Model Carboxyl-Containing Asphaltenes as Potential Acceptor Materials for Bulk Heterojunction Solar Cells

We put forward chemically modified asphaltenes, polycyclic aromatic byproducts of deep oil refining, for use as novel low-cost acceptor materials for bulk heterojunction (BHJ) solar cells. The electronic properties of asphaltenes with varying chemical structures are studied by density functional theory (DFT), while the morphology of DFT-selected carboxyl-containing asphaltenes mixed with poly(3-hexylthiophene) (P3HT) as a model polymer-donor is investigated by means of all-atom molecular dynamics (MD) simulations. DFT calculations show that the chemical modification of asphaltenes with carboxyl groups enables their energy levels to be fine-tuned, thereby obtaining the desirable energy difference between the lowest unoccupied molecular orbitals of the acceptor and donor materials for efficient charge transfer. MD simulations reveal the heterophase morphology of the P3HT/asphaltene mixture, as well as the formation of extended stacks of asphaltenes via p-p stacking between their polyaromatic cores. Overall, from both the electronic and morphological standpoints, carboxyl-containing asphaltenes do indeed represent a potential low-cost acceptor for BHJ solar cells.