Charge Transport in Highly Heterogeneous Natural Carbonaceous Materials
HS Li and TS Zhu and N Ferrolis and JC Grossman, ADVANCED FUNCTIONAL MATERIALS, 29, 1904283 (2019).
Natural carbonaceous materials (NCMs) have recently emerged as promising organic semiconducting materials for electronics and catalysis, although the fundamental picture of charge transport within NCM systems is still incomplete. Morphologically, NCMs exhibit reminiscence of disordered organic solids, yet the experimental measurements demonstrate a transport regime that surprisingly follows Mott's formula derived for variable-range hopping in inorganic noncrystalline materials. With ab initio and kinetic Monte Carlo simulations, a temperature scaling is revealed between the Gaussian-defect model log(sigma) similar to T-2 typical for organic matter and the Mott-like log(sigma) similar to T-1/4 for a wide spectrum of intermolecular connectivity. As dominant transport descriptors, energy levels and coupling strengths are screened among 30 small molecules with varying sizes, shapes, sp(2)/sp(3) ratios, side chains, and functional groups. These analyses provide insight for the design of NCM electronics, and should also be applicable to disordered molecular materials in general.
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