Breaking the efficiency barrier: Tandem DSSCs with benzofuran co-sensitizers achieve better performance gain over N719

In this study, we report the design, synthesis, and application of two novel benzofuran-based organic co-sensitizers ( BF-1 and BF-2 ) featuring a phenyl-pyrazole π-spacer and distinct electron-accepting groups, cyanobenzoic acid for BF-1 and phthalic acid for BF-2 , for high-performance dye-sensitized solar cells (DSSCs). The target compounds were synthesized in high yields via Knoevenagel condensation and Schiff base formation, and fully characterized by FT-IR, 1 H/ 13 CNMR, and elemental analysis. The photophysical, electrochemical, and photovoltaic properties were systematically evaluated using UV–Vis spectroscopy, DFT calculations, and IPCE, J-V, and EIS analyses. Co-sensitization with the benchmark N719 dye significantly enhanced performance, yielding PCEs of 8.85% ( V OC = 0.726 V, J SC = 21.65 mA cm −2 , FF = 56.30%) for BF-1 + N719 and 9.98% ( V OC = 0.731 V, J SC = 22.50 mA cm −2 , FF = 60.67%) for BF-2 + N719 , compared to 7.90% for N719 alone. A parallel tandem DSSC (PT-Tandem) configuration using BF-2 (bottom cell) and N719 (top cell) achieved a PCE of 11.93% ( V OC = 0.755 V, J SC = 23.16 mA cm −2 , FF = 68.22%), representing a 51% improvement over the single N719 device. EIS measurements revealed reduced charge-transfer resistance and prolonged electron lifetimes in the tandem system, consistent with the enhanced V OC and J SC . Stability testing under continuous illumination for 300 h showed >95% retention of the initial efficiency. These findings highlight the potential of benzofuran–phenyl-pyrazole frameworks with tailored acceptors for synergistic co-sensitization and high-efficiency tandem DSSCs. • Novel benzofuran co-sensitizers boost DSSC efficiency beyond benchmark N719 performance. • Tandem DSSCs achieve 51% higher PCE than single N719 devices with enhanced stability. • Phenyl-pyrazole π-spacer design improves light harvesting and electron injection efficiency. • Parallel tandem cells deliver 11.93% PCE and retain >95% efficiency after 300 h illumination. • Reduced charge-transfer resistance and longer electron lifetimes confirmed by EIS analysis.