Spatial-temporal spectroscopy characterizations and electronic structure of methylammonium perovskites
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Research Letter
Spatial–temporal spectroscopy characterizations and electronic structure of methylammonium perovskites Zhaoyu Liu*, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA K. C. Bhamu*, CSIR-National Chemical Laboratory, Pune 411008, Maharashtra, India* Liang Luo, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Satvik Shah, Department of Electrical and Computer Engineering and Microelectronics Research Center, Iowa State University, Ames, IA 50011, USA Joong-Mok Park, and Di Cheng, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Men Long, Division of Chemical and Biological Sciences, Ames Laboratory, Ames, IA 50011, USA; Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA Rana Biswas*, and F. Fungara, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Ruth Shinar, Department of Electrical and Computer Engineering and Microelectronics Research Center, Iowa State University, Ames, IA 50011, USA Joseph Shinar, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Javier Vela, Division of Chemical and Biological Sciences, Ames Laboratory, Ames, IA 50011, USA; Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA Jigang Wang*, Division of Materials Science and Engineering, Ames Laboratory, Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Address all correspondence to Rana Biswas, Jigang Wang at [email protected], [email protected] (Received 2 April 2018; accepted 15 June 2018)
Abstract Using time-resolved laser-scanning confocal microscopy and ultrafast optical pump/THz probe spectroscopy, we measure photoluminescence (PL) and THz-conductivity in perovskite micro-crystals and films. PL quenching and lifetime variations occur from local heterogeneity. Ultrafast THz-spectra measure sharp quantum transitions from excitonic Rydberg states, providing weakly bound excitons with a binding energy of ∼13.5 meV at low temperatures. Ab-initio electronic structure calculations give a direct band gap of 1.64 eV, a dielectric constant of ∼18, heavy electrons, and light holes, resulting in weakly bound excitons, consistent with the binding energies from the experiment. The complementary spectroscopy and simulations reveal fundamental insights into perovskite light-matter interactions.
The methylammonium lead iodide perovskite (CH3NH3PbI3 or MAI) family of materials has revolutionized solar energy conversion, generating power conversion efficiencies as high as 22.7
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