Theretofore Highest Efficiency in Vacuum‐Deposited Organic Solar Cells Originating From Triarylamine‐Based Small‐Molecule Donors Containing Fused Heterocycle Units

ABSTRACT Vacuum‐deposited organic solar cells (v‐OSCs) are alternative candidates for photovoltaics technologies. Their advantages include well‐defined molecular structures, high purity of materials, excellent batch‐to‐batch reproducibility, and solution‐free fabrication process that enables good compatibility with underlying perovskite layer for tandem devices. Triarylamine‐based small‐molecule donors are commonly used in v‐OSCs, however, their power conversion efficiencies (PCEs) are constrained by low short‐circuit current density ( J _sc ). Moreover, to match with the photocurrent of perovskite subcell, enhancing J _sc of v‐OSCs is highly demanded. Herein, four small‐molecule donors (named PT, PF, BT, and BF) based on triarylamine electron‐donating moieties are designed. Compared with linear analogues PT and PF, BT and BF with fused‐ring building blocks including benzothiophene and benzofuran exhibit smaller bandgaps, lower highest occupied molecular orbital (HOMO) energy levels, and higher hole mobilities. Consequently, v‐OSCs based on BT and BF exhibit surprisingly high J _sc values (17.91 and 18.13 mA cm ⁻² , respectively), representing the highest reported J _sc for v‐OSCs. Moreover, the J _sc enhancement leads to improved PCEs of devices based on BT and BF (10.53% and 10.11%, respectively). Remarkably, the PCE of 10.53% for the BT‐based device represents the best PCE reported for v‐OSCs. This work opens a promising avenue to develop high‐performance small‐molecule donors for v‐OSCs.