Constructing Multi‐Functional Polymeric‐Termination Surface Enables High‐Performance Flexible Perovskite LEDs.

Flexible perovskite light‐emitting diodes (f‐PeLEDs) have attracted increasing interest to realize true‐color, low‐cost, and light‐weight wearable optoelectronic and flexible display applications. However, their external quantum efficiency (EQE) and mechanical stability lag far behind because of the inherent surface and brittle issues of polycrystalline perovskite films. In this work, a multi‐functional polymeric‐termination surface of perovskite film is constructed for achieving efficient and mechanically stable f‐PeLEDs. It takes the roles to not only reduce defects through equipping coordination groups to improve emission properties, but also optimize film morphology and eliminate pinholes to solve the long‐standing issue of leakage current. Meanwhile, the polymeric‐termination surface with anchoring points and polymeric soft chains on perovskites demonstrates synergetic effects beyond the corresponding functional group‐only or polymer‐only strategies in reducing the Young's modulus and improving the mechanical flexibility. Ultimately, the record EQE of 22.1% and significantly enhanced mechanical stability of maintaining 82% of the initial performance after 2000 bending cycles with radius of 5 mm are achieved in pure‐green f‐PeLEDs. The work paves the way for the development of high‐performance flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]