Characterisation of the interplay between microstructure and opto-electronic properties of Cu(In,Ga)S₂ solar cells by using correlative CL-EBSD measurements

Abstract

Cathodoluminescence (CL) and electron backscatter diffraction (EBSD) have been applied to exactly the same grain boundaries (GBs) in a Cu(In,Ga)S2solar absorber in order to investigate the influence of microstructure on the radiative recombination behaviour at the GBs. Two different types of GB with different microstructure were analysed in detail: random high angle grain boundaries (RHAGBs) and Σ3 GBs. We found that the radiative recombination at all RHAGBs was inhibited to some extent, whereas at Σ3 GBs three different observations were made: unchanged, hindered, or promoted radiative recombination. These distinct behaviours may be linked to atomic-scale grain boundary structural differences. The majority of GBs also exhibited a small spectral shift of about ±10 meV relative to the local grain interior (GI) and a few of them showed spectral shifts of up to ±40 meV. Red and blue shifts were observed with roughly equal frequency.

Simultaneous mapping of cathodoluminescence spectra and backscatter diffraction patterns in a scanning electron microscope

“…More direct measurement of the crystal lattice can be carried out in an SEM using electron backscatter diffraction (EBSD). This technique is long-established in the mapping of crystal orientations in the grains of polycrystalline materials, and the value of correlating such information with CL maps of the same area has been demonstrated for both geological [3] and semiconductor thin-film [4] samples. In the last few years the EBSD technique has been extended to allow a full strain tensor to be extracted from small distortions in the diffraction pattern, using cross-correlation data analysis methods [5].…”

“…While the two techniques are clearly complementary, simultaneous measurement of the strain (using EBSD) and its effect on emission (using CL) has not been previously demonstrated in a single scan, due to conflicting measurement geometries [7] and/or the need to use different instruments [4]. Both techniques would ideally have access to a large solid angle directly above the sample surface, and so each would obscure the other.…”