Tail states in organic semiconductors have a significant influence on device performances by acting as traps in charge transport. We present a study of the controlled passivation of acceptor tail states in fullerene ${\mathrm{C}}_{60}$ by the addition of electrons introduced by molecular $n$ doping. Using ultralow doping, we are able to successively fill the traps with charges and examine the changes in conductivity, activation energy, mobility, and Fermi-level position. Passivation of the traps leads to an increase of the electron mobility in ${\mathrm{C}}_{60}$ by more than 3 orders of magnitude, to reach $0.21{\mathrm{cm}}^2/(\mathrm{V}\mathrm{s})$.

Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI₂OD-T₂)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp₂]₂, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]₂. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.

CVD graphene has been n- and p-doped using redox-active, solution-processed metal–organic complexes. Electrical measurements, photoemission spectroscopies, and Raman spectroscopy were used to characterise the doped films and give insights into the changes. The work function decreased by as much as 1.3 eV with the n-dopant, with contributions from electron transfer and surface dipole, and the conductivity significantly increased.