Article:Safdar, Amna, Wang, Yue orcid.org/0000-0002-2482-005X and Krauss, Thomas F. orcid.org/0000-0003-4367-6601 (2018) Random lasing in uniform perovskite thin films. Optics Express. A75-A84. ISSN 1094-4087 https://doi.org/10.1364/OE.26.000A75eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract: Following the very promising results obtained by the solar cell community, metal halide perovskite materials are increasingly attracting the attention of other optoelectronics researchers, especially for light emission applications. Lasing with both engineered and selfassembled resonator structures, such as microcrystal networks, has now been successfully observed, with the low cost and the simple solution-based process being a particular attraction. The ultimate in simplicity, however, would be to observe lasing from a continuous thin film, which has not been reported yet. Here, we show random lasing action from such a simple perovskite layer. Our lasers work at room temperature; they are deposited on unpatterned glass substrates and they exhibit a minimum threshold value of 10 µJ/cm 2 . By carefully controlling the solution processing conditions, we can determine whether random lasing occurs or not, using identical precursors. A rather special feature is that some of the films exhibit single and dual mode lasing action, which is rarely observed in random lasers. Our work fully exploits the simplicity of the solution-based process and thereby adds an important capability into the emerging field of perovskite-based light emitters. Heiss, and M. V. Kovalenko, "Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites," Nat. Commun. 6, 8056-8064 (2015). 12. J. Xing, F. Yan, Y. Zhao, S. Chen, H. Yu, Q. Zhang, R. Zeng, H. V. Demir, X. Sun, A. Huan, and Q. Xiong, "High-Efficiency Light-Emitting Diodes of Organometal Halide Perovskite Amorphous Nanoparticles," ACS Nano 10(7), 6623-6630 (2016). Brenner, M. Stulz, D. Kapp, and T. Abzieher, "Highly stable solution processed metal-halide perovskite lasers on nanoimprinted distributed feedback structures," Appl. Random lasing in uniform perovskite