Optoelectronic Materials Research Articles

Harnessing Pb-S Interactions for Long-Term Water Stability in Cesium Lead Halide Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (LHP NCs) have garnered attention as promising light-harvesting materials for optoelectronics and photovoltaic devices, attributed to their impressive optoelectronic properties. However, their susceptibility to moisture-induced degradation has hindered their practical applications. Despite various encapsulation strategies, challenges persist in maintaining their stability and optoelectronic performance simultaneously. Here, a ligand exchange approach is proposed using (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB) to enhance the stability and dispersibility of CsPbBr3 (CPB) NCs in aqueous environments. MUTAB enables effective surface passivation of the CPB NCs via robust Pb-S interactions at the S-terminal while concurrently directing water molecules through the unbound cationic N-terminal or vice versa, ensuring water dispersibility and stability. Spectroscopic analysis confirms retained structural and optical integrity post-ligand exchange. Crucially, MUTAB-bound CPB NCs exhibit sustained charge transfer properties, demonstrated by aqueous colloidal oxidation reactions. This ligand exchange strategy offers a promising pathway for advancing LHP NCs toward practical optoelectronic and photocatalytic applications.

Optoelectronic Material Characterization Platform using RF Topological Edge States

AbstractEfficient characterization of optoelectronic material properties represents a crucial step in the development of next‐generation infrared (IR) materials and devices. For the first time, a sensitive, contact‐free optoelectronic material characterization platform is demonstrated that exploits the unique properties of radio frequency (RF) topological edge states implemented in a topological microstrip waveguide. The topological device is compatible with standard printed circuit board (PCB) processes with no additional materials, stubs, or resonators. The waveguide and topological properties computationally are designed and then experimentally the results are validated with S‐parameter and near‐field measurements. Finally, as a proof of principle, the room temperature spectral response of a micron‐scale thick mid‐wave infrared (MWIR) mercury cadmium telluride (Hg0.70Cd0.30Te) is measured using the topological microstrip and a five‐fold and 20‐fold increase is demonstrated in response when compared to a plain microstrip and trivial bandgap device, respectively. These results open the door to straightforward, low‐cost characterization of optoelectronic films.

In Silico Design and Characterization of a New Molecular Electride: Li@Calix[3]Pyrrole.

Electrides, in which anionic electrons are localized independentof the atoms in the compound, have shown promise especially as catalysts and optoelectronic materials. Here, we present a new computationally designed molecular electride, Li@calix[3]pyrrole (Li@C3P). Electron density and electron localization function analyses unequivocally confirm the existence of localized electride electron density,independent of any specific atoms. Non-covalent interaction plots further validate the character of the isolated localized electron, suggesting that the system can be accurately represented by Li+@calix[3]pyrrole⋅e-, denoting its distinct charge separation. The remarkable non-linear optical properties of Li@C3P, including average polarizability= 412.4 au, first hyperpolarizability= 4.46 × 104 au, and second hyperpolarizability= 18.40 × 106 au, are unparalleled in the previously reported and similar Li@C4P molecular electride. Furthermore, energy decomposition analysisin combination with natural orbital for chemical valencetheory sheds light on the mechanism of electron density transfer from Li to the C3P cage, yielding the charge-separated Li@C3P complex.In addition to the electron transfer, a key factor to its electride nature is the electronic structure of the CnP cage, which has its lowest unoccupied molecular orbitallocated in the void adjacent to the N-H groups at the back of the bowl-shaped CnP cage.

Solution Processed Hybrid Lead Perovskite Films for White Light Emission and Lasing Applications

Abstract2D organic–inorganic hybrid lead halide perovskite films are fascinating optoelectronic materials for white‐light emission and lasing applications. Here, it is demonstrated that nano‐meter‐thick films of perovskites can be formed at room temperature using Langmuir–Schaefer (LS) deposition technique. In situ X‐ray measurements reveal a self‐assembly process of the 2D perovskite formation at the air–water interface. This formation process requires the presence of stearic acid monolayer on the water subphase having a solution of lead‐perovskite in dimethylformamide. Microscopy and X‐ray measurements of these nanofilms transferred onto substrates show crystalline phase formation that deviates from the known orthorhombic structure of the bulk crystals. The nanofilms exhibit novel broad optical emission with sharp band‐edge transition in temperature‐dependent photoluminescence studies. Also, their band‐edge emission is distinctly blue‐shifted compared to that of thicker 2D perovskite flakes prepared by the slow‐cooling chemical synthesis process. 2D flakes exhibit lasing that cannot be obtained in the LS nanofilms as their thicknesses are lower than the lasing wavelength prohibiting wave‐guide formation. The results show that the 2D single‐crystalline nature of the LS films and flakes are suitable materials to develop broad‐band white light emission across the entire visible range and to obtain lasing without external cavities, respectively.

