Patterned waveguide enhanced signal amplification within perovskite nanosheets

Researchers at Busan National University, led by Kwangseuk Kyhm, Professor of Ultra Fast Quantum Optoelectronics from the Department of Optics and Mechatronics, are enhancing signal amplification inside cesium bromide lead perovskite nanosheets through patterned waveguides.

Perovskite is a highly attractive material in solar cell applications, but its nanostructure is now being explored as a new laser medium.

"Light amplification within perovskite quantum dots has been reported, but due to the Auger process, there are inherent limits. It essentially shortens the decay time of population reversal - in this state, most of the system is in a higher excited energy state rather than a lower non excited energy state," said Kyhm. Moreover, due to the two-dimensional structure of perovskite nanosheets arranged in a sheet-like configuration at the nanoscale, the Auger process is relatively suppressed compared to quantum dots.

Efficient laser media require significant gain, so Kyhm's team turned to patterned waveguides to enhance signal amplification of perovskite nanosheets.

In order to enhance signal amplification, researchers chemically synthesized high-quality square CsPbBr3 nanosheets with an average lateral size of~140 ± 40nm. Then, the periodically patterned polyurethane acrylate substrate is filled with small perovskite nanosheets through a deposition process to form nanosheet stripes, and effective light amplification is carried out along these stripes.

"We used a new 'gain profile' gain analysis to overcome the limitations of early gain analysis," said Kyhm. Although the old method provided a gain spectrum, it was unable to analyze the gain saturation of long strip lengths. As the gain contour line shows the variation of gain with spectral energy and strip length, analyzing local gain changes along spectral energy and strip length is very convenient.

It has been proven that the team's patterned waveguide has great potential in efficient and controllable signal amplification. "The optical confinement effect of waveguides is excellent," said Kyhm. "The gain coefficient increases and the thermal stability is also improved."

Researchers say that the improvement in optical confinement and heat dissipation can be attributed to 2D centroid confinement excitons and localized states generated by uneven nanosheet thickness and defect states.

This progress will enable the development of more reliable and versatile devices based on perovskite nanosheets, such as lasers, sensors, and solar cells. In addition, it may also be used for information security, neuromorphic computing, and visible light communication. Of course, compared to traditional silicon-based solar cells, enhanced amplification and higher efficiency can improve the performance of perovskite solar cells.

When strong light is needed at the nanoscale, perovskite nanosheets can be combined with other nanostructures, allowing amplified light to act as optical probes. However, introducing perovskite nanosheets into consumer products such as smartphones and lighting will require overcoming stability, scalability, and toxicity issues.

"Perovskite quantum dots have been studied for use in lasers, but this zero dimensional structure has fundamental limitations," said Kyhm. Our work indicates that the 2D structure of perovskite nanosheets can be another solution.
What is the next step? "The basic physical principle of light amplification in perovskite nanosheets still needs to be verified," said Kyhm.

Source: Laser Net