title: Role of Microstructure in the Electron-Hole Interaction of Hybrid Lead-Halide Perovskites.
abstract: Solar cells based on hybrid inorganic-organic halide perovskites have demonstrated high power conversion efficiencies in a range of architectures. The existence and stability of bound electron-hole pairs in these materials, and their role in the exceptional performance of optoelectronic devices, remains a controversial issue. Here we demonstrate, through a combination of optical spectroscopy and multiscale modeling as a function of the degree of polycrystallinity and temperature, that the electron-hole interaction is sensitive to the microstructure of the material. The long-range order is disrupted by polycrystalline disorder and the variations in electrostatic potential found for smaller crystals suppress exciton formation, while larger crystals of the same composition demonstrate an unambiguous excitonic state. We conclude that fabrication procedures and morphology strongly influence perovskite behaviour, with both free carrier and excitonic regimes possible, with strong implications for optoelectronic devices.
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Grancini
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Ajay Ram
authors.initials: AR
authors.lastname: Srimath Kandada
authors.affiliation: Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Jarvist M
authors.initials: JM
authors.lastname: Frost
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Barker
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.|Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: De Bastiani
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Gandini
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Marras
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Lanzani
authors.affiliation: Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Aron
authors.initials: A
authors.lastname: Walsh
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133, Milan, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: Petrozza