Cesium lead mixed-halide perovskite thin films were fabricated by using a chemical vapor anion exchange procedure. Optical and structural properties of the materials obtained were studied comprehensively.
Inorganic cesium
lead halide perovskite nanowires, generating laser
emission in the broad spectral range at room temperature and low threshold,
have become powerful tools for the cutting-edge applications in the
optoelectronics and nanophotonics. However, to achieve high-quality
nanowires with the outstanding optical properties, it was necessary
to employ long-lasting and costly methods of their synthesis, as well
as postsynthetic separation and transfer procedures that are not convenient
for large-scale production. Here we report a novel approach to fabricate
high-quality CsPbBr3 nanolasers obtained by rapid precipitation
from dimethyl sulfoxide solution sprayed onto hydrophobic substrates
at ambient conditions. The synthesis technique allows producing the
well-separated nanowires with a broad size distribution of 2–50
μm in 5–7 min, being the fastest method to the best of
our knowledge. The formation of nanowires occurs via ligand-assisted
reprecipitation triggered by intermolecular proton transfer from (CH3)2CHOH to H2O in the presence
of a minor amount of water. The XRD patterns confirm an orthorhombic
crystal structure of the as-grown CsPbBr3 single nanowires.
Scanning electron microscopy images reveal their regular shape and
truncated pyramidal end facets, while high-resolution transmission
electron microscopy ones demonstrate their single-crystal structure.
The lifetime of excitonic emission of the nanowires is found to be
7 ns, when the samples are excited with energy below the lasing threshold,
manifesting the low concentration of defect states. The measured nanolasers
of different lengths exhibit pronounced stimulated emission above
13 μJ cm–2 excitation threshold with quality
factor Q = 1017–6166. Their high performance
is assumed to be related to their monocrystalline structure, low concentration
of defect states, and improved end facet reflectivity.
Inexpensive perovskite light-emitting devices fabricated by a simple wet chemical approach have recently demonstrated very prospective characteristics such as narrowband emission, low turn-on bias, high brightness, and high external quantum efficiency of electroluminescence, and have presented a good alternative to well-established technology of epitaxially grown III-V semiconducting alloys. Engineering of highly efficient perovskite light-emitting devices emitting green, red, and near-infrared light has been demonstrated in numerous reports and has faced no major fundamental limitations. On the contrary, the devices emitting blue light, in particular, based on 3D mixed-halide perovskites, suffer from electric field-induced phase separation (segregation). This crystal lattice defect-mediated phenomenon results in an undesirable color change of electroluminescence. Here we report a novel approach towards the suppression of the segregation in single-layer perovskite light-emitting electrochemical cells. Co-crystallization of direct band gap CsPb(Cl,Br)3 and indirect band gap Cs4Pb(Cl,Br)6 phases in the presence of poly(ethylene oxide) during a thin film deposition affords passivation of surface defect states and an increase in the density of photoexcited charge carriers in CsPb(Cl,Br)3 grains. Furthermore, the hexahalide phase prevents the dissociation of the emissive grains in the strong electric field during the device operation. Entirely resistant to 5.7 × 106 V·m−1 electric field-driven segregation light-emitting electrochemical cell exhibits stable emission at wavelength 479 nm with maximum external quantum efficiency 0.7%, maximum brightness 47 cd·m−2, and turn-on bias of 2.5 V.
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