Hybrid Metal Halide Perovskites: Optoelectronic Properties and Stability
Henry J Snaith a, Michael Johnston a, Giles E Eperon a, David McMeekin a, Elizabeth Parrot a, Rebecca Milot a, Laura Herz a, Waqaas Rehman a
a University of Oxford, Clarendon Laboratory, Parks rd, Oxford, 0, United Kingdom
NIPHO
Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
València, Spain, 2017 March 1st - 2nd
Organizers: Hendrik Bolink and David Cahen
Invited Speaker, Laura Herz, presentation 030
Publication date: 18th December 2016

Hybrid metal halide perovskites (stoichiometry AMX3) have recently emerged as low-cost active materials in PV cells with power conversion efficiencies in excess of 20%. We discuss how parameters essential for photovoltaic operation, such as crystallinity, photostability, charge carrier mobility 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 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 limit the charge-carrier diffusion length. However, changes in crystal structure appear to subtly influence the relative alignment of dopant levels with respect to the valence band, offering a route to reduced background hole densities [1]. In addition, we demonstrate that such hole doping introduces a radiative quasi-monomolecular charge recombination channel that supports efficient light emission even in the low charge-carrier density regime [2]. In addition, we demonstrate that charge-carrier diffusion and recombination in FAPb(BryI1-y)3 depends on a complex interplay between changes in morphology and electronic bandstructure with bromide fraction y [3]. In particular, a “stability gap” that leads to photo-induced halide segregation in the central region (y=0.3–0.5) is associated with low crystallinity and charge-carrier mobility [4,5]. We show that the replacement of a small fraction of FA with caesium (e.g. FA0.83Cs0.17Pb(I0.6Br0.4)3) lifts this instability allowing for high charge-carrier mobilities (21 cm2/(Vs)) and diffusion lengths [4]. We find that the substitution range of 10-30% caesium fraction is associated with higher crystallinity which correlates with improved optoelectronic properties and photo-stability [5].

 References

[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. ASAP (2017).



© FUNDACIO DE LA COMUNITAT VALENCIANA SCITO
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info