Intrinsic Limits of Charge Carrier Mobilities in Halide Perovskites: From 3D to Layered Materials

Over the past decade, we have witnessed the emergence of metal halide perovskites as a most formidable building block for emergent solar cells with record-breaking performances. Recently, 2D/3D materials that combine these ABX₃ (3D) metal halide perovskites with their layered (or 2D) counterparts, have enabled the fabrication of photovoltaic devices that are both stable and highly efficient. [1] Yet, it is well-known that layered perovskites exhibit poor charge carrier transport in comparison with 3D perovskites. [2] To date, the underlying mechanisms behind the reported reduced mobilities remain elusive. In this work, we employ a combination of state-of-the-art ab initio approaches [3] and symmetry analysis to explore the electron-phonon coupling mechanisms in layered halide perovskites. We start from the three-dimensional perovskite CsPbBr₃ and model the cases of layered n = 1 (Cs₂PbBr₄) and n = 2 (Cs₃Pb₂Br₇). We show that the diminished charge carrier mobilities in layered systems primarily originate from differences in the carrier's lifetimes. We identify the vibrational modes contributing to charge carrier scattering and associate them with polar-phonon scattering mechanisms arising from long-range Fröhlich coupling and non-polar optical deformation potential scattering processes. Furthermore, we show that the charge carrier mobilities are not only reduced by the increased polar-phonon interactions but also by an abrupt increase in the electronic density of states near the band edges. Our findings uncover the electron-phonon coupling mechanisms that intrinsically limit the charge carrier transport of layered metal halide perovskites, which is critical for their application in any optoelectronic device, such as solar cells.<br/><br/>JE acknowledges the support of the MEranet project Phantastic.<br/><br/>[1] I. Metcalf, S. Sidhik, H. Zhang, A. Agrawal, J. Persaud, J. Hou, J. Even, and A. D. Mohite. <i>Chem. Rev.</i> 123, 9565-9652, <b>2023</b>.<br/><br/>[2] S. G. Motti, M. Kober-Czerny, M. Righetto, P. Holzhey, J. Smith, H. Kraus, H. J. Snaith, M. B. Johnston, L. M. Herz.<i> Adv. Funct. Mater.</i> 33, 2300363,<b> 2023</b>.<br/><br/>[3] H. Lee, S. Poncé, K. Bushick, S. Hajinazar, J. Lafuente-Bartolome, J. Leveillee, C. Lian, F. Macheda, H. Paudyal, W. H. Sio, M. Zacharias, X. Zhang, N. Bonini, E. Kioupakis, E. R Margine, F. Giustino. <i>arXiv:2302.08085</i>, <b>2023</b>.