Structured Single-Walled Carbon Nanotubes and Graphene for Solar Cells.

We propose the concept of structured single-walled carbon nanotubes (SWNTs) for the applications of heterojunction solar cells and dye-sensitized solar cells (DSSCs). The structure of SWNTs was controlled and modified by a simple water vapor treatment, which was originally developed by our group. Compared with the graphene-Si solar cell and the SWNT-Si solar cell using the random-oriented SWNT film, the pristine micro-honeycomb structured SWNT-Si solar cell shows a significant improvement in terms of fill factor and the greater potential to obtain high power conversion efficiency (PCE). Moreover, the performance of the pristine micro-honeycomb structured SWNT-Si solar cells is stable in ambient condition. In addition, the PCE and fill factor of the DSSC with the micro-honeycomb structured SWNT counter electrode are 3.90% and 0.61, respectively, which are comparable to those of the DSSC with Pt as the counter electrode. This result shows that the micro-honeycomb networked SWNTs provide a low-cost alternative to replace Pt in DSSCs.