Unexpected hole transfer leads to high efficiency single-walled carbon nanotube hybrid photovoltaic

We report surprisingly efficient photocurrent generation at individual single-walled carbon nanotube (SWNT) /poly(3-hexylthiophene-2,5-diyl) (P3HT) junctions. Contrary to previous prediction, both semiconducting SWNTs (s-SWNTs) and metallic SWNTs (m-SWNTs) function as efficient hole acceptors. By active tuning of SWNTs' Fermi level, we confirm that P3HT p-dopes both s-SWNT and m-SWNT, and the work function difference between the nanotube and P3HT leads to a built-in voltage driving the efficient exciton dissociation and hole transfer. We further demonstrate square millimeter scale SWNT/P3HT bilayer photovoltaics using horizontally aligned SWNT arrays. Importantly, the devices exhibit greater than 90% effective external quantum efficiency. These key findings will not only enhance our knowledge of photocurrent generation at nanoscale interfaces, but also make selective omission of m-SWNT redundant, promising carbon nanomaterial-based, low-cost, high-efficiency hybrid photovoltaics.