Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 114; no. 29; pp. 7519 - 7524
• Main Authors: Chen, Tianran, Chen, Wei-Liang, Foley, Benjamin J., Lee, Jooseop, Ruff, Jacob P. C., Ko, J. Y. Peter, Brown, Craig M., Harriger, Leland W., Zhang, Depei, Park, Changwon, Yoon, Mina, Chang, Yu-Ming, Choi, Joshua J., Lee, Seung-Hun
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 18-07-2017; National Academy of Sciences, Washington, DC (United States)
• Subjects: Calcium Compounds - chemistry; Carrier lifetime; Current carriers; Electrons; Entropy; Ferroelectric domains; Ferroelectric materials; Iodides; Iodides - chemistry; Luminescence; MATERIALS SCIENCE; Metals, Heavy - chemistry; Neutrons; organic–inorganic hybrid perovskite; Oxides - chemistry; Perovskite; Perovskites; Photochemistry; photoluminescence; Photovoltaic cells; Photovoltaics; Physical Sciences; polaron; Polarons; Recombination; Screening; SOLAR ENERGY; Sunlight; Temperature; Titanium - chemistry; carrier lifetime; photoluminescence; organic–inorganic hybrid perovskite; polaron
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1704421114

Long carrier lifetime is what makes hybrid organic–inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic–inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.