DFT Calculations Reveal Pronounced HOMO-LUMO Spatial Separation in Polypyrrole-Nanodiamond System

Low-cost efficient generation of renewable energy and its blending with society lifestyle is increasing in importance. Diamond-based inorganic-organic hybrid systems may have an immense, yet still mostly unexplored potential in photovoltaic solar cells. In this work, we study interactions of polypyrrole (PPy) with diamond nanoparticles (so-called nanodiamonds - NDs) by computational density functional theory (DFT) methods. We compute structural and electronic properties of such hybrid organic-inorganic system. In the model, PPy is chemisorbed and physisorbed on (111) and (100) ND edge-like surface slabs terminated with oxygen, hydroxyl, carboxyl, and anhydride functional groups, i.e. in the arrangements most common in real NDs. Moreover, NDs terminated with an amorphous surface layer (a-C:H, a-C:O) are considered to approach realistic conditions even further. In a predominant number of cases, we obtain a spatial separation of HOMO and LUMO at the interface facilitating exciton dissociation. There is also a favorable energy level alignment for charge transport. The theoretical results thus show a potential of PPy-ND composites for use in photovoltaics.