Phase Modulation on Low‐Dimensional Perovskite for High Performance Blue Light Emitting Diodes

Abstract Layered low‐dimensional perovskite nanostructures have recently been utilized in blue perovskite light‐emitting diodes (PeLEDs), but excess organic ammonium spacers restrict charge transfer and radiative recombination, as well as device stability. Introducing diammonium can improve the stability due to the short distance between layered slices. However, the small n‐phases ( n = 1, 2, 3) still cause the nonradiative recombination. Herein, 1,3,5‐Tris(1‐phenyl‐1H‐benzimidazole‐2‐yl) benzene (TPBi), is employed to control the film growth and modulate the phase purification for low‐dimensional perovskites. The coordination of imidazole with Pb 2+ helps to mediate the growth and passivate defects. Transient absorption (TA) spectroscopy reveals that the incorporation of TPBi effectively suppresses the formation of the small‐n phase. The N‐type doping uplifts the Fermi energy level by 0.3 eV, ensuring balanced charge injection. Consequently, sky‐blue PeLEDs emitting at 488 nm achieve impressive external quantum efficiency (EQE) of 15.18%, a high brightness of 2358 cd m −2 , and a low turn‐on voltage of 2.6 V. The blue PeLED exhibits a stable electroluminescent (EL) spectrum and a half‐lifetime (L 0 = 100 cd m −2 ) of 740 s.