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Seminar: MRI SEMINAR Prof. Prof. Laura Herz, University of Oxford - Hybrid Metal Halide Perovskites for Photovoltaics: Optoelectronic Properties and Stability

Date(s): 4 October 2017
Time: 15:00 - 16:00
Location: David Sizer Theatre
Details: Hybrid metal halide perovskites (stoichiometry AMX3) have recently emerged as low-cost active materials in PV cells with power conversion efficiencies in excess of 21%. We discuss how optoelectronic properties essential for photovoltaic operation, such as crystallinity, photostability, charge carrier mobility, recombination and diffusion lengths are altered with substitutions of the organic A cation (e.g. methylammonium versus formamidinium), the metal M cation (e.g. Pb2+ or Sn2+) and the halide X anion (I- versus Br-). We focus on two 3D perovskite systems that have attracted much interest lately, lead-free ASnI3 (optical bandgap ~1.3 eV) and the mixed organic lead iodide/bromide system APb(BryI1-y)3 whose band gap can be tailored between ~1.5 eV (FAPbI3) and ~2.3 eV (FAPbBr3). We show that unintentional hole doping in tin iodide perovskites introduces fast recombination pathways that can be moderated by crystal structure [1] and introduces a radiative quasi-monomolecular charge recombination channel [2]. In addition, we examine mixed-halide perovskites with band gap near 1.7eV, ideal for use in two-terminal tandems with silicon bottom cells. We demonstrate that charge-carrier diffusion and recombination in FA1-xCsxPb(BryI1-y)3 can be optimised for high performance that depends on a complex interplay between changes in morphology and electronic bandstructure with bromide fraction y [3,4,5].

[1] Parrott, Milot, Stergiopoulos, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 1321 (2016).
[2] Milot, Eperon, Green, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 4178 (2016).
[3] Rehman, Milot, Eperon, Wehrenfennig, Boland, Snaith, Johnston, Herz, Adv. Mater. 27, 7938 (2015).
[4] McMeekin, Sadoughi, Rehman, Eperon, Saliba, Hörantner, Haghighirad, Sakai, Korte, Rech, Johnston, Herz, Snaith, Science 351, 151 (2016).
[5] Rehman, McMeekin, Patel, Milot, Johnston, Snaith, Herz, Energy Environ. Sci. 10, 361 (2017).

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