Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se₂ thin films for solar cells – a review

Abstract

The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se)2 thin films for high‐efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep‐defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley–Read–Hall recombination is still enhanced with respect to defect‐free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se)2 thin films with two‐dimensional device simulations suggest that these defects are one origin of the reduced open‐circuit voltage of the photovoltaic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Inhomogeneities in Cu(In,Ga)Se2 Thin Films for Solar Cells: Band‐Gap Versus Potential Fluctuations

“…Spatial variations in composition were detected at various line and planar defects in polycrystalline Cu(In,Ga)Se 2 thin films. The reader is referred to a recent review on this topic, which provides a summary on various experimental results obtained by electron energy‐loss spectrometry in scanning transmission electron microscopy (STEM) or by atom‐probe tomography (APT). At planar defects (i.e., stacking faults, twin boundaries, and random grain boundaries), atomic reconstruction was identified, i.e., the changes in composition are generally confined to the atomic planes adjacent to the planar defect.…”

No Evidence for Passivation Effects of Na and K at Grain Boundaries in Polycrystalline Cu(In,Ga)Se2 Thin Films for Solar Cells

“…It is noted that the s GB values at individual GBs (Figure ) overall exhibited magnitudes on a wide range with orders of 10 2 –10 4 cm s −1 . This finding can be linked to the mechanism of atomic/ionic reconstruction at CIGSe GBs described by Abou‐Ras et al The result of this reconstruction is a residual density of point defects, which is always composed differently for different GBs (and thus, also the magnitude and sign of its excess charge densities are different). Therefore, also the barrier heights and the recombination velocities at the GBs can be expected to be (largely) different.…”

“…It is noteworthy that in contrast to the CIGSe/buffer (or to the CIGSe/back contact) interfaces, alkali metals are not expected to form any secondary phases at GBs but rather contribute to the atomic/ionic reconstruction of the adjacent atomic planes at the GBs . atom‐probe tomography analyses determined the concentrations of Na and K at CIGSe GBs to about 0.1–1 at% (order of magnitude) …”

A short review on the advancements in electroplating of CuInGaSe2 thin films

“…Moreover, mimicking such studies in electrochemical route is much easier when compared to vacuum deposition techniques. A detailed recent review on the progress in CIGSe solar cells defects mechanisms and the state-of-the-art CIGSe devices have been discussed in the cited literature [51,52].…”