Background: Quantum-dot (QD) superlattice solar cells can attain quite high energy conversion
efficiencies. The formation of epitaxial QD superlattice is very difficult since extremely delicate
control is required for the QD stacking during the growth to avoid QD deformation and dislocation
generation. It is well known that CQDs are self-assembled to form superlattice in electron microscope
area after sedimentation in a solvent. To apply the colloidal QD superlattice to solar cell,
superlattice size must be expanded from electron microscope order to centimeters or more.
Method: Long-periodic packing was done by slowly depositing PbS QDs with short-chain butylamine
ligands in a solvent into a pyramidal-hole array processed by anisotropic KOH etching of a
Results: QDs' ground state energy reduced by 116 meV together with 1.5-time increase in luminescence
lifetime after the film formation.
Conclusion: We demonstrate that the film prepared by close packing of colloidal QDs with shortchain
ligands exhibited the large red shift of emission wavelength with the increase in emission lifetime.
The results suggest that the carrier wavefunction was well delocalized in the long-periodic
superlattice film on the template.