St. Andrews develops electrically-driven organic semiconductor laser

28 Sep 2023

New approach said to overcome major difficulties of such lasers, while retaining operational benefits.

Cross-section schematic of the electrically driven laser; yellow arrows indicate laser feedback and output.

Scientists at the University of St. Andrews, UK, say they are leading a “significant breakthrough” in a decades-long challenge to develop compact organic laser technology.

While many lasers used for typical applications in communications, medicine, surveying, manufacturing and measurement, are based on rigid, brittle, semiconductor crystals such as gallium arsenide, organic semiconductors are a newer class of electronic material.

Flexible, based on carbon, and emitting visible light, they enable the simple fabrication of electronic devices. They are now widely used for the organic light-emitting diode (OLED) screens found in most mobile phones.

St. Andrews says a limitation of organic semiconductor lasers is that they typically need another laser to power them: “Researchers have been working to overcome this limitation for 30 years, so it is particularly significant that scientists at the University of St Andrews have recently developed an electrically driven organic semiconductor laser,” stated the university’s press release.

The team made this breakthrough, reported on September 27th, in Nature, by first making an OLED with world-record light output and then carefully combining it with a polymer laser structure. This new type of laser emits a green laser beam consisting of short light pulses.

For now, this is mainly a scientific breakthrough, but with future development the laser could potentially be integrated with OLED displays and allow communication between them, or be used for spectroscopy for the detection of disease and environmental pollutants.

Prof. Ifor Samuel commented “Making an electrically driven laser from organic materials has been a huge challenge for researchers across the world. Now, after many years of hard work, we are delighted to have made this new type of laser.”

Prof. Graham Turnbull added “We expect this new laser to use less energy in its manufacture, and in the future will generate laser light across the visible spectrum.”

From the Nature paper

The abstract of the Nature paper explains how the St. Andrews team has overcome the common organic semiconductor problems of low current density and “intolerable losses [arising from] injecting charges into the gain medium”.

It states: “We achieve [reduced losses] by developing an integrated device structure that efficiently couples an OLED, with exceptionally high internal-light generation, with a polymer distributed feedback laser. Under the electrical driving of the integrated structure, we observe a threshold in light output versus drive current, with a narrow emission spectrum and the formation of a beam above the threshold. These observations confirm lasing.

“Our results provide an organic electronic device that has not been previously demonstrated, and show that indirect electrical pumping by an OLED is a very effective way of realizing an electrically driven organic semiconductor laser. This provides an approach to visible lasers that could see applications in spectroscopy, metrology and sensing.”

The paper concludes: “We have demonstrated an integrated device approach to achieve electrically driven laser action in organic semiconductors, and so addressed an important challenge in organic optoelectronics. This approach overcomes the major difficulties commonly faced in the attempts of direct electrical injection of organic or hybrid perovskite lasers, while retaining the operational advantages.”