Sloboda Tamara, Svanström Sebastian, Johansson Fredrik O L, Andruszkiewicz Aneta, Zhang Xiaoliang, Giangrisostomi Erika, Ovsyannikov Ruslan, Föhlisch Alexander, Svensson Svante, Mårtensson Nils, Johansson Erik M J, Lindblad Andreas, Rensmo Håkan, Cappel Ute B
Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, 100 44, Stockholm, Sweden.
Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20, Uppsala, Sweden.
Sci Rep. 2020 Dec 31;10(1):22438. doi: 10.1038/s41598-020-79792-z.
Time-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface.
时间分辨光电子能谱能够深入了解载流子动力学，并通过对芯能级的测量提供元素和位点特异性信息的可能性。在本文中，我们证明了在同步加速器设施BESSY II上进行的单次实验中，该方法可以在从皮秒到微秒的宽时间窗口内获取PbS量子点中的电子动力学信息。该方法对芯能级位置的微小变化敏感。通过使用重复频率低于用于探测芯能级电子的X射线脉冲重复频率的泵浦激光，能够在低泵浦通量下进行快速测量：通过使用时间分辨光谱仪，可以对来自所有同步加速器脉冲的数据进行时间相关分析。此外，通过皮秒级控制泵浦激光相对于X射线脉冲到达样品的时间，可以实现仅受X射线脉冲长度限制的时间分辨率。使用这种方法，我们通过对Pb 5d芯能级的时间分辨测量，研究了n型MgZnO衬底上PbS量子点薄膜样品中的电荷动力学。我们发现了一个时间分辨的芯能级位移，我们将其归因于MgZnO/PbS量子点界面处的电子注入和电荷积累。通过测量不同厚度的PbS薄膜，证实了这一归因。因此，我们的结果深入了解了在MgZnO/PbS界面处特异性产生的光电压的大小、电荷传输和电子注入的时间尺度，以及该界面处电荷复合的时间尺度。我们方法的一个独特之处在于，这两个过程的时间尺度可以在单次实验中获取，并针对特定界面进行研究。
