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).
Bibliographical noteFunding Information:
We thank Jarvist M. Frost and Paul N. Stavrinou for useful discussions, Xiao Li for assistance with sample preparation and Stefan A. Maier for access to equipment. PB and AL are grateful to the EPSRC (EP/J002305/1, EP/M014797/1 and EP/M023532/1) for financial support. JN thanks the EPSRC for funding (EP/J017361 and EP/K030671/1). MCQ and MIA acknowledge financial support from MINECO through project MAT2012-37776. The theory portion of this work was supported by EPSRC (EP/M009602/1, EP/K016288/1 and EP/M009580/1).
© The Royal Society of Chemistry 2016.
All Science Journal Classification (ASJC) codes
- Materials Science(all)