title: Unbalanced Hole and Electron Diffusion in Lead Bromide Perovskites.
abstract: We use scanning photocurrent microscopy and time-resolved microwave conductivity to measure the diffusion of holes and electrons in a series of lead bromide perovskite single crystals, APbBr3, with A = methylammonium (MA), formamidinium (FA), and Cs. We find that the diffusion length of holes (LDh+∼ 10-50 μm) is on average an order of magnitude longer than that of electrons (LDe-∼ 1-5 μm), regardless of the A-type cation or applied bias. Furthermore, we observe a weak dependence of LDacross the A-cation series MA > FA > Cs. When considering the role of the halide, we find that the diffusion of holes in MAPbBr3is comparable to that in MAPbI3, but the electron diffusion length is up to five times shorter. This study shows that the disparity between hole and electron diffusion is a ubiquitous feature of lead halide perovskites. As with organic photovoltaics, this imbalance will likely become an important consideration in the optimization of lead halide perovskite solar cells.
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Giselle A
authors.initials: GA
authors.lastname: Elbaz
authors.affiliation: Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Daniel B
authors.identifier: 0000-0003-2977-5590
authors.initials: DB
authors.lastname: Straus
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Octavi E
authors.initials: OE
authors.lastname: Semonin
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Trevor D
authors.initials: TD
authors.lastname: Hull
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.|Columbia Nano Initiative, Columbia University , New York, New York 10027, United States.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Paley
authors.affiliation: Department of Physics, Harvard University , Cambridge, Massachusetts 02138, United States.
authors.forename: Philip
authors.initials: P
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Jonathan S
authors.identifier: 0000-0001-5502-3267
authors.initials: JS
authors.lastname: Owen
authors.affiliation: Department of Electrical and Systems Engineering, Department of Materials Science and Engineering, and Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Cherie R
authors.initials: CR
authors.lastname: Kagan
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.
authors.forename: Xavier
authors.identifier: 0000-0002-8850-0725
authors.initials: X
authors.lastname: Roy
keywords: Cation effect; carrier diffusion; lifetime; scanning photocurrent microscopy; time-resolved microwave conductivity