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

Abstract

X-ray beam induced current (XBIC) measurements allow mapping of 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.

Defect activation and annihilation in CIGS solar cells: an operando x-ray microscopy study

“…The energy of the incident x-ray photons was set to 10.5 keV, just above the Ga K edge for maximum sensitivity to the absorber elements Ga and Cu. Note that at this incident energy the sensitivity to In is fairly reduced and there is negligible sensitivity to Se, Na or K. The x-ray beam was modulated at a frequency of 318 Hz by an optical chopper upstream of the focusing optics and detectors [21]. The chopper consists of m 300 m spring steel that enables a modulation ratio of > 10 12 between x-ray ON/OFF periods.…”

“…In the case of the SG sample, stick-slip motion of the sample below  40 C and above  80 C did not allow for the measurement of the same area throughout the entire temperature range. Therefore, the comparable temperature range of the SG sample is limited to 40°C- 80 C. For the highest signal-to-noise ratio of the XBIC and XBIV measurements, we utilized lock-in amplification as introduced in detail earlier [21,22,28,39]. The front contact being exposed to the incident x-rays was grounded to suppress contributions of replacement currents for ejected electrons to the measured XBIV & XBIC signal, which should include only the signal from the absorber layer [17].…”

PtyNAMi: ptychographic nano-analytical microscope

“…Here, ptychography was combined with X-ray fluorescence (XRF) and lock-in amplified X-ray beam-induced current (XBIC) measurements (Ossig et al, 2019). This allowed the simultaneous assessment of the X-ray transmittance [ Fig.…”

Resonant x-ray ptychographic nanotomography of kesterite solar cells

“…The most important feature of this technique is the possibility for in situ or operando studies. The impact of these defects and features can be quantified with measurements of x-ray beam induced current or voltage (XBIC/XBIV [50][51][52]), which is the natural extension of this study. The missing requirements for such studies are the ability to electrically contact the prepared samples and a different scheme for the ptychographic scan.…”