Regensburg 2016 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 80: Hybrid and Perovskite Photovoltaics IV (Joint session of CPP, DF, DS and HL, organized by HL)
HL 80.9: Talk
Thursday, March 10, 2016, 17:15–17:30, H2
Dynamics and nature of photo-excited carriers in (CH3NH3)PbI3 organic-inorganic perovskite — •Daniel Niesner1,2, Haiming Zhu1, Tyler J. S. Evans1, Bryan J. Kudisch1, Prakriti P. Joshi1, Kiyoshi Miyata1, M. Tuan Trinh1, Manuel Marks1, and X.-Y. Zhu1 — 1Department of Chemistry, Columbia University, New York, NY 10027, USA — 2Festkörperphysik, FAU Erlangen-Nürnberg, D-91058 Erlangen, Germany
Thin film solar cells based on organic-inorganic perovskites are the rising star in photovoltaics. The photophysics and transport mechanism behind the outstanding device performance remain a matter of debate. I will present the results of a study on carrier dynamics in vapor-deposited thin films of (CH3NH3)PbI3, combining time-resolved two-photon photoemission, transient absorption, and photoluminescence.
After optical excitation with sufficient photon energy (≥ 2.15 eV), highly excited electrons relax quickly (≤ 0.3 ps) to a region of the conduction band with a low density of states, located 0.3 eV above the band minimum. In parallel, polaron formation takes place on a time scale of 0.28± 0.04 ps, matching the time scale of cation motion. Polaronic screening suppresses further energy relaxation and thermalization. The polaron maintains a significant excess energy for more than 60 ps.
The excess energy can be utilized to overcome energy barriers at grain boundaries and contacts. Harvesting it directly would result in a solar cell with an efficiency exceeding the Shockley-Queisser limit.