46. nanoscale halide segregation and charge collection within mixed-halide perovskite solar cells

Department: NanoEngineering
Research Institute Affiliation: Agile - Sustainable Power and Energy Center (SPEC)
Faculty Advisor(s): David Fenning

Primary Student
Name: Yanqi Luo
Email: yal227@ucsd.edu
Phone: 925-216-0991
Grad Year: 2019

The emerging class of lead halide perovskite materials has been actively developed for optoelectronic applications in solar cells, photonic devices, light emitting diodes, and lasers due to their inexpensive fabrication cost and excellent optoelectronic properties. Tremendous amounts of efforts on optimizing cell architecture design, controlling perovskite crystal growth, and exploring a variety chemistry composition have improved perovskite solar cell performance from less than 4% to 22.1% within 6 years. Besides their impressive performance, an attractive aspect of organometal perovskites is their structural flexibility and light absorption tunablility. For example, the bromine-based lead perovskites have a bandgap in the green wavelength range, and this absorption wavelength can be gradually tuned beyond the red to 785 nm when more and more iodine is substituted for Br. To date, the most efficient lead halide perovskite solar cells are composed of both Br and I, giving the chemical composition of MA1/3FA2/3Pb(Br1/6I5/6)3, where the A-site cations MA and FA are the organic groups methylammonium and formamidinium, respectively. In this study, a nanoscale spatial variation of Br incorporation is found in both iodide rich and poor FAPbI3-xBrx solar cells by synchrotron-based nanoprobe X-ray fluorescence (Nano-XRF). The simultaneous collection of X-ray beam induced (XBIC) maps is used to determine the variation of local photocurrent collection. Combining the local elemental information from Nano-XRF and the local optoelectronic response from XBIC reveals the electronic role of Br substitution and opens new directions toward understanding the tuning of mixed-cation and mixed-halide perovskite systems toward optimal device efficiency.

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