Borane Incorporation in a Non-Fullerene Acceptor To Tune Steric and Electronic Properties and Improve Organic Solar Cell Performance

Herein we study the effects of borane incorporation in a perylene diimide (PDI)-based non-fullerene acceptor (NFA). We have previously demonstrated that a PDI-bithiophene-PDI ((PDI)(2)Th-2) compound can be synthesized via direct (hetero)-arylation techniques and is easily modified to incorporate a phosphole in the bithiophene core ((PDI)(2)Th2PO) to tune the electronic and geometric properties. In this work, we have synthesized the borane analogue ((PDI)(2)Th2B) and demonstrated that the organoboron moiety heavily influences the optical, electronic, and geometric properties. To determine the effects of borane functionalization on device performance, green solvent solution-processed bulk-hetero-junction solar cells were fabricated using a medium-gap donor polymer TTFQx-T1 and each PDI compound as the NFA, respectively. Devices with the new borane-containing compound provided the highest efficiency, more than twice that for the other compounds, which was attributed to a highly twisted structure allowing for a more favorable active-layer morphology to be formed.