Scientists from the Soochow University (Suzhou), the Chinese Academy of Sciences, East China Normal University (Shanghai) and Ural Federal University have developed an architecture of red-emitting perovskite LEDs (PeLEDs) that minimizes optical energy loss and significantly increases their efficiency and longevity.
The new work may open the door to high-performance LEDs for lighting devices, displays and other electronic devices. These could be energy efficient and at the same time have high brightness and long operating time.
"Our research team solved the problem by modifying the organic perovskite emitter PeLED and its light-emitting nanostructures. Thus, the surface of the LED was complicated by a certain order of numerous "patterns" - "hemispheres" several nanometers high. This led to a significant improvement in light output and, consequently, to a significant reduction in re-absorption of photons," explains Associate Professor of the Department of Electrophysics at Ural Federal University, research participant and co-author of the article Ivan Zhidkov.
When the light output increases, the voltage of electric current required to provide the brightness of the LED can be reduced. Therefore, when a smaller number of photons are absorbed, the so-called joule heating - heat generation inside the LED device, which is caused by the electric current - also decreases.
If in a flat LED the surface temperature already rose to 32°C in 20 seconds and in 50 seconds to 35°C, in a device with a patterned surface the temperature reached 30°C in 100 seconds and then stabilized at this level. Reducing the temperature of the LED prevented its thermal degradation and prolonged its lifetime.
It was found experimentally that the peak quantum efficiency (the ratio of energy invested to energy output) of the LED device with a patterned surface - 21.2% - is twice as high as that of the LED with a flat surface. At the same current voltage, the modified LED shines almost 2.5 times brighter, and its period of productive operation is 1.75 times longer.
"At a wavelength of 666 nanometers and an initial luminosity of 100 candel/square meter, the resulting peak quantum efficiency of the modified LED was observed for nearly 4807 hours. This is the longest high performance lifetime compared to similar PeLEDs available in the world. For example, the lifetime of the LED with the same brightness parameters and efficiency of 21.3% is only 5 minutes. The efficiency of the LED, whose lifetime at a similar brightness is 694 hours - 6.2%," emphasizes Ivan Zhidkov.
In addition, an article published by the same research team in the journal Advanced Science, describes the process of creating a new high-performance PeLEDs with sky-blue radiation. The method of obtaining these LED devices is simple and efficient, and the LEDs themselves have large for this class of devices (100 and 400 mm2) and a significant peak quantum efficiency - 9.2% and 6.1%, respectively.
