Implications of open circuit voltage of light-emitting diodes installed for plant cultivation

AbstractWe compare the electroluminescence (EL) of three polycrystalline ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells with similar bandgaps but different open circuit voltages, indicating a difference in the electronic quality of the absorber. Temperature dependent electroluminescence measurements reveal that all cells feature transitions from donor-acceptor pair recombination at lower temperatures to band to band recombination at higher temperatures. However, the less efficient cells show a longer transition range with donor-acceptor pair recombination still apparent at room temperature. The thus broadened room temperature luminescence is one effect which reduces the open circuit voltage of the devices below the Shockley-Queisser-limit. The other effect is the existence of non-radiative recombination currents, which determine the efficiency of the device as light emitting diode. To quantify the open circuit voltage losses, we use reciprocity relations between electroluminescent and photovoltaic action of solar cells, which allow us to predict the light emitting diode efficiency. Measurements support the theory and show that Cu(In,Ga)Se2 solar cells reach external LED efficiencies approaching.

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Accelerated Life Testing in Epoxy Packaged High Luminosity Light Emitting Diodes

Journal of Electronic Packaging ◽

10.1115/1.4004659 ◽

2011 ◽

Vol 133 (3) ◽

Cited By ~ 5

Author(s):

Eduardo Nogueira ◽

Manuel Vázquez ◽

Carlos Algora

Keyword(s):

Light Emitting Diodes ◽

Failure Mechanisms ◽

Open Circuit ◽

Accelerated Life Testing ◽

High Luminosity ◽

Light Emitting ◽

Operation Conditions ◽

Accelerated Life ◽

Catastrophic Failures ◽

Temperature And Humidity

In this work, we have evaluated the reliability of epoxy packaged light emitting diodes (LEDs) for outdoor applications by specific tests to enhance catastrophic failures that appear under high temperature and humidity operation conditions. The different failure mechanisms were analyzed observing two main types: one is open circuit catastrophic failures induced by moisture and the other one power luminosity degradation. The influence of temperature and humidity on catastrophic failures was modelled using the Arrhenius–Peck law obtaining an activation energy of 0.87 eV and a Peck parameter of 2.29. MTTF value of 1.582 × 106 h at low bias current, 10 mA, has been evaluated.

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Influence of the Carrier Mobility and Charge Accumulation in Interfacial Layers on Deterioration in Organic Light-emitting Diodes

IEEJ Transactions on Fundamentals and Materials ◽

10.1541/ieejfms.137.291 ◽

2017 ◽

Vol 137 (5) ◽

pp. 291-297

Author(s):

Hirofumi Nakamura ◽

Miki Kuribayashi ◽

Chihaya Adachi

Keyword(s):

Carrier Mobility ◽

Light Emitting Diodes ◽

Organic Light Emitting Diodes ◽

Charge Accumulation ◽

Light Emitting ◽

Interfacial Layers ◽

Organic Light

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Injecting Inter-Layers and the Built-in Potential of Blue Polymer Light-Emitting Diodes

MRS Proceedings ◽

10.1557/proc-660-jj6.9 ◽

2000 ◽

Vol 660 ◽

Author(s):

Thomas M. Brown ◽

Ian S. Millard ◽

David J. Lacey ◽

Jeremy H. Burroughes ◽

Richard H. Friend ◽

...

Keyword(s):

