Determination Of Internal Quantum Efficiency Research Articles

Determination of the internal quantum efficiency for photoelectrochemical reaction in a semiconductor photoelectrode by photoacoustic detection.

We showed for the first time the validity of photothermal measurement for determination of internal quantum efficiency, which is one of the most fundamental parameters for energy conversion systems. The measurement method using photoacoustic detection in the present study can be applied to a wide variety of samples and measurement conditions.

Determination of internal quantum efficiency in GaInN-based light-emitting diode under electrical injection: carrier recombination dynamics analysis

We proposed a method to determine the internal quantum efficiency (IQE) of GaInN-based light-emitting diode (LED). For the accurate determination thereof, we carefully reviewed a conventional carrier rate equation and then proposed a set of advanced formulae, which can comprehensively explain the carrier dynamics in a modern GaInN-based LED. Based on our proposed formula, this convenient method to determine the IQE is presented. Next, to identify the proposed carrier rate equations and recombination dynamics, we investigated carrier lifetime. We also discuss the physical origins of IQE degradation in a modern GaInN-based LED such as efficiency droop and green gap.

Demonstration of omnidirectional photoluminescence (ODPL) spectroscopy for precise determination of internal quantum efficiency of radiation in GaN single crystals

For rating unambiguous performance of a light-emitting semiconductor material, determination of the absolute quantum efficiency (AQE) of radiation, which is basically a product of internal quantum efficiency (IQE) and light-extraction efficiency, is the most delightful way. Here, we propose the use of omnidirectional photoluminescence (ODPL) spectroscopy for quantifying AQE of the near-band-edge (NBE) emission, in order to evaluate bulk GaN crystals and wafers. When the measurement was carried out in the air, the AQE showed a continuous decrease most likely due to the formation of extrinsic nonradiative recombination channels at the surface by photo-pumping. However, such an influence was suppressed by measuring ODPL in an inert ambient such as nitrogen or in vacuum. Consequently, AQE was revealed to depend on the photo-pumping density. The increase in AQE of the NBE emission caused by the increase in the excess carrier concentration was significant, indicating gradual saturation of nonradiative recombination centers in the bulk of GaN. The highest AQE value (8.22%) ever reported for the NBE emission of GaN at room temperature, which corresponds to IQE of 70.9%, was eventually obtained from the GaN wafer grown by hydride vapor phase epitaxy on a GaN seed crystal manufactured by the acidic ammonothermal method, when the cw photo-pumping density was 66 W/cm2.

Evaluation of the internal quantum efficiency in blue and green light-emitting diodes using the rate equation model

A convenient and reliable method for the determination of internal quantum efficiency (IQE) in GaN-based light-emitting diodes (LEDs) is presented. By using the peak point of the efficiency curve as the parameter of the carrier rate equation model, IQE of LEDs is shown to be unambiguously determined without any information on the recombination coefficients or LED structures. The theoretical analysis model was used to determine IQE of LED samples. When the theoretical IQE model is applied to the measured external quantum efficiency (EQE) of a blue and a green LED, good agreements between the measured data and the theoretical fit curves are found.

Electroluminescent measurement of the internal quantum efficiency of light emitting diodes

An experimental method is demonstrated for the determination of internal quantum efficiency (IQE) in III-nitride-based light-emitting diodes (LEDs). LED devices surrounded with an optically absorbing material have been fabricated to limit collected light to photons emitted directly from the quantum wells across a known fraction of the recombination area. The emission pattern for this device configuration was modeled to estimate the extraction efficiency. IQE can then be calculated from the measured input current and output power. This method was applied to c-plane InxGa1−xN-based LEDs emitting at 445 nm. Initial measurements estimate an IQE of 43%±1% at a current density of 7.9 A/cm2.

Angle dependence of external and internal quantum efficiencies in bulk-heterojunction organic solar cells

The realization of highly efficient organic solar cells requires the understanding and the optimization of the light path in the photoactive layer. We present in this article our approach to measure and model the optical properties of our bulk-heterojunction devices, and to control them in order to enhance the photovoltaic performances. We report our recent observations on the dependence of the external quantum efficiency (EQE) on the incidence angle of the light, and our results on the determination of internal quantum efficiency based on EQE measurement and optical modeling cross-checked by reflection measurements. We investigate poly(3-hexylthiophene): 1-(3-methoxy-carbonyl) propyl-1-phenyl[6,6]C61 based solar cells with two different thicknesses of the active layer (170 and 880nm), and show that in the thin ones the absorption is enhanced for oblique incident radiation.

Calibration of silicon photodiodes by photoacoustics

We present a new approach to the calibration of silicon photodiodes that are used for light (radiometric) power measurements. We describe the photoacoustic method for the determination of internal quantum efficiency and absolute spectral response of silicon photodiodes in the photovoltaic short-circuit mode. Measurements were taken for the different structures of silicon photodiodes.