Perovskite LED points the way to perovskite laser diodes

Belgian research lab Imec is claiming to have created a metal halide perovskite LED stack that emits 1,000x more light “than state-of-the-art OLEDs”, it said.

With the assistance of an external laser, the same stack exhibited the electrically-pumped amplified spontaneous emission that would be necessary in a laser.

The “result is a milestone towards a perovskite injection laser, promising applications in image projection, environmental sensing and medical diagnostics,” according to the lab. “While perovskites can withstand very high current densities, laser operation with the emission of high-intensity coherent light has not been reached yet.”

In a nutshell the team achieved:

Electroluminescence (LED behaviour) with only electrical power applied to the device
Amplified spontaneous emission using solely optical pumping from an external laser
Amplified spontaneous emission with a electrical power and with less optical pumping

Imec has dubbed the perovskite-based LEDs ‘PeLEDs’.

“In the project, Imec showed for the first time a PeLED architecture with low optical losses and pumped these PeLEDs to current densities that support the spontaneous emission of light,” said principal investigator Professor Paul Heremans. “This architecture of transport layers, transparent electrodes and perovskite as the active material, can operate at 3kA/cm², tens of thousands of times higher than conventional OLEDs can.”

With electrical and optical stimulation combined, Imec said that electrical injection that contributes 13% to the total amount of spontaneous emission “and thus approaches the threshold to achieve a thin film injection laser”.

The proof-of-concept device was operated at 77K.

40W/cm² of LED-like emission was achieved at 3kA/cm², said Imec in the Nature Photonics paper ‘Electrically assisted amplified spontaneous emission in perovskite light emitting diodes‘.

Stimulated with 2.3ns external laser pulses only, it exhibited amplified spontaneous emission above 9.1μJ/cm².

Applying external laser pulses synchronised with 3.5kA/cm² electrical pulses allowed the external laser to be turned-down ~1.2μJ/cm², while still achieving amplified spontaneous emission – showing that electron-injection has replaced some of the external laser energy.

Electrical pulses also generated electroluminescence close to half the optical output produced by continuous-wave optical pumping at the amplified spontaneous emission threshold.

“It is the goal to reach amplified spontaneous emission, or lasing threshold, by purely electrical pumping,” team member Robert Gehlhaar told Electronics Weekly. “This would be equivalent to an optical threshold reduction of 9.1μJ/cm² for that device. We still have a way to go, but have passed the milestone of demonstrating a significant electrical contribution to the amplified spontaneous emission signal.”

Earlier this week, Pusan National University announced amplified spontaneous emission from a solution-processed perovskite, although this was only optically pumped, without the necessary stack for electron-to-photon conversion – a useful electronic laser component would require all-electrical pumping plus structures that optically-confine a cavity for lasing to occur.