Improvement of solar cell performance using PbS quantum dot superlattices with iodine ligands

We investigated the method to improve the performance of solar cells that use colloidal quantum dots (QDs) as light absorption layers. By replacing ligands of PbS QDs with iodine, adjusting QD concentration in a solvent suitable for the ligands, and preparing QD films by the sedimentation method, photoelectric conversion efficiency of QD solar cells was improved. It is known that by depositing QDs freely onto a substrate in a solvent, QDs are closest packed to form a superlattice. A suitable solvent that aided the free sedimentation of QDs facilitated the QD superlattice formation. Iodine ligands had narrowed QD spacing, promoting intermediate bands formation in the QD superlattices. QD concentration had affected the film quality. To achieve high performance expected for QD superlattice solar cells in future, it is necessary to develop carrier transport layers that extract carriers from high energy bands originating from excited states in QDs.