Synergy of Liquid-Crystalline Small-Molecule and Polymeric Donors Delivers Uncommon Morphology Evolution and 16.6% Efficiency Organic Photovoltaics

Achieving an ideal morphology is an imperative avenue for enhancing key
parameters toward high-performing organic solar cells (OSCs). Among a
myriad of morphological-control methods, the strategy of incorporating a
third component with structural similarity and crystallinity difference to
construct ternary OSCs has emerged as an effective approach to regulate
morphology. A nematic liquid-crystalline benzodithiophene terthiophene
rhodamine (BTR) molecule, which possesses the same alkylthio-thienylsubstituted benzo moiety but obviously stronger crystallinity compared to
classical medium-bandgap polymeric donor PM6, is employed as a third
component to construct ternary OSCs based on a PM6:BTR:Y6 system. The
doping of BTR (5 wt%) is found to be enough to improve the OSC
morphology—significantly enhancing the crystallinity of the photoactive layer
while slightly reducing the donor/acceptor phase separation scale
simultaneously. Rarely is such a morphology evolution reported. It positively
affects the electronic properties of the device—prolongs the carrier lifetime,
shortens the photocurrent decay time, facilitates exciton dissociation, charge
transport, and collection, and ultimately boosts the power conversion
efficiency from 15.7% to 16.6%. This result demonstrates that the successful
synergy of liquid-crystalline small-molecule and polymeric donors delicately
adjusts the active-layer morphology and refines device performance, which
brings vibrancy to the OSC research field.