Understanding Twisted Triarylboranes from Single Crystals to Heterojunction Blends and Their Applications in Organic Photovoltaics

The triarylborane family has expanded rapidly as valuable π electron-accepting moieties in organic materials, yet the performance and application of triarylboranes in organic photovoltaics (OPVs) have thus far been limited. Herein, we present a comprehensive platform of 17 distinct triarylboranes to investigate their structure-property relationships from single crystals to heterojunction blends and further to OPV device performance. We show that twisted triarylboranes exhibit distinct molecular packing behavior in the solid state, characterized by limited π-π stacking and the lack of the face-on orientation required for efficient light-to-electric conversion, in contrast to state-of-the-art OPV materials. However, when incorporated as a third component, triarylboranes induce red-shifted absorption and blue-shifted photoluminescence spectra in OPV materials, thereby reducing reorganization energies in blends. Furthermore, triarylboranes possessing high dipole moments and trap-free energetics enhance power conversion efficiencies (PCEs) in devices. Notably, careful molecular design of triarylboranes is essential, as strong donor moieties lead to high-lying HOMOs in triarylboranes, creating energetic traps in OPV blends and significantly reducing PCEs. Finally, we demonstrate the application of triarylboranes in semitransparent OPVs, achieving improved PCEs and stability without losing semitransparent performance, and in state-of-the-art PM6/L8-BO-based blends, achieving impressive PCEs of 19.56%. These findings offer valuable guidance for the rational design of triarylboranes for OPVs and related organic electronic applications, reducing reliance on trial-and-error approaches.