title: Experimental and theoretical optical properties of methylammonium lead halide perovskites.
abstract: The optical constants of methylammonium lead halide single crystals CH3NH3PbX3 (X = I, Br, Cl) are interpreted with high level ab initio calculations using the relativistic quasiparticle self-consistent GW approximation (QSGW). Good agreement between the optical constants derived from QSGW and those obtained from spectroscopic ellipsometry enables the assignment of the spectral features to their respective inter-band transitions. We show that the transition from the highest valence band (VB) to the lowest conduction band (CB) is responsible for almost all the optical response of MAPbI3 between 1.2 and 5.5 eV (with minor contributions from the second highest VB and the second lowest CB). The calculations indicate that the orientation of [CH3NH3](+) cations has a significant influence on the position of the bandgap suggesting that collective orientation of the organic moieties could result in significant local variations of the optical properties. The optical constants and energy band diagram of CH3NH3PbI3 are then used to simulate the contributions from different optical transitions to a typical transient absorption spectrum (TAS).
authors.affiliation: Physics department, Imperial College London, SW7 2AZ, UK. piers.barnes@imperial.ac.uk.
authors.forename: Aurélien M A
authors.initials: AM
authors.lastname: Leguy
authors.affiliation: Physics department, Kings College London, WC2R 2LS, UK. mark.van_schilfgaarde@kcl.ac.uk.
authors.forename: Pooya
authors.initials: P
authors.lastname: Azarhoosh
authors.affiliation: Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), 08193, Spain.
authors.forename: M Isabel
authors.initials: MI
authors.lastname: Alonso
authors.affiliation: Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), 08193, Spain.
authors.forename: Mariano
authors.initials: M
authors.lastname: Campoy-Quiles
authors.affiliation: Chemistry department, University of Bath, BA2 7AY, UK.
authors.forename: Oliver J
authors.initials: OJ
authors.lastname: Weber
authors.affiliation: Physics department, Imperial College London, SW7 2AZ, UK. piers.barnes@imperial.ac.uk.
authors.forename: Jizhong
authors.initials: J
authors.lastname: Yao
authors.affiliation: Chemistry department, Imperial College, London, SW7 2AZ, UK and SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation and Knowledge Centre, Central Avenue, Baglan, SA12 7AX, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bryant
authors.affiliation: Chemistry department, University of Bath, BA2 7AY, UK.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Weller
authors.affiliation: Physics department, Imperial College London, SW7 2AZ, UK. piers.barnes@imperial.ac.uk and SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation and Knowledge Centre, Central Avenue, Baglan, SA12 7AX, UK.
authors.forename: Jenny
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Chemistry department, University of Bath, BA2 7AY, UK.
authors.forename: Aron
authors.initials: A
authors.lastname: Walsh
authors.affiliation: Physics department, Kings College London, WC2R 2LS, UK. mark.van_schilfgaarde@kcl.ac.uk.
authors.forename: Mark
authors.initials: M
authors.lastname: van Schilfgaarde
authors.affiliation: Physics department, Imperial College London, SW7 2AZ, UK. piers.barnes@imperial.ac.uk.
authors.forename: Piers R F
authors.initials: PR
authors.lastname: Barnes