193 / 2024-07-08 17:01:19

Time and Spatially Resolved Electroluminescence Spectroscopy for QLED Analysis

electroluminescence,quantum dot light-emitting diodes,time-resolved spectroscopy,operational mechanisms

Quantum dots light emitting diodes (QLED) are emerging as new generation self-emissive display technology with the advantages of high brightness, high efficiency, wide color gamut, and low-cost solution fabrication. After about 30 years of effort, the device performance of QLEDs has been greatly improved, which results in the achievements of maximum efficiency over 20% for all the colors. To push forward the display industrialization, there is an urgent need to improve the stability of QLEDs especially the blue ones, which inspired the mechanism study of operational QLED devices.

The time-resolved electroluminescence (TREL) technique is an in-situ non-destructive testing method used to investigate the operational mechanisms of LED devices by recording the real-time brightness under pulsed voltage. Combined with time-resolved current (TRC) results, parameters such as series resistance, parallel resistance, and capacitance can be extracted from the equivalent circuit of the QLED device. These parameters can be used to model the key processes in typical TREL spectra including the delay, rising, and decay stages, and thus quantitatively determine the charge accumulation and recombination in an operational QLED.

Furthermore, time and spatially resolved electroluminescence spectroscopy (TSR-EL) is developed to measure the spatial distribution of light emission from LED devices. By combining a single-photon camera (SPC) with the time-gated sampling method, we derived the time and spatially resolved electroluminescence intensity with increasing time. Benefiting from the high sensitivity of the SPC, this methodology can detect ultralow electroluminescence at the delay stage from the device operated around the turn-on voltage. The spatial light distribution of a typical QLED was investigated under different applied voltages and varied temperatures.

Intended Session: Nano-optoelectronics

Reference:

H. Bao et al. The Journal of Physical Chemistry Letters 2023, 14, 7, 1777-1783

Y. Cao et al. ACS Photonics 2024, 11, 2, 731-736