Search results for "efficiency"

Efficient Photo- and Electroluminescence by Trap States Passivation in Vacuum-Deposited Hybrid Perovskite Thin Films

2018

Methylammonium lead iodide (MAPI) has excellent properties for photovoltaic applications, although it typically shows low photoluminescence quantum yield. Here, we report on vacuum-deposited MAPI perovskites obtained by modifying the methylammonium iodide (MAI) to PbI2 ratio during vacuum deposition. By studying the excitation density dependence of the photoluminescence lifetime, a large concentration of trap states was deduced for the stoichiometric MAPI films. The use of excess MAI during vacuum processing is capable of passivating these traps, resulting in luminescent films which can be used to fabricate planar light-emitting diodes with quantum efficiency approaching 2%.

Short photoluminescence lifetimes in vacuum-deposited ch3nh3pbI3 perovskite thin films as a result of fast diffusion of photogenerated charge carriers

2019

It is widely accepted that a long photoluminescence (PL) lifetime in metal halide perovskite films is a crucial and favorable factor, as it ensures a large charge diffusion length leading to a high power conversion efficiency (PCE) in solar cells. It has been recently found that vacuumevaporated CH3NH3PbI3 (eMAPI) films show very short PL lifetimes of several nanoseconds. The corresponding solar cells, however, have high photovoltage (>1.1 V) and PCEs (up to 20%). We rationalize this apparent contradiction and show that eMAPI films are characterized by a very high diffusion coefficient D, estimated from modeling the PL kinetics to exceed 1 cm2/s. Such high D values are favorable for long di…

2015

Two novel charged organic thermally activated delayed fluorescence (TADF) emitters, 1 and 2, have been synthesized. Their TADF behavior is well-supported by the multiexponential decay of their emission (nanosecond and microsecond components) and the oxygen dependence of the photoluminescence quantum yields. Spin-coated electroluminescent devices have been fabricated to make light-emitting electrochemical cells (LEECs) and organic light-emitting diodes (OLEDs). The first example of a non-doped charged small organic molecule LEEC is reported and exhibited an external quantum efficiency (EQE) of 0.39% using 2. With a multilayer architecture, a solution-processed OLED device using neat 2 as the…

Transient photoresponse and incident power dependence of high-efficiency germanium quantum dot photodetectors

2012

We report a systematic study of time-resolved and power-dependent photoresponse in high-efficiency germanium quantum dot photodetectors (Ge-QD PDs), with internal quantum efficiencies greater than 100 over a broad wavelength, reverse bias, and incident power range. Turn-on and turn-off response times (τ on and τ off) are shown to depend on series resistance, bias, optical power, and thickness (W QD) of the Ge-QD layer, with measured τ off values down to ∼40 ns. Two different photoconduction regimes are observed at low and high reverse bias, with a transition around -3 V. A transient current overshoot phenomenon is also observed, which depends on bias and illumination power. © 2012 American …

Enhancement of spin Hall conductivity in W-Ta alloy

2020

Generating pure spin currents via the spin Hall effect in heavy metals has been an active topic of research in the last decade. In order to reduce the energy required to efficiently switch neighbouring ferromagnetic layers for applications, one should not only increase the charge- to-spin conversion efficiency but also decrease the longitudinal resistivity of the heavy metal. In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} / CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance measurements. Alloying W with Ta leads to a factor of two change in both the damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal resistivity (60 - 120…

Flashlamp-pumped Ti:Sapphire laser: Influence of the rod figure of merit and Ti3+ concentration

1994

A flashlamp-pumped Ti:Sapphire laser is tested with rods of various Figures of Merit (FOM from 100 to 800) and Ti3+ concentrations (0.1 and 0.15% by weight) and we measured the laser energy dependence as a function of these parameters. Output energies above 2 J are obtained without dye converter, leading to a 1.8% overall efficiency and a 2.2% slope efficiency. The effects of pump pulse duration by variation of the discharge capacitance are also monitored.

Synthesis of phenothiazine-based di-anchoring dyes containing fluorene linker and their photovoltaic performance

2015

Abstract A new di-anchoring organic dye based on phenothiazine featuring A-D-π-D-A (acceptor-donor-π-linker-donor-acceptor) configuration with fluorene as the π linker was designed and successfully synthesized. Compared to the corresponding mono-anchoring D-A congener, this new dye exhibited a broader and stronger absorption in the light wavelength ranging from 400 nm to 600 nm and thus showed a more efficient photovoltaic performance for dye-sensitized solar cells (DSSCs). The overall power conversion efficiency (η) of this new dye in a sensitized solar cell amounted to 5.70%, which is 17% higher than that of the equivalent based counterpart (4.87%). On the other hand, the introduction of …

Metal-free organic dyes with di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole as a donor for efficient dye-sensitized solar cells: Effect of mono- and bi-anch…

2019

Abstract Four novel metal-free organic dyes WL1a-b and WL2a-b containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as electron donor were synthesized and applied for dye-sensitized solar cells (DSSCs), where DBTP was firstly employed as a donor in the organic dyes. It has been demonstrated that the dyes WL with DBTP as a donor show better photovoltaic performance than the reference dye PTZ with phenothiazine as a donor. In comparison with WL1a-b with one cyanoacrylic acid as mono-anchor, WL2a-b with two cyanoacrylic acids as bi-anchors show a broader light absorption on the TiO2 film and higher molar extinction coefficients in solution, resulting in higher power conversion efficiency. …

Efficient and Long-Living Light-Emitting Electrochemical Cells

2010

Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6-position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4-position. The phenyl group allows for intramolecular π–π stacking, which renders the complex more stable and yields long-living light-emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory…

High performance p-type segmented leg of misfit-layered cobaltite and half-Heusler alloy

2015

In this study, a segmented p-type leg of doped misfit-layered cobaltite Ca_(2.8)Lu_(0.15)Ag_(0.05)Co_4O_(9+δ) and half-Heusler Ti_(0.3)Zr_(0.35)Hf_(0.35)CoSb_(0.8)Sn_(0.2) alloy was fabricated and characterized. The thermoelectric properties of single components, segmented leg, and the electrical contact resistance of the joint part were measured as a function of temperature. The output power generation characteristics of segmented legs were characterized in air under various temperature gradients, ΔT, with the hot side temperature up to 1153 K. At ΔT ≈ 756 K, the maximum conversion efficiency reached a value of ∼5%, which is about 65% of that expected from the materials without parasitic l…