Caught in a spin: cation rotation is too rapid to support ferroelectric domains
12 February 2018
A recent paper, by Dr Tom Oliver's group, with collaborators at the Rutherford Appleton National Laboratory, describes the use of two-dimensional infrared spectroscopy to investigate the presence of long-lived (anti-) ferroelectric domains in hybrid lead-halide perovskite thin films.
Hybrid organic-inorganic lead halide perovskites have shown great promise as a future photovoltaic material, offering high operating efficiencies and are cheap to manufacture. Previous studies have concluded that devices containing perovskite as the photoactive layer owe their high efficiencies to alignment of the constituent organic cations forming (anti-) ferroelectric domains. These domains funnel oppositely charged electrons and holes away from each other, reducing recombination processes. Taylor et al. definitively refute this hypothesis for thin films of formamidinium lead iodide perovskite films.
Ferroelectric domains had previously been proposed to arise from alignment of adjacent organic cations in the perovskite thin films, and many studies cite such phenomena as the main reason for the remarkably low charge-carrier recombination rates for perovskite thin films. Through these ultrafast spectroscopic measurements, this paper shows that organic cations only remain aligned for a very short period of time (less than 3 picoseconds) and thus refutes the presence of long-lived (anti-) ferroelectric domains.
Investigating the Role of the Organic Cation in Formamidinium Lead Iodide Perovskite Using Ultrafast Spectroscopy, the Journal of Physical Chemistry Letters