Evaluation on over photocurrents measured from unmasked dye-sensitized solar cells

We have investigated the change in photocurrent density (JSC) of dye-sensitized solar cell (DSSC) before and after covering an aperture mask on the cell, especially its dependence on solar absorption range in dye. Four different dyes having absorption threshold at 460 nm (P5), 520 nm (TA-St-CA), 680 nm (N719) and 820 nm (N749) are tested. JSC of the DSSC without mask decreases after mask, where the decreasing rate (△JSC = JSC (no mask) − JSC (with mask)/JSC (no mask)) becomes larger when dye absorption threshold decreases. △JSC at the given TiO2 film thickness of 10 μm is determined to be about 20%, 15% and 13% for P5, TA-St-CA and N719-N749, respectively, which is reduced to 14% (TA-St-CA), 11.3% (N719) and 10.5% (N749) after increasing the thickness to 20 μm, except for P5 dye remaining unchanged. According to the analysis based on IPCE and photon flux data, the over photocurrents observed for the unmasked dye-sensitized solar cells and their dependence on dye absorption range are found to be attributed to diffuse light leaving the dye-adsorbed TiO2 active area.