Phosphosulfide semiconductors for optoelectronics and solar energy conversion

Abstract Inorganic phosphosulfides – materials containing phosphorus, sulfur, and at least one metal – are a vast and chemically-versatile family of materials. Benefiting from a wide range of possible phosphorus oxidation states, phosphosulfide semiconductors exist as thiophosphate compounds with various types of P-S polyanions, as genuine multi-anion compounds with or without P-P bonds, as solid solutions, and as many intermediate cases. Since metal phosphides and metal sulfides are among the highest-performing optoelectronic semiconductors, it seems reasonable to consider the phosphosulfide family as a potential pool of materials for solar cells, photoelectrochemical cells, and light-emitting diodes. Nevertheless, phosphosulfide semiconductors have very rarely been characterized with these applications in mind. In this perspective article, we reflect on the potential applicability of known and hypothetical phosphosulfides as light absorbers and emitters in optoelectronic devices. First, we distill the existing knowledge accessible through the Materials Project database, finding promising phosphosulfides among the compounds already present in the database and identifying what we see as the general advantages and challenges of phosphosulfides as optoelectronic materials. Then, we propose three concrete research directions aimed at finding novel high-quality phosphosulfide semiconductors with high light absorption coefficients, high carrier mobilities, and long carrier lifetimes. In particular, we argue that the versatility of phosphorus in this class of materials could potentially be exploited to engineer defect tolerance. Finally, we describe and explain the advantages of a custom synthesis setup dedicated to high-throughput exploration of thin-film phosphosulfides.

Selected papers from 9th International Conference on Optical, Optoelectronic and Photonic Materials and Applications and 14th Europhysical Conference on Defects in Insulating Materials, 3–7 July 2022, Ghent, Belgium

Selected papers from 9th International Conference on Optical, Optoelectronic and Photonic Materials and Applications and 14th Europhysical Conference on Defects in Insulating Materials, 3–7 July 2022, Ghent, Belgium

4f-4f absorption strength of Eu3+ in La2Zr3(MoO4)9 compared to other Eu3+ activated luminescent materials

This study deals with the optical and luminescent properties of a double molybdate containing rare earth elements, specifically focusing on La2Zr3(MoO4)9:Eu3+ and comparing it with the widely used Y2O3:Eu3+, (Y,Gd)BO3:Eu3+ and YVO4:Eu3+ as well as Y2O2S:Eu3+ and Y(P,V)O4:Eu3+ phosphors. It utilizes Kubelka Munk Theory to estimate the absorption strengths of these materials. Higher absorption coefficients indicate greater efficiency in absorbing light, leading to more intense and brighter luminescence. This investigation aims to assess La2Zr3(MoO4)9:Eu3+ as a promising luminescent material for optoelectronics and solid state lighting by comparing its absorbance properties.

Monolithic back-end-of-line integration of phase change materials into foundry-manufactured silicon photonics

Monolithic integration of novel materials without modifying the existing photonic component library is crucial to advancing heterogeneous silicon photonic integrated circuits. Here we show the introduction of a silicon nitride etch stop layer at select areas, coupled with low-loss oxide trench, enabling incorporation of functional materials without compromising foundry-verified device reliability. As an illustration, two distinct chalcogenide phase change materials (PCMs) with remarkable nonvolatile modulation capabilities, namely Sb2Se3 and Ge2Sb2Se4Te1, were monolithic back-end-of-line integrated, offering compact phase and intensity tuning units with zero-static power consumption. By employing these building blocks, the phase error of a push-pull Mach–Zehnder interferometer optical switch could be reduced with a 48% peak power consumption reduction. Mirco-ring filters with >5-bit wavelength selective intensity modulation and waveguide-based >7-bit intensity-modulation broadband attenuators could also be achieved. This foundry-compatible platform could open up the possibility of integrating other excellent optoelectronic materials into future silicon photonic process design kits.

