Nature of optically active color-centers in two-dimensional lead iodide perovskites identified by photoemission

Two-dimensional perovskites have attracted considerable attention for potential applications in photonics and optoelectronics on the nanoscale due to their outstanding electrical and non-linear optical properties [1]. In particular, they are appealing since their optical emission properties can be controlled by their n value, which labels the number of inorganic monolayers building the quantum well structure (from n = 1, 2, 3 to bulk) [2,3]. We have been able to detect the presence of very narrow and spatially localised optical transitions in n=2 two-dimensional Lead Halide perovskites by micro-photoluminescence and time-decay measurements. These discrete optical transitions are characterized by sub meV linewidths (around 120 μeV) and long decay times (5-8 ns). In this communication, we use x-Ray photoemission and DFT calculations to investigate the chemical origin of electronic states responsible of these discrete optical transitions. In particular, our results show that the association of Phenethylammonium with Methylammonium cations into n=2 2D Ruddlesden-Popper perovskites, (PEA)₂(MA)_n−1Pb_nI_3n+1 promote the formation of donor-acceptor pairs corresponding to the displacement of lead atoms and their replacement by methylammonium. Ionized DAP recombination is identified as the most likely physical

source of the observed discrete optical transtions.

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2. A. G. Ricciardulli, S. Yang, J.H. Smet, M. Saliba. Emerging perovskite monolayers. Nature Materials 20, 1325–1336 (2021).

3. K. Leng, W. Fu, Y. Liu, M. Chhowalla, K.P. Loh. From bulk to molecularly thin hybrid perovskites. Nature Reviews Materials 5, 482–500 (2020).