Complementary triphenylamine sensitizers unlock 23% indoor efficiency in tandem DSSCs with N719

Molecular engineering of organic sensitizers is a powerful strategy for enhancing the spectral utilization and charge-transfer dynamics in dye-sensitized solar cells (DSSCs). Herein, we report two novel triphenylamine-based donor–π–acceptor dyes, TMN-1 (-COOH anchoring acceptor) and TMN-2 (-NO 2 acceptor), which incorporate a thiazole–benzofuran π-system. The dyes were synthesized in high yields and fully characterized using spectroscopic and electrochemical techniques, supported by DFT calculations. TMN-1 exhibited superior planarity, broader charge delocalization, and stronger TiO 2 coupling compared to TMN-2, which is consistent with its narrower optical band gap (2.02 eV vs. 2.10 eV) and enhanced intramolecular charge transfer. When co-sensitized with N719, TMN-1 significantly improved light harvesting and photocurrent generation, whereas tandem DSSCs achieved outstanding efficiencies. In particular, the N719(top)/TMN-1(bottom) parallel tandem delivered a power conversion efficiency of 11.23% under AM 1.5G illumination, outperforming both the single and co-sensitized devices. Strikingly, under indoor lighting (1000 lx, 0.283 mW.cm -2 ), the tandem cell achieved a record 23.43% efficiency, demonstrating excellent spectral complementarity and suppressed recombination loss. Thermogravimetric analysis (TGA) and operational stability tests (300 h continuous illumination) confirmed the robustness of TMN-1 , which was attributed to its strong carboxyl anchoring and extended π-conjugation. These findings highlight TMN-1 as a highly efficient and stable organic co-sensitizer and establish triphenylamine–benzofuran frameworks as a promising platform for next-generation DSSCs targeting both solar and indoor energy-harvesting applications.