Exotic Honeycomb NaCl Structures on a Lead Halide Perovskite Substrate—New Insights from Ab Initio Calculations

Sodium chloride (NaCl) is an ionic compound that plays a crucial role in the fine-tuning of electronic properties at heterogeneous junctions. NaCl is effectively employed in perovskite solar cells as an interlayer between the photoactive material and the charge transport layers. Despite its apparent simplicity, NaCl can exhibit unexpectedly complex interfacial structures, particularly under high pressure or at reduced dimensions.¹ The most stable surface facet of cubic NaCl is the (100) plane. However, recent experiments have revealed different surface terminations depending on the chemical nature and structure of the substrate. For instance, a hexagonal surface of NaCl has been observed on the diamond (110) surface.² In this context, this contribution delves into the interface between NaCl and the prototypical lead halide perovskite methylammonium lead iodide (MAPI) using first-principles calculations at the density functional theory (DFT) level.³ Our results indicate various possible NaCl surface reconstructions depending on the MAPI terminations and the nature of the interactions involved. The impact on the electronic structure of MAPI, including work function and band edge potentials, is also examined. These insights are pivotal for the development of new and more efficient perovskite solar cells. We also investigate the role of the salt in mitigating interface defects and improve charge transport between layers. Our findings highlight the importance of considering interface engineering in the design of perovskite solar cells. The ability to fine-tune the electronic properties of the interface through the choice of interlayer materials like NaCl opens new avenues for enhancing device performance.<br/><br/>1. Y. Zhao, Q. Zhang, Y. Li, L. Chen, R. Yi, B. Peng, D. Nie, L. Zhang, G. Shi, S. Zhang and L. Zhang, ACS Nano, 2022, 16, 2046–2053.<br/>2. K. A. Tikhomirova, C. Tantardini, E. V. Sukhanova, Z. I. Popov, S. A. Evlashin, M. A. Tarkhov, V. L. Zhdanov, A. A. Dudin, A. R. Oganov, D. G. Kvashnin and A. G. Kvashnin, J. Phys. Chem. Lett., 2020, 11, 3821–3827.<br/>3. A. Pecoraro, A.B. Muñoz-García, G.V. Sannino, P. Delli Veneri, M.Pavone, Phys. Chem. Chem. Phys., 2024, 26, 1602