Flexible all-carbon photovoltaics with improved thermal stability

The structurally robust nature of nanocarbon allotropes, e.g., semiconducting single-walled carbon nanotubes (SWCNTs) and C₆₀s, makes them tantalizing candidates for thermally stable and mechanically flexible photovoltaic applications. However, C₆₀s rapidly dissociate away from the basal of SWCNTs under thermal stimuli as a result of weak intermolecular forces that "lock up" the binary assemblies. Here, we explore use of graphene nanoribbons (GNRs) as geometrically tailored protecting layers to suppress the unwanted dissociation of C₆₀s. The underlying mechanisms are explained using a combination of molecular dynamics simulations and transition state theory, revealing the temperature dependent disassociation of C₆₀s from the SWCNT basal plane. Our strategy provides fundamental guidelines for integrating all-carbon based nano-p/n junctions with optimized structural and thermal stability. External quantum efficiency and output current-voltage characteristics are used to experimentally quantify the effectiveness of GNR membranes under high temperature annealing. Further, the resulting C₆₀:SWCNT:GNR ternary composites display excellent mechanical stability, even after iterative bending tests.