Driving fiber diameters to the limit: nanoparticle-induced diameter reductions in electrospun photoactive composite nanofibers for organic photovoltaics

Abstract

Electrospun photoactive nanofibers hold significant potential for enhanced photon absorption and charge transport in organic photovoltaics. However, electrospinning conjugated polymers with fiber diameters comparable to exciton diffusion lengths for efficient dissociation, is difficult. Previously, spinning sub-100 nm poly(3-hexylthiophene) (P3HT) fibers has required the auxiliary polymer, poly(ethylene oxide) (PEO), and large antisolvent additions. Therefore, its success differs considerably across donor polymers, due to variable antisolvent addition limits before precipitation. Herein, plasmonic nanoparticle infusion into P3HT nanofibers is used to modulate viscosity and deliver a novel and unrivaled strategy to achieve reduced fiber diameters. Following PEO removal, the fibers measure 55 nm in diameter, 30% lower than any previous report – providing the shortest exciton diffusion pathways to the heterojunction upon electron acceptor infiltration. The nanoparticle-containing nanofibers present a 58% enhancement over their pristine thin-film counterparts. ~17% is ascribed to plasmonic effects, demonstrated in thin-films, and the remainder to along-fiber polymer chain alignment, introduced by electrospinning. The anisotropy of light absorbed when polarized parallel versus perpendicular to the fibers increases from 0.88 to 0.62, suggesting the diameter reduction improves the alignment, resulting in greater electrospinning-induced enhancements. Controlled by the electrospinning behavior of PEO, our platform may be adapted to contemporary donor-acceptor systems. Graphical Abstract: [Figure not available: see fulltext.] A dramatic reduction in the diameters of electrospun photoactive nanofibers is achieved by introducing nanoparticles, offering shorter exciton pathways towards the heterojunction in nanofibrous OPVs. Thinner fiber diameters enhance the alignment of the polymer chains along the fiber, manifesting in greater photon absorption. Alongside plasmonic effects, the dual-mode enhancement within the fibers offers 58% additional light harvesting versus their thin-film counterparts.