Dual excitonic emissions and structural phase transition of octylammonium lead iodide 2D layered perovskite single crystal

Two dimensional (2D) layered hybrid lead halide perovskites exhibit interesting electronic and optical properties because of their repeating quantum well structure. These materials are now being explored for various optoelectronic applications, including solar cells and light emitting diodes. But still there are surprises regarding the basic band gap or excitonic absorption and emission of these layered hybrid perovskites. Recently, we showed possibility of dual band gaps or dual excitonic emissions from 2D butylammonium lead iodide (BA(2)PbI(4)). In the present paper, we extend the study to octylammonium lead iodide (OA)(2)PbI4 single crystals. The longer organic cations in (OA)(2)PbI4 separates the adjacent inorganic Pb-I layers further, reducing any possible electronic interactions between the inorganic layers. Interestingly, (OA)(2)PbI4 also exhibits dual excitonic emission at room temperature. A minor structural inhomogeneity between near-surface and interior regions of (OA)(2)PbI4 single crystals might be responsible for the two different excitonic emissions. To explore the correlation between crystal structure and excitonic emissions, we have studied single crystal XRD and photoluminescence at variable temperatures. The results show a small change in tilting of Pb-I-6 octahedra can distinctly change the band gap and the excitonic emission energy.