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Organic semiconductors that possess both long exciton diffusion length and high mobility emissive properties are crucial for the development of high-performance organic optoelectronic devices. However, materials with these combined characteristics are currently rare. Herein, a long exciton diffusion length was obtained in the high mobility emissive organic semiconductor trans-1,2-bis(5-phenyldithieno[2,3-b:3′,2′-d]thiophen-2-yl)ethene (BPTTE). Excellent optoelectronic properties with the maximum carrier mobility of 18.1 cm2V–1s–1and high photoluminescence quantum yield (PLQY) of 21.4% were obtained for BPTTE single crystals. Notably, an impressive exciton diffusion length reaching up to 114.2 nm was also achieved, demonstrating the effective integration of optoelectrical properties in BPTTE single crystals. This work offers valuable guidance for exploring the multifunctional capabilities of high mobility organic semiconductors, a crucial aspect for enhancing the performance of organic optoelectronic devices.

Solid-state quantum emitters (QEs) are central components for photonic-based quantum information processing. Recently, bright QEs in III-nitride semiconductors, such as aluminum nitride (AlN), have attracted increasing interest because of the mature commercial application of the nitrides. However, the reported QEs in AlN suffer from broad phonon side bands (PSBs) and low Debye–Waller factors. Meanwhile, there is also a need for more reliable fabrication methods of AlN QEs for integrated quantum photonics. Here, we demonstrate that laser-induced QEs in AlN exhibit robust emission with a strong zero phonon line, narrow line width, and weak PSB. The creation yield of a single QE could be more than 50%. More importantly, they have a high Debye–Waller factor (>65%) at room temperature, which is the highest result among reported AlN QEs. Our results illustrate the potential of laser writing to create high-quality QEs for quantum technologies and provide further insight into laser writing defects in relevant materials.

We have developed an improved physical vapor transport method. This method enables us to decrease the sublimation temperature of small organic molecules, and slow the weight loss process, and then regulate the degree of vapor saturation of materials. Large-size single-crystalline materials with high quality are successfully prepared from small organic functional molecules. The slice crystals are found to be single crystalline with high quality. The surface morphologies and structural information of grown crystals were characterized by optical microscope, atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. The results indicate that the growth mechanism of single crystals is a 2D nucleation, with elementary steps, large straight steps, and layer-by-layer growth.

Layered halide hybrid organic–inorganic perovskites (HOP) have been the subject of intense investigation before the rise of three-dimensional (3D) HOP and their impressive performance in solar cells. Recently, layered HOP have also been proposed as attractive alternatives for photostable solar cells and revisited for light-emitting devices. In this review, we combine classical solid-state physics concepts with simulation tools based on density functional theory to overview the main features of the optoelectronic properties of layered HOP. A detailed comparison between layered and 3D HOP is performed to highlight differences and similarities. In the same way as the cubic phase was established for 3D HOP, here we introduce the tetragonal phase with D4hsymmetry as the reference phase for 2D monolayered HOP. It allows for detailed analysis of the spin–orbit coupling effects and structural transitions with corresponding electronic band folding. We further investigate the effects of octahedral tilting on the band gap, loss of inversion symmetry and possible Rashba effect, quantum confinement, and dielectric confinement related to the organic barrier, up to excitonic properties. Altogether, this paper aims to provide an interpretive and predictive framework for 3D and 2D layered HOP optoelectronic properties.

Owing to spectacular optoelectronic properties, halide perovskites hold great promises in various fields, including photovoltaics and light-emission devices. Although hybrid halide perovskites are known to be unstable when exposed durably to water and oxygen, it has been shown that humid air and oxygen can restore the photoluminescent properties of methylammonium lead tribromide (MAPbBr3) that vanish under vacuum [Fang, H.-H.Sci. Adv.2016, 2, e1600534]. Here, thanks to density functional theory-based calculations, we propose that the quenching and revival of surface photoluminescent properties are due to the formation and passivation of surface charge traps. Moreover, we establish that bulk properties are preserved either because molecules are unlikely to penetrate the bulk or because they do not interfere with the electronic states involved in the optical properties.

