Determination of the Electron Diffusion Length in Dye-Sensitized Solar Cells by Substrate Contact Patterning

A new method to est. the electron diffusion length in dye-sensitized solar cells is presented. Dye-sensitized solar cells were fabricated on conducting glass substrates that were patterned by laser ablation of the fluorine-doped tin oxide coating to form parallel contact strips sepd. by uncontacted strips of the same width. The relative collection efficiency was measured as a function of the gap between the contact strips, which dets. the lateral distance traveled by electrons to reach the contacts. To avoid complications arising from nonlinear recombination kinetics, current measurements were performed using small amplitude perturbations of the electron d. close to open circuit and the max. power point to minimize electron d. gradients in the film. One- and two-dimensional solns. of the continuity equation for electron transport and back reaction predict that the relative collection efficiency should fall as spacing between the contact strips exceeds the electron diffusion length and electrons are lost by back electron transfer during transit to the contacts. Measurements of the relative collection efficiency were fitted to the predicted dependence of the collection efficiency on the spacing between the contact strips to obtain the value of the electron diffusion length. The diffusion length is found to increase with voltage both at open circuit and at the max. power point