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

Abstract

Organic semiconductor nanoparticle dispersions are electrostatically stabilized with the p‐doping agent 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), omitting the need for surfactants. Smallest amounts of F4TCNQ 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 F4TCNQ 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.

Iodine‐Stabilized Organic Nanoparticle Dispersions for the Fabrication of 10% Efficient Non‐Fullerene Solar Cells

“…With increasing ζ I2/J71 , we also observed a reduction of the nanoparticle size (Table S1, Supporting Information) as more charges can stabilize larger surfaces and hence produce smaller nanoparticles. [ 5 ] Smaller amounts of iodine than ζ I2/J71 = 10 wt.% resulted in too large (nano)particles and too low dispersion concentrations that were useless to any of the later device experiments.…”

“…Recent reports also featured acetonitrile as a promising dispersion agent due to its high permittivity and hence its excellent screening of stabilizing charges. [ 5 ] Besides the omission of toxic solvents during coating, this deposition route i) disentangles solution processing from the need of solubility, ii) advances multi‐layer deposition without the need for orthogonal solvents and hence iii) is less dependent on molecular engineering, eventually giving access to a broader choice of semiconductors for optoelectronic applications. [ 6 ] The prevailing challenge of this approach is the colloidal stabilization of the dispersion.…”

“…by electrical p‐doping with F 4 TCNQ or temporarily even by photodoping with visible light, can enhance the colloidal stability of nanoparticle dispersions. [ 5,7 ] Yet, the large ionization potentials of most high‐performance light‐harvesting polymers render electrical doping often inefficient and would call for substantial amounts of dopants that would later conflict with device operation. [ 5 ]…”

“…[ 5,7 ] Yet, the large ionization potentials of most high‐performance light‐harvesting polymers render electrical doping often inefficient and would call for substantial amounts of dopants that would later conflict with device operation. [ 5 ]…”

“…by electrical p-doping with F 4 TCNQ or temporarily even by photodoping with visible light, can enhance the colloidal stability of nanoparticle dispersions. [5,7] Yet, the large ionization potentials of most high-performance light-harvesting polymers render High-performance organic solar cells are deposited from eco-friendly semiconductor dispersions by applying reversible electrostatic stabilization while omitting the need for stabilizing surfactants. The addition of iodine fosters the oxidation (p-doping) of the light-harvesting polymer, effectively promoting the electrostatic repulsion of the nanoparticles and hence the colloidal stability of the respective dispersions.…”