Elaboration of PCBM Coated P3HT Nanoparticles: Understanding the Shell Formation

Abstract

Solvent displacement, or nanoprecipitation, is a well-known process to develop colloidal dispersions in water. Using two successive and selective nanoprecipitation steps, we developed a method to generate [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) shell on poly(3-hexylthiophene) (P3HT) core nanoparticles (P3HT@PCBM). We report herein on the understanding of the shell formation during this process. Using several techniques (dynamic light scattering, zeta-potential, photoluminescence), we evidenced that after the first solvent displacement with dimethyl sulfoxide (DMSO), the PCBM molecules still dissolved in the medium are already in close interaction with the P3HT nanoparticles (NP). Such proximity of the P3HT core with PCBM molecules in the DMSO dispersion explains why PCBM aggregates around the nanoparticles during the second solvent displacement with water. A fast electron transfer from P3HT to PCBM was identified by transient absorption spectroscopy, confirming the core-shell morphology even for low PCBM concentration. This study opens the route for the development of well-defined nano-objects dispersed in water for fabrication of organic photovoltaic devices with eco-friendly processes.

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

“…[ 9,10 ] Recent reports indicated that the inclusions of fullerenes with residual solubility in the dispersion medium help the dispersion stability by displacing the negative countercharges from the positively charged nanoparticles. [ 24,57 ] Earlier investigations on solution‐processed polymer:fullerene light‐harvesting layers demonstrated no detrimental effects of small amounts of F 4 TCNQ on the OSC performance. [ 28,32,37,42 ]…”

Review of Waterborne Organic Semiconductor Colloids for Photovoltaics

“…The addition rate (of the organic solvent into water or reverse) is quite important to obtain stable dispersions exhibiting narrow size distributions . In the literature, the most common approach to form conjugated polymer nanoparticles is to add the organic phase dropwise to water while stirring. ,, However, it is worth mentioning that Chambon et al reported the generation of monomodal nanoparticle dispersions by quickly adding a large amount of water into the organic phase. , …”

“…The solvent/nonsolvent volume ratio also has an impact on the final nanoparticle size. , Prunet et al reported an increase in the size of nanoparticles with the increase in solvent/nonsolvent volume ratio . They studied the influence of the final concentration of the active components in water, keeping a fixed initial concentration in THF.…”

“…Darwis et al reported that the colloidal stability of P3HT:PC 61 BM nanoparticles over time was too low to be considered, so the NP ink should be used immediately after preparation for OPV device fabrication . However, Palacio Valera et al reported high zeta-potentials for dispersions of P3HT:PC 61 BM nanoparticles prepared through nanoprecipitation, with a specific core–shell morphology, as will be discussed further in subsection “Donor–Acceptor Morphology” . Without addition of PC 61 BM, P3HT nanoparticles showed low colloidal stability (zeta-potential of approximately −1.8 mV) for DMSO dispersions, but with the addition of PC 61 BM, the zeta-potential of the P3HT NPs increased up to −29 mV, leading to stable dispersions.…”

“… The first solvent displacement from THF to dimethyl sulfoxide (DMSO) led to the precipitation of P3HT, with PC 61 BM molecules still soluble in the solution (for concentrations below the solubility threshold in DMSO). Then, through a second solvent displacement step from the THF/DMSO mixture to water, PC 61 BM precipitates preferentially on the P3HT nanoparticles, forming a PC 61 BM shell (observed by an increase in the nanoparticle size after the second displacement step). , Therefore, the core–shell morphology is not exclusive to preparation via miniemulsion and can be achieved through nanoprecipitation.…”