Ultra-Bright Thin-Film Light Emitting Devices and Lasers

Project Information

ULTRA-LUX

Grant agreement ID: 835133

DOI

10.3030/835133

Project closed

EC signature date 3 May 2019

Start date 1 October 2019

End date 30 September 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 497 493,00

EU contribution

€ 2 497 493,00

Coordinated by

INTERUNIVERSITAIR MICRO-ELECTRONICA CENTRUM
Belgium

Periodic Reporting for period 4 - ULTRA-LUX (Ultra-Bright Thin-Film Light Emitting Devices and Lasers)

Reporting period: 2024-04-01 to 2024-09-30

Summary of the context and overall objectives of the project

The objective was to demonstrate high brightness thin film LEDs and achieve injection lasing. High brightness is crucial for applications like sensing, spectroscopy, and ranging in various fields. While crystalline III-V semiconductors have been used for decades, thin film devices with organic, quantum dot, or perovskite-based media have lower current densities but are highly customizable and versatile for integration and custom designs.
Our target was a power density of P>30W/cm² for a thin-film light source, achieving an IQE>75% (EQE~15%) at J≤100A/cm². This would ideally also be the lasing threshold for low loss resonators with embedded perovskite LEDs.
During the project, we made significant progress. We developed new perovskite compositions and device stack combinations, including transport layers and electrodes. We advanced in device fabrication and design to support ultrahigh current densities necessary for electrically generated stimulated emission. Newly developed characterization setups and methods provided deep insights into device operation under extreme conditions. We also optimized to reduce optical losses and promote mode amplification.
Overall, our work has been published in over 20 peer-reviewed articles, including highlights in Nature Photonics and Advanced Materials, combining achievements and insights from the past five years.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work was divided into three packages: (1) process development and device fabrication; (2) study of perovskite electro-optical performance and device physics; (3) optical design and characterization of perovskite films and photonic devices.
Strategies were developed to extract device parameters from PeLEDs at high current densities, identifying effects influencing temporal response and demonstrating the advantage of pulsed voltage biasing to reduce hysteresis impact. The focus then shifted to reducing the driving voltage of perovskite LEDs to lower power loss and internal heat generation, achieving a maximum EQE of 11.4% at 330mA/cm² and a T50 stability of >500 hours at 50mA/cm² [DOI: 10.1002/adom.202100586].
To address heat generation and low thermal conductivity, scaling the active area was chosen to reduce the pumping volume, enabling lasing-level current density injection at a low absolute current. PeLEDs were also operated under cryogenic conditions to further reduce Joule heating [DOI: 10.1002/adom.202200024]. Studies on charge transfer and energy migration in quasi-2D perovskites showed charge carrier transfer dominance at low temperatures (15K) [DOI: 10.1002/adfm.202010076]. Alternating cations in the interlayer space improved stability and EQE in PeLEDs [DOI: 10.1515/nanoph-2021-0037].
Vacuum deposition was used to improve parameter control during film preparation, showing potential for light-emitting devices [DOI: 10.1021/acsaelm.1c00252].
Using organic LEDs, we have established a new optical characterization method to analyze the emission zone profile of thin film devices [DOI: 10.1002/adma.202201409].

In collaboration with imec's photovoltaics department, we developed a perovskite composition that improved solar cell performance by reducing interface voltage losses, achieving record high fill factors and power conversion efficiencies, and successfully implemented it in PeLED stacks to achieve ultra-high current densities with low total power input [DOI: 10.1021/acsenergylett.3c00697].

In the workpackage on the optical film and device properties, we have introduced a new characterization method for optically generated gain [DOI: 10.1021/acsphotonics.3c00204]. To improve the comparability of results between the different research groups working on thin film devices for ASE and lasing, we have summarized our learnings on threshold pump conditions by suggesting a unified data reporting [DOI: 10.1002/adpr.202400065]. Distributed feedback (DFB) resonators have been selected as the ideal resonator concept within this project. Early prototypes have been fabricated by electron beam lithography and reproduced by nanoimprint lithography [DOI: 10.1021/acsphotonics.3c00206]. By applying our optical characterization setup, we have been able to spectrally image our devices in various configurations. We have been able to report the coexistence of three different stimulated emission processes (ASE, random lasing and distributed feedback lasing) and have shown that the introduction of transparent conductive oxides in the resonator geometry is feasible to achieve lasing.

We have fabricated DFB resonators in imec’s 200mm wafer line using deep-UV lithography, where thousands of different designs within a single die give new insights into the design parameter dependencies. A combination of device screening and advanced optical device modelling, enabled us to find optimum design parameters for a number of device stack and a method to model future architecture [DOI: 10.1002/adom.202302496].

In Nature Photonics, we demonstrated gain generation by electrical pumping of a scaled PeLED in a transparent architecture, reducing the optical pump ASE threshold by 13% through simultaneous optical and electrical pumping [DOI: 10.1038/s41566-023-01341-7]. We also showed continuous wave pumped ASE from the same device, comparing emission intensity at threshold with maximum intensity from purely electrical pumping, and outlined a route towards injection lasing from perovskite LEDs in a Perspective published in Advanced Materials [DOI: 10.1002/adma.202314193].

We published 20 peer-reviewed articles in high-impact journals and presented 18 talks and posters at major conferences. The project highlight was featured in a press release and we were invited to present in a webinar. An article in "EU Research" magazine is set for December 2024, and we submitted two European patent applications based on our results.

All achievements of this work are used to continue the injection laser development within the EIC Pathfinder project SUPERLASER within a strong European consortium.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have identified Joule heating as the major issue for PeLED efficiency at high current densities. To address this, we introduced methods like layer engineering, pulsed driving, device area scaling, thermally conductive substrates, and cryogenic operation. These steps led to high light power generation at several kA/cm² and demonstrated the contribution of electrically injected carriers to the net gain of amplified spontaneous emission in a PeLED, marking a milestone towards a perovskite injection laser.
The next step is integrating this diode into a resonator geometry. We selected distributed feedback resonators and used our characterization setup and modelling approaches to identify design parameters for the lowest lasing thresholds. Our analysis provides insights into design factors like layer thicknesses, resonator lengths, grating periods, and duty cycles, applicable beyond thin film devices.
We identified 3D perovskites as the most promising for injection lasing. Despite low external quantum efficiencies at low driving powers, their charge transport and thermal properties are beneficial at high current densities for gain generation, which was initially counterintuitive.

Transparent perovskite light emitting diodes on sapphire substrate with scaled emission area for inj