Absorption coefficient and non-equilibrium generalized Planck's law for improved hot carrier photoluminescence spectroscopy

International audienceThe generalized Planck's law describes the light emitted by a blackbody. In the past this law has been generalized to semiconductors. Whereas Planck's orginial formulation roots on a same temperature between the body and the emitted photon gas, the generalized expression for semiconductors has been used to describe electron-hole plasmas in non-equilibrium with the lattice. Here we show experimentally how to determine different electron and hole temperatures in non-equilibrium with the pho-ton gas. Since the absorption coefficient varies with the carrier density and is part of the generalize Planck's law, we particularly emphasize the importance of the absorption coefficient in the analysis of hot carrier photoluminescence spectra. Index Terms-hot carrier solar cells, hot carrier photolumines-cence, non-equilibrium generalized Planck's law, non-equilibrium electron and hole distribution

Accurate radiation temperature and chemical potential from quantitative photoluminescence analysis of hot carrier populations

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Reply to the Comment of Y. Apertet on Optical Imaging of Light-Induced Thermopower in Semiconductors

International audienceIn a Comment on a previously published article in this Journal [Phys. Rev. Applied 5, 024005 (2016)] 1 , Apertet states that the definition of the thermopower given in that article seems erroneous due to a confusion between the different physical quantities needed to derive this parameter. We believe some definitions need to be clarified in order to avoid confusions. We here intend to answer the questions of Apertet by detailing the method and by focusing on the definition of the quantities we optically measured

Two carrier temperatures non-equilibrium generalized Planck law for semiconductors

International audiencePlanck's law of radiation describes the light emitted by a blackbody. This law has been generalized in the past for the case of a non-blackbody material having a quasi Fermi-level splitting: the lattice of the material and the carriers are then considered in an isothermal regime. Hot carrier spectroscopy deals with carriers out of the isothermal regime, as their respective temperatures (≠) T T H e H h are considered to be different than that of the lattice () T L. Here we show that Fermi-Dirac distribution temperature for each type of carrier still determine an effective radiation temperature: an explicit relationship is given involving the effective masses. Moreover, we show how to determine, in principle with an additional approximation, the carrier temperatures () T T , H e H h and the corresponding absolute electrochemical potentials from photoluminescence measurements

Advanced analysis for hot-carriers photoluminescence spectrum

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Quantitative optoelectronic measurements of carrier thermodynamics properties in quantum well hot carrier solar cell

International audienceWe investigated a semiconductor heterostructure based on InGaAsP multi quantum wells using optical and electrical characterizations in the scope of hot carrier solar cell device. The potential of the investigated quantum well structure to overpass the Schockley Queisser limit is discussed. Population density, temperature and quasi-Fermi level splitting of photogenerated carriers are investigated by fitting the full luminescence spectra using generalized Planck's law. A proper optical study is realized thanks to a detailed description of the absorption of excitons and free carriers in the quantum well. Optical measurements are compared to electrical measurements where the open circuit voltage electrically measured is higher than the minimum absorption threshold. To probe the hot carrier effect in such measurements we look at the changes in thermodynamic properties of carriers in the quantum well and in the barriers when changing the excitation power and the electrical bias

Quantitative experimental assessment of hot carrier-enhanced solar cells at room temperature

International audienceIn common photovoltaic devices, the part of the incident energy above the absorption threshold quickly ends up as heat, whichlimits their maximum achievable efficiency to far below the thermodynamic limit for solar energy conversion. Conversely, the conversion of the excess kinetic energy of the photogenerated carriers into additional free energy would be sufficient to approach the thermodynamic limit. This is the principle of hot carrier devices. Unfortunately, such device operation in conditions relevant for utilization has never been evidenced. Here, we show that the quantitative thermodynamic study of the hot carrier population, with luminance measurements, allows us to discuss the hot carrier contribution to the solar cell performance. We demonstrate that the voltage and current can be enhanced in a semiconductor heterostructure due to the presence of the hot carrier population in a single InGaAsP quantum well at room temperature. These experimental results substantiate the potential of increasing photovoltaic performances in the hot carrier regime

Neuroprotection Against Amyloid-b Induced DNA Double-Strand Breaks is Mediated by Multiple Retinoic Acid-Dependent Pathways

