Role of Alkali-Metal Cations in Electronic Structure and Halide Segregation of Hybrid Perovskites.
Nguyen, Nhan V
Anthopoulos, Thomas D.
Hacker, Christina A
KAUST DepartmentMaterial Science and Engineering Program
Material Science and Engineering
Physical Science and Engineering (PSE) Division
KAUST Solar Center (KSC)
Online Publication Date2020-07-01
Print Publication Date2020-07-29
Embargo End Date2021-07-02
Permanent link to this recordhttp://hdl.handle.net/10754/664352
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AbstractThe ability to control or prevent phase segregation in perovskites is crucial to realizing stable and tunable mixed-halide optoelectronic devices. In this work, we systematically examine the impact of alkali-metal-cation (Cs+ and K+) concentration on the band structure, chemical composition, phase segregation, and polycrystalline microstructure on formamidinium-dominated mixed-halide mixed-cation perovskite films. It was found that the incorporation of Cs+ and K+ cations decreases the work function and the core levels of all components shift toward higher binding energy consistent with n-doping the perovskite film, which facilitates electron transfer to the electron transport layer TiO2. A concentration-dependent film structure was observed by X-ray photoemission spectroscopy and grazing incidence wide-angle X-ray scattering where the halides and cations are distributed evenly across perovskite films at low metallic cation concentration (5%). A high metal-cation ratio (20%) leads to halide segregation within the perovskite film and the surface becomes bromide-poor, whereas the bromide and metal cations diffuse more deeply within the film. These differences in electronic properties, element distribution, and film morphology were reflected in the device performance where the power conversion efficiency of low-metallic-cation concentration (5% of Cs+ and K+) perovskite solar cells is ≈5% higher than the high-concentration ones (20%). This study provides valuable chemical and physical insight into the underlying trade-offs in the careful tuning of electrical properties and film structure to optimize multication and mixed-halide hybrid perovskites.
CitationZhang, S., Tang, M.-C., Fan, Y., Li, R., Nguyen, N. V., Zhao, K., … Hacker, C. A. (2020). Role of Alkali-Metal Cations in Electronic Structure and Halide Segregation of Hybrid Perovskites. ACS Applied Materials & Interfaces. doi:10.1021/acsami.0c08396
SponsorsThis work was supported by the National Institute of Standards and Technology (NIST) Financial Assistance Award with Federal Award ID 70NANB16H228, King Abdullah University of Science and Technology (KAUST), and National Natural Science Foundation of China (61974085). Dr. Tang acknowledges support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Physical Measurement Laboratory, Award 70NANB14H209, through the University of Maryland.
PublisherAmerican Chemical Society (ACS)
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