Scanning Kelvin Probe Force Microscopy for investigation of charge transport in carbon-nanotube enhanced organic photovoltaics

As a powerful tool to study surface potential difference at nanometer scale, canning Kelvin Probe Force Microscopy (KPFM) has been applied to investigate the photoexcited charge transport in single-walled carbon nanotubes (SWCNTs) enhanced organic solar cells. By comparing surface potential images of SWCNTs on regioregular poly 3-hesylthiophene (P3HT) and 6,6-phenyl C₆₁-butyric acid methyl ester (PCBM) blended film in the dark and under illumination, it is observed that photoinduced holes flow from active layer to SWCNTs, which indicates that SWCNTs work as donor materials. The transport of holes from organic materials to SWCNTs verifies that the improved performance of P3HT/PCBM/SWCNTs bulk heterojunction solar cells is attributed to the increased hole mobility in ballistic pathways provided by SWCNTs instead of slow hopping and tunneling in disordered organic materials.