| Abstract
| - Two new semiconducting hybrid perovskites based on 2-substituted phenethylammonium cations, (2-XC6H4C2H4NH3)2SnI4 (X = Br, Cl), are characterized and compared with the previously reported X = F compound, with afocus on the steric interaction between the organic and inorganic components. The crystal structure of (2-ClC6H4C2H4NH3)2SnI4 is solved in a disordered subcell [C2/m, a = 33.781(7) Å, b = 6.178(1) Å, c = 6.190(1) Å, β =90.42(3)°, and Z = 2]. The structure is similar to the known (2-FC6H4C2H4NH3)2SnI4 structure with regard to boththe conformation of the organic cations and the bonding features of the inorganic sheet. The (2-BrC6H4C2H4NH3)2SnI4 system adopts a fully ordered monoclinic cell [P21/c, a = 18.540(2) Å, b = 8.3443(7) Å, c = 8.7795(7) Å, β= 93.039(1)°, and Z = 2]. The organic cation adopts the anti conformation, instead of the gauche conformationobserved in the X = F and Cl compounds, apparently because of the need to accommodate the additional volumeof the bromo group. The steric effect of the bromo group also impacts the perovskite sheet, causing notabledistortions, such as a compressed Sn−I−Sn bond angle (148.7°, as compared with the average values of 153.3and 154.8° for the fluoro and chloro compounds, respectively). The optical absorption features a substantial blueshift (lowest exciton peak: 557 nm, 2.23 eV) relative to the spectra of the fluoro and chloro compounds (588 and586 nm, respectively). Also presented are transport properties for thin-film field-effect transistors (TFTs) based onspin-coated films of the two hybrid semiconductors.
- With the halogens X = F, Cl, and Br substituted at the phenyl 2-position in (2-XC6H4C2H4NH3)2SnI4, the steric impact from the organic cation proves effective in modifying the structural and electronic properties of the hybrid perovskites. The large Br atom causes substantial compression of the Sn−I−Sn bond angle in the perovskite sheet. A comparison with related compounds indicates that the compression of the Sn−I−Sn angle generally raises the exciton energy associated with the band gap.
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