Optical Properties of Heterojunction between Hybrid Halide Perovskite and Charge Transport Materials: Exciplex Emission and Large Polaron

The photoluminescence from exciplex states at lower energy than the bandgap of CH3NH3PbI3 (MAPbI(3)) was observed in both MAPbI(3)/Spiro-OMeTAD and MAPbI(3)/PCBM bilayer films. At the same time, using continuous wave photoinduced absorption (PIA) spectroscopy, we observed the PIA band at 0.14 eV, which was due to the positive or negative polarons in perovskite for MAPbI(3)/Spiro-OMeTAD and MAPbI(3)/PCBM film, respectively. The binding energies of both kinds of polarons are about similar to 40 meV, with the radius of phonon cloud of about 5.9 nm. Our finding may supply direct spectroscopic evidence for the existence of exciplex states in heterojunction of hybrid halide perovskite and charge transport materials as well as consequent large polarons in perovskite.