Large Red Shift of Emission of PbS Quantum-dot Superlattice with Butylamine Ligands

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 (001)Si substrate. 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.