title: Direct-indirect character of the bandgap in methylammonium lead iodide perovskite.
abstract: Metal halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) are generating great excitement due to their outstanding optoelectronic properties, which lend them to application in high-efficiency solar cells and light-emission devices. However, there is currently debate over what drives the second-order electron-hole recombination in these materials. Here, we propose that the bandgap in CH3NH3PbI3has a direct-indirect character. Time-resolved photo-conductance measurements show that generation of free mobile charges is maximized for excitation energies just above the indirect bandgap. Furthermore, we find that second-order electron-hole recombination of photo-excited charges is retarded at lower temperature. These observations are consistent with a slow phonon-assisted recombination pathway via the indirect bandgap. Interestingly, in the low-temperature orthorhombic phase, fast quenching of mobile charges occurs independent of the temperature and photon excitation energy. Our work provides a new framework to understand the optoelectronic properties of metal halide perovskites and analyse spectroscopic data.
authors.affiliation: Opto-electronic Materials Section, Department of Chemical Engineering, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Eline M
authors.identifier: 0000-0002-5537-6545
authors.initials: EM
authors.lastname: Hutter
authors.affiliation: Opto-electronic Materials Section, Department of Chemical Engineering, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: María C
authors.initials: MC
authors.lastname: Gélvez-Rueda
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Osherov
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Bulović
authors.affiliation: Opto-electronic Materials Section, Department of Chemical Engineering, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Ferdinand C
authors.initials: FC
authors.lastname: Grozema
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.|Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Stranks
authors.affiliation: Opto-electronic Materials Section, Department of Chemical Engineering, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Savenije