Quantifying Polaron Formation and Charge Carrier Cooling in Lead‐Iodide Perovskites
Abstract
Notwithstanding the success of lead‐halide perovskites in emerging solar energy conversion technologies, many of the fundamental photophysical phenomena in this material remain debated. Here, the initial steps following photogeneration of free charge carriers in lead‐iodide perovskites are studied, and timescales of charge carrier cooling and polaron formation, as a function of temperature and charge carrier excess energy, are quantified. It is found, using terahertz time‐domain spectroscopy (THz‐TDS), that the observed femtosecond rise in the photoconductivity can be described very well using a simple model of sequential charge carrier cooling and polaron formation. For excitation above the bandgap, the carrier cooling time depends on the charge carrier excess energy and lattice temperature, with cooling rates varying between 1 and 6 meV fs−1, depending on the cation. While carrier cooling depends on the cation, polaron formation occurs within ≈400 fs in CH3NH3PbI3 (MAPbI3), CH(NH2)2PbI3 (FAPbI3), and CsPbI3. Its formation time is independent of temperature between 160 and 295 K. The very similar polaron formation dynamics observed for the three perovskites points to the critical role of the inorganic lattice, rather than the cations, for polaron formation.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- May 30, 2018
- Source ID
- 10.1002/adma.201707312
Entities
People
- Hai I Wang
- Ivan G. Ivanov
- Kiyoshi Miyata
- Mischa Bonn
- Simon A Bretschneider
- Xiaoyang Zhu
Organizations
- Columbia University
- Japan Society for the Promotion of Science
- Max Planck Graduate Center
- Max Planck Institute for Polymer Research
- United States Department of Defense