Push or Pull Electrons: Acetoxy and Carbomethoxy-Substituted Isomerisms in Organic Solar Cell Acceptors

Isomerism is a major factor affecting the properties of materials. Herein, two isomeric acceptors based on acetoxy and methyl ester end group substituents, BTIC-OCOMe and BTIC-COOMe are reported. When blended with PBDB-TF, devices based on BTIC-OCOMe achieve an inferior (8.32%) power conversion efficiency (PCE) while the BTIC-COOMe material has a superior PCE of 13.25%. We investigated the reasons why these two devices, which differ only in the isomeric substituents on the terminal site, have such a large difference in photovoltaic performance. Our investigation conducted theoretical calculations and examined UV-vis absorption, energy levels, exciton dissociation and bimolecular recombination, mobilities tests, photoluminescence, and packing modes. It is found that the energy levels of the materials are fine-tuned, the absorption spectra are adjusted, and the energy loss is regulated. Our studies explored the reasons for the properties of materials differing, and the acetoxy and carbomethoxy substitutions provided some useful information concerning high-performance acceptor materials.

Automated summary

The differences in photovoltaic performance between two devices with minor variations in terminal isomeric substitutions are mainly due to fine-tuning of energy levels and adjustments in absorption spectra.