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.
