Electron doping of a crystalline conjugated polymer through cation exchange

Control of electrical doping is indispensable in any semiconductor device, and both efficient hole and electron doping is required for many devices. In organic semiconductors, however, electron doping has been essentially more problematic compared to hole doping because in general organic semiconductors have low electron affinities and require dopants with low ionization potentials that are often air-sensitive. Here, in this study, we adapt an efficient molecular doping method, so called ion-exchange doping, to electron doping in a polymeric semiconductor. Reduction of the polymeric semiconductor is initiated via one electron transfer from molecular dopants, then the ionized dopants in the resulting air-unstable films are replaced with the secondary ions via cation-exchange. When a specific bulky molecular cation was employed as the secondary ion, ambient stability and crystallinity of doped polymeric semiconductors were improved compared to conventional methods. The presented strategy can overcome a trade-off relationship between reducing capability and ambient stability in molecular dopants, and a wider selection of dopant ions will help to realize ambient-stable electron conductors.