Polarization-dependent conversion efficiency of carbon nanotube-Si heterojunction solar cells based on aligned carbon nanotube films

We have fabricated solar cells that implement heterojunctions of Si and aligned carbon nanotube (CNT) films. Polarization-dependent optical absorption of highly aligned CNTs led to polarization-dependent conversion efficiencies, which in turn provided insight into the role of the CNT layer in the power generation mechanism in these heterojunction solar cells. When the incident light polarization was parallel to the CNT alignment direction so that the light absorption in the CNT layer was maximized, the short circuit photocurrent decreased by similar to 25%. This indicates that electron-hole pair generation in the CNT layer does not directly lead to power generation and that the CNT-Si heterojunctions in our devices are Schottky junctions rather than p-n junctions.