Optimization of the Metal Front Contact Design for Single-Walled Carbon Nanotube-Silicon Heterojunction Solar Cells

Single-walled carbon nanotube (SWCNT) transparent conducting films have been combined with silicon (Si) to fabricate solar cells which operate due to the heterojunction formed between the SWCNTs and the Si. Until now, these solar cells have been prepared in proof-of-concept devices with typically very small active areas. However, it is difficult to simply increase the working area of the devices required for commercial application because of the limited conductivity of the transparent SWCNT films. Here, we determine the optimal metal front contact grid design, which can readily to be applied over a much larger area to meet industrial demands. Gold grids, which act as current collecting electrodes with 12 different patterns, are defined on top of an n-type silicon wafer. The deposition of p-type SWCNT films forms the SWCNT-Si heterojunction solar cell. Three different SWCNT films with different thickness, transparency, and conductivity were prepared. The effect of the active area and the porosity of the grid designs on the performance of the solar cells have been explored for each SWCNT film thickness. It was found that by employing a grid-patterned electrode, performance was improved for all films with particular improvement occurring in the fill factor of the devices. The greatest performance improvement (over 100%) was obtained for thinner, more transparent, and less conductive SWCNT films. Our results suggest that employing a patterned metal electrode is a scalable method to achieve solar cells with efficiency above 10%.