Regulating the Molecular Shape of Nonfused Electron Acceptors Enables Efficient Organic Solar Cells

Nonfused electron acceptor based organic solar cells (OSCs) have garnered increasing curiosity, because of their simple synthetic route and versatile chemical modification capabilities. However, nonfused acceptors with varying molecular symmetries have rarely been explored, and their structure-property-performance relationship remains unclear. In this work, two nonfused acceptors, namely, DTBDT-4Cl and DTBTT-4Cl with different molecular shapes, were synthesized and systematically investigated. The asymmetric acceptor DTBTT-4Cl with a C-shape molecular backbone exhibits more compact π-π stacking and higher crystallinity than the centrosymmetric S-shape acceptor DTBDT-4Cl. Remarkably, a promising power conversion efficiency (PCE) of 13.8% with a the open-circuit voltage (V_OC) as high as 0.916 V, a short-circuit current density (J_SC) of 21.9 mA cm^-2, and a fill factor (FF) of 68.5% was achieved, which significantly surpasses 11.3% for the DTBDT-4Cl-based devices. The enhanced performance could primarily be attributed to the enhanced intermolecular interactions, improved charge transfer, and suppressed charge recombination. These findings underscore the importance of precise control of the molecular shape through rational molecular design represents an effective strategy for adjusting the miscibility and thus the photovoltaic performance of nonfused electron acceptor-based OSCs.