Modifying electronic properties of ICBA through chemical substitutions for solar cell applications

Abstract

Fullerene derivatives are the most widely used type of acceptor material in the organic solar cells (OSCs) active layers, but there are still some problems to be overcome, such as increased solubility and adjustment of the frontier electronic levels for a better combination with the donor materials in the active layer. Chemical modification of the materials already employed in active layers is an interesting way to vary the electronic properties in order to find new materials, because it is possible, in principle, to tune the intrinsic properties of the material aiming to improve the solar cell efficiency. Thus, we studied theoretically the effect caused by chemical substitutions on the electronic properties of the ICBA, one of the fullerene derivatives employed in OSCs. Geometry optimizations and electronic structure data were obtained by DFT/PBE/6-311G(d,p) calculations for 13 ICBA derivatives. We show that by chemical substitutions of ICBA, it is possible to modify the energies of the frontier electronic levels, increase the solubility, and find new derivatives that show improvements in open circuit voltage and morphology of the active layer, potentially bringing better efficiency for OSCs.

Theoretical evaluation of chemical substitutions along the main chain of poly(3‐hexylthienylene‐vinylene) for solar cell applications

“…Thus, the geometric structures of all the cases studied were optimized through the semi‐empirical PM6 method implemented in the computational package MOPAC2016 . The choice of the PM6 method is related to its satisfactory performance in studies with conjugated polymers , , …”

“…30 The choice of the PM6 method is related to its satisfactory performance in studies with conjugated polymers. 13,14,18 For the initial conformations of the oligomers of P3HTV and its derivatives, we adopt structures with the main chain restricted to the plane, because this type of conformation is the most likely in the solid state. 24,31,32 We performed some preliminary calculations with structures not restricted to the plane, but the torsions in the main chain were not greater than 10 ∘ out of planarity.…”

“…The use of chemical substitutions in existing organic materials has been a very useful tool when it is desired to modify electronic properties , –. In previous works we have shown that chemical substitutions carried out in the monomeric units of polymers already employed in OSCs, such as poly(3‐hexylthiophene) (P3HT) and polythieno[3,4‐ b ]thiophene‐ co ‐benzodithiophene (PTB7), resulted in new electron donor materials that presented better bandgaps, solubility and/or ionization potential , .…”

“…3 The use of chemical substitutions in existing organic materials has been a very useful tool when it is desired to modify electronic properties. 2,[13][14][15][16][17][18] In previous works we have shown that chemical substitutions carried out in the monomeric units of polymers already employed in OSCs, such as poly(3-hexylthiophene) (P3HT) and polythieno [3,4-b]thiophene-co-benzodithiophene (PTB7), resulted in new electron donor materials that presented better bandgaps, solubility and/or ionization potential. 13,14 Combining these new materials with phenyl-C 61 -butyric-acid-methyl-ester (PCBM) as electron acceptor, we showed that it is possible to obtain new BHJ active layers with P3HT and PTB7 derivatives with predicted higher efficiency.…”

Review: materials and modelling for organic photovoltaic devices

“…HOMO, LUMO, electrode work functions and their relative differences, i.e. ∆ E HD‐HA , ∆ E LD‐LA , ∆ E LA‐HD , and injection/collection barriers) which can be directly predicted from isolated structures (or medium size complexes) and are supposed to play a relevant role in the dynamics of charge carriers and excitons in OPVs 166,190–196 . In addition, QM methods are generally used to describe/tune specific geometrical parameters, 197 stability and degradation processes, 198,199 predictions for ideal donor–acceptor pairs to improve OPV lifetimes and efficiencies, 200,201 chemical reactivity and electrical charges of force fields used in MM/MD simulations 202,203 …”