Molecular Descriptor and Criterion for Efficient N-Doping of Organic Semiconductors

Precursor dopants activated by C-H bond cleavage, especially N-DMBI-H derivates, are the most commonly used n-dopants for organic semiconductors (OSCs), however, their doping mechanism and the structure-activity relationship remain unclear. Here, by rationalizing the thermodynamics and kinetics of the hydrogen atom transfer (HAT) and hydride transfer (HYT) reactions between N-DMBI-H derivates and a variety of OSCs using the density functional theory, we manifest that the HYT via concerted electron and hydrogen atom transfer is the most viable doping mechanism. Furthermore, by correlating important thermodynamic and kinetic parameters of HYT to facile molecular properties, we propose the electron affinity (EA) of OSCs and the ionization energy (IE) of dopant radicals (Ds) as two molecular descriptors of n-doping, and EA(OSC) IE(D) > 1.0 eV as the criterion for high doping efficiency. Finally, new quinoid-structure polymers with EA > 4.0 eV and good backbone planarity are designed as potential n-type OSCs.