Advancing dye–DES synergies in dye-sensitized solar cells for improved indoor efficiency and long-term stability under sustainable conditions

Two carbazole-based donor–acceptor dyes, CBZ-Gly and CBZ-EG, featuring glycerol- and ethylene glycol-like side chains, were designed and synthesized to achieve synergistic compatibility with DES-based electrolytes, and systematically investigate their impact on DSSCs performance. These dyes were tested in DSSCs employing two neat deep eutectic solvent (DES) electrolytes (choline chloride/ethylene glycol and choline chloride/glycerol) under both simulated sunlight (AM 1.5G) and indoor lighting (1000 lux). By combining molecular-level dye design with a tailored DES-based electrolyte, we achieved an improvement in long-term device stability over several months and demonstrated a record indoor power conversion efficiency of 9.4%, thereby establishing a new benchmark for fully sustainable, DES-based DSSCs under low-light conditions. Incorporating deep eutectic solvent (DES) mixtures in dye-sensitized solar cells offers an alternative to the use of volatile organic compounds as part of their electrolyte, which limits their use to outdoor environments. Here, the authors design two carbazole-based donor–acceptor dyes that are compatible with DES-based electrolytes and demonstrate their performance under both simulated sunlight and indoor lighting, with enhanced indoor power conversion efficiency under low-light conditions.