Colloidal quantum dot ligand engineering for high performance solar cells

Colloidal quantum dots (CQDs) are fast-improving materials for next-generation solution-processed optoelectronic devices such as solar cells, photocatalysis, light emitting diodes, and photodetectors. Nanoscale CQDs exhibit a high surface to volume ratio, and a significant fraction of atoms making up the quantum dots are thus located on the surface. CQD surface states therefore play a critical role in determining these materials' properties, influencing luminescence, defect energy levels, and doping type and density. In the past five years, halide ligands were applied to CQD solar cells, and these not only improved charge carrier mobility, but also reduced defects on the surface. With the inclusion of halide ligands, CQD solar cell certified power conversion efficiencies have increased rapidly from an initial 5% in 2010 to the latest certified values over 10%. In this perspective article, we summarize recent advances in ligand engineering that improve the performance of CQD solar cells, focusing on the use of halide inorganic ligands to improve CQD surface passivation and film conductivity simultaneously.