Grain‐Specific Transitions Determine the Band Edge Luminescence in Dion–Jacobson Type 2D Perovskites

Abstract

metal halide octahedra.This opens a rich playing field for tuning the photophysical properties of these 2D compounds targeted to a variety of opto-electronic applications. [1] Many studies have considered 2D compounds to increase the stability of 3D perovskites in solar cells and to facilitate charge extraction or to act as efficient emitters in light emitting devices. [2,3] The choice of the spacer cation can affect factors, such as moisture resistivity, [4] or the degree of distortion in the inorganic slabs, which partially governs the band gap energy [5] or the carrier effective masses. [6] Recently, also the imposition of optical chirality [7] or the mixing of states between spacers and inorganic moieties have become important topics of research. [8] Traditionally, most of the organic spacers have been based on primary amines, such as the prototypical butylammonium (BA + ) or phenylethylammonium (PEA + ) giving rise to A 2 MX 4 chemical formulas in so-called Ruddlesden-Popper (RP) compounds, where A is the spacer cation, M the metal cation, and X the halide anion. [1] More recently, diammonium cations, forming AMX 4 Dion-Jacobson (DJ) structures, have moved into the spotlight of research. [9,10] Instead of two spacer cations per unit cell, these compounds possess only one organic molecule with two functional groups to stabilize the layered structure. Although employed in solar cells and characterized for this purpose, [11][12][13] fundamental studies on their photophysics are so far scarce.The photophysics of 2D perovskites exhibits several intensively studied aspects. In particular, low-temperature studies reveal a rich substructure of the excitonic luminescence and absorption. High-energy features are commonly explained through exciton-phonon interactions. However, there is no consensus on the origin of the vibrational modes responsible for the observed spectral features and the actual mechanisms at play. [14][15][16] Slightly Stokes-shifted band edge emission and split sub-peaks have been analyzed in the framework of dark and bright excitons, [17,18] bright doublets, [19] localized defects, [16,20] and have been shown to depend on the angle of detection. [20,21] At even lower energy, broad emission bands are sometimes attributed to self-trapped excitons, but have recently been proposed to be defect-related. [22] Here, we report on the photophysics of the prototypical compounds PDMAPbI 4 and PDMASnI 4 , which are based on the The photophysics of 2D perovskites incorporating 1,4-phenylenedimethanammonium (PDMA) as spacer cations is studied. PDMAPbI 4 and PDMASnI 4 exhibit absorption and luminescence spectra dominated by excitonic transitions and an emission due to two different states. Low-temperature studies reveal a time-dependent red shift of 12 meV that is correlated with grain-specific luminescence spectra observed in optical micrographs. For the Pb-variant, grains of red-shifted and lower intensity band edge emission simultaneously exhibit a more pronounced luminescence from a broad defect-related band...

Nanosegregation in arene-perfluoroarene π-systems for hybrid layered Dion–Jacobson perovskites

“…S5, ESI †). Likewise, a visual inspection of GIWAXS images shows that (PDMA)PbI 4 crystallites have a preferred orientation, [9][10][11][12]27,34 whereas upon the gradual addition of F-PDMA continuous Debye-Scherrer rings appear, indicating a more random distribution of crystallites (Fig. 2d-f and Fig.…”

“…[6][7][8] In particular, two classes of 2D perovskite materials are of special interest, namely the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases. [9][10][11][12][13][14] RP systems mostly follow the general formula S′ 2 A n−1 M n X 3n+1 , where S′ are monofunctional spacers that interact with the perovskite slabs by forming a bilayer with a half-aunit-cell displacement between the perovskite slabs (Fig. 1b).…”

Enhancing and Extinguishing the Different Emission Features of 2D (EA1−xFAx)4Pb3Br10 Perovskite Films

“…These results also show that care must be taken when studying optical processes because the growth method or solvents may enhance or suppress different emission features. Such variations might explain why lower‐energy features appear inconsistently across a sample of (PDMA)PbI 4 , [ 65 ] or from study to study in (BA) 2 PbI 4 . [ 11,12,56 ]…”

“…These results also show that care must be taken when studying optical processes because the growth method or solvents may enhance or suppress different emission features. Such variations might explain why lowerenergy features appear inconsistently across a sample of (PDMA)PbI 4 , [65] or from study to study in (BA) 2 PbI 4 . [11,12,56] Finally, because a sharp absorbance onset is highly desired for photovoltaics and photodetectors, we measured the electronic disorder near the absorption edge.…”

“…[11,12,56,63,64] Lowerenergy features can also vary in intensity across different locations of the same sample. [65] Recent work shows that film strain can be used to remove the lowestenergy feature of (EA) 4 Pb 3 Br 10 . [52] In order to fully tune the emission color of 2D films, we must further explore how to change the optoelectronic properties of 2D phases through composition and processing.…”