Molecular Surface Doping of Cellulose Nanocrystals: A High-Throughput Computational Study

Cellulose, a linear polymer of glucose residues, is the most abundant biopolymer on Earth. However, its inability to conduct electricity limits its applications in flexible electronics and energy storage devices. Here, we performed high-throughput first-principles computational screening to identify promising molecules for surface doping of cellulose nanocrystals (CNCs). We examined over 1600 molecules, including those from the TABS database, to find candidates for p-type and n-type doping. Our results identified several p-type dopants, such as hexacyano-trimethylene-cyclopropane (CN6-CP) and octacyanoquinodimethane (OCNQ). However, no suitable n-type dopants were found due to the low electron affinity of cellulose. We constructed atomic models of CNCs of cellulose I alpha and I beta crystals, showing how their electronic band structures depend on surface hydrogen bond reconstructions. We propose a novel mechanism for photocurrent generation in CNC I alpha surfaces by manipulating the hydrogen bond network at the surfaces. The selection of potential p-type dopants was further refined through the first-principles calculations of the CNC models with molecular dopants adsorbed on the surface. Finally, we demonstrate that suitable surface functionalization can enhance the electron affinity of CNCs, partially overcoming the challenges of n-type doping.