Polarity-Mediated Antisolvent Control Enables Efficient Lanthanide-Based near-Infrared Perovskite LEDs.

Alloying lanthanide ions (Yb 3+ ) into perovskite quantum dots (Yb 3+ :CsPb(Cl 1- x Br x ) 3 ) is an effective method to achieve efficient near-infrared (NIR) luminescence (>950 nm). Increasing the Yb 3+ alloying ratio in the perovskite matrix enhances the luminescence intensity of Yb 3+ emission at 990 nm. However, high Yb 3+ alloying (>15%) results in vacancy-induced inferior material stability. In this work, we developed a polarity-mediated antisolvent manipulation strategy to resolve the incompatibility between a high Yb 3+ alloying ratio and inferior stability of Yb 3+ :CsPb(Cl 1- x Br x ) 3 . Precise control of solution polarity enables increased uniformity of the perovskite matrix with fewer trap densities. Employing this strategy, we obtain Yb 3+ :CsPb(Cl 1- x Br x ) 3 with the highest Yb 3+ alloying ratio of 30.2% and a 2-fold higher electroluminescence intensity at 990 nm. We lever the engineered Yb 3+ :CsPb(Cl 1- x Br x ) 3 to fabricate NIR-LEDs, achieving a peak external quantum efficiency (EQE) of 8.5% at 990 nm: this represents the highest among perovskite NIR-LEDs with an emission wavelength above 950 nm.