Electron Delocalization in CsPbI3 Quantum Dots Enables Efficient Light-Emitting Diodes with Improved Efficiency Roll-Off

Perovskite quantum dot (QD) charging is prone to occur during light-emitting diode (LED) operation due to the electron accumulation inside the QD emitters, which is caused by the unbalanced charge injection and carrier transportation. Here in order to address this issue, an electron attractor of phenethylammonium (PEA(+)) is introduced to the surface of perovskite QDs. The PEA(+) conjugated ligands can reversibly store and release electrons driven by the electron local density of states redistribution, which enhances the delocalization of electrons in QDs, and thus suppresses QD charging at high carrier concentrations, as evidenced by the excitation energy dependent photoluminescence. Besides, PEA(+) down-shifts the Fermi level of perovskite QDs, consequently increases the hole concentration, leading to greatly improved hole conduction. Halogen-rich synthesis environment also reduces the number of halogen vacancies, consequently narrows the distribution of electronic states at the band edges, leading to slightly improved electron conduction. Taking advantage of the enhanced electron delocalization and improved charge transportation, the CsPbI3 QDs LEDs show the maximum external quantum efficiency (EQE) of 15.6% with a low efficiency roll-off, and the maximum luminance of 1634 cd m(-2).