Attaining control over the surface traps in halide perovskites is critical for the tunability of ultimate device characteristics. Here, we present a study on the modulation of photophysical properties, surface traps, and recombination in MAPbI3single crystals (MSCs) with methylamine (MA) vapor surface treatment. Transient photoluminescence spectroscopy in conjunction with density functional theory calculations reveals that nonradiative recombination related to Pb2+becomes mitigated after MA vaporing while radiative recombination via bimolecular path tends to increase, which originates from the passivation of Pb ions with the Lewis base nitrogen in MA. In contrast to the broad photoresponse in the pristine MSC photodiodes, application of MA surface treatments leads to a spectral narrowing effect (SNE) in MSCs with the response peak width <40 nm. On the basis of the examined photon-cycling effect with MA treatment that indicates a reduction of exciton diffusion into the interior region of MSCs, we attempt to propose an operation mechanism for the SNE which can be related to the overall stronger surface recombination and resulting severe photocarrier losses, such that the charge collection and quantum efficiency from the above-band gap absorption decrease. This work provides a facile approach with chemical means to tune the surface properties and eventual spectral selectivity in MSCs that are promising for photon-detection device applications.

The application of luminescent materials in display screens and devices requires micropatterned structures. In this work, we have successfully printed microstructures of a two-dimensional (2D), orange-colored organic/inorganic hybrid perovskite ((C6H5CH2NH3)2PbI4) using two different soft lithography techniques. Notably, both techniques yield microstructures with very high aspect ratios in the range of 1.5–1.8. X-ray diffraction reveals a strong preferential orientation of the crystallites along the c-axis in both patterned structures, when compared to nonpatterned, drop-casted thin films. Furthermore, (time-resolved) photoluminescence (PL) measurements reveal that the optical properties of (C6H5CH2NH3)2PbI4are conserved upon patterning. We find that the larger grain sizes of the patterned films with respect to the nonpatterned film give rise to an enhanced PL lifetime. Thus, our results demonstrate easy and cost-effective ways to manufacture patterns of 2D organic/inorganic hybrid perovskites, while even improving their optical properties. This demonstrates the potential use of color-tunable 2D hybrids in optoelectronic devices.

Colloidal quantum dots are a class of solution-processed semiconductors with good prospects for photovoltaic and optoelectronic applications. Removal of the surfactant, so-called ligand exchange, is a crucial step in making the solid films conductive, but performing it in solid state introduces surface defects and cracks in the films. Hence, the formation of thick, device-grade films have only been possible through layer-by-layer processing, limiting the technological interest for quantum dot solids. Solution-phase ligand exchange before the deposition allows for the direct deposition of thick, homogeneous films suitable for device applications. In this work, fabrication of field-effect transistors in a single step is reported using blade-coating, an upscalable, industrially relevant technique. Most importantly, a postdeposition washing step results in device properties comparable to the best layer-by-layer processed devices, opening the way for large-scale fabrication and further interest from the research community.

Excitons are quasi-particles composed of electron–hole pairs through Coulomb interaction. Due to the atomic-thin thickness, they are tightly bound in monolayer transition metal dichalcogenides (TMDs) and dominate their optical properties. The capability to manipulate the excitonic behavior can significantly influence the photon emission or carrier transport performance of TMD-based devices. However, on-demand and region-selective manipulation of the excitonic states in a reversible manner remains challenging so far. Herein, harnessing the coordinated effect of femtosecond-laser-driven atomic defect generation, interfacial electron transfer, and surface molecular desorption/adsorption, we develop an all-optical approach to manipulate the charge states of excitons in monolayer molybdenum disulfide (MoS2). Through steering the laser beam, we demonstrate reconfigurable optical encoding of the excitonic charge states (between neutral and negative states) on a single MoS2flake. Our technique can be extended to other TMDs materials, which will guide the design of all-optical and reconfigurable TMD-based optoelectronic and nanophotonic devices.

