a) Schematic diagram of optical interference between two light beams originating from the same point in the emitting pn junction (horizontal black line) in a thin film LEC device, the only difference being that one of the light beams exits the device directly through the transparent electrode and substrate, Another ray of light is directed to the reflective electrode and leaves the device first after specular reflection. Left: The pn junction position is defined as 0 when it is located at the transparent electrode interface and 1 when it is located at the reflective electrode interface. b) Measured (solid line) and best-fit simulated (dashed line) EL spectra as a function of L1-thin viewing angle, recorded at steady state from a device driven by a current density of 10 mA cm2. The derived best-fit value for the pn junction position is 0.59. c) Steady-state position of the emitting pn junction as a function of current density for four LEC devices, as shown in the inset. Credit: advanced materials (2024). DOI: 10.1002/adma.202310156
Luminescent electrochemical cells (LECs) can be fabricated sustainably and cost-effectively on rigid and flexible surfaces, making them suitable for a wide range of applications such as lighting, healthcare and signage. Despite its potential, this technology faces a major challenge: emission efficiency decreases at higher currents, a phenomenon known as “efficiency roll-off.”
A research team at Umea University has now developed a method to identify and quantify the main factors affecting LEC efficiency.
“This insight will help us reduce efficiency losses and enable us to design and develop LEC devices that provide bright emission with high efficiency,” said Xiaoying Zhang, a doctoral student in the Department of Physics at Umea University and one of the authors of the book.research in journals advanced materials.
The breakthrough revolves around the detailed understanding and quantification of an internal so-called quenching process, in which collisions between particles in a device cause energy to be lost in the form of reduced light production.
“Imagine a box with two bouncing balls inside: one that glows and one that doesn’t. If a glowing ball hits another ball, it stops glowing and the light disappears. We discovered that it’s special It is the collision between the luminous ball and the non-luminous ball that is the main reason for the decrease in the efficiency of our equipment,” Zhang Xiaoying said.
“This loss mechanism is called ‘exciton-polaron quenching,’ and we found that more than half of the light is lost in this way,” Xiaoying continued. Therefore, the results of this study suggest that developing materials, device designs, and operating protocols that reduce the impact of this loss mechanism is a viable path toward achieving brighter, more efficient LECs.
The bright LEC device, bearing the May University logo, is thin, flexible and lightweight. Image source: Xiaoying Zhang, Joan Rfols-Rib
More information:
Zhang Xiaoying et al., Efficiency decay in luminescent electrochemical cells, advanced materials (2024). DOI: 10.1002/adma.202310156
Provided by Umeå University
citation: New understanding of energy losses in emerging light sources (2024, April 18), Retrieved April 19, 2024, from https://techxplore.com/news/2024-04-energy-losses-emerging-source.html
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