Predictive Simulations for Tuning Electronic and Optical Properties of SubPc Derivatives

Abstract

Boron subphthalocyanine chloride is an electron donor material used in small molecule organic photovoltaics with an unusually large molecular dipole moment. Using first-principles calculations, we investigate enhancing the electronic and optical properties of boron subphthalocyanine chloride, by substituting the boron and chlorine atoms with other trivalent and halogen atoms in order to modify the molecular dipole moment. Gas phase molecular structures and properties are predicted with hybrid functionals. Using positions and orientations of the known compounds as the starting coordinates for these molecules, stable crystalline structures are derived following a procedure that involves perturbation and accurate total energy minimization. Electronic structure and photonic properties of the predicted crystals are computed using the GW method and the Bethe-Salpeter equation, respectively. Finally, a simple transport model is used to demonstrate the importance of molecular dipole moments on device performance. Introduction.Organic photovoltaics (OPV) are a possible technology for large-scale deployment of renewable energy generation. They have the advantages of being more easily processed, using less material, and being more substrate-independent than traditional inorganic PVs such as silicon. 1 Of the common OPV materials, boron subphthalocyanine chloride is unusual for having a large molecular dipole moment. As opposed to the typically planar geometry of phthalocyanines, which consist of four fused diiminoisoindole rings, boron subphthalocyanine chloride adopts an inverted umbrella shape with only three fused diiminoisoindole rings (Fig. 1). Previously, boron subphthalocyanine chloride has been shown to offer improved efficiency over phthalocyanines, 2 which previous experimental work attributes in part

Recent advances in subphthalocyanines and related subporphyrinoids

“…Geometry, electronic structure, electrochemical and spectroscopic features of SubPcs have been thoroughly investigated by theoretical calculations. 211–233 A detailed study on a series of three SubPc-Cl derivatives bearing different peripheral substituents ( i.e. perhydrogenated, trinitro- and tri- t -butyl SubPc) at Hartree–Fock (HF) and density functional theory (DFT) levels using STO-3G and 6-31G basis sets has been reported by Ferro et al 211 The calculated geometries of the unsubstituted derivative were found to be in accordance with the experimental data from X-ray diffraction studies, and no substantial changes were detected with respect to the substituted derivatives.…”

“…fluorine, bromine, and iodine), respectively. 222 The structure, electronic properties and optical properties of these derivatives were calculated both in the gas phase and in their predicted crystalline solid phase. The degree of openness of the cone was found to depend on the nature of the central atom, and the molecular dipole (pointing from the electronegative halogen toward the trivalent atom) was shown to vary from 1 to 6 D. In the bulk crystalline phase, no net polarization was found due to the alternating arrangement of molecular dipoles.…”

Hexachlorinated Boron(III) Subphthalocyanine as Acceptor for Organic Photovoltaics: A Brief Overview

“…In any heterojunction type, the charge transfer across the D/A interface could also be influenced by the dipole moment of a molecule of one or both components. It bound to occur in the pyramidal subphthalocyanine molecules bearing axially attached halogen (Figure 1) and can further be tuned by the axial/peripheral substitution [4,26,[56][57][58][59]. Mutual orientation of the acceptor/donor molecules at the interface affects both the dissociation distance and the local electric field during the charge transfer and separation, thus modifying the resulting V oc of the device [59].…”

“…Unfortunately, this interesting issue has not been given enough attention in the experiments. Theoretical considerations regarding the influence of a molecular dipole in a series of, mostly hypothetical, subphthalocyanines on the photovoltaic parameters were recently published [58]. The first-principles DFT calculations were also performed in [60] to characterize the electronic structure of the axially substituted SubPc molecules interfaced with C 60 .…”

Let Digons be Bygones: The Fate of Excitons in Curved π-Systems

“…15 The changes in individual chromophore geometry imply a concomitant change in the molecular dipole moment. In particular, the molecular dipole moment is significant in determining electronic properties of interfaces [16][17][18][19] and has been exploited to improve device efficiencies through inclusion of strong-dipole spacer layers in donor-acceptor solar cells. 20 Similarly, the orientation of the transition dipole moment (TDM) is also sensitive to geometry distortions and morphology.…”