Title: Interdot Lead Halide Excess Management in PbS Quantum Dot Solar Cells

Abstract: Light-harvesting devices made from PbS quantum dot (QD) absorbers are one of the many promising technologies of third-generation photovoltaics. Their simple, solution-based fabrication together with a highly tunable and broad light absorption makes their application in newly developed solar cells particularly promising. In order to yield devices with reduced voltage and current losses, PbS QDs need to have strategically passivated surfaces, most commonly achieved through lead iodide and bromide passivation. The interdot spacing is then predominantly filled with residual amorphous lead halide species that remain from the ligand exchange, thus hindering efficient charge transport and reducing device stability. Herein, we demonstrate that a post-treatment by iodide based 2-phenylethlyammonium salts (X-PEAI) and intermediate 2D perovskite formation can be used to manage the lead halide excess in the PbS QD active layer. This treatment results in improved device performance and increased shelf-life stability, demonstrating the importance of interdot spacing management in PbS quantum dot photovoltaics.