Room‐Temperature Stimulated Emission and Lasing in Recrystallized Cesium Lead Bromide Perovskite Thin Films

Abstract

Metal-halide perovskite semiconductors are of tremendous interest for a variety of applications. Only recently, solar cells based on a representative of this family have been certified with an efficiency in excess of 24%.[1] Aside from their remarkable success in photovoltaics, metal-halide perovskites are also highly promising as light emitters, e.g., in light-emitting diodes (LEDs) or lasers. [2][3][4] LEDs based on the fruit-fly of these compounds, i.e., methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPbI 3 ), and other related perovskites have been demonstrated with continuously increasing efficiency. [5][6][7] For lasers, there is the vision that perovskites may overcome/avoid the typical limitations and loss mechanisms present in organic gain media, such as triplet-singlet annihilation or absorption due to triplet excitons and Cesium lead halide perovskites are of interest for light-emitting diodes and lasers. So far, thin-films of CsPbX 3 have typically afforded very low photoluminescence quantum yields (PL-QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX 3 nanoparticles (NPs).Here, thin films of cesium lead bromide, which show a high PL-QY of 68% and low-threshold ASE at RT, are presented. As-deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin-film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX 3 perovskites can only be achieved with NPs.

Thermal properties of CsPbCl3 thin films across phase transitions

“…An initial study by backscattered scanning electron microscopy (SEM) revealed a notable contrast ( figure 1(b)). Note, a similar contrast has previously been evidenced by electron backscatter diffraction (EBSD) for Cs x Pb y Br z perovskite thin films that had undergone a similar procedure [2,32], where the contrast could be clearly assigned to CsPbBr 3 (3D) and CsPb 2 Br 5 (2D) grains in the film. In the present case, the coexistence of 3D phase CsPbCl 3 and the 0D phase Cs 4 PbCl 6 has been confirmed by XRD ( figure 1(c)).…”

“…Individual layers of 10 nm CsCl and 5 nm PbCl 2 were deposited alternately to produce a 200 nm thick pristine layer on glass substrates. Subsequently, a planar hot pressing process (PHP) was carried out with a pressing time of 30 min at 100°C and a pressure of 100 bar to re-crystallize the film and to form the perovskite as reported earlier [2,32]. This re-crystallization step affords thin films consisting of large crystals with a low surface roughness (∼1 nm rms) [34,35].…”

“…Perovskite semiconductors are of tremendous interest for a variety of applications due to their relatively simple processing technology and their outstanding optoelectronic properties. Among then, all-inorganic perovskites are of particular interest for light emitting devices [1] and lasers [2] as organic-inorganic halide perovskites lack intrinsic stability [3,4]. The phase transitions of all-inorganic lead halide perovskites, such as CsPbX 3 (X=Cl, Br, I), are already known for a long time [5].…”

Advances in inorganic and hybrid perovskites for miniaturized lasers

“…Under the excitation of the fs laser (400 nm, 100 fs, 1 kHz), the thresholds of the F-P mode laser were as low as ~19, ~9 and ~25.5 μJ/cm 2 for the stable red, green and blue lasing, respectively. Recently, Pourdavoud et al implemented the CsPbBr 3 thin film featuring large crystals with micrometer lateral extension as a gain layer to demonstrate the high performance VCSEL [83]. The threshold was only ~2.2 μJ/cm 2 and the FWHM was narrowed down to 0.07 nm ( Figure 7C).…”

“…Consequently, the ultralow lasing threshold of 13 W/cm 2 with narrow FWHM of ~0.7 nm was achieved, thus demonstrating a major step toward electrically pumped perovskite lasing. In 2019, Pourdavoud et al used a DFB structure, which was formed by a recrystallized perovskite CsPbBr 3 thin film, to achieve a low threshold (7.2 μJ/cm 2 ) and narrow FWHM (0.14 nm) laser emission ( Figure 7E) [83]. PC refers to an artificial periodic dielectric structure with photonic band gap characteristics and has a wavelength selection function.…”