Interstitial Defect Relaxation DFT Study of Lead Halide Perovskites

Perovskite solar cells have garnered a lot of attention in the last decade. The efficiency obtained for solar cells using metal halide perovskites (MHP) have exceeded 22%. A major reason for this is the high carrier lifetimes in these materials [1]. These high efficiencies have been obtained despite relatively high defect densities as compared to those in Silicon solar cells, giving rise to an appreciation of high defect-tolerance in MHPs. Polycrystalline films made using metal halide perovskites can exhibit high defect densities of (10¹⁵ − 10¹⁶ per ����³), with minimal effect on efficiency. However, the origin of this tolerance is still a matter of active research. Halide defects (vacancies and interstitials) are some of the most common defects in perovskites. This is due to low defect formation energy in these systems. DFT studies exist to quantify the formation energies of halide defects [2]. Our work will study the relaxation of these interstitials back to their lattice site using DFT (Quantum Espresso). The recombination pathway as well as the activation energy for this relaxation will help us better understand how these defects affect the recombination time for photogenerated carriers. The pathway to relaxation can be estimated using Nudged Elastic Band calculations (NEB).<br/><br/>Funding Acknoledgements:<br/>PC acknowledges support from the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), under award DE-SC0022305. Kumar Miskin thanks Johns Hopkins University for his support. The authors acknowledge the support afforded by access to the computing facilities at the petascale Advanced Research Computing at Hopkins (ARCH) facility (rockfish.jhu.edu), supported by the National Science Foundation (NSF), Grant Number OAC 1920103, for providing the extensive computational resources needed here. Partial funding for the infrastructure for ARCH was originally provided by the State of Maryland.<br/><br/>References:<br/>1. Wehrenfennig, C.; Eperon, G. E.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites. Adv. Mater. 2014, 26, 1584−1589.<br/>2. Meggiolaro, D.; De Angelis, F. First-Principles Modeling of Defects in Lead Halide Perovskites: Best Practices and Open Issues. ACS Energy Lett. 2018, 3 (9), 2206– 2222