Search results for "LIFETIME"
showing 10 items of 212 documents
Influence of the intermediate density-of-states occupancy on open-circuit voltage of bulk heterojunction solar cells with different fullerene accepto…
2010
Electron density of states (DOS) and recombination kinetics of bulk heterojunction solar cells consisting of a poly(3-hexylthiophene) (P3HT) donor and two fullerene acceptors, either [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or 4,4′-dihexyloxydiphenylmethano[60]fullerene (DPM6), have been determined by means of impedance spectroscopy. The observed difference of 125 mV in the output open-circuit voltage is attributed to significant differences of the occupancy of the DOS in both fullerenes. Whereas DPM6 exhibits a full occupation of the electronic band, occupancy is restricted to the tail of the DOS in the case of PCBM-based devices, implying a higher rise of the Fermi level in the D…
Study of the e<sup>+</sup> Distribution in a Layered Stack Sample Using Positron Lifetime Spectroscopy
2010
The results of the Monte Carlo (MC) simulations, using GEANT4 codes, indicate the enhancement of the fraction of the e+ in the denser regions of the sample embedded by the less dense environment. The positron lifetime measurements, performed for two stacks of layers consisting of pure aluminum and silver do not seem to reveal this effect. Some features of the e+ distribution detected in the experiments are not reproduced by the MC simulations.
Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts
2011
We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for…
The Single Molecule Probe: Nanoscale Vectorial Mapping of Photonic Mode Density in a Metal Nanocavity
2009
International audience; We use superresolution single-molecule polarization and lifetime imaging to probe the local density of states (LDOS) in a metal nanocavity. Determination of the orientation of the molecular transition dipole allows us to retrieve the different LDOS behavior for parallel and perpendicular orientations with respect to the metal interfaces. For the perpendicular orientation, a strong lifetime reduction is observed for distances up to 150 nm from the cavity edge due to coupling to surface plasmon polariton modes in the metal. Contrarily, for the parallel orientation we observe lifetime variations resulting from coupling to characteristic λ/2 cavity modes. Our results are…
Donor/Acceptor Heterojunction Organic Solar Cells
2020
The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF &asymp
New process of silicon carbide purification intended for silicon passivation
2017
Abstract In this work, we report on a new, efficient and low cost process of silicon carbide (SiC) powder purification intended to be used in photovoltaic applications. This process consists on the preparation of porous silicon carbide layers followed by a photo-thermal annealing under oxygen atmosphere and chemical treatment. The effect of etching time on impurities removal efficiency was studied. Inductively coupled plasma atomic emission spectrometry (ICP-AES) results showed that the best result was achieved for an etching time of 10 min followed by gettering at 900 °C during 1 h. SiC purity is improved from 3N (99.9771%) to 4N (99.9946%). Silicon carbide thin films were deposited onto s…
Minority Carrier Lifetime Variations in Multicrystalline Silicon Wafers with Temperature and Ingot Position
2017
The minority carrier lifetimes of multicrystalline silicon wafers are mapped using microwave photoconductive decay for different temperatures and ingot positions. Wafers from the top of the ingot display larger areas with lower lifetimes compared to wafers from the bottom. The lifetimes of low-lifetime areas are found to increase with the temperature, while the lifetimes of some high-lifetime areas decrease or remain unchanged. The relative improvement of the low-lifetime areas is considerably larger than the relative change in the high-lifetime areas. We suggest that the above-mentioned observations explain, at least partially, why previous studies have found the relative temperature coeff…
Photoconductivity and photovoltaic effect in indium selenide
1983
Transport and phototransport properties of crystalline indium monoselenide (InSe) doped with a variety of elements are reported. Measured mobilities, lifetimes, and effective diffusion lengths of photoexcited carriers are used to interpret electrical and photovoltaic properties of several different structures. These include p‐n junctions, bismuth/p‐type InSe, platinum/n‐type InSe, and indium tin oxyde (ITO)/p‐type InSe. External solar efficiencies of the best devices are between 5% and 6%. The influence on the efficiency of the various parameters is evaluated, and ways of improvement are discussed.
Degradation mechanisms in organic lead halide perovskite light-emitting diodes
2019
Organic–inorganic metal halide perovskites have attracted significant attention for low-cost, high-efficiency, color-pure light-emitting applications. However, as seen in many reports so-far, perovskite light-emitting diodes (PeLED) suffer from poor operational lifetime, limiting their practical use. The underlying degradation mechanism is a topic of crucial importance. Here, the degradation mechanisms of methylammonium lead bromide based PeLED are investigated. When the PeLED is electrically biased, there is an initial raise in the luminance followed by a rapid reduction in luminance and current density. Microscopic studies reveal the formation of micrometer-sized spots that are photolumin…
Positron studies of hydrogen-defect interactions in proton irradiated molybdenum
1985
Molybdenum single crystals are irradiated at 20 K with 6 MeV protons. The radiation damage and lattice defect annealing is studied by positron lifetime spectroscopy in the temperature range from 15 to 720 K. Loss of vacancies due to recombination with mobile interstitials is observed at 40 K (Stage I) in agreement with resistivity measurements. This is the first time Stage I is observed by positrons below 77 K. The implanted hydrogen decorates the vacancies around 100 K, which is consistent with a hydrogen migration energy in molybdenum:E H = 0.3–0.4 eV. Clustering of spatially correlated vacancies takes place in a wide temperature region below the usual vacancy clustering stage (Stage III)…