Lead halide perovskite (LHP) nanocrystals (NCs) are witnessing
tremendous success in LED and display technology applications for
their defect tolerance properties and near-unity photoluminescence
quantum yield (PLQY). Despite this success, thermally assisted PL
quenching in LHP NCs is a major obstacle during the operation of devices
at a higher temperature. To overcome this obstacle, we have introduced
an effective washing-assisted short-chain capping ligand engineering
by 4-fluorobenzylammonium bromide (4FBABr) for the first time to obtain
the CPB-4FBABr NC, which is simple and cost-effective. We observed
a retention of about 74% PL intensity for the CPB-4FBABr NC at 373
K compared to its PL intensity at 283 K, whereas for the CPB-parent
NC, only 2% of the initial PL intensity was found to be retained in
the same temperature range. We argued the importance of optimum washing
prior to surface engineering in this report. We also highlighted that
the F-atom in 4FBABr enhances the positive charge density on the N
atom of the ammonium headgroup, facilitating exceptional ligand-NC
binding, while the bromide ion eliminates detrimental halide vacancy-related
trap states. These two factors synergistically enhanced the heat tolerance
of the engineered NC. Time-resolved PL (TRPL) measurements shed more
light on the charge carrier dynamics, where shallow trap state-mediated
charge carrier trapping and detrapping in the engineered NC reduced
the permanent loss of excitons under extreme thermal conditions. An
insight into reversibility during the cooling cycle (PL recovery by
lowering the temperature) has also been established by TRPL measurements.
Our findings underscore the critical role of washing before postsynthetic
treatment and the effectiveness of using short-chain fluorinated aryl
ammonium ligands in suppressing the thermally assisted PL quenching.
This investigation will be highly beneficial to fabricating high-temperature
stable perovskite-based LEDs.