Entropy Stabilization Effects and Ion Migration in 3D “Hollow” Halide Perovskites

Abstract

A recently discovered new family of 3D halide perovskites with the general formula (A)1–x (en) x (Pb)1–0.7x (X)3–0.4x (A = MA, FA; X = Br, I; MA = methylammonium, FA = formamidinium, en = ethylenediammonium) is referred to as “hollow” perovskites owing to extensive Pb and X vacancies created on incorporation of en cations in the 3D network. The “hollow” motif allows fine tuning of optical, electronic, and transport properties and bestowing good environmental stability proportional to en loading. To shed light on the origin of the apparent stability of these materials, we performed detailed thermochemical studies, using room temperature solution calorimetry combined with density functional theory simulations on three different families of “hollow” perovskites namely en/FAPbI3, en/MAPbI3, and en/FAPbBr3. We found that the bromide perovskites are more energetically stable compared to iodide perovskites in the FA-based hollow compounds, as shown by the measured enthalpies of formation and the calculated formation energies. The least stable FAPbI3 gains stability on incorporation of the en cation, whereas FAPbBr3 becomes less stable with en loading. This behavior is attributed to the difference in the 3D cage size in the bromide and iodide perovskites. Configurational entropy, which arises from randomly distributed cation and anion vacancies, plays a significant role in stabilizing these “hollow” perovskite structures despite small differences in their formation enthalpies. With the increased vacancy defect population, we have also examined halide ion migration in the FA-based “hollow” perovskites and found that the migration energy barriers become smaller with the increasing en content.

Exploring Solar Cells Based on Lead- and Iodide-Deficient Halide Perovskite (d-HP) Thin Films

“…Each of these systems has undergone few optimizations as thin films yet, but the crucial point is that an improvement in the stability for both systems was observed. Similar structures have been reported based on the use of other large cations such as ethylenediammonium [ 57 , 58 , 59 , 60 , 61 , 62 , 63 ], propylenediammonium [ 64 ], and trimethylenediammonium [ 64 ] by Kanatzidis et al They have called this family “Hollow” perovskites.…”

Design rules for obtaining narrow luminescence from semiconductors made in solution

“…[412][413][414][415][416][417][418] The superior environmental stability of 2D hybrid lead iodide perovskites and their inherent structural flexibility has rendered them attractive alternatives to 3D perovskites for the fabrication of environmentally robust optoelectronic devices. 68,366,417,[419][420][421][422][423][424][425][426][427] Photophysical studies have mainly been focused on lead halide perovskites due to their strong, excitonic PL emission. In the early 1990s, Thorn and colleagues published the first evidence of thick-layer lead halide perovskites (n>1) producing thin films with the compositions (C9H19NH3)2(CH3NH3)Pb2I7 and (C9H19NH3)2(CH3NH3)n-1PbnBr3n+1 (n=1-3) incorporating the nonylamine spacer cation, along with films of (PhNH3)2(CH3NH3)Pb2I7 with Ph: phenylamine cation.…”

Stable organic lead iodides with three-dimensional crystallographic and electronic structures showing high photoresponse

“…Recently, a new type of 3D MHP-like structure has been reported that accommodates large diammonium cations. [32][33][34][35][36] The basic unit consists of rigid [Pb 2 I 10 ] 6− building blocks in edge-sharing mode and the dimers share corners to extend in all three directions. The expanded inorganic sublattice can be derived from the perovskite lattice by translating alternating slices cut along the (110) crystallographic plane to form edge-sharing dimers of the octahedra.…”

“…E-mail: hanxiangbin@seu.edu.cn, zhangwen@seu.edu.cn organic A-site cations than MA can be included, which provides the possibility of expanding the family of novel 3D MHPs. 34,35 However, research on the electronic dimensionality related to this type of structure is still restricted in theoretical work, and there is no report on the study of large-size single crystals and their corresponding optoelectronic properties.…”