Optimizing Efficiency in Conducting Polymer/Single-walled Carbon Nanotube Hybrids for Organic Photovoltaics

Several unique properties of single-walled carbon nanotubes (SWCNTs) have motivated their investigation as potential replacements for fullerene derivatives as the acceptor phase of organic photovoltaic (OPV) devices. Although replacement of the ubiquitous fullerene acceptors by SWCNTs in OPV devices has shown limited success thus far, better understanding of charge transfer between SWCNTs and conjugated polymers has promoted its viability. We provide experimental evidence that m-SWNTs limit the generation efficiency and lifetime of the charge-separated state in these composites. We also probe the photo-carrier generation and decay dynamics in poly(3-hexylthiophene) (P3HT) paired with a broad diameter range of SWCNTs. We witness electron transfer from the polymer to SWCNT and \textit{selective} hole transfer from the SWCNT to polymer by varying the nanotube HOMO via its diameter. We finally extend our investigation to additional semi-conducting polymers that have contributed to high OPV efficiencies, pBTTT and PCDTBT.