In the last few years, non-coherent sensitized photon up-conversion (SUC) in multi-component systems has been developed to achieve significantly high quantum yields for various chromophore combinations at low excitation powers, spanning from the ultraviolet (UV) to near infrared (NIR) spectrum. This promising photon energy management technique became indeed suitable for wide applications in lighting technology and especially in photovoltaics, being able to recover the sub-bandgap photons lost by current devices. A full and general description of the SUC photophysics will be presented, with the analysis of the parameter affecting the photon conversion quantum yield and the quantities which define the optimal working range of any SUC system, namely the threshold and saturation excitation intensity. It will be shown how these quantities depend on intrinsic photophysical properties of the moieties involved and on the SUC solid host matrix. The model proposed represents a powerful tool for evaluation of a newly proposed system, and its reliability will be discussed in respect to an optimized system with SUC yield of 0.26 ± 0.02. The results obtained will outline the research guidelines which must be pursued to optimize the SUC efficiency for its perspective technological applications.

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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 have analyzed the dynamics of the upconversion-induced delayed fluorescence for a model multicomponent organic system, in which high concentrations of triplet states can be sustained in steady-state conditions. At different excitation powers, two regimes have been identified depending on the main deactivation channel for the triplets, namely, the spontaneous decay and the bimolecular annihilation. The excitation power density at which triplet bimolecular annihilation becomes dominant is the threshold (I(th)) to have efficient upconversion generation. The simple equation obtained for I(th) allows us to predict the theoretical efficiency of a generic system on the basis of few parameters of the constituent molecules

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

A comprehensive study of the photophysical properties of a series of monoaza[5]helicenes is presented on the basis of joint optical spectroscopy and quantum chemistry investigations. The molecules have been characterized by absorption and CW/time-resolved luminescence measurements. All quantities related to spin-orbit-coupling processes, such as intersystem crossing rates and radiative phosphorescence lifetimes, were found to depend strongly on the nitrogen position within the carbon backbone. Density functional theory and semiempirical quantum-chemical methods were used to evaluate the molecular geometries, the characteristics of the excited singlet and triplet states, and the spin-orbit coupling matrix elements. We demonstrate that the magnitude of spin-orbit coupling is directly correlated with the degree of deviation from planarity. The trends from the calculated photophysical quantities, namely, radiative fluorescence and phosphorescence decay rates and intersystem crossing rates, of the mono-aza-helicenes are fully consistent with experiment.

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