Harmonizing the Synthetic Complexity and Efficiency of Organic Solar Cells Using an Asymmetric Coumarin–Phenothiazine-Based Fullerene-Free Acceptor

Phenothiazine-based molecules are often used as electron donors in organic solar cells (OSCs). Herein, for the first time, we present the design and synthesis of a coumarin-phenothiazine dyad (AM-3) as a wide-band-gap fullerene-free acceptor (FFA) for OSCs. Most importantly, the molecule was synthesized in a simple and cost-effective two-step condensation reaction. Air-processed binary OSCs, containing AM-3 as an acceptor and PTB7-Th as the donor, yield a power conversion efficiency (PCE) of 12.46% and an open-circuit voltage (<i>V</i>_OC) of 0.99 V. Further, an improved PCE of 14.96% is achieved by introducing AM-3 as a third component in the PTB7-Th:NFA-5 blend, marking an enhancement of 40% over its PTB7-Th:NFA-5 binary counterpart (10.66%). Considering the synthetic simplicity and low cost, the obtained PCEs for AM-3 are comparable to those of several high-performance acceptors. We further evaluate the synthetic complexity (SC) and figure of merit (FoM) of AM-3 and compare them with commonly used fused- and nonfused-ring electron acceptors to evaluate its prospects for future applications.