René A. J. Janssen's team at Eindhoven University of Technology published a research paper titled "Local halide heterogeneity drives surface wrinkling in mixed-halide wide-bandgap perovskites" in the journal Nature Communications. Kunal Datta is the first author, and Kunal Datta & René A. J. Janssen are co-corresponding authors.
Key Highlights: This paper reveals the formation mechanism of surface wrinkles by studying the formation dynamics of mixed-halide perovskite films and their influence on local composition and optoelectronic properties. Using in situ X-ray scattering, nano-X-ray fluorescence, and hyperspectral photoluminescence imaging, the authors investigated the crystallization process and compositional distribution of perovskite films with varying compositions. They found that the uneven distribution of local halides leads to the formation of surface wrinkles, affecting the band gap and photoluminescence properties of the films.
Wide-bandgap (1.8−2.1 eV) mixed-halide perovskites present a critical bottleneck in the preparation of high-quality solution-processed films, hindering their application in high-efficiency multijunction solar cells. In particular, mixed-cation (ammonium formamide-methylammonium) wide-bandgap perovskite films are prone to the formation of micrometer-scale wrinkles, which conflict with the smooth surface required for multijunction devices. The formation of these wrinkles is attributed to compressive stress generated during film crystallization, resulting in morphological inhomogeneity and residual stress, which degrades device performance and stability.
In light of this, the team of Kunal Datta and René A. J. Janssen at Eindhoven University of Technology investigated the formation dynamics of wrinkled mixed-halide perovskite thin films and their impact on the local composition and optoelectronic properties. Using in situ X-ray scattering during perovskite film formation, they demonstrated that the crystallization of the bromide-rich perovskite precedes that of the mixed-halide phase in wrinkled films cast using an antisolvent-based process. Nanoscale X-ray fluorescence and hyperspectral photoluminescence imaging also revealed the formation of iodine- and bromine-rich phases in the wrinkled regions. This intrinsic spatial halide segregation leads to local bandgap shifts and increased Urbach energies. Morphological disorder and compositional heterogeneity also exacerbate the formation of sub-bandgap electronic defects, reducing photostability and accelerating the photoinduced segregation of iodine and bromide ions in thin films and solar cells.
This study not only reveals the impact of surface wrinkling and halide heterogeneity on the optoelectronic properties and stability of mixed-halide perovskite films, but also provides potential strategies for suppressing these defects, providing important theoretical insights and experimental data for the application of perovskite materials in high-efficiency solar cells.
