Conjugated Ditertiary Ammonium Templated (100)-Oriented 2D Perovskite with Efficient Broad-Band Emission

Two-dimensional (2D) perovskites have emerged as potential single-source white-light emitters in solid-state lighting. However, the quantum yields (PLQY) remain modest, probably ascribed to the limitation of octahedral distortion modulation. Herein, it is demonstrated that the PLQY of 2D lead bromide perovskites can be further enhanced to 12.8% if they contain a bulk and optically active conjugated ditertiary ammonium cation N,N,N′,N′-tetramethyl-1,4-phenylenediammonium (TMPDA). The pristine alkyl ditertiary ammonium cation N,N,N′,N′-tetramethyl-1,6-hexanediammonium (TMHDA) can only form a 1D lead bromide perovskite with much inferior emission. The robust emission derives from the ultrahigh octahedral distortions associated with self-trapped excitons in 2D TMPDAPbBr4. Our experimental and theoretical results further suggest that the efficient broad-band emission in 2D TMPDAPbBr4 probably involves Förster resonant energy transfer where the optically active organic TMPDA2+ acts as a donor and the inorganic PbBr6 slab acts as an acceptor. Moreover, a 2D perovskite based on the conjugated ligand exhibits superior electrical properties compared to a 1D perovskite templated by an alkyl ligand. This work highlights the importance of molecular engineering to enhance the broad-band emission efficiency of 2D perovskites.