Synergistic control of multilength-scale morphology and vertical phase separation for high-efficiency organic solar cells

Abstract

Controlling the morphology of organic solar cells (OSCs) presents a significant challenge due to their complex structure and composition. In particular, attaining synergistic control over the multi-length-scale morphology and vertical phase separation poses a substantial obstacle to the advancement of OSC technology. Here, we designed and synthesized two Y-series acceptors, BTP-9F and BTP-17F, with precisely controlled semi-fluorinated side chains attached to the pyrrole rings. The results indicate that BTP-9F-based organic solar cells (OSCs) exhibited more efficient polaron generation dynamics, reduced trap density, and charge recombination due to their optimized hierarchical morphology compared to PM6:BTP-17F-based OSCs. Consequently, PM6:BTP-9F-based OSCs achieved a promising power conversion efficiency (PCE) of 17.2%, significantly outperforming PM6:BTP-17F-based devices (14.1%). Furthermore, a remarkable PCE of 19.1%, coupled with an enhanced open-circuit voltage, was achieved in PM6:BTP-eC9:BTP-9F-based ternary systems. This achievement was attributed to the suppression of non-radiative recombination facilitated by synergistically controlled multilength-scale morphology and vertical phase separation. Our work shows that precise manipulation of the semi-fluorinated side-chain of NFAs is a compelling strategy for fine-tuning hierarchical morphology and minimizing energy loss to realize highly efficient OSCs.