Formation of Corrugated n = 1 2D Tin Iodide Perovskites and Their Use as Lead-Free Solar Absorbers

Abstract

Major strides have been made in the development of materials and devices based around low-dimensional hybrid group 14 metal halide perovskites. Thus far, this work has mostly focused upon compounds containing highly toxic Pb, with the analogous less toxic Sn materials being comparatively poorly evolved. In response, the study herein aims to (i) provide insight into the impact of templating cation upon the structure of 2D tin iodide perovskites, and (ii) examine their potential as light absorbers for photovoltaic (PV) cells. It was discovered through systematic tuning of organic dications, that imidazolium rings are able to induce formation of (110)-oriented materials, including the first examples of "3 × 3" corrugated Sn-I perovskites. This structural outcome is a consequence of a combination of supramolecular interactions of the two endocyclic N-atoms in the imidazolium functionalities with the Sn-I framework and the higher tendency of Sn 2+ ions to stereochemically express their 5s 2 lone pairs relative to the 6s 2 electrons of Pb 2+ . More importantly, the resulting materials feature very short separations between their 2D inorganic layers with iodide-iodide (I•••I) contacts as small as 4.174 Å, which is amongst the shortest ever recorded for 2D tin iodide perovskites. The proximate inorganic distances, combined with the polarizable nature of the imidazolium moiety, eases the separation of photogenerated charge within the materials. This is evident from the excitonic activation energies as low as 83(10) meV, measured for ImEA[SnI4]. When combined with superior light absorption capabilities relative to their lead congeners, this allowed fabrication of lead-free solar cells with incident photon-to-current and power conversion efficiencies of up to 70 % and 2.26 %, respectively, which are amongst the highest values reported for pure 2D group 14 metal halide perovskites. In fact, these values are superior to the corresponding lead iodide material, which demonstrates that 2D Sn-based materials have significant potential as less toxic alternatives to their Pb counterparts. Supporting InformationCrystal structures of hybrid lead iodide perovskites (cif files).Experimental procedures, materials synthesis, additional spectra and crystallographic data (pdf).The Supporting Information is available free of charge on the ACS Publications website.

Exciton Localization for Highly Luminescent Two‐Dimensional Tin‐Based Hybrid Perovskites through Tin Vacancy Tuning

“…These isolated [SnI 6 ] 4− metal‐halide octahedra exhibit significantly larger structural deformation than those in the ideal tin halide crystal lattice, thereby enabling the intense coupling between excited excitons and deformed [SnI 6 ] 4− octahedra that favor the formation of STEs (Figure 3d, e). [11a, 16] Accordingly, E b for the Sn 2+ ‐poor (OA) 2 SnI 4 PNSs was calculated to be as high as ≈90.6 meV by fitting the temperature‐dependent PL intensity with the Arrhenius equation [4e] . This value is significantly higher than that of their Sn 2+ ‐rich counterparts irrespective of their identical crystalline phase and morphology (≈32.3 meV, Figure 3f and S13).…”

Tunable phase transition temperature and nonlinear optical properties of organic–inorganic hybrid perovskites enabled by dimensional engineering

“…The theoretical calculations in this work using the Vienna ab initio simulation package (VASP 5.0) based on density functional theory (DFT). 42,43 The band structure and density of states were calculated based on CIF files using generalized gradient approximation (GGA) exchange-correlation functional and Perdew-Burke-Ernzerhof (PBE). For related calculations, a 3 Â 3 Â 1 k-point was selected and the cutoff energy was set to 340 eV, the force convergence criterion was 0.01 eV Å À1 .…”

Perovskite-transition metal dichalcogenides heterostructures: recent advances and future perspectives

“…There also exist studies that combine the solution process and va-por-phase conversion, providing extra angles over the formability of the materials 195 . Due to the enormous number of preceding reviews on the subject 186,187,196,197 , the above strategies are not elaborated at length in this review. Instead, the focus will be given to the 2D counterparts where relatively rare reports exist discussing the topic.…”