Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been intensively studied in optoelectronic applications due to several advantages such as band gap tunability, high charge carrier mobility, and low internal reorganization energy. However, the fundamental aspects of exciton dissociation at heterojunctions between s-SWCNT and electron acceptors still remain elusive. Here, we investigate the detailed photodynamics at the heterojunction between (6,5) SWCNTs and perylene diimide (PDI) based electron acceptors. While a number of studies have demonstrated efficient charge transfer at interfaces between s-SWCNTs and fullerenes, as well as s-SWCNT-fullerene photovoltaic devices with high internal quantum efficiencies, studies paring s-SWCNTs with non-fullerene acceptors are rare. PDI-based electron acceptors have several potential advantages over fullerene acceptors such as broader absorption, cheaper cost, higher robustness, and greater spectral tunability.

Two novel PDI-based electron acceptors were synthesized and coated on (6,5) SWCNT films to form donor-acceptor heterojunctions. The PDI-based electron acceptors are hPDI2-pyr-hPDI2, where pyrene (electron donor) is covalently connected to PDI oligomers (hPDI2), and Trip-hPDI2, where hPDI2 is connected to each side of triptycene. The steric hindrance from these acceptors prevents excessive aggregation, which has been a significant problem for PDI-based electron acceptors. Transient absorption studies reveal that the photoinduced electron/hole transfer at the (6,5)/PFO-bpy – PDI-based acceptor heterojunction occurs, and the separated charges live longer than 1.5 μs. For the photoinduced electron transfer from (6,5) SWCNTs to PDI-based acceptors, the electron transfer to hPDI2-pyr-hPDI2 occurs more efficiently than to Trip-hPDI2, and it is attributed to weaker electron transfer driving force for Trip-hPDI2 due to its higher LUMO level than that of hPDI2-pyr-hPDI2. Charge transfer across these s-SWCNT/PDI interfaces will be compared to the more commonly studied SWCNT/C₆₀ interfaces.

These fundamental photophysical studies provide insight into how different electron acceptor materials can impact the s-SWCNT heterojunction energetics and how the energetics impacts the kinetics of exciton dissociation and charge recombination. The results help to inform design strategies for s-SWCNT-based solar photoconversion systems.