Meta-analysis: the molecular organization of non-fullerene acceptors

Abstract

The rapid development of Non-Fullerene Acceptors (NFAs) for organic solar cells has recently pushed the Power Conversion Efficiencies (PCE) over the 15% threshold, surpassing fullerene-based state-of-the-art devices. However, for the commercialization of large-scale photovoltaic modules, thick active layers films (150–300 nm) with high PCE and fill factors are required. The realization of materials with higher charge mobilities is fundamental for the roll-to-roll printing industry, and therefore understanding the factors that limit charge transport properties of NFAs becomes crucial for commercialization. The study of the molecular packing and arrangement of NFAs in the solid-state provides direct insight to the propensity of the pristine materials to crystallize and contribute efficiently to the charge transport. In this work we combine experimental techniques and molecular modelling, with the aim of analyzing the way in which NFAs interact in the solid-state and the key components of their structures for building efficient percolation pathways for charge transport. To this end, several new molecules were synthesized and crystallized by solvent vapour diffusion, which were then characterized by single crystal X-Ray Diffraction (XRD). These structures were further compared to a wide selection of literature materials. Density Functional Theory (DFT) calculations were also carried out to examine the electronic transport of these materials with respect to their molecular packing motifs.