High Efficiency and Low Roll-Off Pure-Red Perovskite LED Enabled by Simultaneously Inhibiting Auger and Trap Recombination of Quantum Dots

CsPbI₃ perovskite quantum dots (QDs) could achieve pure-red emission by reducing their size, but the increased exciton binding energy (E_B) and surface defects for the small-sized QDs (SQDs) cause severe Auger and trap recombinations, thus worsening their electroluminescence (EL) performance. Herein, we utilize the dangling bonds of the SQDs as a driving force to accelerate KI dissolution to solve its low solubility in nonpolar solvents, thereby allowing K⁺ and I^- to bond to the surface of SQDs. The E_B of the SQDs was decreased from 305 to 51 meV because of the attraction of K⁺ to electrons, meanwhile surface vacancies were passivated by K⁺ and I^-. The Auger and trap recombinations were simultaneously suppressed by this difunctional ligand. The SQD-based light-emitting diode showed a stable pure-red EL peak of 639 nm, an external quantum efficiency of 25.1% with low roll-off, and a brightness of 5934 cd m^-2.