Tunable White-Light Emission from Self-Trapped Excitons in Ultrathin Sheets of a Low-Dimensional Hybrid Perovskite

Low-dimensional organic-inorganic perovskites complement the advantages of two classes of materials for next-generation optoelectronics: They combine customized building blocks for atomically thin, layered materials with the enhanced light-harvesting and -emitting capabilities of perovskites. These materials promise a playground for exploring novel phenomena driven by the dynamic interplay of electronic, photonic, and vibrational excitations.<br/> <br/>Traditionally, the prevailing belief has been that in-plane covalent interactions are an absolute prerequisite for forming atomically thin materials. This belief has, in turn, limited the range of candidates for 2D materials.<br/> <br/>In this study, we challenge this prevailing paradigm and present single layers of the one-dimensional organic-inorganic perovskite [C₇H₁₀N]₃[BiCl₅]Cl.^[1] Its unique crystal structure facilitates the exfoliation of single layers and the formation of self-trapped excitons, resulting in tunable white-light emission. Remarkably, the thickness-dependent behavior of exciton self-trapping leads to an unprecedented photoluminescence shift of 0.4 eV between bulk crystals and ultrathin sheets.<br/> <br/>Our research demonstrates that even 1D covalent interactions suffice to create atomically thin materials, granting access to unique photophysics. These findings enable a versatile construction principle for identifying and creating two-dimensional materials, eliminating the prior constraint of covalently bonded 2D sheets.<br/><br/>[1] Klement, P.; Dehnhardt, N.; Dong, C.-D.; Dobener, F.; Bayliff, S.; Winkler, J.; Hofmann, D. M.; Klar, P. J.; Chatterjee, S.; Heine, J. (2021): Atomically Thin Sheets of Lead-Free 1D Hybrid Perovskites Feature Tunable White-Light Emission from Self-Trapped Excitons. <i>Adv. Mater.</i> <b>33</b>, 2100518, DOI: 10.1002/adma.202100518