Suppressing electron-phonon coupling in perovskite nanoplatelets for efficient pure-red light-emitting diodes with narrow spectral emission.

Perovskite light-emitting diodes are promising for next-generation ultrahigh-definition displays, yet efficient pure-red emission (620-650 nm) with high spectral purity remains challenging, with emission linewidths commonly exceeding 30 nm. CsPbI nanoplatelets feature the potential for narrow-linewidth emission owing to strong vertical quantum confinement and atomic-level flat surface. Nonetheless, the dynamic motion of native long-chain oleylamine exacerbates lattice vibrations in ultrathin soft lattices, inducing strong electron-phonon coupling and undermining optical advantages. Here, we introduce the rigid 4-(2-aminoethyl)benzenesulfonamide molecule, which partially replaces oleylamine and vertically anchors on the nanoplatelets, sterically restricting the dynamic motion of neighboring oleylamine, thereby mitigating electron-phonon coupling. The resulting light-emitting diodes achieve pure-red electroluminescence at 641 nm with a narrow linewidth of 24 nm, an average external quantum efficiency of 23.2 ± 2.4% (maximum 29.8%), and an operational lifetime of 128.2 h. This work underscores the critical role of electron-phonon coupling modulation in optimizing perovskite optoelectronic devices.