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In a recent study, scientists have demonstrated an electrically driven perovskite laser using a dual-cavity design, addressing a challenge that has persisted in the field for over a decade.

The dual-cavity laser device developed by a team from Zhejiang University shows a lasing threshold an order of magnitude lower than state-of-the-art electrically driven organic lasers and offers superior operational stability with rapid modulation capabilities.

Â鶹ÒùÔº spoke with the research team about their work.

"Realizing electrically driven perovskite lasers is viewed by many researchers as the grandest challenge in the field of perovskite optoelectronics," said Chen Zou, Research Fellow at Zhejiang University and first author of the study. "As a research group actively working on perovskite LEDs and lasers, we are very excited to tackle this great challenge."

The persisting challenge

Perovskite semiconductors have emerged as exceptional materials for laser applications due to their high gain coefficients, long carrier lifetimes, and tunable emission wavelengths.

Even though these materials demonstrated impressive lasing performance under optical pumping (where an external laser excites the perovskite), electrically driven lasing stayed elusive.

"Solution-processed perovskites offer advantages including low cost, the ease of integration with other materials, spectrum tunability, and low optically pumped lasing thresholds, making them very attractive laser materials," explained Baodan Zhao, Associate Professor at Zhejiang University and co-author.

"However, these optically-driven perovskite lasers require external light sources to operate, significantly limiting their usefulness."

The challenge lay in overcoming fundamental barriers at both material and device levels.

At the material level, forming high-quality perovskite single crystals embedded within microstructures remains the main obstacle. The high electrical currents needed for lasing caused perovskite materials to suffer severe degradation and a dramatic roll-off in efficiency.

At the device level, two critical issues demanded resolution: improving the radiant exitance of microcavity perovskite LED components and maximizing optical coupling efficiency between cavity elements.

The dual-cavity solution

The research team's approach centers on an integrated dual-cavity architecture that splits the functions of electrical-to-optical conversion and optical amplification between two specialized components.

"Under electrical pulses, the intense directional emission from the perovskite LED in the first microcavity is absorbed by the perovskite single crystal in the second microcavity, which supports light amplification and the subsequent lasing," explained Prof. Dawei Di, Professor at Zhejiang University and co-author.

The mechanism exploits careful engineering of optical coupling between the two cavities. The first microcavity contains a high-power perovskite LED sub-unit, while the second houses a low-threshold single-crystal perovskite microcavity.

"Microcavity I is responsible for generating the intense directional photon flux that goes into the microcavity II, while the microcavity II is responsible for light amplification and lasing," said Zou.

The architectural structure focused on solving technical challenges related to crystal quality and optical coupling efficiency.

Engineering precision

The dual-cavity system required engineering two distinct perovskite components with different functions.

The lasing component required growing high-quality single crystals of formamidinium lead iodide (FAPbI₃) using space-confined inverse temperature crystallization. This technique involves growing the perovskite material within a controlled space between two surfaces over a carefully controlled temperature cycle, which lasted about two days.

The method produced crystals of exceptional quality: a surface roughness of only 0.7 nm and an optimized thickness of approximately 180 nm.

The electrical pumping component used a different perovskite composition, Csâ‚€.â‚…FAâ‚€.â‚…PbIâ‚‚Br, fabricated into a high-power LED through solution processing methods.

Both components were embedded between distributed Bragg reflectors with carefully engineered optical properties to maximize light coupling between the cavities.

"The optical coupling efficiency between the two microcavities was improved to 82.7% by reducing the divergence of emission from microcavity I and the coupling distance between the two microcavities," said Zhao.

This efficiency proved to be critical. Comparative studies showed the dual-cavity design achieved a 4.7-fold reduction in lasing threshold compared to a single-cavity architecture.

Performance and metrics

The device achieved notable performance metrics, particularly the lasing threshold, which is a measure of the current density needed to achieve lasing. The lasing threshold reached a minimum of 92 A/cm², with an average threshold of 129 A/cm². This represents an order of magnitude improvement over the best electrically-driven organic lasers.

Beyond the low threshold, the perovskite laser demonstrated an operational half-life of 1.8 hours under pulsed excitation (64,000 voltage pulses at 10 Hz), outperforming existing electrically pumped organic lasers.

"As the first demonstration, we were already surprised by the device's half-life of 1.8 hours," said Di. "Of course, the lifetime is considered very short from an application standpoint."

The researchers identified the primary limiting mechanisms as ion migration under electric fields and Joule heating under intense currents.

"These might be resolved in the future by improved heat dissipation of the devices and suppressed ion migration in the perovskite materials," Zhao noted.

Further, the device achieved impressive modulation capabilities, giving it rapid laser switching capabilities for digital information encoding during transmission.

The laser achieved a bandwidth of 36.2 MHz, indicating it can switch on and off 36.2 million times per second, with rise and fall times of 5.4 and 5.1 nanoseconds, respectively. This suggests that the device is feasible for optical data transmission applications.

Future work and applications

"The perovskite laser may be used in various applications such as optical data transmission, coherent light source in integrated photonic chips, and wearable devices," said Zou.

The researchers emphasized that this represents the beginning of further development.

"The demonstration of the electrically-driven perovskite lasers is just the beginning. The transition from an integrated pumping architecture we currently use to a simple laser diode structure would be a potential direction, as this would enable more compact and scalable optoelectronic applications," Di explained.

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