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SPIE Optics + Photonics Digital Forum: perovskite progress yields blue VCSEL

26 Aug 2020

University of Toronto team's optically pumped device is one of many avenues of research into next-generation LEDs and lasers.

Researchers at the University of Toronto in Canada have fabricated a perovskite-based vertical cavity surface-emitting laser (VCSEL) operating at 425 nm.

The optically pumped structure, described in a plenary talk by Toronto professor Ted Sargent at this week’s SPIE Optics + Photonics Digital Forum, is one of a number of examples showing progress in the light-emitting potential of perovskite materials that are thus far better known for their photovoltaic applications.

The unpublished work by Joao Pina, a graduate student in Sargent’s research group, involved converting a cesium-lead perovskite structure from a brominated form into a chlorinated compound, which shifted its lasing wavelength deeper into the blue spectrum when sandwiched between mirrors and illuminated with a 337 nm pump source.

Color purity
Sargent used his presentation to outline a number of developments involving perovskites, in both LED and laser devices.

He explained that quantum-dot (QD) devices incorporating the novel materials could end up finding applications in the displays sector, where the high color purity of both QD structures and perovskites could yield wider color gamuts and screen brightness.

Blue sources could prove particularly valuable, because of the greater difficulty meeting commercial requirements with QD emitters operating at that end of the visible spectrum.

Members of the Sargent group have previously devised high-efficiency near-infrared LEDs based on lead sulfide (PbS) QDs in perovskite sheets, and come up with a way to reduce problems caused by phase segregation when using materials featuring a combination of bromide and chloride perovskites.

Strong results achieved in recent work include blue emitters with a record external quantum efficiency (EQE) of 12 per cent, and green emitters with an EQE of 20 per cent.

Technical challenges
Several challenges remain, however: perovskite materials tend to be based around lead atoms, which is problematic when it comes to environmental regulations in the electronics industry, and they remain susceptible to the effects of moisture and oxygen.

However, QD lasers incorporating the novel structures would have some highly attractive features, notably a low gain threshold and good tunability across different colors, as well as likely being extremely cheap to produce.

“The holy grail of the field is to move to electrically injected lasing,” Sargent said of the laser development, referencing work by Victor Klimov and his research team at Los Alamos National Laboratory as leading the way towards practical implementation of such devices.

• The SPIE Optics + Photonics Digital Forum, running 24-28 August, is free to access for all registered virtual attendees. For more information and registration details, visit the dedicated web site.

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