Effects of a dianion compound as a surface modifier on the back reaction of photogenerated electrons in TiO2-based solar cells

Enhancement in Photovoltaic Performance of Solar Cells by Electrostatic Adsorption of Dyes on ZnO Nanorods

ZnO nanorods were formed by chemical bath deposition on fluorine-doped tin oxide (FTO) glass and the photovoltaic performance of ZnO-based dye-sensitized solar cells (DSCs) was investigated. A DSC with 8 h-grown ZnO nanorods showed a higher power conversion efficiency (PCE) than devices with 4, 6, and 10 h-grown ones. Further improvement in PCE was achieved in a cell with a silver-ion-deposited ZnO/FTO electrode. By deposition of Ag+ on the surface of the 8 h-grown ZnO nanorods, the dye-loading amount increased by approximately 210%, compared to that of pristine ZnO nanorods, resulting in a 1.8-times higher PCE. A DSC with the pristine ZnO/FTO electrode showed a PCE of 0.629%, while in a device with the silver-ion-deposited ZnO/FTO, the PCE increased to 1.138%. In addition, interfacial resistance at the ZnO/dye/electrolyte was reduced to approximately 170 Ω from 460 Ω for the control cell with the pristine ZnO/FTO. We attributed the higher dye-loading amount in the silver-ion-deposited ZnO/FTO to the electrostatic attraction between the positively charged ZnO and carboxylate anions (-COO-) of the N719 dyes.

Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO2 Photoanode

By simple soaking titanium dioxide (TiO₂) films in an aqueous Na₂S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (V_oc) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV–visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na₂S modification led to the formation of anions on the TiO₂ surface, and thereby shifted the conduction band edge of TiO₂ in the negative (upward) direction, inducing an increase of 29 mV in the V_oc. It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.