We introduce a simple and low-cost approach -drop-coating method -for preparation of in-situ self-assembled perovskite nanocrystals for efficient light-emitting diodes. The PL spectrum of the self-assembled NFPI4 nanocrystals thin film prepared by the drop-coating method shows blue shift compared with that of the typical NFPI4 thin film prepared by spin-coating method. In addition, the PL spectra of these self-assembled nanocrystals are tuned from 765 nm to 725 nm by changing usage amounts of the perovskite precursor solution. More importantly, efficient light-emitting diodes with EQEs up to 6.8% are achieved based on these self-assembled NFPI4 nanocrystals.