Efficient and Stable PbS Quantum Dot Solar Cells by Triple-Cation Perovskite Passivation

Solution-processed quantum dots (QDs) have a high potential for fabricating low-cost, flexible, and large-scale solar energy harvesting devices. It has recently been demonstrated that hybrid devices employing a single monovalent cation perovskite solution for PbS QD surface passivation exhibit enhanced photovoltaic performance when compared to standard ligand passivation. Herein, we demonstrate that the use of a triple cation Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.9Br_0.1)₃ perovskite composition for surface passivation of the quantum dots results in highly efficient solar cells, which maintain 96% of their initial performance after 1200 h shelf storage. We confirm perovskite shell formation around the PbS nanocrystals by a range of spectroscopic techniques as well as high-resolution transmission electron microscopy. We find that the triple cation shell results in a favorable energetic alignment to the core of the dot, resulting in reduced recombination due to charge confinement without limiting transport in the active layer. Consequently, photovoltaic devices fabricated via a single-step film deposition reached a maximum AM1.5G power conversion efficiency of 11.3% surpassing most previous reports of PbS solar cells employing perovskite passivation.