Bandgap narrowing and piezochromism of doped two-dimensional hybrid perovskite nanocrystals under pressure

Abstract

Two-dimensional (2D) halide perovskites that incorporate organic interlayers show greatly improved environmental stability and optical tunability. Here, we provide a facile pressure engineering approach to achieve control over the optical features in Mn doped 2D perovskite (PEA)₂PbBr₄ (PEA⁺ = C₆H₅C₂H₄NH₃⁺) nanocrystals (NCs). Successive bandgap narrowing and marked piezochromism, which change the emission from orange to bluish violet, were realized. The bandgap of the Mn doped 2D perovskite (PEA)₂PbBr₄ NCs was steadily reduced by 480 meV under high pressure, which is much larger than that of conventional Mn-doped three-dimensional (3D) perovskite CsPbBr₃ NCs (with a bandgap tuning of about 100 meV). In addition, the intrinsic band edge emission of Mn doped 2D perovskite (PEA)₂PbBr₄ NCs was stabilized up to 9.2 GPa. The unique steric and spring effects of asymmetric organic PEA⁺ bilayers accommodated the slow octahedral deformation under pressure. Furthermore, the doping of elemental Mn greatly facilitated the local lattice distortion of the 2D perovskite (PEA)₂PbBr₄ NCs under high pressure, which was attributed to the appearance of enhanced self-trapped exciton (STE) emission. Our studies elucidated the structure–property relationship of Mn doped layered (PEA)₂PbBr₄ NCs, thus providing a basis for their applications in opto-pressure sensing.