title: Effect of Thermal and Structural Disorder on the Electronic Structure of Hybrid Perovskite Semiconductor CH3NH3PbI3.
abstract: In this Letter, we investigate the temperature dependence of the optical properties of methylammonium lead iodide (MAPbI3 = CH3NH3PbI3) from room temperature to 6 K. In both the tetragonal (T > 163 K) and the orthorhombic (T < 163 K) phases of MAPbI3, the band gap (from both absorption and photoluminescence (PL) measurements) decreases with decrease in temperature, in contrast to what is normally seen for many inorganic semiconductors, such as Si, GaAs, GaN, etc. We show that in the perovskites reported here, the temperature coefficient of thermal expansion is large and accounts for the positive temperature coefficient of the band gap. A detailed analysis of the exciton line width allows us to distinguish between static and dynamic disorder. The low-energy tail of the exciton absorption is reminiscent of Urbach absorption. The Urbach energy is a measure of the disorder, which is modeled using thermal and static disorder for both the phases separately. The static disorder component, manifested in the exciton line width at low temperature, is small. Above 60 K, thermal disorder increases the line width. Both these features are a measure of the high crystal quality and low disorder of the perovskite films even though they are produced from solution.
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai, India 400076.
authors.forename: Shivam
authors.initials: S
authors.lastname: Singh
authors.affiliation: Organic and Hybrid Electronics, Macromolecular Chemistry I, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.affiliation: Experimental Physics II & Bayreuth Institute of Macromolecular Research (BIMF), Universität Bayreuth , Bayreuth 95440, Germany.|Department of Functional Materials, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Panzer
authors.affiliation: Department of Electrical Engineering, Indian Institute of Technology Bombay , Powai, Mumbai, India 400076.
authors.forename: K L
authors.initials: KL
authors.lastname: Narasimhan
authors.affiliation: Organic and Hybrid Electronics, Macromolecular Chemistry I, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Graeser
authors.affiliation: Applied Functional Polymers, Macromolecular Chemistry I, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Tanaji P
authors.initials: TP
authors.lastname: Gujar
authors.affiliation: Experimental Physics II & Bayreuth Institute of Macromolecular Research (BIMF), Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Köhler
authors.affiliation: Applied Functional Polymers, Macromolecular Chemistry I, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Mukundan
authors.initials: M
authors.lastname: Thelakkat
authors.affiliation: Organic and Hybrid Electronics, Macromolecular Chemistry I, Universität Bayreuth , Bayreuth 95440, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Huettner
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai, India 400076.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Kabra