Langmuir-Schaefer deposition of 2D PbS quantum dot superlattices with millimetre square coverage.

Superlattices of lead chalcogenide colloidal quantum dots hold promise to revolutionise the field of infrared optoelectronics due to their unique combination of optical and transport properties. However, the main challenge remains to form a homogeneous thin-film with long-range order avoiding cracking upon ligand exchange. To overcome these issues, we introduce an approach where external lateral pressure is applied during the self-assembly and ligand exchange, thus avoiding the formation of cracks due to volume shrinking. The formed monolayer superlattices are crack-free over several millimetres square. Transport measurements in an ionic gel-gated field-effect transistor reveal that increasing the external pressure during the superlattice formation leads to higher electron mobilities above 25 cm2V-1s-1 thanks to better compactness, high ordering, and a higher number of nearest neighbours. These results demonstrate that colloidal quantum dot superlattices with high charge mobility can be fabricated over large areas with important implications for technological applications.