Fig. 2: The impact of ambient water on the CQD nanostructure and film morphology.

a–e The TEM images of PbS CQDs prepared under different conditions. The samples were prepared on carbon meshes by (a) droplet deposition (b) followed by ligand exchange and annealing process at 85 °C under dry air, (c–e) or under humid air with different annealing times. The scale bars: left column 10 nm and right column 5 nm. f, g Molecular dynamic simulation of the water effect on hydroxylated CQDs. Atom color: brown, Pb; yellow, S; red, O; white, H. Snapshots of two CQDs with surface hydroxyls covered on {111} facet with a gap distance of 1 nm at 300 K after (f) 10 ps and (j) 1000 ps. The ambient water could work as H-bonding bridges, which significantly promote the close attachment of neighboring CQDs. h, l The focused ion beam (FIB) cross-sectioned bright-field TEM images of CQD stacks prepared through (h) spin coating and (l) CA. Scale bars: 10 nm. The GISAXS patterns of CQD films prepared by (i) spin coating before ligand exchange and (j) after ligand exchange under dry air annealing or (k) under humid air annealing, or by (m) CA deposition before ligand exchange and (n) after ligand exchange under dry air annealing or (o) under humid air annealing. p The illustration of meniscus-guided coating and spin-coating process for the preparation of PbS CQD solids. The densely packed CA films show the self-draining effect against ambient water intrusion.