Organic Solar Cells: Electrostatic Stabilization of Organic Semiconductor Nanoparticle Dispersions by Electrical Doping

Organic semiconductor nanoparticle dispersions are electrostatically stabilized with the p-doping agent 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F$_4$TCNQ), omitting the need for surfactants. Smallest amounts of F$_4$TCNQ stabilize poly(3-hexylthiophene) dispersions and reduce the size of the nanoparticles significantly. The concept is then readily transferred to synthesize dispersions from a choice of light-harvesting benzodithiophene-based copolymers. Dispersions from the corresponding polymer:fullerene blends are used to fabricate organic solar cells (OSCs). In contrast to the widely used stabilizing surfactants, small amounts of F$_4$TCNQ show no detrimental effect on the device performance. This concept paves the way for the eco-friendly fabrication of OSCs from nanoparticle dispersions of high-efficiency light-harvesting semiconductors by eliminating environmentally hazardous solvents from the deposition process.