  Halide perovskite nanocrystals (NCs) have emerged as a promising material for
applications ranging from light-emitting diodes (LEDs) to solar cells and
photodetectors. Still, several issues impede the realization of the
nanocrystals' full potential, most notably their susceptibility to degradation
from environmental stress. This work demonstrates highly stable perovskite
nanocrystals (NCs) with quantum yields as high as 95 % by exploiting a
ligand-assisted copolymer nanoreactor-based synthesis. The organic ligands
thereby serve a dual function by enhancing the uptake of precursors and
passivating the NCs. The polymer micelles and ligands thus form a double
protection system, shielding the encapsulated NCs from water-, heat- and
UV-light-induced degradation. We demonstrate the optoelectronic integrability
by incorporating the perovskite NCs as spectrally pure downconverters on top of
a deep-blue-emitting organic LED. These results establish a way of stabilizing
perovskite NCs for optoelectronics while retaining their excellent optical
properties.
