The LED technology is seen today as the most promising approach to manufacture high luminance color microdisplays for augmented reality application. So far, it mostly involves blue micro-LED technology and quantum dots-based layers for green and red color generation by light down-conversion. Despite significant progress, the viability of this technology still raises many questions. Among them, the stability of the color conversion layer under nominal display operating conditions is still an issue which has not been thoroughly addressed yet. This paper provides experimental data on the aging behavior of CdSexS1-x quantum platelets (QP) for blue-to-red conversion, under a wide range of blue irradiation power. A modeling of the photoluminescence (PL) decrease versus aging time is proposed, that enables to reliably predict the lifetime of a color LED microdisplay in real operating conditions. At room temperature, the alumina encapsulated CdSexS1-x QPs exhibit a lifetime (t70) of 35,000 h under operating conditions representative of a microdisplay emitting 100,000 nits white light, in video mode. With an average daily use of 3 hours, it would represent for a microdisplay more than 30 years. In addition, the study highlights that display heating induces a lifetime decrease related to a thermally activated enhancement of the annihilation rate of PL emission centers. As a result, a display operated at 100,000 nits and 45°C would see its lifetime t70 reduced by a factor 4 (∼8 years), which remains acceptable for most micro-display applications.

Graphene/lead sulfide (PbS) quantum dot (QD) hybrid infrared photodetectors have gained a lot of attention in recent times due to their high resolution and cost effective fabrication process. In spite of exhibiting remarkably high responsivity, such hybrid detectors are slow as a result of their internal gain mechanism process. In this work, we present a convenient strategy to modulate the correlation between their responsivity and response time giving access to high resolution fast photodetectors in the broadband wavelength range for imaging purpose. Using a layer-by-layer deposition technique including simultaneous ligand exchange and surface passivation at each layer, homogeneous PbS QD films on chemical vapour deposition grown single layer graphene could be achieved. The obtained hybrid phototransistors exhibit a high responsivity of 108A W-1and sensitivity down to 0.1 pW incident light power in the near-infrared wavelength range. By modulating the incident light at a modulation frequency up to 50 kHz, we achieve a response time as low as 5μs while preserving a much higher responsivity (144 A W-1) compared to existing commercial room temperature infrared photodetectors.

In the field of augmented reality, there is a need for very bright color microdisplays to meet the user specifications. Today, one of the most promising technology to manufacture such displays involves a blue micro-LED technology and quantum dots-based color conversion layers. Despite recent progress, the external power conversion efficiencies (EPCE) of these layers remain under ∼25%, below the needs (>40%) to reach a white luminance of 100,000 cd/m2. In this work, we have synthesized CdSexS1-x nanoplatelet-based conversion layers for red and green conversion, and measured their absorption properties and EPCE performances with respect to layer thickness. On this basis, a model was developed that reliably predicts the layer EPCE while using only few input data, namely the layer absorption coefficients and the photoluminescence quantum yield (PLQY) of color photoresist. It brings a new insight into the conversion process at play at a micro-LED level and provides a simple method for extensive optimization of conversion materials. Finally, this study highlights the outstanding red conversion efficiency of photoresist layers made of core-double shell CdSexS1-x nanoplatelets with 31% EPCE (45% external PLQY) for 8 µm-thick conversion layer.

This paper focuses on the dimensioning of a very bright full color 10 mu m-pitch light-emitting device (LED) microdisplay for avionics application. Starting from the specifications of head-mounted display to be used in an augmented reality optical system, a theoretical approach is proposed that enables predicting the specifications of the main technology building blocks entering into the microdisplay manufacturing process flow. By taking into account various material and technological parameters, kept as realistic as possible, it is possible to assess the feasibility of a very bright LED microdisplay (1 Mcd/m(2) full white) and to point out the main limitations. The theoretical specifications are then compared with the technical results obtained so far in the framework of the H2020 Clean Sky "HILICO" project. It shows that 350 000 cd/m(2) of white emission may be accessible with the present gallium nitride (GaN)-micro-LED technology provided a color conversion solution with stable external quantum efficiency of 30% is available. Beyond such level of luminance, the inherent limitations of driving circuit (4 V, 15 mu A per pixel) commands working with materials enabling higher external quantum efficiency (EQE). In particular, 10-mu m-pitch micro-LEDs with electroluminescence EQE of 15% and color conversion EQE approaching 60% are needed, opening the way to future challenging material and technology research developments.

