Metal halide perovskites (MHPs) have numerous advantages as light emitters such as high photoluminescence quantum efficiency with a direct bandgap, very narrow emission linewidth, high charge-carrier mobility, low energetic disorder, solution processability, simple color tuning, and low material cost. Based on these advantages, MHPs have recently shown unprecedented radical progress (maximum current efficiency from 0.3 to 42.9 cd A-1 ) in the field of light-emitting diodes. However, perovskite light-emitting diodes (PeLEDs) suffer from intrinsic instability of MHP materials and instability arising from the operation of the PeLEDs. Recently, many researchers have devoted efforts to overcome these instabilities. Here, the origins of the instability in PeLEDs are reviewed by categorizing it into two types: instability of (i) the MHP materials and (ii) the constituent layers and interfaces in PeLED devices. Then, the strategies to improve the stability of MHP materials and PeLEDs are critically reviewed, such as A-site cation engineering, Ruddlesden-Popper phase, suppression of ion migration with additives and blocking layers, fabrication of uniform bulk polycrystalline MHP layers, and fabrication of stable MHP nanoparticles. Based on this review of recent advances, future research directions and an outlook of PeLEDs for display applications are suggested.

Improving the Stability of Metal Halide Perovskite Materials and Light-Emitting Diodes

A review of recent advances in thermophysical properties at the nanoscale: From solid state to colloids

This paper summarizes the basics of pulsed thermal nondestructive testing (TNDT) including theoretical solutions, data processing algorithms and practical implementation. Typical defects are discussed along with 1D analytical and multi-dimensional numerical solutions. Special emphasis is focused on defect characterization by the use of inverse solutions. A list of TNDT terms is provided. Applications of active TNDT, mainly in the aerospace industry, are discussed briefly, and some trends in the further development of this technique are described.

Review of pulsed thermal NDT: Physical principles, theory and data processing

An overview of corrosion defect characterization using active infrared thermography

Organic light emitting diodes (OLEDs) have been well known for their potential usage in the lighting and display industry. The device efficiency and lifetime have improved considerably in the last three decades. However, for commercial applications, operational lifetime still lies as one of the looming challenges. In this review paper, an in-depth description of the various factors which affect OLED lifetime, and the related solutions is attempted to be consolidated. Notably, all the known intrinsic and extrinsic degradation phenomena and failure mechanisms, which include the presence of dark spot, high heat during device operation, substrate fracture, downgrading luminance, moisture attack, oxidation, corrosion, electron induced migrations, photochemical degradation, electrochemical degradation, electric breakdown, thermomechanical failures, thermal breakdown/degradation, and presence of impurities within the materials and evaporator chamber are reviewed. Light is also shed on the materials and device structures which are developed in order to obtain along with developed materials and device structures to obtain stable devices. It is believed that the theme of this report, summarizing the knowledge of mechanisms allied with OLED degradation, would be contributory in developing better-quality OLED materials and, accordingly, longer lifespan devices.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202002254

Approaches for Long Lifetime Organic Light Emitting Diodes.

Current work presents a quantitative analysis of Joule heating by temperature measurements using infrared thermography and heat estimation of organic light emitting diodes (OLEDs) and their correlation with device life time. These temperature measurements were performed at 10, 20, 30, 40, and 50 mA/cm2 current densities and studied with operational time. The temperature rise of the device has increased from 9.8 to 16.6 °C within 168 h at an operating current density of 40 mA/cm2. This has been ascribed as due to the external contamination by water, oxygen, and dust particles as well as by internal heat generation. Encapsulation of the device avoids external degradation of OLEDs by preventing the destruction caused by these external contaminations. In this way, encapsulation has led to the decreased temperature rise of 12.4 °C within the duration of 168 h, which reflects the improved stability of the device. The temperature measured has been used to calculate the heat generated inside the device by solving the heat conduction equation using a transverse matrix approach. It has been found by these calculations that about 97%–98% of the power supplied to the device are converted into the heat for un-encapsulated device and results in rapid degradation of device with time, which in turns leads to the increase in operating voltage and decrease in luminous intensity with operational time. Proper encapsulation has reduced the heat generated inside the device by about 3%–4%, thereby, increasing the life time of the device. However, the glass encapsulation reduces the possibilities of the device cooling by heat convection to the atmosphere and prohibited the maximum utilization of encapsulation.

/pdf/elucidation-on-joule-heating-and-its-consequences-on-the-4d2ewhdlxs.pdf

Elucidation on Joule heating and its consequences on the performance of organic light emitting diodes

Thermal diffusivity measurements of templated nanocomposite using infrared thermography

The visualization of electromagnetic field intensity can be easily achieved by infrared thermography using an absorption screen of carbon loaded polymers. The electromagnetic waves falling on the absorption screen increase its temperature which is monitored by an infrared camera. The measured temperature profile can further be correlated to the electric field intensity. Measurement of electromagnetic field distribution is typically done by a small scanning antenna and is a time consuming process. Furthermore the scanning antenna will itself disturb the measurement process which is not the case with an absorption screen, even if the screen is kept very near to the electromagnetic wave source. Therefore fields very near to the source can also be visualized and measured. Also the length of the scanning antenna depends on wavelength of electromagnetic field to be measured, therefore it is improper to apply it to measure various fields. In order to show the utility of the above technique, an example of a patch antenna operating at a frequency of 2.45 GHz is given. Initial experiments show good agreement between simulated and measured results.

Suneet Tuli

Papers

Elucidation on Joule heating and its consequences on the performance of organic light emitting diodes

Thermal diffusivity measurements of templated nanocomposite using infrared thermography

Infrared thermography for electromagnetic field pattern recognition

Beam width estimation of microwave antennas using lock-in infrared thermography

Frequency modulated infrared imaging for thermal characterization of nanomaterials