Improving Charge Carrier Delocalization in Perovskite Quantum Dots by Surface Passivation with Conductive Aromatic Ligands

Long-chain saturated hydrocarbons and alkoxysilanes are ligands that are commonly used to passivate perovskite quantum dots (PQDs) to enhance their stability and optical properties. However, the insulating nature of these capping ligands creates an electronic energy barrier and impedes interparticle electronic coupling, thereby limiting device applications. One strategy to solve this problem is the use of short conductive aromatic ligands that allow delocalization of the electronic wave function from the PQDs, which, in turn, facilitates charge transport between PQDs by lowering the energy barrier. This is demonstrated with methylammonium lead bromide (MAPbBr3) QDs prepared using benzylamine (BZA) and benzoic acid (BA) capping ligands. Optimized BZA-BA-MAPbBr3 QDs are highly stable and show very high photoluminescence (PL) quantum yield (QY) (86%). More importantly, the BZA-BA-MAPbBr3 QD film exhibits higher conductivity and carrier lifetime and more efficient charge extraction compared to PQDs with insulating ligands, as indicated by electrochemical measurements and transient photocurrent and photovoltage spectroscopy.