A Multifunctional Additive Strategy Enables Efficient Pure‐Blue Perovskite Light‐Emitting Diodes

Abstract Lead halide perovskites have shown exceptional performance in light‐emitting devices (PeLEDs), particularly in producing significant electroluminescence in sky‐blue to near‐infrared wavelengths. However, PeLEDs emitting pure‐blue light at 465–475 nm are still not satisfactory. Herein, efficient and stable pure‐blue PeLEDs are reported by controlling phase distribution, passivation of defects, as well as surface modifications using multifunctional phenylethylammonium trifluoroacetate (PEATFA) in reduced‐dimensional p‐F‐PEA₂Cs_n−1Pb_n(Br_0.55Cl_0.45)_3n+1 polycrystalline perovskite films. Compared with 4‐fluorophenylethylammonium (p‐F‐PEA⁺) in the pristine films, phenylethylammonium (PEA⁺) has lower adsorption energy while interacting with perovskites, resulting in large‐n low‐dimensional perovskites, which can greatly facilitate charge transport within the low‐dimensional perovskite films. The interaction between the CO group in trifluoroacetate (TFA⁻) and perovskites significantly reduces defects in the perovskite films. Additionally, the electron‐giving CF₃ group in TFA‐ uplifts surface potential in the films, resulting in smooth electronic injection in devices. The multifunctional additive strategy leads to elevated radiative recombination and efficient carrier transport in the films and devices. As a result, the devices exhibit a maximum external quantum efficiency (EQE) of 11.87% at 468 nm with stable spectral output, the highest reported to date for pure‐blue PeLEDs. Thus, this study extends the way for high‐efficiency pure‐blue LED with perovskite polycrystal films.