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

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Halide perovskite nanocrystals (NCs) are promising solution-processed emitters for low-cost optoelectronics and photonics. Doping adds a degree of freedom for their design and enables us to fully decouple their absorption and emission functions. This is paramount for luminescent solar concentrators (LSCs) that enable fabrication of electrode-less solar windows for building-integrated photovoltaic applications. Here, we demonstrate the suitability of manganese-doped CsPbCl3 NCs as reabsorption-free emitters for large-area LSCs. Light propagation measurements and Monte Carlo simulations indicate that the dopant emission is unaffected by reabsorption. Nanocomposite LSCs were fabricated via mass copolymerization of acrylate monomers, ensuring thermal and mechanical stability and optimal compatibility of the NCs, with fully preserved emission efficiency. As a result, perovskite LSCs behave closely to ideal devices, in which all portions of the illuminated area contribute equally to the total optical power. These results demonstrate the potential of doped perovskite NCs for LSCs, as well as for other photonic technologies relying on low-attenuation long-range optical wave guiding.

Ternary I-III-VI 2 semiconductor nanocrystals (NCs), such as CuInS 2 , are receiving growing attention as they offer the possibility to overcome the toxicity concerns related to heavy metals for numerous technologies spanning from solar cells, luminescent solar concentrators (LSCs) and artificial lighting to bioimaging. Despite the intense research activity, the fundamental mechanisms underpinning the optical properties of CuInS 2 NCs are still not fully understood. Studies suggest that the characteristic Stokes-shifted and long-lived luminescence arises from radiative decay of conduction band electrons to copperrelated defects that are particularly abundant in non-stoichiometric NCs or into a strongly localized HOMO based on Cu(3d) states. However, a recent theoretical model points to a further phenomenon; namely the detailed structure and odd-even parity states of the valence band. Crucially, this model, which has not been experimentally validated, predicts a distinctive optical behaviour in defect-free NCs: the quadratic dependence of both the radiative decay rate and the Stokes shift on the NC radius. If this origin was confirmed, this would have crucial implications for LSC devices as the large solar spectral coverage ensured by low bandgap (large size) NCs would come with a cost in terms of increased reabsorption of the guided near-IR luminescence. Here, we test this hypothesis by studying stoichiometric CuInS 2 NCs of varying sizes. Data reveal, for the first time, the spectroscopic signatures theoretically predicted for the free band edge exciton of I-III-VI 2 NCs, thus providing experimental support to the valence-band structure model. At very low temperatures the same NCs also show dynamic signatures of dark-state emission likely originating from enhanced electron-hole spin interaction. We then evaluated the trade-off between the enhanced solar harvesting of large NCs and their progressively smaller Δ SS on the efficiency of LSCs by performing Monte Carlo ray tracing simulations based on the experimental data that provided useful guidelines for the design of efficient LSCs based on stoichiometric CuInS 2 NCs. Finally, based on such theoretical insights, we fabricated largearea plastic LSC devices showing optical grade quality and an optical power efficiency as high as 6.8%, corresponding to the highest value reported to date for large-area LSC devices.

Hybrid devices employing organic semiconductors interfaced with an aqueous solution represent a new frontier in bioelectronics and energy applications. Understanding of the energetics and photoinduced processes occurring at the organic/water interface is fundamental for further progress. Here, we investigate the interfacial electronic structure of poly-3-hexylthiophene (P3HT) sandwiched between an indium tin oxide (ITO) electrode and a liquid water electrolyte. The aqueous solution is found to polarize the polymer outermost layers, which together with the polymer p-(photo) doping by dissolved oxygen localizes photogenerated electrons at the P3HT/water interface, while holes can be transferred to the ITO electrode. Under illumination, the polymer/water interface is negatively charged, attracting positive ions from the electrolyte solution and perturbing the ion distribution in the aqueous solution. The observed mechanism is of general character and could underlie the behavior of a variety of devices characterized by an organic/water interface, such as prosthetic devices for artificial vision and organic-based systems for photoelectrochemical applications.