The large mobilities and carrier lifetimes of hybrid perovskite single crystals and the high atomic numbers of Pb, I and Br make them ideal for X-ray and gamma-ray detection. Here, we report a sensitive X-ray detector made of methylammonium lead bromide perovskite single crystals. A record-high mobility–lifetime product of 1.2 × 10–2cm2V–1and an extremely small surface charge recombination velocity of 64 cm s–1are realized by reducing the bulk defects and passivating surface traps. Single-crystal devices with a thickness of 2–3 mm show 16.4% detection efficiency at near zero bias under irradiation with continuum X-ray energy up to 50 keV. The lowest detectable X-ray dose rate is 0.5 μGyairs–1with a sensitivity of 80 μC Gy−1aircm–2, which is four times higher than the sensitivity achieved with α-Se X-ray detectors. This allows the radiation dose applied to a human body to be reduced for many medical and security check applications.

In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing.

Colloidal semiconductor quantum dots (QDs) are extraordinarily appealing for the development of cheap and large area solar cells due to high absorption efficiency, tunable bandgap energies, and solution processability. Understanding and controlling electronic wave function delocalization in QD thin films is therefore pivotal for realizing efficient optoelectronic devices. Here, a detailed study of the exciton recombination dynamics in PbS/CdS core/shell films as a function of temperature and surface chemistry is reported. By decreasing the temperature from 295 to 5.4 K, electronic wave function delocalization from the PbS core to the monolayer CdS shell is observed, demonstrating a reduction of the conduction band offset at low temperature and the formation of a quasi-type II band alignment. Interestingly, films made with core–shell particles, where the shell is thicker than a monolayer, display type I alignment also at low temperature.

Initial nanointerfacial electron transfer dynamics are studied in dye‐sensitized solar cells (DSSCs) in which the free energy and kinetics vary over a broad range. Surprisingly, it is found that the decay profiles, reflecting the electron transfer behavior, show a universal shape despite the different kinds of dye and semiconductor nanocrystalline films, even across different device types. This renews intuitive knowledge about the electron injection process in DSSCs. In order to quantitatively comprehend the universal behavior, a static inhomogeneous electronic coupling model with a Gaussian distribution of local injection energetics is proposed in which only the electron injection rate is a variant. It is confirmed that this model can be extended to CdSe quantum dot‐sensitized films. These unambiguous results indicate exactly the same physical distribution in electron injection process of different sensitization films, providing limited simple and important parameters describing the electron injection process including electronic coupling constant and reorganization energy. The results provide insight into photoconversion physics and the design of optimal metal‐free organic dye‐sensitized photovoltaic devices by molecular engineering.

Organic crystals have great potential for the applications in laser devices. This article presents an effective approach for fabrication of distributed feedback single crystal lasers. With the laser interference ablation method, high quality grating structures have been fabricated on the organic single‐crystalline thin film materials. The relationship between the depth, periodicity, and laser fluence is discussed. The optical properties, such as photoluminescence, and diffractive properties are studied in detail. With the appropriate period, strong laser emission has been observed from these devices. Distributed feedback lasing is demonstrated from the laser interference ablated organic single crystals for the first time.

We report the effective two-photon absorption-induced upconversion amplified spontaneous emission (ASE) in the cyano-substituted oligo(p-phenylenevinylene) 1,4-bis[1-cyano-2-(4-(diphenylamino)phenyl)vinyl]benzene (TPCNDSB) organic crystals. The material shows enhanced emission in the solid state (31% quantum yield in crystal) and efficient two-photon absorption. The ASE under the one-photon and two-photon excitation were observed. It is demonstrated that the organic crystals of TPCNDSB might be practically used as fluorescent materials for potential upconversion laser applications.

