No abstract

Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to colouring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymerized poly(lauryl methacrylate), we obtain freestanding, colourless slabs that introduce no distortion to perceived colours and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state associated with a native defect.

We report a high-yield, low cost synthesis route to colloidal Cu 1-x InS 2 nanocrystals with a tunable amount of Cu vacancies in the crystal lattice. These are then converted into quaternary Cu−In−Zn−S (CIZS) nanocrystals by partial exchange of Cu + and In 3+ cations with Zn 2+ cations. The photoluminescence quantum yield of these CIZS nanocrystals could be tuned up to a record 80%, depending on the amount of copper vacancies.

Building-integrated photovoltaics is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend architectural integration to the urban environment by realizing electrode-less photovoltaic windows. Crucial for large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate the use of indirect-bandgap semiconductor nanostructures such as highly emissive silicon quantum dots. Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids the limitations to the industrial scaling of quantum dots composed of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal LSCs with an optical efficiency of η = 2.85%, matching state-of-the-art semi-transparent LSCs. Monte Carlo simulations indicate that optimized silicon quantum dot LSCs have a clear path to η > 5% for 1 m 2 devices. We are finally able to realize flexible LSCs with performances comparable to those of flat concentrators, which opens the way to a new design freedom for building-integrated photovoltaics elements. MainThe continuous increase in performance of silicon-based photovoltaic (Si-PV) systems and the economic incentive programmes that have characterized the fiscal policies of

We report a new colloidal synthesis of niobium-doped TiO2 anatase nanocrystals (NCs) that allows for the preparation of ∼10 nm NCs with control over the amount of Nb doping up to ∼14%. The incorporation of niobium ions leads to the appearance of a tunable, broad absorption peak that ranges from the visible range to the mid-infrared. This optical behavior is attributed to the substitution of Nb5+ on Ti4+ sites generating free carriers inside the conduction band of the TiO2 NCs as supported by optical and electron paramagnetic resonance spectroscopic investigations. At the same time, the incorporation of progressively more niobium ions drives an evolution of the shape of the NCs from tetragonal platelets to “peanutlike” rods.

The absorption properties of materials are emerging as a forefront issue of present-day research boosted by strategic industrial and environmental applications such as gas storage, selective gas recognition, and separation.[1] Molecular selfassembled materials and organic zeolites [2] are still to be explored extensively as a competing alternative in the field, although they are promising as a result of their unique features. In fact, they can be prepared simply by exploiting soft interactions: the ease of formation results in a surprising modularity of the preparation approach. The available space for absorbates can be engineered in the shape of nanochannels lined with an infinite number of receptors for targeted and selective physisorption. Selectivity is provided not only by the channel opening, as in conventional zeolites, but also by organic groups that focus specific interactions on the channel core and fabricate supramolecular structures that cooperatively stabilize gases that diffuse in. Relatively narrow channels with interacting walls provide greater stability and thus milder absorption conditions than those necessary in the widely reported large-cavity systems, as in the case of metalorganic frameworks.[3] Moreover, the network of soft interactions is often amenable to switching properties and to fabricating actuators, as reversible changes from an absorbing state to a close-packed inactive polymorph can be triggered by thermal, mechanical, or radiative stimuli.[4]Herein we show the remarkable sorption properties of molecular crystals of tris-o-phenylenedioxycyclotriphosphazene (1; TPP) [5] with respect to important gases that participate in a network of soft interactions. In fact, methane and carbon dioxide, key gases in the global economy, could be incorporated with high efficiency in the novel adducts (60 % and 100 % occupation, respectively, of the available sites, guest-host molar fraction of up to 1.25) with neat selectivity over other gases. Unprecedented observations of the gases in van der Waals crystals and their topology could be provided by fast MAS NMR spectroscopy.The empty-pore hexagonal structure was solved for the first time after isolation of diffraction-quality single crystals and showed no residual electron density in the large unoccupied volume, shaped as straight nanochannels with a minimum diameter of 4.6 (Supporting Information). Weak intermolecular interactions consolidate molecular stacks along the c axis (repeat period of 10.16 ) and layers on the a-b plane (a = 11.45 ), ensuring the stability of the assembly (Figure 1). The crystal density is low (1 calcd = 1.321 g cm À3 ) and 25 % of the volume is available to guests in the noncovalent architecture.

Optically active materials able to up‐convert the frequency of the incident radiation can be used to enhance the performance of photovoltaic and photocatalityc cells, recovering sub‐bandgap photons not directly absorbed by the devices. Actually, sensitized up‐conversion (SUC) based on multi‐component organic systems is the most promising approach for these photon energy managing processes, being efficient also at the solar irradiance. However, applications of SUC on real devices have not been yet accomplished because its conversion yield usually drops dramatically in the solid state where the low dye mobility inhibits the diffusion controlled mechanisms ruling SUC photophysics. To overcome this limit, we prepared a single‐phase elastomer (poly‐butylacrilate) doped with proper dyes (platinum (II) octaetyl‐porphyrin and 9,10‐diphenylanthracene) to fabricate an efficient photon up‐converting material. Thanks to the residual molecular diffusion provided by the soft host, and to the quenching reduction of involved metastable electronic excited‐states in a solid environment compared to a liquid one, we obtained a record SUC yield of 17% at the solid state. SUC efficiency has been studied as function of the excitation power and sample temperature, elucidating the photophysical processes at the base of the high observed yield and assessing the guidelines for the fabrication of technologically appealing low power up‐converting materials.

Single-file diffusion behavior is expected for atoms and molecules in one-dimensional gas phases of nanochannels with transverse dimensions that do not allow for the particles to bypass each other. Although single-file diffusion may play an important role in a wide range of industrial catalytic, geologic, and biological processes, experimental evidence is scarce despite the fact that the dynamics differ substantially from ordinary diffusion. We demonstrate the application of continuous-flow laser-polarized 129 Xe NMR spectroscopy for the study of gas transport into the effectively one-dimensional channels of a microporous material. The novel methodology makes it possible to monitor diffusion over a time scale of tens of seconds, often inaccessible by conventional NMR experiments. The technique can also be applied to systems with very small mobility factors or diffusion constants that are difficult to determine by currently available methods for diffusion measurement. Experiments using xenon in nanochannel systems can distinguish between unidirectional diffusion and single-file diffusion. The experimental observations indicate that single-file behavior for xenon in an organic nanochannel is persistent even at long diffusion times of over tens of seconds. Finally, using continuousflow laser-polarized 129 Xe NMR spectroscopy, we describe an intriguing correlation between the observed NMR line shape of xenon within the nanochannels and the gas transport into these channels.