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.

2D pentamethylenediammonium lead bromide single crystal with distinctive smooth and continuous morphology and decreased interlayer distance exhibits promising photoconductivity performance.

Two-dimensional (2D) perovskite broadband emitters are gaining intensive attention in light-emitting fields. However, the limitation of structure distortion modulation hinders the increase of emission intensity, and the high toxicity of organic diamine causes potential damage to human health. Herein, we utilize a green organic spacer 5-ammonium valeric acid (Ava) to template novel 2D lead chloride hybrids, Ava2PbCl4, where intermolecular O1···H–O2 interactions form between the adjacent organic cation layers. The intermolecular hydrogen bonding in Ava2PbCl4 causes a larger cation penetration depth which enables larger structural deformation than the pentamethylenediammonium lead chloride (PDAPbCl4) reference. This octahedral deformation further leads to ultrabroadband emission in Ava2PbCl4, which achieves enhanced photoluminescence quantum yield (2.83%) compared to PDAPbCl4 (0.4%). Further mechanism investigation indicates that these broadband emissions could be assigned as the transient self-trapped excitons luminescence. Density functional theory calculation indicates that the octahedral distortions are traced to an electronic origin as well. The above findings reveal the key role of intermolecular hydrogen bonding in modulating the photophysical properties of 2D perovskites and will benefit the design of green perovskites for optoelectronic applications.

Lead-free zero-dimensional (0D) hybrid bismuth halide perovskites have aroused great interest due to their promising emission properties and good chemical stability. Herein, we report the design and synthesis of mixed-cation-phase 0D guanidinium−formamidinium bismuth chloride, [C(NH 2 ) 3 ] 2 [CH(NH 2 ) 2 ] 3 Bi 2 Cl 11 (denoted as Gua 2 FA 3 Bi 2 Cl 11 ), where an individual corner-sharing [Bi 2 Cl 11 ] 5− dimer is completely isolated and surrounded by the mixed Gua + and FA + organic cations. The corner-sharing connectivity mode in Gua 2 FA 3 Bi 2 Cl 11 differs from that in pristine Gua 3 BiCl 6 , featuring an isolated [BiCl 6 ] 3− unit. Importantly, Gua 2 FA 3 Bi 2 Cl 11 yields remarkable broadband emission spanning from 350 to 750 nm, different from the pristine Gua 3 BiCl 6 , showing distinct narrowband emission. Further investigation of photophysical properties reveals that the broadband emission has contributions from both free excitons and selftrapped excitons. Moreover, Gua 2 FA 3 Bi 2 Cl 11 not only exhibits excellent photostability under continuous high-power UV lamp irradiation during 70 min but also is humidity stable for over 6 months under ambient conditions. This finding presents a novel molecular engineering strategy for the development of eco-friendly and stable 0D perovskite broadband emitters.