Wide-Band-Gap Mixed-Halide 3D Perovskites: Electronic Structure and Halide Segregation Investigation
Siyuan Zhang, Ming Chun Tang, Nhan V. Nguyen, Thomas D. Anthopoulos, Christina A. Hacker
Mixed-halide organolead perovskites (MAPbX3) are of great interest for both single junction and tandem solar cells because their bandgap can be effectively tuned by varying the halide ratio. In this study, we investigate the family of mixed iodide/bromide (I/Br) and bromide/chloride (Br/Cl) perovskites, revealing the strong influence of halide substitution on the bandgap, electronic properties, morphology, film composition, and phase segregation. A qualitatively blue- shift along with the I →Br →Cl series was observed, and the resulting light absorption covers the entire visible region from 420 nm to 800 nm. The ionization potential increases from ≈6.0 eV to ≈7.0 eV as the halide composition changing from I to Br. However, when Cl substitutes Br, the valence band position shows little variation, while a monotonic trend is found for the conduction band edge. Through XPS depth profile, we found that halide segregation was observed in both I/Br and Br/Cl mixed halide perovskite films, where the large halide ion (I and Br in I/Br and Br/Cl mix) phase segregates to the surface of the film and the small halide ion (Br and Cl in I/Br and Br/Cl mix) accumulates at the bottom of the film. These differences in the band structure, electronic properties, morphology, and film composition were reflected in the device performance: a decreased short-circuit current density and increased open-circuit voltage was observed as the bandgap increases along with the I →Br →Cl series. This study highlights the role of halides in the band structure and phase segregation in mixed halide perovskite solar cells and provides a foundational framework for future optoelectronic applications of these materials.
, , M.
, Nguyen, N.
, Anthopoulos, T.
and Hacker, C.
Wide-Band-Gap Mixed-Halide 3D Perovskites: Electronic Structure and Halide Segregation Investigation, ACS Applied Electronic Materials, [online], https://doi.org/10.1021/acsaelm.1c00191, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=931525
(Accessed October 22, 2021)