Researchers at Imec have reported a metal halide perovskite LED (PeLED) stack that emits 1,000x more light “than state-of-the-art OLEDs”. The team developed a transparent PeLED architecture, that combines low optical losses with excellent current-injection properties.
In this work, the team showed that perovskite semiconductor optical amplifiers and injection lasers are within reach using this type of transparent PeLED.
Metal halide perovskites have emerged as promising gain materials for thin-film laser diodes. However, achieving electrically excited amplified spontaneous emission (ASE) in perovskite light-emitting diodes (PeLEDs), a pre-condition for perovskite laser diodes, is usually hindered by the conflicting requirements of high conductivity and high net modal gain of the device stack.
The Imec “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.”
Imec is working within a EU Horizon 2020 funded project called Ultra-Lux, which ends in September 2024.
“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 stimulated emission of light,” said Imec 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.”
The architecture is described as ‘an electrical assist of the conventional optical pumping’ and Imec said that electrical injection that contributes 13% to the total amount of stimulated emission “and thus approaches the threshold to achieve a thin film injection laser”.
The proof-of-concept device was operated at 77K.
Stimulated with 2.3ns optical pulses, it exhibited amplified stimulated emission above 9.1μJ/cm2.
The 3kA/cm2 was achieved with ‘sub-μs’ electrical excitation “with irradiance values above 40W/cm2” said Imec in the paper.
Co-pumping optical pulses synchronized with the leading edge of an electrical pulse reduced the amplified stimulated emission threshold by ~1.2μJ/cm2 “showing that electrically injected carriers contribute to optical gain”, said Imec in the paper. “We probe the PeLED with 1μs long optical excitation and observe continuous-wave amplified stimulated emission at a threshold of 3.8kW/cm2.”
Electrical pulses also generated electroluminescence close to half the irradiance produced by continuous-wave optical pumping at the amplified stimulated emission threshold.
