Modulating Spin Concentrations in Self-Doped Organic Molecules

N-type doping methods in organic systems typically combine small ionizable species with a semiconductor scaffold in solution before casting the pair into films. How dopants distribute within the cast semiconductor is unpredictable. The distribution of dopants, which vary from small to very large in their relative sizes, may affect semiconductor continuity, grain boundaries, morphology and packing of the semiconductor, electronic state distribution near the Fermi-energy, and yield topological variations in the electronic structure. Direct comparisons between different doping concentrations can therefore be rather nebulous, making the selection of the proper dopant for a given organic semiconductor highly convoluted. These challenges may be mitigated using self-dopants, where the electron source is covalently attached to the semiconductor. We have investigated the effects of steric hinderance, counterions, and dopant/semiconductor proximity on the efficiency of self-doping in a variety of perylene diimides. We believe our findings offer design considerations for the fabrication of effective self-dopants in n-type organic semiconductors.