Cooperative chelation for high-performance Perovskite light-emitting diodes

Molecular additives are frequently employed to enhance the performance of perovskite light-emitting diodes (PeLEDs), either through surface defect passivation or crystal growth control. In general, such passivation is attained through the chelation of the molecular additive to a defective Pb site along a lattice plane. Unfortunately, nano-crystallites often display multiple lattice planes and defects that a single additive is inadequate in passivating. Here, we report a dual additive system, comprising 5-aminopentanoic acid and (4-fluoropheny)thiourea to enhance the performance of FAPbI₃ PeLEDs. Our results and calculations reveal that the dual additives chelate cooperatively and synergistically with defective sites along the (100), (110) and (111) lattice planes, leading to significantly improved performance compared to the use of a single additive. The strong binding of the dual additives towards multiple lattice planes further slows down the growth of the nucleated crystallites, leading to small and uniform crystal grains as well as smoother thin films that exhibit higher exciton binding energy and improved luminescence quantum yields. The resulting PeLEDs attained a peak external quantum efficiency (EQE) of 26.3% at a high current density of 298 mA·cm^-2 and a peak radiance of 1843 W·sr^-1·m^-2 at 795 nm. Such high efficiency and radiance, together with enhanced stability, could allow PeLEDs to become viable for commercial use.