Photovoltaic and photoelectric properties of Al/mixed monolayers of Chl a-SQDG/Ag sandwich cells

With a view to examining the effect of the lipid sulphoquinovosyldiacylglycerol (SQDG) on the photovoltaic and photoelectric properties of chlorophyll a (Chl a) sandwich cells of the type Al/mixed monolayers of Chl a-SQDG/ Ag have been fabricated. Various photovoltaic parameters of the cells, i.e. short-circuit photocurrent, open-circuit photovoltage, fill factor and power conversion efficiency, have been measured at 672 nm (the maximum of Chl a absorption in the red region). For incideident light power of 21ωW cm^-2 these parameters are 20 nA cm^-2, 450 mV, 0.27 and 0.02% respectively for cells of Chl a-SQDG in a 1:0.025 molar ratio, while for cells of Chl a-SQDG in a 1:0.25 molar ratio they are 18 nA cm^-2, 40 mV, 0.26 and 0.002% respectively. This indicates that the introduction of an increased quantity of SQDG in Chl a decreases the cell efficiency. This is possibly due to the intervening effect of SQDG which makes the transport of photogenerated charge carriers (in Chla) across the multilayers of Chl a-SQDG and to the electrodes rather difficult. The introduction of recombination sites by SQDG as seen from the lower values of γ (about 0.7) may also be a reason for the lower efficiency of cells with increased quantities of SQDG.