Thick-Layer Lead Iodide Perovskites with Bifunctional Organic Spacers Allylammonium and Iodopropylammonium Exhibiting Trap-State Emission.

The nature of the organic cation in two-dimensional (2D) hybrid lead iodide perovskites tailors the structural and technological features of the resultant material. Herein, we present three new homologous series of (100) lead iodide perovskites with the organic cations allylammonium (AA) containing an unsaturated C═C group and iodopropylammonium (IdPA) containing iodine on the organic chain: (AA) 2 MA n -1 Pb n I 3 n +1 ( n = 3-4), [(AA) x (IdPA) 1- x ] 2 MA n -1 Pb n I 3 n +1 ( n = 1-4), and (IdPA) 2 MA n -1 Pb n I 3 n +1 ( n = 1-4), as well as their perovskite-related substructures. We report the in situ transformation of AA organic layers into IdPA and the incorporation of these cations simultaneously into the 2D perovskite structure. Single-crystal X-ray diffraction shows that (AA) 2 MA 2 Pb 3 I 10 crystallizes in the space group P 2 1 / c with a unique inorganic layer offset (0, <1/2), comprising the first example of n = 3 halide perovskite with a monoammonium cation that deviates from the Ruddlesden-Popper (RP) halide structure type. (IdPA) 2 MA 2 Pb 3 I 10 and the alloyed [(AA) x (IdPA) 1- x ] 2 MA 2 Pb 3 I 10 crystallize in the RP structure, both in space group P 2 1 / c . The adjacent I···I interlayer distance in (AA) 2 MA 2 Pb 3 I 10 is ∼5.6 Å, drawing the [Pb 3 I 10 ] 4- layers closer together among all reported n = 3 RP lead iodides. (AA) 2 MA 2 Pb 3 I 10 presents band-edge absorption and photoluminescence (PL) emission at around 2.0 eV that is slightly red-shifted in comparison to (IdPA) 2 MA 2 Pb 3 I 10 . The band structure calculations suggest that both (AA) 2 MA 2 Pb 3 I 10 and (IdPA) 2 MA 2 Pb 3 I 10 have in-plane effective masses around 0.04 m 0 and 0.08 m 0 , respectively. IdPA cations have a greater dielectric contribution than AA. The excited-state dynamics investigated by transient absorption (TA) spectroscopy reveal a long-lived (∼100 ps) trap state ensemble with broad-band emission; our evidence suggests that these states appear due to lattice distortions induced by the incorporation of IdPA cations.