Publication date: 21st July 2025
Hybrid lead halide perovskites are among the most promising materials today, combining excellent optical properties from the inorganic framework with the tunability and stability provided by organic cations. Within this class, PEA:CsPbBr₃ has gained particular attention for its remarkable optical performance, making it a strong candidate for diverse optoelectronic applications. However, while its optical properties are well established, much less is known about the underlying processes, especially the lattice response to photoexcitation and its role in the following light emission.
For this reason, low-temperature (87 K) time-resolved XRD measurements were carried out at FemtoMAX beamline (MAX IV),[1] investigating the behavior of a thin film of PEA:CsPbBr₃. The sample was photoexcited using a 400 nm femtosecond laser pump with 5 Hz repetition rate and fluences in the 0.5 – 8 mJ/cm2 range and subsequently probed with femtosecond X-ray pulses at 10 Hz. After photoexcitation we could observe a 12 picoseconds clear expansion along [110] and [220] directions followed by 2 ns relaxation of the lattice. The observed expansion suggests an octahedral rearrangement that increases the symmetry of the orthorhombic phase. This interpretation is further supported by the concurrent increase in peak intensity and narrowing, which indicates improved ordering within the crystal lattice. Moreover, strain and peak-shape parameters appear to depend on laser fluence, emphasizing its critical role in governing the structural dynamics of these materials.
This study provides insights into the processes of photoexcitation and subsequent emission, which are crucial for guiding the future development of perovskite-based optoelectronic devices with enhanced emissive properties.
We acknowledge the MAX IV Laboratory for beamtime on the FemtoMAX beamline under proposal 20241468. Research conducted at MAX IV, a Swedish national user facility, is supported by Vetenskapsrådet (Swedish Research Council, VR) under contract 2018-07152, Vinnova (Swedish Governmental Agency for Innovation Systems) under contract 2018-04969 and Formas under contract 2019-02496. We thank colleagues Prasenjit Mandal, Chenxu Jiao, Lorenzo Tallarini, and the FemtoMAX beamline staff for participation in and assistance with the beamtime #20241468, respectively. The work of G.L. and D.B. was funded by the European Union (ERC Starting Grant PROMETHEUS, project no. 101039683). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.
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