A CPL intensity of up to 3 × 10−2 is achieved in π-extended 6-helicene derivatives, owing to an intense helicene-mediated exciton coupling. Corresponding top-emission CP-OLEDs afforded a promising gEl of around 8 × 10−3.

A low reflectance green top-emitting OLED using a cermet Ag:WO3 thin film as a top cathode has been fabricated and fully characterized. The cermet film has been made by co-evaporating Ag and WO3 materials. Depending on the Ag concentration in the WO3 matrix, the optical and electrical properties vary a lot, as this will be investigated by optical simulations as well as by studying single film properties deposited on silicon and glass wafers. A plasmonic absorption of Ag occurs for metal concentrations around 60-70%, which confirms the "nano" nature of the cermet material, with Ag nanocrystals embedded in an amorphous WO3 oxide matrix (also confirmed by TEM). Using an optimal (optical, electrical) Ag:WO3 (70%) cermet composition as a top electrode in the OLED allows to strongly reduce the device mean reflectance in the visible while its contrast ratio becomes far better (maximum + 76% at 1000 lux) than a reference green device (with Ag as top electrode instead of Ag:WO3). The device with the cermet shows very good lifetimes when driven at constant current drive: an extrapolated lifetime of 90 000 h at 100 cd/m2 has been estimated, based on accelerating ageing tests done for 1000 cd/m2 to 20 kcd/ m2 initial luminance values.

Molecular designs merging circularly polarized luminescence (CPL) and thermally activated delayed fluorescence (CP-TADF) using the concept of chiral perturbation appeared recently as a cornerstone for the development of efficient CP-organic light emitting diodes (CP-OLED). Such devices could strongly increase the energy efficiency and performances of conventional OLED displays, in which 50% of the emitted light is often lost due to the use of antiglare filters. In this context, herein, ten couples of enantiomers derived from novel chiral emitter designs are reported, exhibiting CPL, TADF, and aggregation induced enhancement emission properties (AIEE). Representing the first structure properties relationship investigation for CP-TADF materials, this thorough experimental and theoretical work highlights crucial findings on the key structural and electronic parameters (isomerism, nature of the carbazole substituents) governing the synergy between CPL and TADF properties. To conclude this study, the first top emission CP-OLED is elaborated as a new approach of generating CP light in comparison with classical bottom-emission CP-OLED architecture. Indeed, the top-emission configuration represents the only relevant device architecture for future microdisplay applications. Thereby, in addition to offer molecular guidelines to combine efficiently TADF and CPL properties, this study opens new avenues toward practical applications for CP-OLEDs.

Infrared (IR) photodetectors have a wide range of applications in various fields such as telecommunication, thermal imaging, remote sensing, night assistance car driving etc. Combining highly efficient light absorbing nanomaterials with high mobility 2D materials, a new kind of hybrid photodetector has been introduced which dramatically increases the responsivity and gain of the photodetector. Such low dimensional IR phototransistor based on graphene/PbS QD hybrid was first proposed in literature [1, 2] in 2012. Later in 2017, a highresolution broadband image sensor based on such hybrid materials was demonstrated [3], which is sensitive to ultraviolet, visible and infrared light (300–2000 nm).

We present a new cermet cathode Ag:WO3 for top‐emission OLEDs. The silver nano‐particles in the layer lead to a tunable plasmonic resonance from 500 to 800 nm which limits ambient light reflection. Furthermore, the introduction of WO3 in the cathode improves the lifetime of the device.

This paper, “Faisabilitité d'un separateur spectral integre: étude de filtres optiques localisés et d'un diaphragme absorbant," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.

