Probing Strain-Induced Band Gap Modulation in 2D Hybrid Organic–Inorganic Perovskites

In photovoltaics and flexible electronics applications, two-dimensional (2D) hybrid organic–inorganic perovskites (HOIPs) are often subjected to mechanical strain arising from materials processing, device functioning, and thermal expansion. Here we report for the first time a study of the band gap response to uniaxial tensile strain in thin 2D HOIP flakes with a general formula of (CH3(CH2)3NH3)2(CH3–NH3)n−1PbnI3n+1. At large n (n > 3), the band gap will increase as the strain increases, and the strain response of band gap can be as high as 13.3 meV/% for n = 5, which is due to the rotation of the inorganic [PbI6]4– octahedra and the consequential Pb–I bond stretching and increase of Pb–I–Pb. Our findings provide a route to engineer the electronic properties of 2D HOIPs. The observed band gap–strain relationship can be harnessed to map the local mechanical strain in 2D HOIP-based devices and allow 2D HOIPs for sensing applications.