Non-Halogenated Polymer Donor-Based Organic Solar Cells with a Nearly 15% Efficiency Enabled by a Classic Ternary Strategy

Organic solar cells (OSCs) are expected to attain a satisfactory power conversion efficiency (PCE) and acceptable production cost to guarantee strong competitiveness. However, state-of-the-art PCEs are all achieved by polymer donors with halogen atom-based active layers, which leaves room for researchers to develop efficient systems without the currently widely used halogenated polymer donors. Here, we combined a recent well-known non-fullerene acceptor (NFA) Y6 with our previously proposed donor PBDTNS-BDD (possessing no halogen atoms) and successfully acquired a moderate PCE of 12.55%. By utilizing a classic ternary strategy of introducing a fullerene acceptor PC71BM into the blend, the PCE of the device is significantly increased to 14.88%, close to the 15% milestone. The improvement in the device performance due to PC71BM is attributed to the fact the improved blend morphology (molecular packing and domain size) enables suppressed exciton recombination and more efficient and balanced charge transport. Our work extends the applicable range of the classic ternary design of adding fullerene into an efficient NFA-based binary system, e.g., non-halogenated polymer:Y6 combination, to achieve a nearly 15% efficiency for its ternary device, providing new directions for applications of OSCs.