Charge Carrier Dynamics upon Sub-bandgap Excitation in Methylammonium Lead Iodide Thin Films
Effects of Urbach Tail, Deep Defects, and Two-Photon Absorption
V. M. Caselli (TU Delft - ChemE/Opto-electronic Materials)
Zimu Wei (TU Delft - ChemE/Opto-electronic Materials)
M.M. Ackermans (AMOLF Institute for Atomic and Molecular Physics)
Eline M. Hutter (AMOLF Institute for Atomic and Molecular Physics, Universiteit Utrecht)
Bruno Ehrler (Systems Biophysics)
T. J. Savenije (TU Delft - ChemE/Opto-electronic Materials)
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Abstract
To further understand the optoelectronic properties of metal halide perovskites, we investigate sub-bandgap absorption in methylammonium lead iodide (MAPbI3) films. Charge carrier dynamics are studied using time-resolved microwave conductivity measurements using sub-bandgap excitation. From changes in the decay dynamics as a function of excitation energy and intensity, we have identified three regimes: (i) Band-like charge transport at photon energies above 1.48 eV; (ii) a transitional regime between 1.48 and 1.40 eV; and (iii) below 1.40 eV localized optically active defects (8 × 1013 cm-3) dominate the absorption at low intensities, while two-photon absorption is observed at high intensities. We determined an Urbach energy of approximately 11.3 meV, indicative of a low structural and/or thermal disorder. Surprisingly, even excitation 120 meV below the bandgap leads to efficient charge transfer into electron (C60) or hole (spiro-OMeTAD) transport layers. Therefore, we conclude that for MAPbI3, the band tail states do not lead to nonradiative losses.
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