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

Abstract

The ability to control or prevent phase segregation in perovskites is crucial to realizing stable and tunable mixed-halide optoelectronic devices. Here, 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 chemicalmore » 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.« less

Authors:

Zhang, Siyuan  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0221-9407"

Tang, Ming-Chun ^[2]; Fan, Yuanyuan ^[3]; Li, Ruipeng ^[4]; Nguyen, Nhan V. ^[5]; Zhao, Kui ^[3]; Anthopoulos, Thomas D.  ^[6];

• Search DOE PAGES for author "Anthopoulos, Thomas D."
• Search DOE PAGES for ORCID "0000-0002-0978-8813"

Hacker, Christina A. ^[5]

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+ Show Author Affiliations

1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Theiss Research, La Jolla, CA (United States)
2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudi Arabia); Univ. of Maryland, College Park, MD (United States)
3. Shaanxi Normal Univ., Xi’an (China)
4. Brookhaven National Lab. (BNL), Upton, NY (United States)
5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
6. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudi Arabia)

Publication Date:

Wed Jul 01 00:00:00 EDT 2020

Research Org.:

Brookhaven National Lab. (BNL), Upton, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Institute of Standards and Technology (NIST); National Natural Science Foundation of China (NSFC)

OSTI Identifier:

1658811

Report Number(s):

BNL-216344-2020-JAAM
Journal ID: ISSN 1944-8244

Grant/Contract Number:  

SC0012704; 70NANB16H228; 70NANB14H209

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 12; Journal Issue: 30; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; mixed-cation and mixed-halide perovskites; band structure; depth profile; microstructure; phase segregation