In this study we have investigated the role of all-trans retinoic acid (RA) as neuroprotective agent against Ab1-42-induced DNA double-strand breaks (DSBs) in neuronal SH-SY5Y and astrocytic DI TNC1 cell lines, and in murine brain tissues, by single-cell gel electrophoresis. We showed that RA does not only repair Ab1-42-induced DSBs, as already known, but that it also prevents their occurrence. This effect is independent of that of other anti-oxidants studied, such as vitamin C, and appears to be mediated, at least in part, by changes in expression, not of the RARa but of the PPARb/g and of anti-amyloidogenic proteins, such as ADAM10, implying a decreased production of endogenous Ab. Whereas Ab1-42 needs transcription and translation for DSBs production, RA protects against Ab1-42-induced DSBs at the post-translational level through both, the RARa/b/g and the PPARb/d receptors as demonstrated by using specific antagonists. Furthermore, it could be shown by Proximity Ligation Assay that the PPARb/d-RXR interactions, not the RARa/b/g-RXR interactions, increased in the cells when a 10 min RA treatment was followed by a 20 min Ab1-42 treatment. Thus, the PPARb/d receptor, known for its anti-apoptotic function, might for these short-time treatments play a role in neuroprotection via PPARb/d-RXR heterodimerization and possibly expression of anti-amyloidogenic genes. Overall, this study shows that RA can, not only repair Ab1-42-induced DSBs, but also prevent them via the RARa/b/g and the PPARb/d receptors. It suggests that the RA-dependent pathways belong to an anti-DSBs Adaptative Gene Expression (DSB-AGE) system that can be targeted by prevention strategies to preserve memory in Alzheimer’s disease and aging

Preferential Involvement of BRCA1/BARD1, Not Tip60/Fe65, in DNA Double-Strand Break Repair in Presenilin-1 P117L Alzheimer Models

Recently, we showed that DNA double-strand breaks (DSBs) are increased by the Aβ42-amyloid peptide and decreased by all-trans retinoic acid (RA) in SH-SY5Y cells and C57BL/6J mice. The present work was aimed at investigating DSBs in cells and murine models of Alzheimer’s disease carrying the preseniline-1 (PS1) P117L mutation. We observed that DSBs could hardly decrease following RA treatment in the mutated cells compared to the wild-type cells. The activation of the amyloidogenic pathway is proposed in the former case as Aβ42- and RA-dependent DSBs changes were reproduced by an α-secretase and a γ-secretase inhibitions, respectively. Unexpectedly, the PS1 P117L cells showed lower DSB levels than the controls. As the DSB repair proteins Tip60 and Fe65 were less expressed in the mutated cell nuclei, they do not appear to contribute to this difference. On the contrary, full-length BRCA1 and BARD1 proteins were significantly increased in the chromatin compartment of the mutated cells, suggesting that they decrease DSBs in the pathological situation. These Western blot data were corroborated by in situ proximity ligation assays: the numbers of BRCA1-BARD1, not of Fe65-Tip60 heterodimers, were increased only in the mutated cell nuclei. RA also enhanced the expression of BARD1 and of the 90 kDa BRCA1 isoform. The increased BRCA1 expression in the mutated cells can be related to the enhanced difficulty to inhibit this pathway by BRCA1 siRNA in these cells. Overall, our study suggests that at earlier stages of the disease, similarly to PS1 P117L cells, a compensatory mechanism exists that decreases DSB levels via an activation of the BRCA1/BARD1 pathway. This supports the importance of this pathway in neuroprotection against Alzheimer’s disease

Experimental investigation of performances enhancement in hot carrier solar cells: improvements and perspectives (Conference Presentation)

International audienceIn single junction solar cells a large part of the incident energy ends up as heat which limits their maximum achievable efficiency. Thus the achievement of maximum power conversion efficiencies relies on complex multijunction devices. Here we show the possibility to harvest the available solar energy using hot carrier devices and evidence a positive contribution of the hot carrier effect on photovoltaic performances. We investigated a semiconductor heterostructure based on a single InGaAsP quantum well using quantitative optoelectrical characterization, especially luminance measurements. The quantitative thermodynamic study of the hot carrier population allows us to discuss the hot carrier contribution to the solar cell performance. We demonstrate that voltage and current are enhanced due to the presence of the hot carrier population in the quantum well. These experimental results substantiate the potential of increasing photovoltaic performances in the hot carrier regime. Moreover, by developing a suitable analytic theoretical framework, we show how to obtain separate (hot) temperatures of electrons and holes from photoluminescence spectra analysis. The individual thermalization coefficients of each carrier type are also discussed. The method developed in this article paves the way towards the design of new energy harvesting devices and to the development of advanced characterization tools. Finaly, to increase the PV performance enhancement and reduce the concentration factor, an optimize design is investigated