Indium Tin Oxide ◽

Light Emitting Diodes ◽

Basic Structure ◽

Thin Layers ◽

Carrier Injection ◽

Semiconducting Polymer ◽

Light Emitting ◽

Physical Mechanisms ◽

Organic Solid ◽

Polymer Light Emitting Diodes

ABSTRACTThe semiconducting-polymer/injecting-electrode heterojunction plays a crucial part in the operation of organic solid state devices. In polymer light-emitting diodes (LEDs), a common fundamental structure employed is Indium-Tin-Oxide/Polymer/Al. However, in order to fabricate efficient devices, alterations to this basic structure have to be carried out. The insertion of thin layers, between the electrodes and the emitting polymer, has been shown to greatly enhance LED performance, although the physical mechanisms underlying this effect remain unclear. Here, we use electro-absorption measurements of the built-in potential to monitor shifts in the barrier height at the electrode/polymer interface. We demonstrate that the main advantage brought about by inter-layers, such as poly(ethylenedioxythiophene)/poly(styrene sulphonic acid) (PEDOT:PSS) at the anode and Ca, LiF and CsF at the cathode, is a marked reduction of the barrier to carrier injection. The electro- absorption results also correlate with the electroluminescent characteristics of the LEDs.

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Microcrystalline (Si,Ge):H Solar Cells

MRS Proceedings ◽

10.1557/proc-762-a7.6 ◽

2003 ◽

Vol 762 ◽

Cited By ~ 1

Author(s):

Jianhua Zhu ◽

Vikram L. Dalal

Keyword(s):

Solar Cells ◽

Buffer Layer ◽

Quantum Efficiency ◽

Fill Factor ◽

Open Circuit Voltage ◽

Defect Density ◽

Cell Structure ◽

Open Circuit ◽

Base Layer ◽

Ecr Plasma

AbstractWe report on the growth and properties of microcrystalline Si:H and (Si,Ge):H solar cells on stainless steel substrates. The solar cells were grown using a remote, low pressure ECR plasma system. In order to crystallize (Si,Ge), much higher hydrogen dilution (∼40:1) had to be used compared to the case for mc-Si:H, where a dilution of 10:1 was adequate for crystallization. The solar cell structure was of the p+nn+ type, with light entering the p+ layer. It was found that it was advantageous to use a thin a-Si:H buffer layer at the back of the cells in order to reduce shunt density and improve the performance of the cells. A graded gap buffer layer was used at the p+n interface so as to improve the open-circuit voltage and fill factor. The open circuit voltage and fill factor decreased as the Ge content increased. Quantum efficiency measurements indicated that the device was indeed microcrystalline and followed the absorption characteristics of crystalline ( Si,Ge). As the Ge content increased, quantum efficiency in the infrared increased. X-ray measurements of films indicated grain sizes of ∼ 10nm. EDAX measurements were used to measure the Ge content in the films and devices. Capacitance measurements at low frequencies ( ~100 Hz and 1 kHz) indicated that the base layer was indeed behaving as a crystalline material, with classical C(V) curves. The defect density varied between 1x1016 to 2x1017/cm3, with higher defects indicated as the Ge concentration increased.

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Low-Temperature Operation of Green, Blue and UV InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes

MRS Proceedings ◽

10.1557/proc-764-c5.5 ◽

2003 ◽

Vol 764 ◽

Author(s):

X. A. Cao ◽

S. F. LeBoeuf ◽

J. L. Garrett ◽

A. Ebong ◽

L. B. Rowland ◽

...

Keyword(s):

Quantum Well ◽

Light Emitting Diodes ◽

Multiple Quantum Well ◽

Light Output ◽

Localized States ◽

Multiple Quantum ◽

Nonradiative Recombination ◽

Light Emitting ◽

Temperature Range ◽

Green Leds

Absract:Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission energies ranging from 2.3 eV (green) to 3.3 eV (UV) has been studied over a wide temperature range (5-300 K). As the temperature is decreased from 300 K to 150 K, the EL intensity increases in all devices due to reduced nonradiative recombination and improved carrier confinement. However, LED operation at lower temperatures (150-5 K) is a strong function of In ratio in the active layer. For the green LEDs, emission intensity increases monotonically in the whole temperature range, while for the blue and UV LEDs, a remarkable decrease of the light output was observed, accompanied by a large redshift of the peak energy. The discrepancy can be attributed to various amounts of localization states caused by In composition fluctuation in the QW active regions. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED. The large number of localized states in the green LEDs are crucial to maintain high-efficiency carrier capture at low temperatures.

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