Journal
NANO LETTERS
Volume 17, Issue 4, Pages 2554-2560Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b00289
Keywords
Perovskite; solar cells; photovoltaic; nanoscale imaging; open-circuit voltage
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Funding
- UMD Department of Physics through The Thomas Mason Interdisciplinary Physics Fund
- National Science Foundation [ECCS-1610833, DMR-1505535, DMR-1420645]
- Directorate For Engineering
- Div Of Electrical, Commun & Cyber Sys [1610833] Funding Source: National Science Foundation
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Hybrid organic inorganic perovskites based on methylammonium lead (MAPbI(3)) 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 (V-oc) 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 V-oc are 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 V-oc in 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.
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