Equations describing the electroluminescence (EL) intensity as a function of material properties are derived for thin film solar cells and experimentally validated using Cu(In,Ga)Se2 solar cells. EL intensity at constant voltage is controlled by the electronic properties of the neutral bulk even when the diode current is controlled by recombination in the space charge region. Using a combination of techniques, it is found that recombination in the quasineutral bulk does not correlate with recombination in the space charge region. Differences between EL measurements on thin film cells and crystalline silicon cells are discussed including the effects of secondary barriers.
Equations describing the effect of electronic nonuniformities on electroluminescence ͑EL͒ and electron beam induced current ͑EBIC͒ images are derived and tested on Cu͑In, Ga͒Se 2 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 m while the band gap varied almost linearly across the cell. The influence of shunt, series, and stack resistances on EL images is also discussed.
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