Proton-Prompted Ligand Exchange to Achieve High-Efficiency CsPbI Quantum Dot Light-Emitting Diodes.

CsPbI perovskite quantum dots (QDs) are ideal materials for the next generation of red light-emitting diodes. However, the low phase stability of CsPbI QDs and long-chain insulating capping ligands hinder the improvement of device performance. Traditional in-situ ligand replacement and ligand exchange after synthesis were often difficult to control. Here, we proposed a new ligand exchange strategy using a proton-prompted in-situ exchange of short 5-aminopentanoic acid ligands with long-chain oleic acid and oleylamine ligands to obtain stable small-size CsPbI QDs. This exchange strategy maintained the size and morphology of CsPbI QDs and improved the optical properties and the conductivity of CsPbI QDs films. As a result, high-efficiency red QD-based light-emitting diodes with an emission wavelength of 645 nm demonstrated a record maximum external quantum efficiency of 24.45% and an operational half-life of 10.79 h.