(665e) Electrostatic Assembly of Aqueous Colloids for Polymer Solar Cell Applications

The recent development of aqueous dispersions of conjugated polymer/fullerene composite nanoparticles (CNPs) has enabled the use of electrostatic assembly (EA) of active layers for the production of organic photovoltaics. EA is the spontaneous deposition of a charged material onto an oppositely charge surface. CNPs are readily produced using a number of anionic and cationic surfactants (i.e. sodium dodecyl sulfate (SDS) and dodecyl trimethyl ammonium bromide (DTAB)). Therefore, their charge can be easily customized for electrostatic deposition on a wide range of charged surfaces. We have recently demonstrated the spontaneous EA of poly(3-hexlythiophene) (P3HT)/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) CNPs onto poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated indium tin oxide (ITO). PEDOT:PSS coated ITO substrates assume a negative charge when immersed in water. When these substrates are immersed in a solution containing P3HT/PCBM CNPs stabilized with DTAB, spontaneous EA of monolayers of P3HT/PCBM CNPs results. By tuning the concentration of DTAB in the bulk phase of P3HT/PCBM CNPs as to minimize competitive surfactant adsorption, the surface density of the nanoparticles can be tuned for a fixed dipping time. This process opens up the prospect of producing thin-film active layers composed of monolayers of fully optimized conjugated polymer/fullerene CNPs. Because photovoltaic modules are composed of number of other materials which also have pH and salt dependent charging behavior in water, layer-by-layer (LBL) assembly of entire photovoltaic modules is possible. LBL processing for photovoltaic modules would be an inexpensive and scalable processing technique that could be applied to substrates with complex form factors (e.g. woven fibers) at low temperatures and without the release of volatile organic solvents during the drying process.