Efficient Electrical Doping of Organic Semiconductors Via an Orthogonal Liquid-Liquid Contact

Doping is an effective strategy to tune the electrical properties of organic semiconductors. Traditional solution-processed doping methods, including “host-dopant mixing-doping” and “post-fabrication doping” methods, present challenges for their use in applications in optoelectronic devices. This work reports about a novel method to prepare electrically doped films, the authors call orthogonal liquid-liquid-contact (OLLC) doping. In OLLC doping, dopant and polymer semiconductors are dissolved in water and an organic solvent, respectively, and electrical doping occurs during film formation at the orthogonal liquid-liquid (aqueous-organic) interface. A large free volume of polymer and dopant in their solutions enables diffusion for effective doping. Thanks to the high surface tension of water, nanometer-thick polymer films form spontaneously on the aqueous surface and simultaneously get doped. The doped thin polymer films on the aqueous surface can be easily transferred to devices to facilitate hole collection/injection in organic photovoltaics and light-emitting diodes with solution-processed top electrodes.