From Electrically Assisted Amplified Spontaneous Emission to Injection Lasing with Metal Halide Perovskites

Metal halide perovskites have emerged as promising gain media for thin-film laser diodes. However, achieving electrically excited amplified spontaneous emission (ASE) and lasing in perovskite light-emitting diodes (PeLEDs) is challenged by the conflicting requirements of high conductivity and high net modal gain of the device stack. We break this trade-off by developing a transparent PeLED architecture that combines excellent current-injection properties with low optical losses [1]. The device is operated at 77 K and delivers current densities above 3 kA cm^-2 with irradiance values above 40 W cm^-2, whilst displaying an ASE threshold of 9.1 μJ cm^-2 using 2.3 ns optical laser pulses. By co-exciting the PeLED with optical pulses that are synchronized with the leading edge of an intense electrical pulse, we achieve a reduction of the ASE threshold by 1.2 μJ cm^-2, showing that electrically injected carriers contribute to optical gain. This breakthrough addresses the first essential pre-condition for perovskite laser diodes. A perovskite gain layer with a three-dimensional morphology has been used in this work, showing that there is potential for the reduction of the amplification threshold through elaborate quantum confinement engineering.<br/><br/>Integration of an optical cavity, which does not compromise PeLED performance, is a critical next step in transitioning from optical amplifier structures to laser diodes. It is noteworthy that reaching injection lasing might turn out to be more accessible than cavity-free electrically stimulated ASE. Specifically, when studying standalone perovskite films deposited over distributed feedback structures, we have achieved an optically pumped lasing threshold that is a factor of ~2 lower than the ASE threshold of neat films [2]. Consequently, we propose an integration route where the resonators are embedded into the substrate with a planarized arrangement of alternating materials with differing refractive indices. This approach eliminates challenges associated with the thin-film deposition atop corrugated surfaces, such as increased leakage currents, strong local electric fields, and nonuniform current distribution. Finally, we show that such a planarized grating can be married with the proposed transparent PeLED architecture, where efficient mode coupling is facilitated by the use of a thin bottom transparent electrode [3]. We believe that this alternative integrating scheme will accelerate the development of thin-film perovskite injection lasers.<br/><br/>[1] Elkhouly, K., Goldberg, I., Zhang, X. et al. Electrically assisted amplified spontaneous emission in perovskite light-emitting diodes. Nat. Photon. (2024). https://doi.org/10.1038/s41566-023-01341-7<br/>[2] Annavarapu, N., Goldberg, I., Hamdad, S. et al. Four-Dimensional Design Space of High-Q Second-Order Distributed Feedback Perovskite Lasers. Advanced Optical Materials (2024). Accepted (adom.202302496).<br/>[3] Goldberg, I., Annavarapu, N., Leitner, S. et al. Multimode Lasing in All-Solution-Processed UV-Nanoimprinted Distributed Feedback MAPbI₃ Perovskite Waveguides. ACS Photonics (2023). https://doi.org/10.1021/acsphotonics.3c00206.