Plasma-etched nanoporous TiO₂ using Ag nanoparticle masks: application for photoanodes of dye-sensitized solar cells

We investigate dye-sensitized solar cells (DSSCs) with nanoporous TiO₂ photoanodes etched by inductively coupled plasmas (ICPs). Thermally Shrunk Ag nanoparticles are used as the etching masks during the ICP etching procedure. The efficiency of the assembled DSSC increases first and then decreases as the ICP etching time increases. The enhancement of light trapping/scattering is observed after ICP etching with Ag nanoparticle masks, however, over-etching may mitigate the effect. Interfacial charge transfer impedance of TiO₂/dye/electrolyte also decreases first and then increases as the etching time increases, a trend highly correlated to the variation of the cell efficiency. Our experimental results indicate that the enhancement of light trapping (which leads to the increase of photocurrent), increase of open circuit voltage and reduction of charge transport resistance lead to the improvement of cell efficiency. The optimized etching time is around 30 s to 1 min. In comparison to the counterpart experiment, the DSSC with TiO₂ photoanode etched by ICP without Ag nanoparticle shadow masks, the cell reveals monotonic decreases of photocurrent level, open circuit voltage, and efficiency with the ICP etching time. (papers)