ON THE SIGMOIDAL SHAPE OF CURRENT-VOLTAGE CURVES OF PHOTOELECTROCHEMICAL SOLAR-CELLS

Current-voltage (J-V) curves of n-GaAs/KOH(aq)-Se-2(2-)/Se2- and n-Si/ acetone-LiClO4-Fc(+/0) (ferrocenium ion/ferrocene) solar cells exhibit sigmoidal shapes near the open-circuit potential. J-V and flatband po tential measurements indicate that the deviation of the J-V curves fro m the ideal square-like shape to S shape is due to the light-induced d isplacement of the bandedges. Analytical expressions describing the de pendence of light-induced bandedge shifts on the anodic photocurrent, the density of surface states, and the interfacial charge-transfer vel ocity are derived and verified experimentally Application of the expre ssions to J-V data yields quantitative information on the kinetics of interfacial charge transfer.