Advancing OLEDs: New Spectroscopy Boosts Lifespan
High-resolution, full-color displays—like those in foldable smartphones and ultrathin TVs—depend on organic light-emitting diodes (OLEDs). OLEDs are gaining popularity due to their flexibility, self-illumination, light weight, slim design, high contrast, and low power consumption.
An OLED consists of several ultrathin organic layers placed between two electrodes, each with a distinct function. When voltage is applied, charges build up at the interfaces between layers, and these charges recombine, emitting light in the process.. While the multilayer structure allows precise control of charge movement and light production, it also causes gradual degradation of the organic materials, reducing lifespan and efficiency.
Understanding the behavior of electronic structures at OLED interfaces during operation remains a major challenge. Professor Takayuki Miyamae, Mr. Tatsuya Kaburagi, and Dr. Kazunori Morimoto from Chiba University used sum-frequency generation (SFG) spectroscopy to study the vibrational and electronic properties at OLED interfaces, providing key insights into their real-time behavior.
As voltage is applied, charges recombine at the organic interfaces, producing light and altering the SFG signal. This change helps researchers observe how charges build up and how the electronic structure evolves under various operating conditions. The team published their innovative, nondestructive approach to studying charge dynamics in OLEDs online in the Journal of Materials Chemistry C on March 10, 2025.
Analyzing Charge Dynamics in Multilayer OLEDs Using ESFG Spectroscopy
In this research, they analyzed three distinct multilayer OLEDs, each featuring different types and combinations of organic layers. The team used electronic sum-frequency generation (ESFG) spectroscopy to track changes in spectral features related to charge activity and electronic structure at OLED interfaces. Prof. Miyamae explains, “We observed how variations in electric field strength affect internal charge movement and light emission, marking the first clear demonstration of these field differences on device performance.”
The researchers identified ESFG spectral bands for each organic layer by comparing the absorption spectra and structural configurations across the three OLED devices. When they applied voltage, they observed changes in the intensity of the spectral signals, which linked to variations in the internal electric field and charge dynamics within the OLEDs.
Specifically, applying voltage caused an increase in signal intensity at the absorption band of the hole transport layer (which carries positive charges), while the signal intensity at the light-emitting layer’s absorption band decreased. These changes indicate that charge movement varies across different organic layers, resulting in shifts in the observed spectra.
Impact of BAlq on Light Emission and Efficiency in OLEDs
The team also used square-wave pulse voltages on the devices to investigate how the internal electric fields changed over time. Their experiments revealed that incorporating BAlq—a material commonly used for electron transport in OLEDs—alters the location of light emission within the device. This change influences not only the color and pattern of the emitted light but also the overall efficiency of converting electrical energy into light.
Professor Miyamae commented on the significance of the study, stating that the ESFG technique offers a groundbreaking, highly efficient, and non-invasive spectroscopic method for analyzing how injected charges generate electric fields in solid-state thin-film devices.
This technique helps design OLEDs with longer lifespans, better energy efficiency, and lower costs, speeding up the integration of ultrathin organic devices. Prof. Miyamae adds, “It can also streamline the materials development process, reducing reliance on trial-and-error and lengthy degradation testing.”
Read the original article on: Scitech Daily
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