研究目的
To probe the electronic and geometric structure of centres formed by photoexcitation of solar materials such as polymorphs and inorganic Cs-based perovskites using picosecond X-ray absorption spectroscopy.
研究成果
The study demonstrated the advantages of an element-selective, time-resolved probe of photoexcited solar materials. It showed electron localization at Ti defects in TiO2 anatase and rutile and small hole polaron formation in the valence band of CsPbBr3, all within 80 ps. The method is promising for the study of the ultrafast time scales of such processes, especially with the advent of the Swiss X-ray Free Electron Laser (SwissFEL).
研究不足
The study was limited to probing charge localization due to the strong signals generated by an oxidation state change of elements. The time resolution was typically 70–100 ps, which may not capture all aspects of charge dynamics.
1：Experimental Design and Method Selection:
The study implemented time-resolved X-ray absorption spectroscopy (XAS) at synchrotrons to probe the fate of electrons in transition metal oxides (TMOs) and perovskites. The optical pump/X-ray spectroscopy probe scheme at MHz repetition rates was used, combined with a sample delivery in the form of a liquid jet.
2：Sample Selection and Data Sources:
The study investigated photoexcited rutile TiO2 nanoparticles (NPs) and inorganic Cs-based perovskite NPs (CsPbBr3 and CsPb(ClBr)3) in solution.
3：List of Experimental Equipment and Materials:
The experiments were conducted at the microXAS, PHOENIX, and SuperXAS beamlines of the Swiss Light Source (SLS). The picosecond pump laser system operated at half the repetition rate of the synchrotron source.
4：Experimental Procedures and Operational Workflow:
The transient signal consisted of the difference between the X-ray absorption of the photoexcited sample minus that of the unexcited sample, averaged over several laser/X-ray pairs of pulses at a given time delay between the pump and the probe pulses.
5：Data Analysis Methods:
The transient XAS spectra were analyzed to reflect photoinduced modifications of both the electronic and the geometric structure of the centers.
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