Anisotropic Electric Field Effect on the Photoluminescence of CH₃NH₃PbI₃ Perovskite Sandwiched between Conducting and Insulating Films

Photoluminescence (PL) of a nanocrystalline film of methylammonium lead iodide perovskite (MAPbI₃) sandwiched between an electrode of a fluorine-doped tin oxide (FTO) layer and an insulating film of poly(methyl methacrylate) is found to increase and decrease significantly with the application of an external electric field (F_ext), depending on the direction of the applied field, based on the measurements of electrophotoluminescence (E-PL) spectra, i.e., field-induced change in PL spectra. The field-induced change in PL intensity is confirmed to originate from the field-induced change in the number of free carriers which induce radiative recombination, based on temporally resolved E-PL measurements. We propose that an internal field (F_int) exists even without application of F_ext. The anisotropic behavior of the effect of F_ext on PL is interpreted in terms of a synergy effect of F_int and F_ext; both fields are additive with the applied field direction from Ag to FTO electrode (positive direction) or subtractive with the opposite applied field direction (negative direction), where FTO is the positive electrode, resulting in an increased or decreased total electric field as well as quenching or enhancement of PL, respectively. The PL lifetime in the nanosecond region increased and decreased with an application of an electric field in the positive and negative directions, respectively, which is attributed to a field-induced change in the concentration of free carriers. (Graph Presented).