Jülich Online Semiconductor Growth Experiment for Photovoltaics (JOSEPH)

JOSEPH is a cluster tool at IMD-3. As shown in the figure below, it consists of two clusters, each with several chambers. The left cluster has several deposition chambers, including sputtering, atomic layer deposition and coevaporation. The deposition chambers are connected via a central handling system to a cluster responsible for analyzing surfaces using microscopic and spectroscopic techniques. The characterization cluster includes a surface probe measurement system (SPM) that can be used for conductive AFM measurements, scanning tunneling microscopy (STM) and Kelvin Probe Force Microscopy (KPFM) measurements. These methods allow us to measure the conductivity and work function of the surface of the deposited layers. In addition, the cluster has a UPS/XPS system that enables measurements of the work functions using UPS (ultraviolet photoemission spectroscopy) and the chemical composition using XPS (X-ray photoemission spectroscopy). With the LEEM/PEEM system, the user can investigate various properties of surfaces with high spatial resolution and simultaneously perform spectroscopic measurements. The PEEM system, for example, illuminates the layer with ultraviolet light and then generates an image of the emitted electrons, which can be spectrally filtered.

Photothermische Deflektionsspektroskopie (PDS)

Photothermal deflection spectroscopy is based on the illumination of a sample placed in a cuvette filled with a liquid. The light heats the sample and consequently also the liquid. The liquid must be selected so that its refractive index is temperature-dependent. Thus, there is a light-induced temperature gradient in the liquid, as shown in Fig. 2, which can be detected with a laser directed perpendicular to the monochromatic light used to excite the sample. This laser beam is then deflected by the refractive index gradient, which is detected by a position-selective photodetector. The signal detected by the photodetector is directly proportional to the amount of light absorbed and therefore to the absorption coefficient of the sample. If the thickness is known, the absorption coefficient (normally the parameter of interest) can also be determined with a high dynamic range of about 4 orders of magnitude.

Transiente Photolumineszenz

The knowledge gained from transient photoluminescence (PL) has contributed to a better understanding of recombination and transport in a wide range of semiconductors. Transient photoluminescence is attractive because it allows contactless measurements of films on glass, layer stacks or complete devices, investigating processes on different time and length scales. In particular, it makes it possible to analyze the various recombination processes that take place in photovoltaic absorber materials and that can reduce the open-circuit voltage and thus the efficiency of solar cells made from these materials. However, analyzing the transients is challenging due to the large number of (nonlinear) effects that contribute to the shape of the PL transient. Recent work has focused on combining transient photovoltage and photoluminescence measurements to gain an understanding of the overall significance of decay times and the differences and similarities between electrically and optically sensed transients [1].

[1] Krückemeier, L., Liu, Z., Krogmeier, B., Rau, U., & Kirchartz, T. (2021). Consistent Interpretation of Electrical and Optical Transients in Halide Perovskite Layers and Solar Cells. Advanced Energy Materials, 11(n/a), 2102290. doi:
https://doi.org/10.1002/aenm.202102290