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

Abstract

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 DFTselected 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 π−π 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.

Influence of Asphaltene Modification on Structure of P3HT/Asphaltene Blends: Molecular Dynamics Simulations

“…The molecular dynamics (MD) simulations of the carboxyl-containing asphaltenes/P3HT blend revealed the heterophase morphology of the studied blend, as well as the formation of extended stacks of the asphaltenes, all of the above being essential for efficient charge transfer in the active layer. We also observed a slight ordering of the P3HT backbones, possibly due to the impact of the addition of asphaltenes [24].…”

“…Asphaltenes occur in nature as a mixture of molecules of different chemical structures. Although various complicated asphaltene architectures were used in MD simulations [7,41,42], in this study, we considered the following previously investigated and well-established types of model molecules (Figure 1): the asphaltene with aliphatic side groups proposed by Mullins [33], Li and Greenfield [34] (denoted as Asp in the text and figures); the same model molecule with side aliphatic chains cut off (Asp-Core) [35]; another modification of the Asp molecules -the carboxyl-containing asphaltene with three −COOH groups (Asp-COOH) [24]. The Asp molecule contains 7 aromatic rings with a single sulfur atom.…”

“…As we have shown previously by means of density functional theory (DFT) calculations [24], the chemical modification of asphaltenes with carboxyl groups enables their energy levels to be fine tuned, thereby obtaining the required energy difference between the lowest unoccupied molecular orbitals (LUMO) of the acceptor and donor materials for efficient charge transfer.…”

“…To gain a better understanding of the factors governing the perspective morphological properties of the P3HT/carboxyl-containing asphaltene blend observed previously [15], in the present study, we test which type of interaction has the major contribution to the formation of ordered stacks of the carboxyl-containing asphaltenes. To this end, we perform MD simulations of P3HT-based blends containing model asphaltene molecules of the following three types: the model asphaltene molecule with aliphatic side groups proposed by Mullins [33], Li and Greenfield [34]; the model molecule with aliphatic chains cut off [35]; and another modification of the model molecule containing the carboxyl groups studied previously [24]. The asphaltene model molecule with aliphatic groups is expected to have high compatibility with P3HT due to the presence of both aromatic and aliphatic constituents in the chemical structure.…”

Size matters: asphaltenes with enlarged aromatic cores promote heat transfer in organic phase-change materials

“…A potential solution to this issue is to utilize asphaltenes for various applications such as the production of asphalt pavements, 6 polymer composites, [7][8][9] and solar cells. [10][11][12][13] Thus, diversifying the applications of asphaltenes can aid in preventing their accumulation in the environment as well as in developing novel, high-value products.…”