Unravelling the structural complexity and photophysical properties of adamantyl-based layered hybrid perovskites

Abstract

Layered hybrid perovskites comprising adamantyl spacer (A) cations based on the A2FAn–1PbnI3n+1 (n = 1–3, FA = formamidinium) compositions have recently been shown to act as promising materials for photovoltaic...

Organic Spacers in 2D Perovskites: General Trends and Structure‐Property Relationships from Computational Studies

“…for BA‐based systems, EBEs vary between 470 and 125 meV for n =1–4) [41,42] . Increasing n also leads to a considerable charge mobility increase, [43] in agreement with ab initio calculated hole and electron effective masses [28,30] . In addition, mixing MAPbI 3 with t ‐BA‐based 2DHPs has been reported to help mitigate moisture instability [44] .…”

“…It is however worth noting that in many of the cases listed above, pure 2‐dimensional perovskites have been observed to form merely in the case of lower n values, i. e ., in a limited range of inorganic layer thickness (or in some cases even only for n =1) whereas mixed 2D/3D phases are evidently formed for higher n [8,27–30,40] . This can be rationalized by a direct correlation between the thickness of the inorganic layer and the enthalpies of formation of 2DHP, [28,30] that becomes increasingly unfavorable with respect to the 3D counterpart as a function of n . In addition to the interplay between the inorganic layer thickness and the enthalpies of formation, EBEs of these systems also vary with the inorganic thickness as formerly mentioned ( e. g .…”

“…Accordingly, reported effective masses for the out‐of‐plane direction largely suggest the break‐down of the band model of transport. The effective masses in the in‐plane directions on the contrary, are comparable to those in 3D halide perovskites and decrease as the thickness of the inorganic layer increases [8,28,30] . Notable exceptions to this trend are cases where the organic spacer directly contributes to the band edges, such as in the NDI molecules, some oligothiophenes and pyrene [5,39,48] .…”

“…Extensive research has been conducted in an attempt to unravel different characteristics of both RP and DJ phases of 2DHPs ranging from structural to electronic and finite temperature properties as a function of n [7,8,11–13] . Some of the ligands that have been examined so far include ammonium ions of aliphatic or aromatic hydrocarbon molecules with either linear or more bulky shapes, such as butylammonium (BA), [8,19] phenethylammonium (PEA), [20–22] hexylammonium (Hex), [23,24] anilinium (Anyl), [25] benzylammonium, [26] (adamantan‐1‐yl)methanammo‐ nium (A), adamantylammonium (A‐prime), [27,28] or (1,4‐phenylene)dimethanammonium (PDMA), [29,30] as well as functionalized spacers with hydrogen‐bonding possibilities such as 4‐ammonium butyric acid (4‐ABA), [31] and 5‐ammonium valeric acid (5‐AVA), [32–37] guanine, [38] and naphthalene diimide (NDI) [39] . It is however worth noting that in many of the cases listed above, pure 2‐dimensional perovskites have been observed to form merely in the case of lower n values, i. e ., in a limited range of inorganic layer thickness (or in some cases even only for n =1) whereas mixed 2D/3D phases are evidently formed for higher n [8,27–30,40] .…”

“…A band gap opening accompanied by octahedral distortion away from cubic symmetry was observed in BA‐based 2D systems upon fluorination of the spacers, [45] as well as in Pb−Sn 2DHP systems [46] . Charge transport properties of 2D halide perovskites have been characterized by time‐resolved microwave conductivity (TRMC) measurements, [30,47] and modeled by calculating the effective masses through the band transport model [28,30] . Owing to the mostly insulating nature of the organic spacer layer, charge transport in the direction perpendicular to the inorganic layers (out‐of‐plane direction) through the organic layer is found to be an order of magnitude slower than within the inorganic sheets (in‐plane direction) [47] .…”