Linn Leppert1
University of Twente1
Halide double perovskites are an emerging class of photoactive materials with considerable structural and electronic diversity [1,2, 3] and reliable stability towards heat and moisture under ambient conditions. However, in contrast to ABX<sub>3</sub> perovskites like CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, most halide double perovskites have comparably large band gaps and exhibit signatures of strongly bound and self-trapped excitons [4, 5]. In the first part of this talk, I will show how the band gap of Cs<sub>2</sub>AgBiBr<sub>6</sub> can be dramatically altered by dilute alloying with symmetry-matched impurities leading to significantly reduced band gaps while preserving long carrier lifetimes [6]. I will also discuss the challenges that first principles numerical modelling techniques face for accurately describing defects in this chemically and electronically diverse family of materials [7].<br/><br/>In the second part of my talk, I will focus on the migration dynamics of halide vacancies in CsPbBr<sub>3</sub>. Migration of halide vacancies is one of the primary sources of phase segregation and material degradation in lead-halide perovskites. We use first principles density functional theory to compare migration energy barriers and paths of bromine vacancies in the bulk and at a surface of CsPbBr<sub>3</sub>. We find that surfaces facilitate bromine vacancy migration due to their soft structure that allows for bond length variations larger than in the bulk. Our calculations also demonstrate that this effect can be mitigated by lattice-matched passivation with alkali halide salts [9].<br/><br/>[1] F. Giustino, H. Snaith, ACS Energy Lett. 1, 1233 (2016).<br/>[2] M. Filip, F. Giustino, Proc. Nat. Acad. Sci. 115, 5397 (2018).<br/>[3] M. Wolf, B. Connor, A. Slavney, H. Karunadasa, Ang. Chem. Int. Ed. 60, 16264 (2021).<br/>[4] R. I. Biega, M. Filip, L. Leppert, J. B. Neaton, J. Phys. Chem. Lett. 12, 2057 (2021).<br/>[5] L. R. V. Buizza, H. C. Sansom, A. D. Wright, A. M. Ulatowski, M. B. Johnston, H. J. Snaith, L. M. Herz, Adv. Funct. Mater. 32, 2108392 (2022).<br/>[6] A. H. Slavney, L. Leppert, D. Bartesaghi, A. Gold-Parker, M. F. Toney, T. J. Savenije, J. B. Neaton, H. I. Karunadasa, J. Am. Chem. Soc., 139, 5015 (2017).<br/>[7] L. Leppert, T. Rangel, J. B. Neaton, Phys. Rev. Materials 3, 103803 (2019).<br/>[8] R.-I. Biega, L. Leppert, J. Phys. Energy 3, 034017 (2021).