P‑Doped Carbon Nanotubes as Light-Absorbing Electron Donors in Photovoltaics

Semiconductor doping has yielded performance enhancements in organic thermoelectrics, light-emitting diodes, transistors, and photovoltaics. In analogous devices using semiconducting single-walled carbon nanotubes (s-SWCNTs), similar doping strategies have been studied for the enhancement of thermoelectrics, light-emitting diodes, and transistors, but virtually no studies have examined the impact of doping on photovoltaic behavior. Here, we investigate chemically p-doped (6,5) s-SWCNTs as light-absorbing donor materials in photovoltaic donor-acceptor heterojunctions with C₆₀. Although doping reduces absorption, the photocurrent generated per absorbed photon remains constant up to a dopant density of ∼80 μm^-1. This unexpected outcome contrasts with the sharp quenching of photoluminescence observed at similar doping levels. We attribute this divergence to the ultrafast electron transfer from s-SWCNTs to C₆₀, and we quantitatively describe this system by using a diffusion-limited contact quenching model. We also demonstrate that doping sensitizes s-SWCNTs to generate photocurrent from trions near 1.07 eV. While trion photocurrent is weakerlikely due to reduced diffusivity and a lower driving force for dissociationit provides a direct route to electrically probe trionic states. These findings establish that doped s-SWCNTs can operate efficiently in photovoltaic devices and serve as a platform for studying trion dynamics in excitonic semiconductors.