Role of the colossal frequency and temperature dependent dielectric constant in the performance of the organo-metallic tri-halide perovskites

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Organo-metallic perovskites have emerged as a promising next generation semiconducting material. Despite achievements in the efficiencies of perovskite devices, and although crucial to future success, little is known about the fundamental dielectric behavior of these materials. The measurement of the dielectric behavior in perovskites has proven to be both difficult and controversial. This work reports the dielectric properties of tri-halide perovskites over broad frequency (10 mHz–6 MHz) and temperature (100 K–300 K) ranges. A colossal dielectric constant in the materials is observed. The dielectric constant is found to drop abruptly above the PbI3 polarization frequency of ∼106 Hz and is shown to be largely structure dependent. The immense dielectric constant is found to diminish the exciton binding energies to negligible, ∼10 meV, at 300 K, thus guaranteeing exciton separation and explaining previously observed impressive perovskite device performance. This work provides fundamental information about the photo-physics of the materials, resolves some experimental controversy, and enables opto-electrical performance optimization.