Role of Alkali-Metal Cations in Electronic Structure and Halide Segregation of Hybrid Perovskites.

Siyuan Zhang, Ming-Chun Tang, Yuanyuan Fan, Ruipeng Li, Nhan V Nguyen, Kui Zhao, Thomas D. Anthopoulos, Christina A Hacker

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


The 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.
Original languageEnglish (US)
JournalACS Applied Materials & Interfaces
StatePublished - Jul 2 2020

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This 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.


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