A Heteronuclear W/Cu/S Clusters‐Based Donor–Acceptor Polymer for Perovskite Solar Cells

AbstractDonor–acceptor polymers containing the repeating moiety of electron‐rich unit (donor) and electron‐deficient group (acceptor), impair their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) considerably localized on the donors and acceptors, respectively. Their band gaps can be well‐tuned by the electron‐donating ability of donors and the electron‐withdrawing ability of acceptors. The efficient splitting of photo‐generated excitons by electronic pull–push effect between donor and acceptor could promote the effective charge transport within polymer. Therefore, donor–acceptor polymers have the merits of versatile molecule structure, accessible functionalization, and adjustable electronic structure, becoming one of the most promising organic optoelectronic materials. For instance, by adjusting the alternating array of donor and acceptor moieties, a series of donor–acceptor polymers with lower band gaps and good light‐harvesting ability are prepared and used as potential photoelectronic materials.

Construction of the Red‐Green‐Blue Luminescence Conversion System Based on Donor‐Acceptor Dyes Exchange with Diels‐Alder Dynamic Covalent Bonds

The construction of full‐color fluorescence systems has received widespread attention because of their applications in lighting materials, optoelectronic materials, and fluorescent probes. However, for the full‐color luminescence system based on trichromatic materials, there are no connections between materials of different luminescent colors. Herein, A new donor‐acceptor dye with red fluorescence was synthesized. The dye displays excellent optical properties of short half‐peak width and strong fluorescence emission. An effective energy transfer process from the dansyl donor to the acceptor was observed with a transfer efficiency of 81%. Further, dyes with green and blue fluorescence were introduced to construct a full‐spectrum fluorescent system. Through exchange reactions of Diels‐Alder dynamic covalent bonds, red, green, and blue luminescence can be converted. This work provides a new idea for the design of full‐color fluorescent materials.

Photonic Properties of Thin Films Composed of Gallium Nitride Quantum Dots Synthesized by Nonequilibrium Plasma Aerotaxy.

Gallium nitride quantum dots (GaN QDs) are a promising material for optoelectronics, but the synthesis of freestanding GaN QDs remains a challenge. To date, the size-dependent photonic properties of freestanding GaN QDs have not been reported. Here, we examine the photonic properties exhibited by thin films composed of GaN QDs synthesized by nonequilibrium plasma aerotaxy. Each film exhibited two photoluminescence peaks after exposure to ambient air. The first peak was in the ultraviolet spectral region, and the second peak was in the visible region. Both peak positions depended on the QD size. Our findings, supported by transient absorption spectroscopy experiments, suggest that conduction band to valence band recombination was the cause of the ultraviolet photoluminescence and that recombination between the conduction band and an acceptor level was the cause of visible photoluminescence. Furthermore, we show that coating the surface of fresh QDs with Al2O3 suppressed the visible region photoluminescence, corroborating the conclusion that the photoactive defect was caused by oxidation in air.

The strain regulated physical properties of PbI2/g-C3N4 for potential optoelectronic device

The van der Waals (vdW) heterostructures of Z-scheme PbI2/g-C3N4 with an indirect bandgap have gained much attention in recent years due to their unique properties and potential applications in various fields. However, the optoelectronic characteristics and strain-modulated effects are not yet fully understood. By considering this, six stacking models of PbI2/g-C3N4 are proposed and the stablest structure is selected for further investigation. The uniaxial and biaxial strains (−10%–10%) regulated band arrangement, charge distribution, optical absorption in the framework of density functional theory are systematically explored. The compressive uniaxial strain of −8.55% changes the band type from II→I, and the biaxial strains of −7.12%, −5.25%, 8.91% change the band type in a way of II→I→II→I, acting like the ‘band-pass filter’. The uniaxial strains except −10% compressive strain, and the −6%, −4%, 2%, 4%, 10% biaxial strains will enhance the light absorption of PbI2/g-C3N4. The exerted strains on PbI2/g-C3N4 generate different power conversion efficiency ( ηPCE ) values ranging from 3.64% to 25.61%, and the maximum ηPCE is generated by −6% biaxial strain. The results of this study will pave the way for the development of new electronic and optoelectronic materials with customized properties in photocatalytic field and optoelectronic devices.

