PtyNAMi: ptychographic nano-analytical microscope

Ptychographic X-ray imaging at the highest spatial resolution requires an optimal experimental environment, providing a high coherent flux, excellent mechanical stability and a low background in the measured data. This requires, for example, a stable performance of all optical components along the entire beam path, high temperature stability, a robust sample and optics tracking system, and a scatter-free environment. This contribution summarizes the efforts along these lines to transform the nanoprobe station on beamline P06 (PETRA III) into the ptychographic nano-analytical microscope (PtyNAMi

Multi-Modal Scanning X-Ray Microscopy for Solar Cell Characterization

Thin-film photovoltaic devices are used to harvest solar energy. To be economically competitive, three aspects are particularly challenging, which we addressed in this work: cost efficiency, defect passivation, and spatial homogeneity. Comprehensive analysis is required to elucidate the underlying mechanisms that limit the conversion efficiency of thin-film solar cells. Traditionally, several probes are sequentially employed to evaluate different properties. Multi-modal hard X-ray scanning microscopy provides an alternative to sequential measurements and is available at micro- and nano-imaging beamlines of synchrotron facilities.In this work, we extended the range of available scanning X-ray modalities and applied them to two types of thin-film solar cells. Hereby, we utilized the deep penetration depth of hard X-rays to evaluate fully operational solar cells on a point-by-point basis with a sub-micrometer resolution, which allowed us to identify the origin of performance variations.Specifically, we developed an X-ray excited optical luminescence (XEOL) detection unit to resolve the signal in the spectral and temporal domain with a high signal-to-noise ratio. Combining XEOL with X-ray fluorescence (XRF), we studied wrinkled triple-cation metal-halide perovskite solar cells and directly related the inhomogeneous optical performance to the inhomogeneous absorber composition.For X-ray beam induced current (XBIC) measurements, we established a guide to using lock-in amplification. By correlating the XBIC with the XRF signal, we found that economically favorable Cu(In,Ga)Se2 solar cells with a high Ga/In ratio suffer from defect clusters that cannot be sufficiently passivated with the standard Rb post-deposition treatment.Conflicting requirements pose a challenge for the simultaneous evaluation of multiple modalities. However, we demonstrated that four-fold multi-modal measurements are feasible and provide new insights into the relation between structure, composition, optical performance, and electrical performance, enabling the targeted synthesis of high-efficiency, low-cost solar cells

Image Registration in Multi-Modal Scanning Microscopy: A Solar Cell Case Study

Scanning probe measurements are an indispensable tool of solar cell research today, and the compatibility with simultaneous acquisition of complementary measurement modes is a particular strength. However, multi-modal data acquisition is often limited by different scan-parameter requirements. As a consequence, the modalities may be assessed subsequently rather than simultaneously. In this instance, image registration serves as a tool to align two-dimensional datasets at nanoscale. Here, we showcase an example of two subsequent scanning Xray microscopy measurements of solar cells with a Cu(In,Ga)Se2 absorber, the first measurement being optimized for X-ray beam induced current and the second for X-ray fluorescence. We discuss different approaches and pitfalls of image registration and its potential combination with Gaussian filtering. This finally allows us to proceed with the investigation of point-by-point correlations

X-ray Beam Induced Current Measurements for Multi-Modal X-ray Microscopy of Solar Cells

X-ray beam induced current (XBIC) measurements allow mapping out the nanoscale performance of electronic devices such as solar cells. Ideally, XBIC is employed simultaneously with other techniques within a multi-modal X-ray microscopy approach. An example is given herein combining XBIC with X-ray fluorescence to enable point-by-point correlations of the electrical performance with chemical composition. For the highest signal-to-noise ratio in XBIC measurements, lock-in amplification plays a crucial role. By this approach, the X-ray beam is modulated by an optical chopper upstream of the sample. The modulated X-ray beam induced electrical signal is amplified and demodulated to the chopper frequency using a lock-in amplifier. By optimizing low-pass filter settings, modulation frequency, and amplification amplitudes, noise can efficiently be suppressed for the extraction of a clear XBIC signal. A similar setup can be used to measure the X-ray beam induced voltage (XBIV). Beyond standard XBIC/XBIV measurements, XBIC can be measured with bias light or bias voltage applied such that outdoor working conditions of solar cells can be reproduced during in-situ and operando measurements. Ultimately, the multi-modal and multi-dimensional evaluation of electronic devices at the nanoscale enables new insights into the complex dependencies between composition, structure, and performance, which is an important step towards solving the materials’ paradigm

The nanoscale distribution of copper and its influence on charge collection in CdTe solar cells

