Exciton state in two-dimensional perovskite semiconductor (C10H21NH3)2PbI4

Reflection, luminescence and absorption spectra are measured in an exciton region of (C10H21NH3)2PbI4. Crystal structure is determined to be of layered perovskite type by X-ray diffraction. PbI4 layers are sandwiched by barrier layers consisting of alkylammonium chains. The exciton state has a large binding energy of 370 meV and is very stable even at room temperature. Its oscillator strength is estimated to be about 0.7 per a formula unit. The binding energy is too large to be explained only by the two-dimensional character of the exciton and is ascribed to the small dielectric constant of the barrier layer, which makes Coulomb interaction between an electron and a hole stronger.