Researchers from the Rensselaer Polytechnic Institute established the reason behind the loss of efficiency of light-emitting diodes (LEDs). The so-called “efficiency droop” causes as much as 20% greater electrical currents, preventing major improvements in LED lights for household needs.
The study, published in the journal Applied Physical Letters, describes a phenomenon referred to as “electron leakage” and provides a method to over come the limitations.
The team is led by E. Fred Schubert, the Wellfleet Senior Constellation Professor of Future Chips at Rensselaer, founding director of the university’s National Science Foundation-funded Smart Lighting Engineering Research Center. Together with his colleagues, Schubert looked into the causes behind efficiency droop, unlike previous researchers, who focused on reducing it without finding the reasons for its occurrence.
The basic working principle of LEDs is based on the movement of high-energy electrons, which emit light, or photons, as they move between the different energy levels. The negatively electrons are injected into one of the sections within the LEDs, while the positively charged “holes” are injected into another. As part of an electrical current, the electrons and the holes move in opposite directions to each other.
In general, when an electron meets a hole they recombine and emit photons. The efficiency of LEDs is then determined by the amount of electrical current that runs through the diodes. The more current is applied, the less efficient the LEDs are.
The researchers established that electrons escape under higher currents due to the development of an electric field. Although this concept, also known as electron leakage” has been proposed five years ago, this study is the first one to present solid evidence relating it to efficiency droop.
According to David Meyaard, first author on the study and a doctoral student in electrical engineering, the study demonstrates the principle of electron leakage. The main cause was identified to be the difference in mobility of electrons and holes, resulting in diffusion of electrons.
The next step for the team is to implement these findings into a design of a new structure for LEDs, which is much more efficient than current technology.