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.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites are drawing significant attention in optoelectronic fields because of their enhanced out-of-plane electron coupling and improved structure stability. However, the structural effects of organic cations on the in-plane charge transport properties of 2D DJ lead bromide perovskites have remained less explored. Herein, we adopt asymmetric 3-(dimethylamino)-1-propylammonium (DMPD) and symmetric butane-1,4-diammonium (BDA) to systematically investigate the influence of organic cations on the structural, optical, and in-plane charge transport properties of 2D lead bromide perovskites. The large penetration depth of DMPD 2+ induces a decreased perovskite layer distortion and a lower bandgap in DMPDPbBr 4 , compared with that of BDAPbBr 4 . Moreover, DMPDPbBr 4 is shown to possess a low exciton binding energy, a low defect density, and a low ion migration activation energy, thereby yielding a more efficient in-plane charge collection efficiency than BDAPbBr 4 . Density functional theory calculations suggest that the improved in-plane charge transport can be traced to the enlarged antibonding coupling between Pb−6s and Br−4p orbitals that enables a high band dispersion and a low carrier effective mass in the in-plane direction of DMPDPbBr 4 . Finally, the planar Ag/ DMPDPbBr 4 /Ag photodetector delivers a satisfying detectivity of 1.73 × 10 12 Jones under an incident power intensity of 0.16 mW cm −2 and a high on/off ratio of 5.3 × 10 3 . The above findings offer novel insight for the design of 2D DJ lead bromide perovskites for optoelectronic devices.