Suppressing Strong Exciton–Phonon Coupling in Blue Perovskite Nanoplatelet Solids by Binary Systems

Quasi‐two‐dimensional (2D) perovskites are promising candidates for light generation owing to their high radiative rates. However, strong exciton–phonon interactions caused by mechanical softening of the surface act as a bottleneck in improving their suitability for a wide range of lighting and display applications. Moreover, it is not easily available to tune the phonon interactions in bulk films. Here, we adopt bottom‐up fabricated blue emissive perovskite nanoplatelets (NPLs) as model systems to elucidate and as well as tune the phonon interactions via engineering of binary NPL solids. By optimizing component domains, the phonon coupling strength can be reduced by a factor of 2 driven by the delocalization of 2D excitons in out‐of‐plane orientations. It shows the picosecond energy transfer originated from the Förster resonance energy transfer (FRET) efficiently competes with the exciton–phonon interactions in the binary system. The effective suppression of exciton–phonon interactions of blue emissive CsPbBr3 nanoplatelets (NPLs) is realized by constructing binary NPL systems. The exciton–phonon coupling strength can be significantly reduced two times. Additionally, the energy transfer between binary NPLs originated from Förster resonance energy transfer (FRET) effect occurs within picoseconds, efficiently competing with the phonon interactions.