Quantitative imaging of electronic nonuniformities in Cu(In,Ga)Se2 solar cells

Equations describing the effect of electronic nonuniformities on electroluminescence (EL) and electron beam induced current (EBIC) images are derived and tested on Cu(In,Ga)Se2 solar cells. EL images are sensitive to fluctuations in band gap and carrier collection across a cell. EBIC images are only sensitive to variations in carrier collection allowing the two nonuniformities to be separated. Equations are derived connecting the distribution of EL intensities to the open circuit voltage loss from band gap fluctuations. Experimentally, the samples studied show the largest variation in carrier collection function on a length scale of over 100 μm while the band gap varied almost linearly across the cell. The influence of shunt, series, and stack resistances on EL images is also discussed.