Dithienogermole-Based Nonfullerene Acceptors: Roles of the Side-Chains’ Direction and Development of Green-Tinted Efficient Semitransparent Organic Solar Cells
Yongjoon Cho, Tack Ho Lee, Seonghun Jeong, Song Yi Park, Byongkyu Lee, Jin Young Kim, Changduk Yang
Abstract
Inspired by the encouraging properties of Ge-fused heterocyclic dithienogermole (DTG) in optoelectronic applications, we here report two narrow-bandgap acceptor–donor′–donor–donor′–acceptor (A–D′–D–D′–A)-type isomeric nonfullerene acceptors based on DTG (DTG-IW with inward-facing side chains vs DTG-OW with outward-facing side chains) for use in organic solar cells (OSCs). The introduction of the inward-facing side chains into the backbone results in extremely confined face-on crystallites in the solid state, as verified by grazing-incidence wide-angle X-ray scattering measurements. This result is attributed mainly to a better power conversion efficiency (PCE) of 9.16% in the OSC based on a blend of DTG-IW with a narrow-bandgap PTB7-Th donor polymer, as compared with the corresponding DTG-OW-based one. Furthermore, the appealing feature of the blend mixing of the narrow-bandgap donor and acceptor pair is that it enables the construction of a green-tinted efficient semitransparent OSC with a PCE of 6.19% and transmittance of 50.4% in the green wavelength region through incorporation of the recently formulated semitransparent Ag/Sb2O3/Ag electrode. Overall, in addition to providing useful perspectives into the side-chain engineering of nonfullerene acceptors, this work highlights that OSC based on the A–D′–D–D′–A-type DTG is a promising narrow-bandgap acceptor for further improvement of the performance of semitransparent OSCs.