No more droop: LED future looks bright
UC SANTA BARBARA (US) — Researchers have conclusively identified what causes light emitting diodes (LEDs) to dim and be less efficient at high drive currents.
Until now, scientists had only theorized the cause behind the phenomenon known as LED “droop”—a mysterious drop in the light produced when a higher current is applied. The cost per lumen of LEDs has held the technology back as a viable replacement for incandescent bulbs for all-purpose commercial and residential lighting.
This could all change now that the cause of LED efficiency droop has been explained, according to researchers James Speck and Claude Weisbuch of the Center for Energy Efficient Materials at the University of California, Santa Barbara.
Knowledge gained from this study is expected to result in new ways to design LEDs that will have significantly higher light emission efficiencies. LEDs have enormous potential for providing long-lived high quality efficient sources of lighting for residential and commercial applications.
The results of the study are to be published in the journal Physical Review Letters. The US Department of Energy recently estimated that the widespread replacement of incandescent and fluorescent lights by LEDs could save electricity equal to the total output of fifty 1GW power plants.
“Rising to this potential has been contingent upon solving the puzzle of LED efficiency droop,” comments Speck, professor of materials. “These findings will enable us to design LEDs that minimize the non-radiative recombination and produce higher light output.”
Chris van de Walle, a professor at UC Santa Barbara, and colleagues theorized in 2011 that a complex non-radiative process known as Auger recombination was behind nitride semiconductor LED droop, whereby injected electrons lose energy to heat by collisions with other electrons rather than emitting light.
Speck, Weisbuch, and their research team have now accomplished a definitive measurement of Auger recombination in LEDs.
The experiment used an LED with a specially prepared surface that permitted the researchers to directly measure the energy spectrum of electrons emitted from the LED. The results unambiguously showed a signature of energetic electrons produced by the Auger process.
The research was supported by the US Department of Energy Office of Science and the French government.
Source: UC Santa Barbara