Search results for "RECOMBINATION"
showing 10 items of 270 documents
Influence of stoichiometry on high temperature intrinsic defects in fused silica
1992
Abstract The set of intrinsic defects, their generation, interactions and recombination reactions are discussed, including the participation of atomic and molecular oxygen, which allows one to take into account the stoichiometry of fused silica. The mathematical solution of the set of equations, which characterizes the equilibrium concentrations of intrinsic defects, gives the specific values of intrinsic defect concentrations at different temperatures and stoichiometries. The influence of such intrinsic defects frozen in at room temperature on the spectroscopic characteristics of fused silica is analyzed.
Angular dependence of recombination luminescence-detected EPR in a ZnO crystal
2015
Angular dependency of electron paramagnetic resonance, optically detected by UV-excited recombination luminescence (RL-EPR), was measured for nominally pure ZnO single crystals. Observed magnetic resonances belong to the broad yellow RL band with slow decay centred at 610 nm, which is characteristic of untreated ZnO crystals. In the sample, irradiated with the 266 nm UV laser, an additional RL band centred at 740 nm appears, which has considerably faster decay time than the yellow one. This RL band is characteristic of the luminescence of Fe3+ ions in the ZnO crystals. It could be observed only after the UV laser treatment. No RL-EPR signal was detected for this RL band. Our spectral simula…
Doped TiO2 Nanomaterials and Applications
2008
This special issue brieflyreviews some trends and factors that have impacted heterogeneous photocatalysis with next generation TiO2 nanophotocatalysts that could absorband make use of both UV (290–400 nm) and visible (400–700 nm) sunlight to enhance process efficiencies, along with some issues of current debate in the fundamental understanding of the science that underpins the field. Preparative methods and some characteristics features of doped TiO2 as well as its environmental applications are presented and described. The next generation of doped TiO2 photocatalysts should enhance overall process photoefficiencies in many cases, since doped TiO2s absorb a greater quantity of solar radiati…
Charge Transport Layers Limiting the Efficiency of Perovskite Solar Cells: How To Optimize Conductivity, Doping, and Thickness
2019
Perovskite solar cells (PSCs) are one of the main research topics of the photovoltaic community; with efficiencies now reaching up to 24%, PSCs are on the way to catching up with classical inorganic solar cells. However, PSCs have not yet reached their full potential. In fact, their efficiency is still limited by nonradiative recombination, mainly via trap-states and by losses due to the poor transport properties of the commonly used transport layers (TLs). Indeed, state-of-the-art TLs (especially if organic) suffer from rather low mobilities, typically within 10(-5) and 10(-2) cm(-2) V-1 s(-1), when compared to the high mobilities, 1-10 cm(-2) V-1 s(-1), measured for perovskites. This work…
How does an In-containing underlayer prevent the propagation of defects in InGaN QW LEDs?: identification of SRH centers and modeling of trap profile
2021
Recent reports indicated that the use of an InAlN underlayer (UL) can significantly improve the efficiency of InGaN/GaN quantum well (QW) LEDs. Currently, this result is explained by considering that the UL reduces the density of nonradiative recombination centers in the QWs. However, an experimental proof of the reduction of defects in the QWs is not straightforward. In this paper, we use combined electrical (I-V), optical (L-I), capacitance (C-V), steady-state photocapacitance (SSPC) and light-assisted capacitance-voltage (LCV) measurements to explain why devices with UL have a much higher efficiency than identical LEDs without UL. Specifically, we demonstrated an improvement in both elec…
Recombination in Perovskite Solar Cells
2017
Trap-assisted recombination, despite being lower as compared with traditional inorganic solar cells, is still the dominant recombination mechanism in perovskite solar cells (PSCs) and limits their efficiency. We investigate the attributes of the primary trap assisted recombination channels (grain boundaries and interfaces) and their correlation to defect ions in PSCs. We achieve this by using a validated device model to fit the simulations to the experimental data of efficient vacuum-deposited p-i-n and n-i-p CH3NH3PbI3 solar cells, including the light intensity dependence of the open circuit voltage and fill factor. We find that, despite the presence of traps at interfaces and grain bounda…
Reduced Recombination Losses in Evaporated Perovskite Solar Cells by Postfabrication Treatment
2021
The photovoltaic perovskite research community has now developed a large set of tools and techniques to improve the power conversion efficiency (PCE). One such arcane trick is to allow the finished devices to dwell in time, and the PCE often improves. Herein, a mild postannealing procedure is implemented on coevaporated perovskite solar cells confirming a substantial PCE improvement, mainly attributed to an increased open-circuit voltage (V\(_{OC}\)). From a V\(_{OC}\) of around 1.11 V directly after preparation, the voltage improves to more than 1.18 V by temporal and thermal annealing. To clarify the origin of this annealing effect, an in-depth device experimental and simulation character…
Temperature dependent optical properties of stacked InGaAs/GaAs quantum rings
2008
4 páginas, 3 figuras, 2 tablas.-- MADICA 2006 Conference, Fifth Maghreb-Europe Meeting on Materials and their Applicatons for Devices and Physical, Chemical and Biological Sensors
Thermal Creation of Defects in GaTe
2008
Photoluminescence spectra of as-grown and annealed GaTe single crystals in the 0.7–1.8 eV range have been analyzed at different temperatures. Annealing up to 200 °C produces an increase in the recombination intensity of an excitonic characteristic. The annealing at 400 °C generates an intense optically active recombination in the infrared region (0.76 eV). The thermal generation of defects is possible, owing to the low melting temperature of GaTe (800 °C).
Luminescence of localized states in oxidized and fluorinated silica glass
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.