Enhancing DSSCs and Photocatalytic Hydrogen Production with D‐A1‐A2‐π‐A Sensitizers Containing 10′H‐Spiro Fluorene‐9,9′‐Phenanthren‐10′‐one and Benzoc1,2,5Thiadiazole

Abstract Novel D‐A 1 ‐A 2 ‐π‐A organic sensitizers ( FZ ‐sensitizer), utilizing spiro fluorene‐9,9′‐phenanthren‐10′‐one and benzo c1,2,5thiadiazole moiety as two auxiliary acceptors, are synthesized and applied in dye‐sensitized solar cells (DSSCs) and hydrogen production. By incorporating a bulky spiro fluorene‐9,9′‐phenanthrene‐10′‐one (A 1 ) and benzoc1,2,5thiadiazole (A 2 ) between the donor (D) and π‐bridge moiety, structural modifications inhibit molecular aggregation, while the carbonyl group enhances the capture of Li + ions, thereby delaying charge recombination. Furthermore, the extended π‐conjugation broadens the light absorption range and enhances the power conversion efficiency (PCE) of FZ ‐ 2 under AM1.5 conditions, achieving up to 5.72%. Co‐sensitization with N719 and FZ ‐ 2 shows PCE of 9.60% under one sun. Under TL84 indoor light conditions, the efficiency is 29.69% at 2500 lux. The superior co‐sensitization performance of N719 and FZ ‐ 2 can be attributed to FZ ‐ 2 ′s high absorptivity at short wavelengths, compensating for N719′s shortcomings in this range. FZ ‐sensitizers also exhibit high efficiency in photocatalytic hydrogen production. The hydrogen production activities of FZ ‐ 2 are 9190 μmol/g (1 hour) and 76582 μmol/g (12 hours) respectively, while those of FZ ‐ 1 are 7430 μmol/g (1 hour) and 64004 μmol/g (12 hours), indicating that FZ ‐ 2 can inject charges into TiO 2 more efficiently and utilize them for water splitting. Stability testing of photocatalytic water splitting after 12 hours shows a turnover number (TON) of 4249 for FZ ‐ 1 and 5378 for FZ ‐ 2 .