To further understand the optoelectronic properties of metal halide perovskites, we investigate sub-bandgap absorption in methylammonium lead iodide (MAPbI(3)) 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 X 10(13) 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 MAPbI(3), the band tail states do not lead to nonradiative losses.

American Chemical Society (ACS)
NWO
doi.org/10.1021/acsenergylett.0c02067
ACS Energy Lett.
Hybrid Solar Cells

Caselli, V.M, Wei, Z, Ackermans, M.M, Hutter, E.M, Ehrler, B, & Savenije, T.J. (2020). Charge Carrier Dynamics upon Sub-bandgap Excitation in Methylammonium Lead Iodide Thin Films: Effects of Urbach Tail, Deep Defects, and Two-Photon Absorption. ACS Energy Lett., 5(12), 3821–3827. doi:10.1021/acsenergylett.0c02067