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 andtechnological features of the resultant material. Herein, we presentthree new homologous series of (100) lead iodide perovskites withthe organic cations allylammonium (AA) containing an unsaturatedC = C group and iodopropylammonium (IdPA) containing iodine onthe organic chain: (AA)(2)MA(n-1)Pb(n)I(3n+1)(n=3-4),[(AA)(x)(IdPA)(1-x)](2)MA(n-1)Pb(n)I(3n+1)(n=1-4), and (Id-PA)(2)MA(n-1)Pb(n)I(3n+1)(n=1-4), as well as their perovskite-relatedsubstructures. We report the in situ transformation of AA organiclayers into IdPA and the incorporation of these cations simulta-neously into the 2D perovskite structure. Single-crystal X-raydiffraction shows that (AA)(2)MA(2)Pb(3)I(10)crystallizes in the spacegroup P2(1)/c with a unique inorganic layer offset (0, <1/2), comprising thefirst example of n= 3 halide perovskite with amonoammonium 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 P2(1)/c. The adjacent I center dot center dot center dot I interlayer distance in(AA)(2)MA(2)Pb(3)I(10) is similar to 5.6 A, drawing the [Pb3I10](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-planeeffective 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 (similar to 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.

Automated summary

This article introduces three new homologous series of two-dimensional lead iodide perovskites with different organic cations and discusses their structural and technological features. The different organic cations have an impact on the structure and optical properties of the material. The study reveals that the incorporation of specific organic cations leads to lattice distortions and the formation of trap states.