Enhancing the Efficiency and Stability of CsPbI3 Nanocrystal-Based Light-Emitting Diodes through Ligand Engineering with Octylamine

Bright perovskite nanocrystals with high color purity are promising for high-definition displays; however, their complex postprocessing process limits their large-scale production. Using a trace of octylamine to regulate the dynamic balance between surface ligand adsorption and desorption, we develop a facile method to obtain stable CsPbI3 nanocrystal films that combine excellent optical and electrical properties. The octylamine additive maintains the integrity of nanocrystals and inhibits the formation of defects, greatly enhances the phase- and the photoluminescence-stability, and thus the operational stability of the corresponding light-emitting devices (LEDs); enables in situ substitution of oleylamine, which reduces the spacing between adjacent nanocrystals and thus leads to closely packed nanocrystal films with promoted charge carrier transport capability; and also increases the activation energy for ion migration, indicating that the number of ion vacancies─namely, the ion migration paths─has been decreased. As a result, the octylamine additive leads to a 4- and 6-fold increase in LED external quantum efficiency (EQE) and operational lifetime, respectively. LEDs based on octylamine-assisted Zn-doped CsPbI3 nanocrystals show a high EQE of 15.3%.