The field of organic photovoltaics has seen extensive investigation and innovation within the past decade involving functional group modifications. Importantly, side-chain engineering has been inextricable towards the performance gains. Changes in solubilizing groups are key for solution processing and bulk self-assembly in the film; factors that have enabled organic materials to achieve power conversion efficiencies over 13% with planar molecular acceptors. Inspired by this development, we investigated the effects of appending hexyl- or hexyloxy- groups on two positions of zinc-chelated azadipyrromethene (ADP)-based molecular acceptor developed in our lab, which is non-planar. The nature and placement of the side-chains had a strong impact on self-assembly of the molecules in crystals and films. The molecule with hexyloxy- groups on the distal phenyls showed a unique morphology, and calculations derived from the crystal structure showed unusually high overlap integral for these types of non-planar molecules. Since charge transport is related to the square of the overlap integral, these results suggest that the modification is promising for improving charge transport and device performance.

Effect of solubilizing groups on non-planar molecular acceptors based on azadipyrromethenes for organic photovoltaics applications

ACS Spring Meeting 2021

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