Ligand engineering of perovskite quantum dots for efficient and stable solar cells

Lead halide perovskite quantum dots (PQDs) have recently emerged as promising light absorbers for photovoltaic application due to their extraordinary optoelectronic properties. Surface ligands are of utmost importance for the colloidal stability and property tuning of PQDs, while their highly dynamic binding nature not only impedes further efficiency improvement of PQD-based solar cells but also induces intrinsic instability. Tremendous efforts have been made in ligand engineering with good hopes to solve such challenging issues in the past few years. In this review, we first present a fundamental understanding of the role of surface ligands in PQDs, followed by a brief discussion and classification of various ligands that have the potential for improving the electronic coupling and stability of PQD solids. We then provide a critical overview of recent advances in ligand engineering including the strategies of in-situ ligand engineering, post-synthesis/-deposition ligand-exchange, and interfacial engineering, and discuss their impacts on changing the efficiency and stability of perovskite QD solar cells (QDSCs). Finally, we give our perspectives on the future directions of ligand engineering towards more efficient and stable perovskite QDSCs.