Methylated diammonium spacer modulated three-dimensional lead bromide perovskitoid hybrids with distinct photoconductivity anisotropy†
Abstract
The emerged 3D APb2X6 (A represents diammonium; X is Cl, Br and I) perovskitoids hold huge potential to inherit the desirable charge transport properties and functional tunability of 3D APbX3 perovskites. Limited by the Goldschmidt tolerance factor rule, the reported 3D perovskitoid species remain sparse, hindering us from exploring their structural effect dictated photoelectronic behavior. Herein, we construct novel 3D (NMDAP)Pb2Br6 (NMDAP = N-methyl propane diammonium) composed of Pb2Br10 dimer unit, modulated by methylated diammonium spacer and the synthetically controlled stoichiometric ratio of reactants. Significantly, 3D (NMDAP)Pb2Br6 shows remarkable self-trapped exciton (STE) emission induced by high octahedra distortion associated with strong electron–phonon coupling. The STE emission features broadband photoluminescence (PL) spectra ranging from 525 to 750 nm with a large Stokes redshift of ∼0.91 eV. Photophysical investigation further reveals a large Huang–Rhys factor of ∼146 and a long STE emission lifetime of 17 ns. DFT calculations suggest that the band edge states are mainly contributed by the Pb 6s/Br 4p orbitals along the equatorial direction rather than the axial direction in 3D (NMDAP)Pb2Br6. Moreover, the asymmetric structure enables 3D (NMDAP)Pb2Br6 anisotropic charge transport behavior, as underpinned by the experimental and theoretical investigations. As a consequence, a photoconductive detector based on 3D (NMDAP)Pb2Br6 single crystal delivers anisotropic photoconductivity performance, with the [001] direction showing a responsivity and detectivity of 0.28 A W−1 and 2.12 × 1012 Jones, about 3-fold enhancement compared to those along the [100] and [010] directions. These observations offer extended functional tunability in 3D perovskitoids and reveal the potential of 3D perovskitoids in advanced optoelectronic devices.