Intrinsic femtosecond charge generation dynamics in single crystal CH3NH3PbI3

By David A. Valverde-Ch'avez, C. Ponseca, C. Stoumpos, A. Yartsev, M. Kanatzidis, V. Sundstrom, D. Cooke. 2015

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Hybrid metal–organic perovskite solar cells have astounded the solar cell community with their rapid rise in efficiency while maintaining low-cost fabrication. The intrinsic material photophysics related to the generation of free charges, their dynamics and efficiency, however, remains to be understood. As fabrication techniques improve, larger crystal grain sizes have been shown to be a critical factor for improving both the optical and transport properties of the hybrid metal halide perovskites. In this work, we use pulses of multi-THz frequency light in the ultra-broadband 1–30 THz (4–125 meV) range to observe the ac conductivity in large single crystal CH3NH3PbI3. Our spectra reveal the ultrafast dynamics and efficiencies of free charge creation and extremely high charge carrier mobility as high as 500–800 cm2 V−1 s−1. While quasi-equilibrium analysis of efficiencies through the Saha equation suggests a binding energy on the order of 49 meV, an observed reflectance feature appearing at high pump fluence occurs at 12 meV and is consistent with an orbital transition of the exciton, indicating a much lower Rydberg energy of 17 meV at room temperature. The signature of the exciton is found to vanish on a 1 ps time scale commensurate with the appearance of mobile carriers, consistent with thermal dissociation of the exciton to the continuum in the room temperature tetragonal phase.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/d00d767ba048956f5b77be5f2c028279d6ae6a10

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The 2023 terahertz science and technology roadmap (2023, background): “The short duration combined with the smooth and broad spectrum of THz air photonics signals makes appealing for broadband spectroscopy across the 1–30 THz range [110], also in ultrafast transient pump-probe studies [111].”