Excitonic states of alkylammonium lead-iodide layered perovskite semiconductors under hydrostatic pressure to 25 GPa

Optical absorption and photoluminescence (PL) spectra of the layered perovs kite semiconductor (C8H17NH3)(2)PbI4 were measured under hydrostatic pressu re to 25 GPa in order to investigate the effect of pressure-induced perturb ations on the electronic structure and the excitonic states of the two-dime nsional sublattice of corner-sharing [PbI6](4-) octahedra. The predominant PL band, which originates from a free exciton state, shirts to lower energi es sublinearly with pressure, and then disappears abruptly above P-C congru ent to 12 GPa. The exciton absorption hand also disappears at P-C, and a br oad absorption tail appears at a higher energy above P-C. It is found that the pressure dependence of the band gap energy above P-C is significantly d ifferent from that of the exciton band energy below P-C, indicating that th e electronic band structure of the two-dimensional sublattice changes at P- C. A large hysteresis on the recovery of the exciton band was observed upon decreasing pressure.