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

Optical absorption and photoluminescence (PL) spectra of the layered perovskite semiconductor (C8H17NH3)(2)PbI4 were measured under hydrostatic pressure to 25 GPa in order to investigate the effect of pressure-induced perturbations on the electronic structure and the excitonic states of the two-dimensional sublattice of corner-sharing [PbI6](4-) octahedra. The predominant PL band, which originates from a free exciton state, shirts to lower energies sublinearly with pressure, and then disappears abruptly above P-C congruent to 12 GPa. The exciton absorption hand also disappears at P-C, and a broad 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 different from that of the exciton band energy below P-C, indicating that the 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.