Semiconducting polymers; from free standing insoluble materials to water processed nanoparticles

In the early eighties a free standing shiny film hit the scientific.headlines. It was polyacetylene insoluble and infusible, to get film it was necessary to coat the wall vessel by the catalytic system before introducing the gas. Other materials as polythiophene and polyphenylene were black powders hard to handle. The introduction of alkyl chains at suitable positions of thienylene or phenylene rings allowed for developing a huge am ount of materials which could be processed from solution of chlorinated or aromatic or mixture of both solvents. Many type of devices optoelectronic, electronic, electrochemical could be fabricated OLED, polymer solar cells (OPV), Field effect transistors (FET), sensors, dye Synthesized Solar Cells (DSSC) Thanks to chemistry supply the polymer backbone has been modified and always more tricky structures have been designed even in two directions to increase conjugation and planarity hence optoelectronic and electronic properties. The solubility needs became more important and branched long chains were used to impart solubility and processability to get homogenous thin large area films for devices fabricated by continuous processes, as roll to roll for example. Chlorinated solvent mostly the aromatic ones became compulsory to process these materials very frequently associated to high temperature or solvent annealing and to additive use for obtaining the suitable morphology for the charge transport in the different devices. The amount of environment dangerous solvents which must be disposed correctly ( e,g.16 milion liters of chlorobenzene for the production of 1 GWp of polymer solar ) make the Energy payback time (EPBT ) risen.To dispose the before cited waste chlorinated solvent 880 TJ of comulative thermal energy production that means 10 days more to EPBT; versus 17 TJ only 4 days if water were used.1 Employing side chains able to dissolve photoactive polymers in aqueous medium reveiled useful only for PAT of LBG oligomers. Since ten years many research groups have been working on the use of aqueous colloidal solution of these semiconducting polymers, mostly PAT as benchmark. Moreover the preparation of water-processable nanoparticles (NPs) composed of a blend containing a semiconducting polymer and a fullerene derivative recently emerged as a smart strategy to control the nanoscale morphology. Different strategy have been employed to produce these colloidal solution: mini emulsion by using surfactats2, microprecipitation3 giving normally unstable NPs, chemical modification4 of the polymer backbone . Amphiphilic blockcopolymers can be use for this porpose too. Designing well defined block copolymers we were able to prepare active layers for organic solar cells showing an efficiency equal to 75% of that obtained using the established procedure with chlorinated solvent (oDCB).5 By determining the right length of the flexible hydrophilic segment with respect to the nature and size of the rigid hydrophobic block it is possible to develop a new tool for producing aqueous inks for active layers of may devices, OLED OFET and OPV.