Electronic, magnetic, and optical properties of ferrimagnet Heusler alloys Zr2VX (X=Al, Ga, and In)

We present a comprehensive study of the half-metallic, spin-gapless, and optical properties of Zr2VX (X = Al, Ga, and In) Heusler alloys using density functional theory (DFT). Our estimation of the band gap shows different results from those in the literature and predicts that Zr2VAl and Zr2VGa are half-metallic ferrimagnets. The electronic structure of Zr2VIn is a spin-gapless ferrimagnet that is also different from the reported one in the literature. Zr2VAl has the largest positive value of the dielectric constant and, therefore, exhibits the highest optical properties in the visible range. This is attributed to the noticeable presence of the density of states at Fermi energy in the spin minority channel of this material. Calculated optical conductivity suggests these alloys readily absorb light in the infrared-visible spectrum. Our results suggest that Zr2VX alloys are promising materials for various applications, including spintronics and optoelectronics.

Synthesis, optical, and spectroscopic studies of bismuth boro-tellurite glass system containing BaO and V2O5

A melt quenching technique was used for the preparation of xBaO–(30-x)TeO2–35Bi2O3–33B2O3–2V2O5 (5 ≤ x ≤ 25 mol%) glasses. The structural modifications are studied by X-ray diffraction, DSC, optical, infrared spectroscopy, and Raman as a function of BaO mol%. The progressive incorporation of BaO mol% in the BTBiBV glasses decreases the optical band gap values as the number of free electrons increases with the creation of additional NBOs. The FTIR spectra of the prepared glasses consist of BO3 trigonal and BO4 tetrahedral units while TeO2 changes to TeO3 andTeO4 structural units. The Raman spectra shows that the replacement of BaO with TeO2 decreases the concentration of Te–O–Te linkages within the volume of host glass, which increases the concentration of Ba–O–Te linkages along with BO3 units. Due to this, the overall glass formers connectivity decreases which intern to the creation of NBOs. Moreover, the research highlighted that BTBiBV-5 glasses have exceptional optical properties making them promising materials for photonics, optoelectronics, and optical communication device applications.

Phonon-Driven Femtosecond Dynamics of Excitons in Crystalline Pentacene from First Principles.

Nonradiative exciton relaxation processes are critical for energy transduction and transport in optoelectronic materials, but how these processes are connected to the underlying crystal structure and the associated electron, exciton, and phonon band structures, as well as the interactions of all these particles, is challenging to understand. Here, we present a first-principles study of exciton-phonon relaxation pathways in pentacene, a paradigmatic molecular crystal and optoelectronic semiconductor. We compute the momentum- and band-resolved exciton-phonon interactions, and use them to analyze key scattering channels. We find that both exciton intraband scattering and interband scattering to parity-forbidden dark states occur on the same ∼100  fs timescale as a direct consequence of the longitudinal-transverse splitting of the bright exciton band. Consequently, exciton-phonon scattering exists as a dominant nonradiative relaxation channel in pentacene. We further show how the propagation of an exciton wave packet is connected with crystal anisotropy, which gives rise to the longitudinal-transverse exciton splitting and concomitant anisotropic exciton and phonon dispersions. Our results provide a framework for understanding the role of exciton-phonon interactions in exciton nonradiative lifetimes in molecular crystals and beyond.

Thickness‐Dependent Microstructural Evolution of CsPbBr3 Nanobricks Induced by Electron Beam Irradiation

All‐inorganic halide perovskites exhibit exceptional optical properties and are promising photoactive materials for optoelectronics. However, their stability remains a key challenge, exacerbated by a limited understanding of degradation mechanisms. Herein, in situ transmission electron microscopy (TEM) is used to investigate the effect of thickness on the structural stability of CsPbBr3 nanobricks under electron beam irradiation. CsPbBr3 nanobricks with different thicknesses have been prepared using a traditional hot‐injection method, giving rise to a distinctive cubic structure. A modulated structure, caused by bromine vacancy ordering, has been observed in the thin nanobricks. The degradation behaviors of nanobricks are related to thickness‐dependent bromine vacancy formation in the CsPbBr3 lattice. More bromine vacancies exist in thin nanobricks than thick ones, resulting in a greater number of undercoordinated Pb atoms which accelerate irradiation‐induced degradation. Decomposition products include Pb nanoparticles, which also demonstrate thickness‐dependent characteristics. TEM images of Pb nanoparticles formed from thin nanobricks show evidence of irradiation‐induced amorphization. In thicker nanobricks, Pb nanoparticle size increases with the duration of electron beam irradiation, while the remaining Cs atoms bond with Br atoms to form relatively stable CsBr nanoparticles. These results contribute to understanding of degradation mechanisms in cesium lead halide perovskites under electron beam irradiation.

