Organic Radical Accelerates Charge Carrier Funneling in Quasi-2D Perovskite LEDs

Quasi-2D metal halide perovskites (MHP) have emerged as promising candidates for light-emitting diodes (PeLEDs) due to their intrinsic advantages in color purity, bandgap tunability, and stability. The prime working principle realizing high radiative emission in quasi-2D MHP is the ultrafast, consecutive charge transfer (CT) process toward the low-bandgap crystallites across multiple quantum wells, called charge carrier funneling. Ironically, such a key process is intrinsically limited in the quasi-2D MHP by the molecular spacers, which have electronically insulating natures. To challenge this limit, herein, we explore the impact of a judiciously designed, stable, and conductive organic radical, (5H-pyrido[3,2-b]indole-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl as a molecular additive in the MHP matrix. It is found that the spatially delocalized singly occupied molecular orbital offers an electronic bridge accelerating interfacial CT and the carrier funneling by surface adsorption, thus maximizing radiation recombination yield. As a result, the radical-incorporating PeLEDs (peaking at ≈ 684 nm) achieve a remarkable external quantum efficiency of 26.8% with an operational half-lifetime of ≈ 340 min, ranking among the best deep-red devices reported to date. This work demonstrates that rational radical molecular design offers a powerful route to resolve intrinsic CT limitations in quasi-2D MHP, unlocking both high efficiency and long-term stability in next-generation PeLEDs.