New Efficiency Record Set for Perovskite LEDs

Compared to OLEDs, which are widely used in high-end consumer electronics, the perovskite-based LEDs, developed by researchers at the University of Cambridge, can be made at much lower costs, and can be tuned to emit light across the visible and near-infrared spectra with high colour purity.

The researchers have engineered the perovskite layer in the LEDs to show close to 100% internal luminescence efficiency, opening up future applications in display, lighting and communications, as well as next-generation solar cells.

These perovskite materials are of the same type as those found to make highly efficient solar cells that could one day replace commercial silicon solar cells. While perovskite-based LEDs have already been developed, they have not been nearly as efficient as conventional OLEDs at converting electricity into light.

Earlier hybrid perovskite LEDs, first developed by Professor Sir Richard Friend’s group at the University’s Cavendish Laboratory four years ago, were promising, but losses from the perovskite layer, caused by tiny defects in the crystal structure, limited their light-emission efficiency.

Now, Cambridge researchers from the same group and their collaborators have shown that by forming a composite layer of the perovskites together with a polymer, it is possible to achieve much higher light-emission efficiencies, close to the theoretical efficiency limit of thin-film OLEDs. Their results are reported in the journal Nature Photonics.

This perovskite-polymer structure effectively eliminates non-emissive losses, the first time this has been achieved in a perovskite-based device,” said Dr Dawei Di from Cambridge’s Cavendish Laboratory, one of the corresponding authors of the paper. “By blending the two, we can basically prevent the electrons and positive charges from recombining via the defects in the perovskite structure.”


New Quantum Sensor Improves Cancer Treatment

A new quantum sensor developed by researchers at the University of Waterloo’s Institute for Quantum Computing (IQC) in Canada, has proven it can outperform existing technologies and promises significant advancements in long-range 3D imaging and monitoring the success of cancer treatments.

The sensors are the first of their kind and are based on semiconductor nanowires that can detect single particles of light with high timing resolution, speed and efficiency over an unparalled wavelength range, from ultraviolet to near-infrared.

The technology also has the ability to significantly improve quantum communication and remote sensing capabilities.

Interaction of single incident photon pulses and a tapered semiconductor nanowire array photodetector

A sensor needs to be very efficient at detecting light. In applications like quantum radar, surveillance, and nighttime operation, very few particles of light return to the device,” said principal investigator Michael Reimer, an IQC faculty member and assistant professor in the Faculty of Engineering’s electrical and computer engineering department. “In these cases, you want to be able to detect every single photon coming in.

The next generation quantum sensor designed in Reimer’s lab is so fast and efficient that it can absorb and detect a single particle of light, called a photon, and refresh for the next one within nanoseconds. The researchers created an array of tapered nanowires that turn incoming photons into electric current that can be amplified and detected.

Remote sensing, high-speed imaging from space, acquiring long range high resolution 3D images, quantum communication, and singlet oxygen detection for dose monitoring in cancer treatment are all applications that could benefit from the kind of robust single photon detection that this new quantum sensor provides.

The semiconducting nanowire array achieves its high speed, timing resolution and efficiency thanks to the quality of its materials, the number of nanowires, doping profile and the optimization of the nanowire shape and arrangement. The sensor detects a broad spectrum of light with high efficiency and high timing resolution, all while operating at room temperature. Reimer emphasizes that the spectrum absorption can be broadened even further with different materials.

This device uses Indium Phosphide (InP) nanowires. Changing the material to Indium Gallium Arsenide (InGaAs), for example, can extend the bandwidth even further towards telecommunications wavelengths while maintaining performance,” Reimer said. “It’s state of the art now, with the potential for further enhancements.”

Once the prototype is packaged with the right electronics and portable cooling, the sensor is ready for testing beyond the lab.  “A broad range of industries and research fields will benefit from a quantum sensor with these capabilities,” said Reimer.