Diffusion-Dominated Luminescence Dynamics of CsPbBr3 Studied Using Cathodoluminescence and Microphotoluminescence Spectroscopy.

Time-resolved or time-correlation measurements using cathodoluminescence (CL) reveal the electronic and optical properties of semiconductors, such as their carrier lifetimes, at the nanoscale. However, halide perovskites, which are promising optoelectronic materials, exhibit significantly different decay dynamics in their CL and photoluminescence (PL). We conducted time-correlation CL measurements of CsPbBr3 using Hanbury Brown-Twiss interferometry and compared them with time-resolved PL. The measured CL decay time was on the order of subnanoseconds and was faster than PL decay at an excited carrier density of 2.1 × 1018 cm-3. Our experiment and analytical model revealed the CL dynamics induced by individual electron incidences, which are characterized by highly localized carrier generation followed by a rapid decrease in carrier density due to diffusion. This carrier diffusion can play a dominant role in the CL decay time for undoped semiconductors, in general, when the diffusion dynamics are faster than the carrier recombination.

Short excitonic lifetimes of MoSe2 monolayers grown by molecular beam epitaxy on the hexagonal boron nitride

We present a time-resolved optical study of recently developed narrow-line MoSe2 monolayers grown on hexagonal boron nitride with means of molecular beam epitaxy. We find that the photoluminescence decay times are significantly shorter than in the case of the exfoliated samples, even below one picosecond. Such a short timescale requires measurements with better resolution than achievable with a streak camera. Therefore, we employ an excitation correlation spectroscopy pump-probe technique. This approach allows us to identify two distinct non-radiative recombination channels attributed to lattice imperfections. The first channel is active at helium temperatures. It reduces the lifetime of the neutral exciton to below one picosecond. The second channel becomes active at elevated temperatures, further shortening the lifetimes of both neutral and charged exciton. The high effectiveness of both radiative and non-radiative recombination makes epitaxial MoSe2 a promising material for ultrafast optoelectronics.

Dynamic Covalent Synthesis Applied to Optoelectronic and Energy Materials: Design, Applications and Limitations

Dynamic Covalent Chemistry, consisting in the use of dynamic covalent bonds (DCBs) to create complex objects by working at the thermodynamic equilibrium, has undeniable advantages for the preparation of conjugated systems with tailored optoelectronic properties for organic electronics. Chemists can combine simple building blocks with simple functional groups of appropriate geometry, structure and stoichiometry to build multidimensional conjugated architectures. Dynamic covalent reactions are often precious metal‐free, generate little to no side products and are very efficient. DCBs however afford sensitive materials, and consequently a balance needs to be found between the ease of synthesis, the stability and the performances. The dynamicity of the target materials hence can considerably reduce their applicability in organic electronics where strongly stable materials are needed, but opens the door to stimuli‐responsive behaviour and recyclability. A way to overcome dynamicity issues is to lock DCBs, but often at the cost of decreased conjugation. In this review, we will highlight how DCBs are employed to prepare functional optoelectronically active materials, such as discrete molecules, polymers or covalent organic frameworks, applied in fields ranging from organic light‐emitting diodes and solar cells to organic batteries and transistors. We will also discuss their limitations, benefits and  current challenges to overcome.

Sustainable Recycling of Selenium-Based Optoelectronic Devices.

Selenium (Se), the world's oldest optoelectronic material, has been widely applied in various optoelectronic devices such as commercial X-ray flat-panel detectors and photovoltaics. However, despite the rare and widely-dispersed nature of Se element, a sustainable recycling of Se and other valuable materials from spent Se-based devices has not been developed so far. Here a sustainable strategy is reported that makes use of the significantly higher vapor pressure of volatile Se compared to other functional layers to recycle all of them from end-of-life Se-based devices through a closed-space evaporation process, utilizing Se photovoltaic devices as a case study. This strategy results in high recycling yields of ≈ 98% for Se and 100% for other functional materials including valuable gold electrodes and glass/FTO/TiO2 substrates. The refabricated photovoltaic devices based on these recycled materials achieve an efficiency of 12.33% under 1000-lux indoor illumination, comparable to devices fabricated using commercially sourced materials and surpassing the current indoor photovoltaic industry standard of amorphous silicon cells.