Design of diblock co-oligomers as low bandgap small molecules for organic solar cells

Abstract

The properties of a particular kind of small molecule that is built from two oligomers of different monomers, i.e. a diblock co-oligomer, as the electron donor in the active layer of organic solar cells are investigated theoretically. For these molecules, this work shows that it is possible to predict the energies of the frontier molecular orbitals by knowing the same energies for the oligomers that constitute the diblock, opening the possibility of designing new materials with optimal energy levels and optical properties. Furthermore, it was observed that the optical absorption bands of these diblock co-oligomers were broader than that of the constituent oligomers and also of the homopolymers, allowing greater absorption of photons and possibly an improved electric current in the device. It was also shown that these phenomena are sizedependent.

Molecular modeling of low bandgap diblock co-oligomers with π-bridges for applications in photovoltaics

“…According to these observations we can point out the relevance of the π-bridge to the transition intensities. The insertion of an appropriate π -bridge results in low energy optical transitions (HOMO→LUMO transitions) with the same amplitude (and sometimes more intense) than that observed in the unmodified diblock co-oligomer [21,51].…”

“…In this context, a recent study has pointed out that the use of diblock co-oligomers could be considered as a relevant alternative for the design of improved low bandgap materials for applications in photovoltaics [21]. Given their reduced extension, such materials present the typical advantages associated with organic small molecules, as ease of synthesis and higher purity [1,10,22], at the same time that it allows the mitigation of relevant setbacks associated with morphological problems and low fill factors (FF) commonly associated with polymeric systems [22,23].…”

“…However, given the spatial separation between the employed blocks (and then between their frontier orbitals spatial distributions) a good balance between the oligomers extension is vital to favor optical transitions between these states. For example, it was shown that for a oligothiophene-oligopyrrole system the optimal blocks extension is around 5 units ([Th] 5 -[Py] 5 ) [21].…”

“…1 illustrates the compounds evaluated in this study. The choice of thiophene and pyrrole structures with five units (pentamers) for the design of the diblock co-oligomers ([Th] 5 -[Py] 5 ) was based on a previous work of our group, where it was demonstrated that such systems result in low bandgap materials with improved opto-electronic properties [21]. In particular, in that work it was shown that the diblock cooligomers properties are modulated by the resulting HOMO/LUMO overlap, mainly at the diblocks interface.…”

Chemical sensors based on N-substituted polyaniline derivatives: reactivity and adsorption studies via electronic structure calculations

“…The choice of a semi-empirical method for geometry optimization was based on the number of distinct structures evaluated and their relative large size, aiming to minimize the computational cost. We do not consider that this approach is a severe limitation since a number of works show that a reasonable description of opto-electronic properties of similar systems can be obtained by considering geometries coming from semi-empirical calculations in conjunction more sophisticated ab initio or density functional theory (DFT)-based methods [34][35][36]. Local reactivities were evaluated via condensed-to-atoms Fukui indexes (CAFI) [37].…”