal is mandatory. In this context, we present the development of a high-entropy layered double hydroxide electrocatalyst for the oxygen evolution reaction. MgAl-based LDH is a kind of material with a higher number of hydroxyl groups, which are expected to boost OER. [4] Here, we proceed to substitute the Mg cation with four other cations at different molar fractions using a metastable entropy-stabilized solution. The characterization of high entropy LDHs using XRD, XPS, TEM, and UV-visible spectroscopy indicates the effective substitution of Mg by different cations. We found that HE-LDHs material performs better than commercial IrO₂, and the Mg substitution leads to an optimal composition, which can lower the d-band center position as an effective method to improve the OER performance.

Optoelectronics applications require control over the generation, separation, and extraction of photoexcited charges and control over heat. Yet, in many material systems, energy carrier transport must navigate defects of various natures over a broad range of length and time scales. There are many approaches to inferring microscopic energy transport through energetic, temporal, or spatial markers, but each faces limitations. Moreover, heterogeneous systems are often elusive to simple kinetic models that reveal fundamental transport parameters. To understand the principles that govern electronic and thermal relaxation dynamics in complex systems relevant to optoelectronic applications, advanced experimental techniques and theoretical models rooted in fundamental physical phenomena are needed. This presentation will focus on the following questions: How do heterogeneous environments and interfaces impact microscopic energy transport? How can we access information about energy carriers that traditionally do not have clear spectroscopic signals? How can we control the directionality of energy carrier flow? I will describe pump–probe optical measurements and modeling of both charge-carrier and thermal transport in nanocrystal assemblies.