Ion-Assisted Ligand Exchange for Efficient and Stable Inverted FAPbI₃ Quantum Dot Solar Cells

Perovskite quantum dot (QD) has emerged as a promising material for photovoltaics with its superior stability compared to their three-dimensional bulk counterparts, owing to its thermodynamically stabilized photoactive phase. However, ligand management on perovskite QD surfaces is extremely difficult due to the ionic nature of the perovskite lattice, which often leads to either incomplete removal of the native insulating ligands or formation of trap states during the ligand-exchange process, greatly hampering the photovoltaic performances. In this work, we report an ion-assisted ligand-exchange method for FAPbI3 QDs using A-OAc (A = formamidinium (FA+), guanidinium (GA+), and phenethylammonium (PEA+), OAc = acetate), with the A+ and OAc– ions promoting the removal of native long-chain insulating ligands. The more complete ligand exchange results in dense and well-oriented packing of QDs, together with the enhancement of electronic coupling and charge transport across QDs. In addition, the A+ and OAc– ions can fill the surface A-/X-site vacancies, respectively, reducing the QD surface trap state density and hence suppressing charge recombination and iodide migration. The p–i–n inverted QD solar cells fabricated with this ligand-exchange method exhibit significant enhancement in short-circuit current density (JSC), reaching a PCE of 10.13%. Moreover, unencapsulated devices show impressive stabilities of more than 7300 h (10 months) storage time in a N2-filled glovebox.