Influence of grain boundaries on current collection in Cu(In,Ga)Se 2 thin-film solar cells

Abstract

Electron backscatter diffraction (EBSD) in combination with electron beam-induced current (EBIC) measurements in a scanning electron microscope were used to investigate grain boundaries in Cu(In,Ga)Se 2 thin-film solar cells. The measurements were performed on polished cross sections of working devices. EBIC maps enable the analysis of charge-carrier collection with a high spatial resolution and the extraction of the local minority charge-carrier diffusion length. EBSD images reveal the microstructure of the Cu(In,Ga)Se 2 absorber-layer. A combination of these techniques makes it possible to investigate the influence of the microstructure of the Cu(In,Ga)Se 2 absorber-layer and especially of grain boundaries on charge-carrier collection. It is shown that collection properties are grain specific and that there are positions of grain boundaries exhibiting a reduced EBIC signal. These grain boundaries might be regions of enhanced recombination with a recombination velocity of about 1 × 10 4 cm/s.