For decades, Cu has been the primary dopant in CdTe photovoltaic absorbers. Typically, Cu acceptor concentrations in these devices are on the order of 1 10$^{14}$ cm$^{−3}$, which has made it notoriously difficult to directly correlate nanoscale Cu distributions to the local charge transport properties of these devices. To measure and correlate these properties, measurement techniques require high sensitivity to elemental concentration, large penetration depth, and operando compatibility. Techniques such as secondary-ion mass spectroscopy and X-ray energy dispersive spectroscopy are widely adopted to measure Cu concentrations, but they are limited by penetration depth, sensitivity, or spatial resolution. Additionally, they lack the operando capabilities required to correlate one-to-one Cu concentrations to electrical performance. In this work, correlative X-ray microscopy is used to investigate the spatial distribution of Cu and its impact on charge collection through the depth and breadth of CdTe photovoltaic devices. Plan-view, nanoscale X-ray fluorescence maps clearly demonstrate the spatial segregation of copper around regions thought to be CdTe grain boundaries. Complementary cross-section imaging unveils the transition of the maximum charge-collection efficiency from the ZnTe–CdTe interface to the CdS–CdTe interface as a function of Cu incorporation. The copper concentration through the depth of the CdTe layer is characterized by slow and fast diffusion components, and cross-section charge-transport modeling shows that the experimentally obtained charge collection can be explained by the modeled acceptor distribution through the depth of the CdTe layer

Quantifying the Elemental Distribution in Solar Cells from X-Ray Fluorescence Measurements with Multiple Detector Modules

Within the analysis of solar cells with multi-modalX-ray microscopy, X-ray fluorescence (XRF) measurements havebecome a reliable source for evaluating elemental distributions.While XRF measurements can unveil the elemental distributionat unparalleled sensitivity and spatial resolution, the quantitativeanalysis is challenged by effects such as self-absorption and furthercomplicated by the inclusion of multiple detector modules.Here, we showcase the exemplary analysis of XRF spectraobtained from a Cu(In,Ga)Se2 solar cell utilizing four detectormodules. After cataloging typical features found in XRF spectra,we demonstrate the inclusion of detector modules with individualabsorption correction. This results in quantitative stoichiometricratios of the critical absorber elements Cu, In, and Ga that arein good agreement with the nominal ratios.These results are particularly relevant in view of futuremeasurements at diffraction-limited synchrotron beamlines: inorder to profit from the boost of nano-focused photon flux, XRFmeasurements will require multiple detector modules, for whichwe demonstrate an approach of quantitative analysis

X‐ray diffraction with micrometre spatial resolution for highly absorbing samples

X‐ray diffraction with high spatial resolution is commonly used to characterize (poly)crystalline samples with, for example, respect to local strain, residual stress, grain boundaries and texture. However, the investigation of highly absorbing samples or the simultaneous assessment of high‐Z materials by X‐ray fluorescence have been limited due to the utilization of low photon energies. Here, a goniometer‐based setup implemented at the P06 beamline of PETRA III that allows for micrometre spatial resolution with a photon energy of 35 keV and above is reported. A highly focused beam was achieved by using compound refractive lenses, and high‐precision sample manipulation was enabled by a goniometer that allows up to 5D scans (three rotations and two translations). As experimental examples, the determination of local strain variations in martensitic steel samples with micrometre spatial resolution, as well as the simultaneous elemental distribution for high‐Z materials in a thin‐film solar cell, are demonstrated. The proposed approach allows users from the materials‐science community to determine micro‐structural properties even in highly absorbing samples.A demonstration of high‐resolution micro X‐ray diffraction at high photon energies for highly absorbing samples

X-ray diffraction with micrometre spatial resolution for highly absorbing samples

X-ray diffraction with high spatial resolution is commonly used to characterize(poly)crystalline samples with, for example, respect to local strain, residualstress, grain boundaries and texture. However, the investigation of highlyabsorbing samples or the simultaneous assessment of high-Zmaterials by X-rayfluorescence have been limited due to the utilization of low photon energies.Here, a goniometer-based setup implemented at the P06 beamline of PETRAIII that allows for micrometre spatial resolution with a photon energy of 35 keVand above is reported. A highly focused beam was achieved by using compoundrefractive lenses, and high-precision sample manipulation was enabled by agoniometer that allows up to 5D scans (three rotations and two translations).As experimental examples, the determination of local strain variations inmartensitic steel samples with micrometre spatial resolution, as well as thesimultaneous elemental distribution for high-Zmaterials in a thin-film solar cell,are demonstrated. The proposed approach allows users from the materials-science community to determine micro-structural properties even in highly absorbing samples

Comparison of XBIC and LBIC measurements of a fully encapsulated c-Si solar cell

A fully encapsulated c-Si solar cell was evaluatedusing focused X-ray and laser beams to probe the microscopicelectrical performance and composition. Particular emphasiswas placed on the influence of the silver fingers on the laser(LBIC) and X-ray beam induced current (XBIC). Therefore,an uncommonly high X-ray energy of 28 keV was utilized formaximum sensitivity to the Ag distribution measured by X-rayfluorescence through the back sheet. The direct comparison ofLBIC and XBIC measurements yields a comprehensive pictureof these techniques, illustrating the advantages and challenges ofboth approaches. Specifically, the effect of heavy elements actingas a secondary photon source that increase the XBIC signal isdiscussed and supported by Monte-Carlo simulations