Life Of Light-emitting Diodes Research Articles

Passivating CsPbBrxI3−x quantum dots via modifiers film to achieve efficient red light-emitting diodes

Although CsPbBrxI3−x quantum dots (QDs) have wide prospects for application in red light-emitting diodes (LEDs) due to their superior optoelectronic properties, the presence of defects and insulating long-chain ligands severely limits their luminescence performance. A novel strategy of spinning-coated CsPbBrxI3−x QDs on a PEABr or PEAI modified layer is designed to obtain red LEDs with efficient performance. The systematic studies on the structural evolution and optoelectronic properties of CsPbBrxI3−x QDs are discussed. The structural stability and electrical conductivity of CsPbBrxI3−x QDs are significantly improved because the halogen vacancies and insulating long-chain ligands (oleic acid and oleylamine) in CsPbBrxI3−x QDs are passivated and replaced by halogens and short-chain PEA from PEAX (X = Br and I), respectively. Modifying PEABr and PEAI obviously enhances the maximum external quantum efficiency (EQEmax) of CsPbBrxI3−x LEDs from 1.6 % to 11.7 %, and 14.9 %, respectively. Additionally, the electroluminescence (EL) spectral stability and useful life of LEDs are also ameliorated. The interfacial layer formed by the modified solution during the fabrication process of LEDs can effectively passivate the defects in QD films and improve the performance of LEDs. This preparation method is simple and easy to operate, which facilitates the design of efficient and stable QD-LEDs.

Performance Analysis of Various Types of High Power Light Emitting Diodes

Solid state, energy efficient light emitting diode (LED) technology is coming up to replace the conventional gas discharge, etc. light sources. Although declared life of LED is very high but in tropical countries their life time appears very short. This phenomenon is becoming the most drawbacks for usage of LED. To search out the reason for the failure lead to undertake thorough study on the performance of LED specifically on the various environmental conditions. Experimentation was carried out with various types of commercially available high power LED. Failure in tropical countries may be due to effect of temperature. Test results have been noted at various major parts of LEDs, e.g. die, and sink area. Detail analysis of test results at various parts of LEDs in different conditions tends to have some idea about the cause of failure of the LEDs in tropical countries with high ambient temperature and less scope of heat generation by the light source.

Prognostic algorithms for L70 life prediction of solid state lighting

The life of light-emitting diodes (LEDs) is difficult to measure by traditional testing methods as they are not likely to fail completely. The Illuminating Engineering Society of North America (IESNA) uses a standard regression approach based on short-term collected lumen data to predict the L70 lifetime of LEDs. In this paper, a model-based prognostics method is employed to determine the life of luminaires using LEDs. Unscented Kalman filter and particle filter algorithms are used for degradation model parameter estimation. An analytical approach based on three statistical models (Weibull, normal, lognormal) is employed and a best fit is determined by the Akaike information criterion. The resulting L70 is compared with L70 derived from the IESNA approach to accurately determine the best prognostic method.

A Low Firing Temperature Copper Conductor for use on an Aluminum Metal Compatible Dielectric in LED Thermal Substrate Applications

One of the most important contributing factors in the long life of LEDs (Light Emitting Diode) is keeping them cool, i.e., lowering the junction temperature, which can get as high as 150 °C. One way to accomplish this when building a circuit containing many LED packages is to use a thermal substrate. The majority of High Power/High Brightness (HP/HB) LED thermal circuits manufactured today are based on Metal Core Printed Circuit Board (MCPCB) technology. The MCPCB system consists of a copper foil, polymer dielectric layer and either an aluminum or copper base layer that are laminated together. The process of making MCPCB is a subtractive process, where most of the copper foil is removed. The copper foil is etched to create a circuit layer, the polymer dielectric provides the insulation between the copper foil and the metal base, and the aluminum or copper base provides thermal dissipation. The thick film copper paste discussed in this document is processed using an additive process, like screening printing, where the copper conductor is deposited only in the chosen area. The copper thick film paste is screen printed to create a circuit design on top of a thick film dielectric (insulated area) layer which is also printed on a metal base layer. The selective deposition allows for less material usage, and potentially lower overall cost as well as improved thermal performance with inclusion of thermal vias. This paper discusses the results of a newly developed lead (Pb) and cadmium (Cd) free low firing temperature (580–600°C) copper thick film conductor paste on top of a low temperature firing dielectric paste. This study includes evaluations based on SEM photos, solderability, leach resistance, and initial and long term adhesions using SAC 305 solder and RMA flux. There are many different applications for HP/HB LED circuits, from general lighting to street lighting to automotive lighting and more. All of them have varying degrees of performance testing requirement. To try to cover as much of the reliability testing as possible we have included tests such as thermal aging (150°C), thermal cycling from −50 to+150°C, as well as 85°C/85% RH reliability testing under bias.

Photometric method of study of semiconductor heterostructures

The problems of diagnostics of the parameters of light-emitting diodes are considered. The method of study described is applicable for the study of degradation phenomena in any emitting structures and devices based on them, as well as in classical emitters, lamps (incandescent, luminescent, metal-halogen, and others). The method of study of degradation phenomena in semiconductor emitting heterostructures is based on measurements of the spatial distribution of luminous intensity by the goniophotometric method. By example of the technology of thermal ultrasound welding of contact conductors, the physical mechanisms affecting the degradation of characteristics of emitting dies and light diodes based on them are described. The ways of increasing the reliability and useful life of light-emitting diodes are demonstrated.