While dielectric/metal/dielectric (DMD) multilayer thin films have raised considerable interest as transparent and conductive electrodes in various optoelectronic devices, the knowledge of optical characteristics of thin metallic layers integrated in such structures is still rather approximate. The multispectral surface plasmon resonance characterization approach described in this work precisely aims at providing a rigorous methodology able to accurately determine the optical constants of ultra-thin metallic films. As a practical example, the refractive index and extinction dispersion curves of 8 to 25 nm-thick silver layers have been investigated. As a result, their extreme dependence on the layer thickness is highlighted, in particular in a thickness range close to the critical threshold value (∼10 nm) where the silver film becomes continuous and its electrical conductance/optical transmittance ratio particularly interesting. To check the validity of the revisited Ag layers constant dispersion curves deduced from this study, they were introduced into a commercial optical model software to simulate the behavior of various optoelectronic building blocks from the simplest ones (DMD electrodes) to much more complex structures [full organic light emitting device (OLED) stacks]. As a result, a much better prediction of the emission spectrum profile as well as the angular emission pattern of top-emitting OLEDs is obtained. On this basis, it is also shown how a redesign of the top encapsulation thin film of OLEDs is necessary to better take benefit from the advanced DMD electrode. These results should particularly interest the micro-OLED display field where bright and directive single color pixel emission is required.

This paper reports on the investigation of Al x Ga 1-x As y Sb 1-y alloys lattice-matched to GaSb for multi-junction solar cell applications. Optical and electrical characterizations of Al x Ga 1-x As y Sb 1-y alloys are carried out to provide accurate material parameters for simulations. Simulations are then performed with these experimental data to propose an optimized and promising structure for Al x Ga 1-x As y Sb 1-y subcells.

With thousands of publications per year, graphene has raised a particularly great attention these last years. It is true that with an extraordinary combination of physical and technical properties including high flexibility, lightness, electronic mobility and ability to easily change its chemical properties by surface chemistry, graphene appears as an outstanding material which characteristics can interest many fields of application. Among them, energy conversion, production or storage are of such interest that the European's biggest research initiative, the “Graphene Flagship[1]” dedicated a specific work package only to that topic. The present talk aims at reviewing some of these energy applications where graphene and graphene related materials are thought to provide disruptive performances. Actually, fulfil of these promises will depend on the control of the full value chain going from graphene production to integration into the energy devices. Moreover, to fully benefit from graphene properties, the integration strategies have to address the interfacing issue of graphene with hosting material. Further graphene functionalization steps are thus often necessary to adapt the surface graphene properties. It leads to the development of various graphene functionalization technologies without which a successful transfer of graphene into energy applications would be impossible. Various examples dealing with graphene doping, nano-structuring or nano-decorating will be discussed to illustrate the key role of these enabling technologies. [1] http://graphene-flagship.eu/

Here we report on technology developments implemented into the Graphene Flagship European project for the integration of graphene and graphene-related materials (GRMs) into energy application devices. Many of the technologies investigated so far aim at producing composite materials associating graphene or GRMs with either metal or semiconducting nanocrystals or other carbon nanostructures (e.g., CNT, graphite). These composites can be used favourably as hydrogen storage materials or solar cell absorbers. They can also provide better performing electrodes for fuel cells, batteries, or supercapacitors. For photovoltaic (PV) electrodes, where thin layers and interface engineering are required, surface technologies are preferred. We are using conventional vacuum processes to integrate graphene as well as radically new approaches based on laser irradiation strategies. For each application, the potential of implemented technologies is then presented on the basis of selected experimental and modelling results. It is shown in particular how some of these technologies can maximize the benefit taken from GRM integration. The technical challenges still to be addressed are highlighted and perspectives derived from the running works emphasized.

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

This study is devoted to elucidate the interplay of catalyst thickness and growth conditions in the activation and selectivity of single-walled carbon nanotube growth using cobalt deposited on Si/SiO2 as a model system. In situ Raman studies reveal that thin catalyst layers require a higher pressure of carbon precursor to initiate nanotube growth. However, if the catalysts are pre-reduced, all catalyst thicknesses display the same low threshold pressure and a higher yield of single-walled carbon nanotubes. To explain these results, catalysts formed from a gradient of cobalt thickness are studied. Surface analyses show that during the catalyst preparation, catalyst atoms at the interface with silica form small and hard-to-reduce silicate nanoparticles while the catalyst in excess leads to the formation of large oxide particles. Weakly-reducing conditions of pretreatment or synthesis are sufficient to reduce the large oxide particles and to lead to the growth of large-diameter multi-walled carbon nanostructures. However, highly-reducing conditions are required to reduce the small silicate domains into small cobalt particles able to grow single-walled carbon nanotubes. These results show that reaction of the catalyst with the support to form more refractory compounds greatly impact the nucleation yield and the growth selectivity of single-walled carbon nanotubes.