title: Real-Time Nanoscale Open-Circuit Voltage Dynamics of Perovskite Solar Cells.
abstract: Hybrid organic-inorganic perovskites based on methylammonium lead (MAPbI3) are an emerging material with great potential for high-performance and low-cost photovoltaics. However, for perovskites to become a competitive and reliable solar cell technology their instability and spatial variation must be understood and controlled. While the macroscopic characterization of the devices as a function of time is very informative, a nanoscale identification of their real-time local optoelectronic response is still missing. Here, we implement a four-dimensional imaging method through illuminated heterodyne Kelvin probe force microscopy to spatially (<50 nm) and temporally (16 s/scan) resolve the voltage of perovskite solar cells in a low relative humidity environment. Local open-circuit voltage (Voc) images show nanoscale sites with voltage variation >300 mV under 1-sun illumination. Surprisingly, regions of voltage that relax in seconds and after several minutes consistently coexist. Time-dependent changes of the local Vocare likely due to intragrain ion migration and are reversible at low injection level. These results show for the first time the real-time transient behavior of the Vocin perovskite solar cells at the nanoscale. Understanding and controlling the light-induced electrical changes that affect device performance are critical to the further development of stable perovskite-based solar technologies.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Garrett
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Tennyson
authors.affiliation: Department of Mechanical Engineering, University of Nebraska , Lincoln, Nebraska 68588, United States.
authors.forename: Miao
authors.initials: M
authors.lastname: Hu
authors.affiliation: Department of Mechanical Engineering, University of Nebraska , Lincoln, Nebraska 68588, United States.
authors.forename: Jinsong
authors.identifier: 0000-0002-0509-8778
authors.initials: J
authors.lastname: Huang
authors.affiliation: Department of Electrical and Computer Engineering, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: Jeremy N
authors.identifier: 0000-0002-0881-9876
authors.initials: JN
authors.lastname: Munday
authors.forename: Marina S
authors.identifier: 0000-0003-4888-8195
authors.initials: MS
authors.lastname: Leite
keywords: Perovskite; nanoscale imaging; open-circuit voltage; photovoltaic; solar cells