Colloidal photonic crystals (CPhCs) consisting of iron oxide magnetic spheres possess high lattice tunability but are generally unstable and difficult to manage in liquid form. We solve the problem by introducing the colloidal spheres into a resin system, which can “freeze” three-dimensional (3D) patterns by photopolymerization. Robust solid-form CPhCs with various structural colors were, therefore, achieved. The “frozen” 3D patterns would permit not only a systematic exploration on self-assembling dynamics, colloidal crystallography, and PhC physics but also may pave a new application avenue if a solid, but still soft, PhC is shaped or sliced.

Two-beam interference ablation of 1,4-Bis(4-methylstyryl)benzene organic crystal by short laser pulses (10 ns, 355 nm) is presented. The influence of laser fluence, interference period, and pulse number on the morphology have been studied. The morphology is closely associated with the molecular interactions in the crystals, and it could be well controlled by adjusting the laser fluence and pulses number. Through interference ablating the crystals with high fluence pulses, and then treated with low fluence laser pulses, grating structures with smooth surface could be fabricated without any additional process.

We have studied the ultrafast dynamics of two-photon-pumped amplified spontaneous emission (ASE) from a single crystal by the time-resolved fluorescence upconversion technique. With the increase of two-photon pump intensities, the emission decay time is dramatically shortened by 30 times (from 3ns to ~87 ps), and the energy migration rate is acutely enhanced when ASE occurs. The stripe length is also found to play an important role in the formation of the ASE. Meanwhile, the gain coefficient is evaluated to be 15cm^−1 for 560nm at an excitation intensity of 2.3mJ/pulse/cm^2 by the variable stripe length technique.

Effective upconversion emission from an organic crystal of cyano-substituted oligo (p-phenylenevinylene) (CNDPASDB) based on two-photon absorption is presented. Frequency upconverted cavityless lasing, or amplified spontaneous emission, from the crystal pumped by a femtosecond laser of 800 nm was observed when the excitation energy exceeded the threshold of 1.3 mJpulse^−1cm^−2. Its polarization contrast was estimated to be ~0.93. This large ratio is due to the unified unidirectional configuration of the molecular long axis in crystal, beneficial to the stimulated emission with a low threshold. These results indicate that the present CNDPASDB crystal has a potential for upconversion laser device application.

The stability of the active layer is an underinvestigated aspect of metal halide perovskite solar cells. Furthermore, the few articles on the subject are typically focused on thin films, which are complicated by the presence of defects and grain boundaries. Herein, a different approach is taken: a perovskite composition that is known to be stable in single crystal form is used, and its (photo‐)physical properties are studied in the form of spin‐coated thin films. The perovskites are lead‐based with cesium and formamidinium as the A‐site cations and iodide and bromide as the halide anions, with the formula Cs0.1FA0.9PbI3−xBrx. These compounds show high potential in terms of stability in single crystal form and closely resemble the compounds that have successfully been used in highly efficient perovskite–silicon tandem solar cells. It is found that a small difference in bromine content (x= 0.45 vs 0.6) has a significant impact in terms of the phase purity and charge carrier lifetimes, and conclude that the thin films of Cs0.1FA0.9PbI2.55Br0.45have good potential for the use in optoelectronic devices. Stability is an underdeveloped aspect of metal halide perovskite solar cells. Herein, a structurally stable single crystal perovskite is selected to facilitate the step to thin films. Slightly increasing the bromine content in films of cesium formamidinium (FA) lead halide perovskite Cs0.1FA0.9PbI3−xBrxmakes a big difference in purity: the film with more bromine has detrimental non‐perovskite impurities.

On page 33, Jing Feng, Hong‐Bo Sun, and co‐workers report the use of an interference ablation method to fabricate an organic single‐crystalline distributed feedback laser. Organic single crystals are difficult to treat using traditional fabrication methods because of their fragility and sensitivity to organic solvents and this method resolves these difficulties. The method may be applied to fabricate high‐quality organic devices based on the single‐crystalline materials.