  We report the first doping of crystalline methylammonium lead bromide
(MAPbBr$_3$) perovskite thin-films with CdSe/CdZnS core/shell quantum dots
(QDs), using a soft-chemistry method that preserves their high quantum yield
and other remarkable fluorescence properties. Our approach produces MAPbBr$_3$
films of 100 nm thickness doped at volume ratios between 0.025 and 5% with
colloidal CdSe/CdZnS QDs whose organic ligands are exchanged with halide ions
to allow for close contact between the QDs and the perovskite matrix. Ensemble
photoluminescence (PL) measurements demonstrate the retained emission of the
QDs after incorporation into the MAPbBr$_3$ matrix. Ensemble photoluminescence
excitation (PLE) spectra exhibit signatures of wavelength-dependent coupling
between the CdSe/CdZnS QDs and the MAPbBr$_3$ matrix. Spatially-resolved PL
experiments reveal a strong correlation between the positions of QDs and an
enhancement of the PL signal of the matrix. Fluorescence lifetime imaging
(FLIM)of the doped films furthermore show that the emission lifetime of
MAPbBr$_3$ is slower in the vicinity of QDs, which, in combination with the
increased PL signal of the matrix, suggests that QDs can act as nucleation
seeds that improve the crystallinity of MAPbBr$_3$, boosting its emission
quantum yield. Antibunching measurements provide clear evidence of
single-photon emission from individual QDs-in-perovskite. Finally, the analysis
of blinking statistics indicates an improvement of the photostability of
individual QDs in perovskite as compared to bare CdSe/CdZnS QDs. At high doping
levels, this work opens the route to hybrid-based LEDs. Low-doping content
would lead to hybrid single-photon sources embedded in field-effect devices to
serve as an alternative to solid-state QDs and help building nanophotonic
devices with high-quantum-yield CdSe-based QDs.

Chemical Physics