posted on 2015-12-17, 10:14authored byYuxi Tian, Aboma Merdasa, Eva Unger, Mohamed Abdellah, Kaibo Zheng, Sarah McKibbin, Anders Mikkelsen, Tõnu Pullerits, Arkady Yartsev, Villy Sundström, Ivan G. Scheblykin
Photoluminescence
(PL) of organo-metal halide perovskite semiconductors
can be enhanced by several orders of magnitude by exposure to visible
light. We applied PL microscopy and super-resolution optical imaging
to investigate this phenomenon with spatial resolution better than
10 nm using films of CH3NH3PbI3 prepared
by the equimolar solution-deposition method, resulting in crystals
of different sizes. We found that PL of ∼100 nm crystals enhances
much faster than that of larger, micrometer-sized ones. This crystal-size
dependence of the photochemical light passivation of charge traps
responsible for PL quenching allowed us to conclude that traps are
present in the entire crystal volume rather than at the surface only.
Because of this effect, “dark” micrometer-sized perovskite
crystals can be converted into highly luminescent smaller ones just
by mechanical grinding. Super-resolution optical imaging shows spatial
inhomogeneity of the PL intensity within perovskite crystals and the
existence of <100 nm-sized localized emitting sites. The possible
origin of these sites is discussed.