Blue Perovskite Light‐Emitting Diodes Using Multifunctional Small Molecule Dopants

Unbalanced charge carrier injections and high densities of non-radiative recombination channels are still major obstacles to advancing high-efficiency blue perovskite light-emitting diodes (LEDs). Here, a deep-HOMO level p-type small molecule, (2-(3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid, doped in blue perovskites for building a better-balanced injection and controlling over defects is demonstrated. During the perovskite film deposition process, most small molecules are extruded from the precursor solution to the bottom and top surfaces of the perovskite films. This unique distribution of molecules can construct a better-balanced carrier injection due to improved hole and retarded electron injection by its suitable energy-level structure, along with modulation of all defects in bulk and at the surface of doped films due to the formation of covalent bonds by its functional moiety. With this approach, a series of blue perovskite LEDs is designed with external quantum efficiencies (EQEs) of up to 24.03% (at a luminance of 113 cd m^-2 and emission peak of 485 nm), 16.61% (at a luminance of 51 cd m^-2 and emission peak of 476 nm) and 8.55% (at a luminance of 30 cd m^-2 and emission perk of 467 nm), and encouraging operational stability.