Selecting
suitable outermost aromatic rings of the central cores is of particular
importance for the design of fused-ring electron acceptors (FREAs)
because the direct electronic communication between the outermost
aromatic rings and termini exerts a strong impact on the optoelectronic
properties of FREAs. In most cases, the outermost rings of the FREA
cores are thiophene. This work reported the first example of using
pyrrole as the outermost rings of the core. Fused hexacyclic electron
acceptor, P6IC, using pyrrole in place of the often-used thiophene
as the outermost rings of the central core was synthesized. Compared
with its structural analogue F6IC with thiophene as the outermost
rings, P6IC exhibits a remarkably upshifted highest occupied molecular
orbital energy level (P6IC: −5.43 eV, F6IC: −5.71 eV),
a slightly upshifted lowest unoccupied molecular orbital energy level
(P6IC: −3.94 eV, F6IC: −4.00 eV), 54 nm red-shifted
absorption, a narrower band gap (P6IC: 1.30 eV, F6IC: 1.37 eV), and
an enhanced mobility (P6IC: 8.8 × 10–4 cm2 V–1 s–1, F6IC: 7.4 ×
10–4 cm2 V–1 s–1). Organic photovoltaic cells using PTB7-Th/P6IC as
a photoactive layer exhibit an efficiency of 12.2%, far surpassing
that based on PTB7-Th/F6IC active layer (5.57%). The semitransparent
devices using PTB7-Th/P6IC as the active layer yield efficiency of
10.2% with an average visible transmittance (AVT) of 17.0%, far surpassing
that based on PTB7-Th/F6IC (5.26% with an AVT of 18.4%).