Search results for "Kite"
showing 10 items of 1123 documents
Dry Mechanochemical Synthesis of Highly Luminescent, Blue and Green Hybrid Perovskite Solids
2019
A simple method to obtain bright photoluminescent wide bandgap mixed‐halide 3D perovskites is reported. The materials are prepared by dry mechanochemical synthesis (ball‐milling) starting from neat binary precursors, and show enhanced photoluminescence upon the addition of an adamantane derivative in the precursors' mixture. The structural characterization suggests that the additive does not participate in the crystal structure of the perovskite, which remains unvaried even with high loading of amantadine hydrochloride. By simple stoichiometric control of the halide precursors, the photoluminescence can be finely tuned from the UV to the green part of the visible spectrum. Photoluminescence…
Hole transporting materials based on benzodithiophene and dithienopyrrole cores for efficient perovskite solar cells
2018
The development of highly efficient hole transporting materials (HTMs) for perovskite solar cells (PSCs) is still one of the most thrilling research subjects in the development of this emerging photovoltaic technology. Inner ring engineering of the aromatic core of new HTMs – consisting of three fused rings endowed with four triarylamine units – reveals major performance effects over the fabricated devices. In particular, substitution of the central pyrrole ring in dithienopyrrole (DTP) by a benzene ring – benzodithiophene (BDT) – allows enhancing the power conversion efficiency from 15.6% to 18.1%, in devices employing mixed-perovskite (FAPbI3)0.85(MAPbBr3)0.15 (MA: CH3NH3+, FA: NHCHNH3+) …
Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)2PbI4 Perovskite Thin Films: Implications fo…
2021
An outstanding potentiality of layered two-dimensional (2D) organic–inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundament…
Continuous-Flow Synthesis of Orange Emitting Sn(II)-Doped CsBr Materials
2021
An ongoing demand toward lead-free all-inorganic cesium metal halide perovskites has presented Sn(II) as an ideal substitute of Pb(II) for applications in optoelectronic devices. The major concern regarding Sn(II) is the instability due to the ambient oxidation to Sn(IV). To expand the scope of traditional perovskite and analogues, herein the synthesis and optical performance of Sn(II)-doped CsBr, a new material formed by interstitial doping of Sn(II) into the CsBr matrix, are reported for the first time. This material is prepared following an antisolvent mediated recrystallization method using a continuous flow reactor, which is beneficial for scaling up the production compared to traditio…
Quantification of spatial inhomogeneity in perovskite solar cells by hyperspectral luminescence imaging
2016
Vacuum evaporated perovskite solar cells with a power conversion efficiency of 15% have been characterized using hyperspectral luminescence imaging. Hyperspectral luminescence imaging is a novel technique that offers spectrally resolved photoluminescence and electroluminescence maps (spatial resolution is 2 micrometer) on an absolute scale. This allows, using the generalized Planck’s law, the construction of absolute maps of the depth-averaged quasi-Fermi level splitting (Δμ), which determines the maximum achievable open circuit voltage (Voc) of the solar cells. In a similar way, using the generalized reciprocity relations the charge transfer efficiency of the cells can be obtained from the…
Size-And Wavelength-Dependent Two-Photon Absorption Cross-Section of CsPbBr3 Perovskite Quantum Dots
2017
All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 +- 0.2. The …
Charge Transport and Recombination Layers for Perovskite Solar Cells
2020
El trabajo de esta tesis ha sido estructurado en tres secciones. En el capítulo 3, se estudió el rendimiento y la estabilidad de células solares tipo p–i–n de perovskita con y sin capa de transporte de cargas dopada. En el contacto p, el reemplazo de las capas de transporte de carga dopadas por alternativas no dopadas mejoró el rendimiento del dispositivo. En primer lugar, se identificó una barrera Schottky de inyección/extracción de carga en la interfaz ITO-TaTm. Mediante la inserción de una capa muy fina de la molécula de dopante tipo p entre el ITO y la HTL se consiguió aliviar dicha barrera. Esta estrategia da como resultado una reducción importante de la absorción parasítica. Esto cond…
Liikunnallisuus ja hyvä kunto ehkäisevät tyypin 2 diabetesta ja valtimotautien riskitekijöitä lapsesta lähtien
2021
Lasten ylipaino on saavuttanut epidemian mittasuhteet maailmanlaajuisesti. Vaikka viime vuosina tilanne on hiukan parantunut, ylipaino on edelleen yksi merkittävimmistä kansanterveydellisistä ongelmista. Riskitekijöiden kasautumisen ehkäisy ja hoito tulisi aloittaa mahdollisimman varhain: mielellään jo sikiöaikana tai viimeistään varhaislapsuudessa. nonPeerReviewed
Palladium local structure of La1-xSrxCo1-yFey-0.03Pd0.03O3-δperovskites synthesized using a one pot citrate method
2014
Nanostructured La1-xSrxCo1-yFey-0.03Pd0.03O3-δ(LSCF-Pd) perovskites with fixed La-Sr composition (x = 0.4) and two different Fe contents (y = 0.2 and 0.8) were successfully synthesized using a one pot citrate method starting from nitrates of the metal cations. Pd-free La1-xSrxCo1-yFeyO3-δ(LSCF) systems were prepared for comparison. LSCF powders were calcined at 1300 °C and characterized by XRD and Rietveld refinement, EXAFS, XPS, TPR analyses. Promotion of La0.6Sr0.4Co0.8Fe0.2O3-δand of La0.6Sr0.4Co0.2Fe0.8O3-δby incorporation of palladium was evidenced by solving the local environment of Pd using EXAFS spectroscopy. XPS analyses, in agreement with TPR measurements, demonstrated an inc…
Enhanced ferroelectric phase-transition temperature in perovskite-based solid solutions
2004
We explain how the phenomena of ferroelectric phase transition temperature ${T}_{c}$ enhancement beyond the end members in perovskite solid solution such as $\mathrm{Bi}M{\mathrm{O}}_{3}\text{\ensuremath{-}}{\mathrm{PbTiO}}_{3}$ ($M=\mathrm{Sc}$, In, etc.) is related to nonlinear and spatial correlation effects. The explanation is based on the calculation of ${T}_{c}$ in the framework of our random field theory with additional account for nonlinear effects in the above substances. We show that the maximum of ${T}_{c}$ for certain ${\mathrm{PbTiO}}_{3}$ content takes place when coefficient of nonlinearity is positive, the value of this coefficient is found from best fit between theory and ex…