Ultrafast Hole Transfer from (6,5) SWCNT to P3HT:PCBM Blend by Resonant Excitation.

Nowadays, SWCNTs are envisaged to enhance the charge separation or transport of conjugated polymer-fullerene derivatives blends. In this work we studied, by means of ultrafast transient absorption spectroscopy, three components blends in which commercially available SWCNTs are added to the standard bulk heterojunction. We explored three different configurations that give rise to diverse interfacing scenarios. We found strong evidence of a direct hole transfer from photoexcited SWCNTs to the P3HT polymer. The transfer efficiency depends on the interface configuration. It is the highest for the blend where we achieve closer contact between the (6,5) SWCNTs and the polymer. When the polymer blend is deposited on top of the nanotube film or the nanotube film is deposited onto the polymer blend, the process is slowed down due to less or missing interfacing of the carbon nanotubes with the polymer chains. Additionally we demonstrate a cascading effect in the electron path, which stabilizes charge separation by further transferring the electron left behind by hole transfer to the polymer to the adjacent (7,5) SWCNTs. Our results highlight the potential of semiconducting SWCNTs to improving the performance of organic solar cells.