Limited depth-electrical p-doping of semiconducting polymer films by post-process immersion in polyoxometalate solutions

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Most of the organic semiconductors (OSCs) are intrinsic semiconductors and are usually used without further doping. However, electrical doping should allow for adjustment of Fermi level leading to more efficient carrier injection, quasi-Ohmic contacts between organic layers and metal electrodes, and increase of conductivity. In order to obtain a controlled doping, large molecules must be used to avoid instability due to diffusion. Only recently, the potential of molecular electrical doping of OSCs for obtaining of more efficient organic-based devices has been demonstrated . However, most of this work focused on doping of evaporated organic layers with molecules . A solution-based method, compatible with organic electronics printing processes, mostly for organic photovoltaics (OPV), is highly desirable, but remains challenging in terms of dopant diffusion control. Recently, p-doping of a polymeric semiconductor film by immersion into a solution of a polyoxometalate (POM), a polyatomic ion, for use in OPV has been demonstrated. Researchers from USA, apan and  The Netherlands have extended this approach and report a solution-based strategy for electrical p-doping of semiconducting polymer films over a limited depth by post-process immersion in POM (phosphomolybdic acid (PAM) and phosphotungstic acid (TPA)) solutions in nitromethane.