Multicolor Biexciton Lasers Based on 2D Perovskite Single Crystalline Flakes

Abstract The biexciton is a quasi‐particle created from two free excitons and can be applied for basic quantum operations, entangled light sources, and lasers. 2D lead‐halide layered perovskites (LPs) naturally form organic–inorganic quantum wells (QWs), leading to high exciton binding energy and tunable band‐gaps dependent on the QW thickness of <n> . Although excitonic lasing has been reported for thicker LP‐QWs, biexciton emissions and lasers from phase‐pure LP‐QWs as a function of <n> remain largely unexplored. Here, a facile solution growth method for fabricating single‐crystalline flakes (SCFs) of LP‐QWs of (PEA) 2 (MA) n −1 Pb n I 3 n +1 (PEA = phenylethylammonium, <n> = 1, 2, and 3) is reported. Further, multicolor amplified spontaneous emissions from biexciton states of (PEA) 2 (MA) n −1 Pb n I 3 n +1 ( <n> = 1, 2, and 3) SCFs are demonstrated at 541 (green), 588 (yellow), 627 nm (red) with thresholds of 35.4, 15.1, and 5.8 µJ cm −2 at 20 K, respectively. In order to offer cavities for these single‐crystalline flakes, they are exfoliated into smaller flakes. Multimode lasing is shown at 586 and 627 nm for <n> = 2 and 3 with threshold of 10.5 and 4.8 µJ cm −2 , respectively. The results of this study not only enrich the basic understanding of many‐body excitonic interactions in 2D LPs but also provide insights for developing solution‐processed multicolor lasers.