Continuous wave (CW) operation of perovskite lasers is of critical importance for many applications. However, most reports on perovskite lasers solely investigate the lasing behavior under short pulsed excitation, since it was found that stimulated emission in methylammonium lead triiodide (MAPI) typically ceases after a few tens to hundreds of nanoseconds for unknown reasons [1, 2]. To date, sustained photon lasing in perovskite thin films was only clearly proved in a pump-induced tetragonal-orthorhombic mixed crystal phase in MAPI, which can only exist at a very special operation temperature [3].

We will present a study on triple cation perovskites (TCP), which shows that CW amplified spontaneous emission (ASE) can be achieved in these kinds of perovskites at any temperatures between 80 K to 140 K. Temperature dependent photoluminescence (PL) from 290 K to 80 K indicates that the phase of the TCP remains the same from room to cryogenic temperatures. A comparison between CW and pulsed excitation over a wide range of pump energies unambiguously demonstrates the ability of TCP to support CW ASE in a single crystalline phase. As the emission of our TCPs occurs from a single phase, the same crystalline phase that they possess at room temperature, this opens a route towards perovskite CW lasers operating at room temperature.

The investigations are performed on TCP, whose emission properties have been optimized by small stoichiometric deviations [4] and imprint lithography [5]. For nanosecond pulsed excitation, the ASE threshold of these TCP is found to decrease exponentially from 95 µJ/cm² at 290 K to 2.2 µJ/cm² at 80 K. The relations between the temperature dependent thresholds, the carrier lifetimes and the recombination mechanisms will be discussed. To support the conclusions, time and temperature dependent PL measurements will be presented. The ASE threshold for CW excitation at 80 K will then be shown to be 387 W/cm². The plausibility of such a CW threshold is discussed in the context of the Bernard-Duraffourg condition [6] and based on the results from the time dependent PL measurement. Furthermore, investigations on the ASE stability under CW excitation will be shown, which reveal that the CW ASE stability is similar to the previously reported ASE stabilities under pulsed excitation. Temperature dependent measurements of the ASE spectra show that ASE can be maintained up to 140 K, where the material degradation threshold drops below the CW ASE threshold. Possibilities for a further increase of the operation temperature will be discussed.