Suppressing the Jahn‐Teller Effect in 0D Manganese‐Based Perovskite Derivatives for Transparent and Flexible Light‐Emitting Diodes

Abstract The development of stable and deformation‐free crystal structures of perovskites and their derivatives are crucial for electroluminescent devices. In this article, a novel transparent manganese‐based perovskite derivative K 4 MnBr 1.33 Cl 4.67 is synthesized with mixed halogens. For the unique octahedral crystal structure, the Jahn‐Teller distortion, typically present in such structures, is completely suppressed, resulting in high environmental stability of the luminescence spectrum. In transparent flexible devices, the peak current density, average external quantum efficiency on each side and maximum brightness is 45 mA cm −2 , 4.9%, and 2800 cd m −2 , respectively. The best half‐life of the LED reaches 10 h with a starting luminance of 100 cd m −2 . As the first lead‐free transparent flexible perovskite derivative LED, it features an outstanding transparency of 76% and excellent flexibility with a luminescence intensity maintenance of 90% after 2000 bending cycles. This work shows that lead‐free manganese perovskite derivatives can provide a promising way to fabricate stable and high‐performance LEDs.